[browser][coreclr] WASM-specific GC OS layer; no mmap/decommit

[pavelsavara]

Fixes#121036
Fixes#117813
Fixes#118943

Summary

This PR adds a dedicated WASM implementation of the GC's OS abstraction layer
(GCToOSInterface) and updates the GC and PAL to handle the fact that on WASM
there is no virtual memory: pages cannot be reserved without committing,
partial unmaps don't return memory to the engine, and MAP_FIXED / madvise
are not supported.

The previous approach reused gcenv.unix.cpp with #ifdef TARGET_WASM patches
and overloaded use_large_pages_p to mean "decommit is a no-op". This change
splits those concerns:

• A new gc/wasm/gcenv.cpp replaces gc/unix/gcenv.unix.cpp on WASM and
  implements VirtualReserve / VirtualCommit / VirtualDecommit /
  VirtualRelease on top of posix_memalign / free. WASM-specific patches
  in gcenv.unix.cpp are removed.
• A new GC flag never_decommit_p replaces every "is decommit a no-op" check
  that was previously expressed as use_large_pages_p. It is set on WASM
  unconditionally and on other platforms whenever use_large_pages_p is set.
• gc/CMakeLists.txt now selects gc/wasm for WASM targets while still
  including unix/configure.cmake to generate config.gc.h.
• The PAL's virtual.cpp is similarly cleaned up to use posix_memalign /
  free on WASM and to zero memory on MEM_DECOMMIT, so the next
  VirtualCommit (a no-op on WASM) sees zeroed memory.
• A new minipal_getpagesize abstraction is introduced. On WASM it returns a
  compile-time constant of 16 KB (the GC's page granularity, distinct from the
  64 KB memory.grow granularity that getpagesize() reports). On Windows it
  returns the 4 KB constant inline. On other POSIX systems it caches
  getpagesize() once per process. CoreCLR PAL callers are updated to use it.

Why a separate never_decommit_p

On large pages, decommit is a no-op because the OS pre-commits the entire
range. On WASM, decommit is a no-op because there is no way to give linear
memory back to the engine. The two cases share the same set of GC code paths
that must be skipped or modified (decommit_ephemeral_segment_pages,
decommit_step, decommit_region, decommit_heap_segment_pages,
decommit_heap_segment, distribute_free_regions tail-decommit,
reset_memory, virtual_commit, virtual_decommit assert), but they have
nothing else in common. Reusing use_large_pages_p on WASM was misleading and
made it easy to forget large-pages-only behavior (e.g., pre-touch). The new
flag captures only the "decommit is a no-op" semantics; non-WASM behavior is
unchanged because never_decommit_p == use_large_pages_p everywhere except
WASM.

Why minipal_getpagesize

The GC needs the OS page size to be a compile-time constant on WASM (16 KB)
so that alignment math folds. getpagesize() on emscripten returns 64 KB
(the memory.grow granularity), which is too coarse for GC alignment and
thresholds. Centralizing this in minipal lets PAL and GC agree on a single
value and avoids #ifdefs at every call site.

Notes

• VirtualReserveAndCommitLargePages on WASM falls through to the regular
  reserve/commit path; the GC does not request large pages on WASM.
• posix_memalign may return either freshly grown linear memory (zeroed by
  the WASM spec) or a recycled block from emscripten's allocator free list.
  We always memset to zero on reserve and on decommit so callers can rely
  on the standard "memory starts zeroed" contract.
• VirtualReset returns false on WASM, forcing the GC to use the
  decommit+commit fallback (memset to zero) rather than relying on
  madvise, which is a no-op on emscripten.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @dotnet/gc
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR separates WebAssembly-specific GC OS interface behavior from the shared Unix implementation by introducing a dedicated gcenv.wasm.cpp, and adjusts the PAL virtual memory implementation on WASM to avoid relying on Emscripten’s incomplete mmap/munmap support.

Changes:

• Added a dedicated WASM GCToOSInterface implementation (gcenv.wasm.cpp) and CMake wiring for building it.
• Routed WASM GC builds to the new gc/wasm directory and removed WASM-specific #ifdef paths from gcenv.unix.cpp.
• Updated PAL virtual memory reserve/release on WASM to use posix_memalign/free instead of mmap/munmap.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/coreclr/pal/src/map/virtual.cpp	Switches WASM reserve/release behavior to posix_memalign/free and adjusts related error/cleanup paths.
src/coreclr/gc/wasm/gcenv.wasm.cpp	New WASM-specific GC OS interface implementation (virtual memory, CPU/NUMA stubs, memory stats).
src/coreclr/gc/wasm/CMakeLists.txt	Adds build definition for the WASM GC PAL object library.
src/coreclr/gc/unix/gcenv.unix.cpp	Removes WASM-specific branches and fixes nanosleep EINTR retry logic.
src/coreclr/gc/CMakeLists.txt	Routes WASM builds to gc/wasm instead of gc/unix.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated no new comments.

[janvorli]

LGTM, thank you!

[pavelsavara]

/ba-g unrelated CI fail

[pavelsavara]

Fixes#121036
Fixes#117813
Fixes#118943

Summary

This PR adds a dedicated WASM implementation of the GC's OS abstraction layer
(GCToOSInterface) and updates the GC and PAL to handle the fact that on WASM
there is no virtual memory: pages cannot be reserved without committing,
partial unmaps don't return memory to the engine, and MAP_FIXED / madvise
are not supported.

The previous approach reused gcenv.unix.cpp with #ifdef TARGET_WASM patches
and overloaded use_large_pages_p to mean "decommit is a no-op". This change
splits those concerns:

• A new gc/wasm/gcenv.cpp replaces gc/unix/gcenv.unix.cpp on WASM and
  implements VirtualReserve / VirtualCommit / VirtualDecommit /
  VirtualRelease on top of posix_memalign / free. WASM-specific patches
  in gcenv.unix.cpp are removed.
• A new GC flag never_decommit_p replaces every "is decommit a no-op" check
  that was previously expressed as use_large_pages_p. It is set on WASM
  unconditionally and on other platforms whenever use_large_pages_p is set.
• gc/CMakeLists.txt now selects gc/wasm for WASM targets while still
  including unix/configure.cmake to generate config.gc.h.
• The PAL's virtual.cpp is similarly cleaned up to use posix_memalign /
  free on WASM and to zero memory on MEM_DECOMMIT, so the next
  VirtualCommit (a no-op on WASM) sees zeroed memory.
• A new minipal_getpagesize abstraction is introduced. On WASM it returns a
  compile-time constant of 16 KB (the GC's page granularity, distinct from the
  64 KB memory.grow granularity that getpagesize() reports). On Windows it
  returns the 4 KB constant inline. On other POSIX systems it caches
  getpagesize() once per process. CoreCLR PAL callers are updated to use it.

Why a separate never_decommit_p

On large pages, decommit is a no-op because the OS pre-commits the entire
range. On WASM, decommit is a no-op because there is no way to give linear
memory back to the engine. The two cases share the same set of GC code paths
that must be skipped or modified (decommit_ephemeral_segment_pages,
decommit_step, decommit_region, decommit_heap_segment_pages,
decommit_heap_segment, distribute_free_regions tail-decommit,
reset_memory, virtual_commit, virtual_decommit assert), but they have
nothing else in common. Reusing use_large_pages_p on WASM was misleading and
made it easy to forget large-pages-only behavior (e.g., pre-touch). The new
flag captures only the "decommit is a no-op" semantics; non-WASM behavior is
unchanged because never_decommit_p == use_large_pages_p everywhere except
WASM.

Why minipal_getpagesize

The GC needs the OS page size to be a compile-time constant on WASM (16 KB)
so that alignment math folds. getpagesize() on emscripten returns 64 KB
(the memory.grow granularity), which is too coarse for GC alignment and
thresholds. Centralizing this in minipal lets PAL and GC agree on a single
value and avoids #ifdefs at every call site.

Notes

• VirtualReserveAndCommitLargePages on WASM falls through to the regular
  reserve/commit path; the GC does not request large pages on WASM.
• posix_memalign may return either freshly grown linear memory (zeroed by
  the WASM spec) or a recycled block from emscripten's allocator free list.
  We always memset to zero on reserve and on decommit so callers can rely
  on the standard "memory starts zeroed" contract.
• VirtualReset returns false on WASM, forcing the GC to use the
  decommit+commit fallback (memset to zero) rather than relying on
  madvise, which is a no-op on emscripten.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @dotnet/gc
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR separates WebAssembly-specific GC OS interface behavior from the shared Unix implementation by introducing a dedicated gcenv.wasm.cpp, and adjusts the PAL virtual memory implementation on WASM to avoid relying on Emscripten’s incomplete mmap/munmap support.

Changes:

• Added a dedicated WASM GCToOSInterface implementation (gcenv.wasm.cpp) and CMake wiring for building it.
• Routed WASM GC builds to the new gc/wasm directory and removed WASM-specific #ifdef paths from gcenv.unix.cpp.
• Updated PAL virtual memory reserve/release on WASM to use posix_memalign/free instead of mmap/munmap.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/coreclr/pal/src/map/virtual.cpp	Switches WASM reserve/release behavior to posix_memalign/free and adjusts related error/cleanup paths.
src/coreclr/gc/wasm/gcenv.wasm.cpp	New WASM-specific GC OS interface implementation (virtual memory, CPU/NUMA stubs, memory stats).
src/coreclr/gc/wasm/CMakeLists.txt	Adds build definition for the WASM GC PAL object library.
src/coreclr/gc/unix/gcenv.unix.cpp	Removes WASM-specific branches and fixes nanosleep EINTR retry logic.
src/coreclr/gc/CMakeLists.txt	Routes WASM builds to gc/wasm instead of gc/unix.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated no new comments.

[janvorli]

LGTM, thank you!

[pavelsavara]

/ba-g unrelated CI fail

[pavelsavara]

Fixes#121036
Fixes#117813
Fixes#118943

Summary

This PR adds a dedicated WASM implementation of the GC's OS abstraction layer
(GCToOSInterface) and updates the GC and PAL to handle the fact that on WASM
there is no virtual memory: pages cannot be reserved without committing,
partial unmaps don't return memory to the engine, and MAP_FIXED / madvise
are not supported.

The previous approach reused gcenv.unix.cpp with #ifdef TARGET_WASM patches
and overloaded use_large_pages_p to mean "decommit is a no-op". This change
splits those concerns:

• A new gc/wasm/gcenv.cpp replaces gc/unix/gcenv.unix.cpp on WASM and
  implements VirtualReserve / VirtualCommit / VirtualDecommit /
  VirtualRelease on top of posix_memalign / free. WASM-specific patches
  in gcenv.unix.cpp are removed.
• A new GC flag never_decommit_p replaces every "is decommit a no-op" check
  that was previously expressed as use_large_pages_p. It is set on WASM
  unconditionally and on other platforms whenever use_large_pages_p is set.
• gc/CMakeLists.txt now selects gc/wasm for WASM targets while still
  including unix/configure.cmake to generate config.gc.h.
• The PAL's virtual.cpp is similarly cleaned up to use posix_memalign /
  free on WASM and to zero memory on MEM_DECOMMIT, so the next
  VirtualCommit (a no-op on WASM) sees zeroed memory.
• A new minipal_getpagesize abstraction is introduced. On WASM it returns a
  compile-time constant of 16 KB (the GC's page granularity, distinct from the
  64 KB memory.grow granularity that getpagesize() reports). On Windows it
  returns the 4 KB constant inline. On other POSIX systems it caches
  getpagesize() once per process. CoreCLR PAL callers are updated to use it.

Why a separate never_decommit_p

On large pages, decommit is a no-op because the OS pre-commits the entire
range. On WASM, decommit is a no-op because there is no way to give linear
memory back to the engine. The two cases share the same set of GC code paths
that must be skipped or modified (decommit_ephemeral_segment_pages,
decommit_step, decommit_region, decommit_heap_segment_pages,
decommit_heap_segment, distribute_free_regions tail-decommit,
reset_memory, virtual_commit, virtual_decommit assert), but they have
nothing else in common. Reusing use_large_pages_p on WASM was misleading and
made it easy to forget large-pages-only behavior (e.g., pre-touch). The new
flag captures only the "decommit is a no-op" semantics; non-WASM behavior is
unchanged because never_decommit_p == use_large_pages_p everywhere except
WASM.

Why minipal_getpagesize

The GC needs the OS page size to be a compile-time constant on WASM (16 KB)
so that alignment math folds. getpagesize() on emscripten returns 64 KB
(the memory.grow granularity), which is too coarse for GC alignment and
thresholds. Centralizing this in minipal lets PAL and GC agree on a single
value and avoids #ifdefs at every call site.

Notes

• VirtualReserveAndCommitLargePages on WASM falls through to the regular
  reserve/commit path; the GC does not request large pages on WASM.
• posix_memalign may return either freshly grown linear memory (zeroed by
  the WASM spec) or a recycled block from emscripten's allocator free list.
  We always memset to zero on reserve and on decommit so callers can rely
  on the standard "memory starts zeroed" contract.
• VirtualReset returns false on WASM, forcing the GC to use the
  decommit+commit fallback (memset to zero) rather than relying on
  madvise, which is a no-op on emscripten.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @dotnet/gc
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR separates WebAssembly-specific GC OS interface behavior from the shared Unix implementation by introducing a dedicated gcenv.wasm.cpp, and adjusts the PAL virtual memory implementation on WASM to avoid relying on Emscripten’s incomplete mmap/munmap support.

Changes:

• Added a dedicated WASM GCToOSInterface implementation (gcenv.wasm.cpp) and CMake wiring for building it.
• Routed WASM GC builds to the new gc/wasm directory and removed WASM-specific #ifdef paths from gcenv.unix.cpp.
• Updated PAL virtual memory reserve/release on WASM to use posix_memalign/free instead of mmap/munmap.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/coreclr/pal/src/map/virtual.cpp	Switches WASM reserve/release behavior to posix_memalign/free and adjusts related error/cleanup paths.
src/coreclr/gc/wasm/gcenv.wasm.cpp	New WASM-specific GC OS interface implementation (virtual memory, CPU/NUMA stubs, memory stats).
src/coreclr/gc/wasm/CMakeLists.txt	Adds build definition for the WASM GC PAL object library.
src/coreclr/gc/unix/gcenv.unix.cpp	Removes WASM-specific branches and fixes nanosleep EINTR retry logic.
src/coreclr/gc/CMakeLists.txt	Routes WASM builds to gc/wasm instead of gc/unix.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated no new comments.

[janvorli]

LGTM, thank you!

[pavelsavara]

/ba-g unrelated CI fail

[pavelsavara]

Fixes#121036
Fixes#117813
Fixes#118943

Summary

This PR adds a dedicated WASM implementation of the GC's OS abstraction layer
(GCToOSInterface) and updates the GC and PAL to handle the fact that on WASM
there is no virtual memory: pages cannot be reserved without committing,
partial unmaps don't return memory to the engine, and MAP_FIXED / madvise
are not supported.

The previous approach reused gcenv.unix.cpp with #ifdef TARGET_WASM patches
and overloaded use_large_pages_p to mean "decommit is a no-op". This change
splits those concerns:

• A new gc/wasm/gcenv.cpp replaces gc/unix/gcenv.unix.cpp on WASM and
  implements VirtualReserve / VirtualCommit / VirtualDecommit /
  VirtualRelease on top of posix_memalign / free. WASM-specific patches
  in gcenv.unix.cpp are removed.
• A new GC flag never_decommit_p replaces every "is decommit a no-op" check
  that was previously expressed as use_large_pages_p. It is set on WASM
  unconditionally and on other platforms whenever use_large_pages_p is set.
• gc/CMakeLists.txt now selects gc/wasm for WASM targets while still
  including unix/configure.cmake to generate config.gc.h.
• The PAL's virtual.cpp is similarly cleaned up to use posix_memalign /
  free on WASM and to zero memory on MEM_DECOMMIT, so the next
  VirtualCommit (a no-op on WASM) sees zeroed memory.
• A new minipal_getpagesize abstraction is introduced. On WASM it returns a
  compile-time constant of 16 KB (the GC's page granularity, distinct from the
  64 KB memory.grow granularity that getpagesize() reports). On Windows it
  returns the 4 KB constant inline. On other POSIX systems it caches
  getpagesize() once per process. CoreCLR PAL callers are updated to use it.

Why a separate never_decommit_p

On large pages, decommit is a no-op because the OS pre-commits the entire
range. On WASM, decommit is a no-op because there is no way to give linear
memory back to the engine. The two cases share the same set of GC code paths
that must be skipped or modified (decommit_ephemeral_segment_pages,
decommit_step, decommit_region, decommit_heap_segment_pages,
decommit_heap_segment, distribute_free_regions tail-decommit,
reset_memory, virtual_commit, virtual_decommit assert), but they have
nothing else in common. Reusing use_large_pages_p on WASM was misleading and
made it easy to forget large-pages-only behavior (e.g., pre-touch). The new
flag captures only the "decommit is a no-op" semantics; non-WASM behavior is
unchanged because never_decommit_p == use_large_pages_p everywhere except
WASM.

Why minipal_getpagesize

The GC needs the OS page size to be a compile-time constant on WASM (16 KB)
so that alignment math folds. getpagesize() on emscripten returns 64 KB
(the memory.grow granularity), which is too coarse for GC alignment and
thresholds. Centralizing this in minipal lets PAL and GC agree on a single
value and avoids #ifdefs at every call site.

Notes

• VirtualReserveAndCommitLargePages on WASM falls through to the regular
  reserve/commit path; the GC does not request large pages on WASM.
• posix_memalign may return either freshly grown linear memory (zeroed by
  the WASM spec) or a recycled block from emscripten's allocator free list.
  We always memset to zero on reserve and on decommit so callers can rely
  on the standard "memory starts zeroed" contract.
• VirtualReset returns false on WASM, forcing the GC to use the
  decommit+commit fallback (memset to zero) rather than relying on
  madvise, which is a no-op on emscripten.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @dotnet/gc
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR separates WebAssembly-specific GC OS interface behavior from the shared Unix implementation by introducing a dedicated gcenv.wasm.cpp, and adjusts the PAL virtual memory implementation on WASM to avoid relying on Emscripten’s incomplete mmap/munmap support.

Changes:

• Added a dedicated WASM GCToOSInterface implementation (gcenv.wasm.cpp) and CMake wiring for building it.
• Routed WASM GC builds to the new gc/wasm directory and removed WASM-specific #ifdef paths from gcenv.unix.cpp.
• Updated PAL virtual memory reserve/release on WASM to use posix_memalign/free instead of mmap/munmap.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/coreclr/pal/src/map/virtual.cpp	Switches WASM reserve/release behavior to posix_memalign/free and adjusts related error/cleanup paths.
src/coreclr/gc/wasm/gcenv.wasm.cpp	New WASM-specific GC OS interface implementation (virtual memory, CPU/NUMA stubs, memory stats).
src/coreclr/gc/wasm/CMakeLists.txt	Adds build definition for the WASM GC PAL object library.
src/coreclr/gc/unix/gcenv.unix.cpp	Removes WASM-specific branches and fixes nanosleep EINTR retry logic.
src/coreclr/gc/CMakeLists.txt	Routes WASM builds to gc/wasm instead of gc/unix.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated no new comments.

[janvorli]

LGTM, thank you!

[pavelsavara]

/ba-g unrelated CI fail

[pavelsavara]

Fixes#121036
Fixes#117813
Fixes#118943

Summary

This PR adds a dedicated WASM implementation of the GC's OS abstraction layer
(GCToOSInterface) and updates the GC and PAL to handle the fact that on WASM
there is no virtual memory: pages cannot be reserved without committing,
partial unmaps don't return memory to the engine, and MAP_FIXED / madvise
are not supported.

The previous approach reused gcenv.unix.cpp with #ifdef TARGET_WASM patches
and overloaded use_large_pages_p to mean "decommit is a no-op". This change
splits those concerns:

• A new gc/wasm/gcenv.cpp replaces gc/unix/gcenv.unix.cpp on WASM and
  implements VirtualReserve / VirtualCommit / VirtualDecommit /
  VirtualRelease on top of posix_memalign / free. WASM-specific patches
  in gcenv.unix.cpp are removed.
• A new GC flag never_decommit_p replaces every "is decommit a no-op" check
  that was previously expressed as use_large_pages_p. It is set on WASM
  unconditionally and on other platforms whenever use_large_pages_p is set.
• gc/CMakeLists.txt now selects gc/wasm for WASM targets while still
  including unix/configure.cmake to generate config.gc.h.
• The PAL's virtual.cpp is similarly cleaned up to use posix_memalign /
  free on WASM and to zero memory on MEM_DECOMMIT, so the next
  VirtualCommit (a no-op on WASM) sees zeroed memory.
• A new minipal_getpagesize abstraction is introduced. On WASM it returns a
  compile-time constant of 16 KB (the GC's page granularity, distinct from the
  64 KB memory.grow granularity that getpagesize() reports). On Windows it
  returns the 4 KB constant inline. On other POSIX systems it caches
  getpagesize() once per process. CoreCLR PAL callers are updated to use it.

Why a separate never_decommit_p

On large pages, decommit is a no-op because the OS pre-commits the entire
range. On WASM, decommit is a no-op because there is no way to give linear
memory back to the engine. The two cases share the same set of GC code paths
that must be skipped or modified (decommit_ephemeral_segment_pages,
decommit_step, decommit_region, decommit_heap_segment_pages,
decommit_heap_segment, distribute_free_regions tail-decommit,
reset_memory, virtual_commit, virtual_decommit assert), but they have
nothing else in common. Reusing use_large_pages_p on WASM was misleading and
made it easy to forget large-pages-only behavior (e.g., pre-touch). The new
flag captures only the "decommit is a no-op" semantics; non-WASM behavior is
unchanged because never_decommit_p == use_large_pages_p everywhere except
WASM.

Why minipal_getpagesize

The GC needs the OS page size to be a compile-time constant on WASM (16 KB)
so that alignment math folds. getpagesize() on emscripten returns 64 KB
(the memory.grow granularity), which is too coarse for GC alignment and
thresholds. Centralizing this in minipal lets PAL and GC agree on a single
value and avoids #ifdefs at every call site.

Notes

• VirtualReserveAndCommitLargePages on WASM falls through to the regular
  reserve/commit path; the GC does not request large pages on WASM.
• posix_memalign may return either freshly grown linear memory (zeroed by
  the WASM spec) or a recycled block from emscripten's allocator free list.
  We always memset to zero on reserve and on decommit so callers can rely
  on the standard "memory starts zeroed" contract.
• VirtualReset returns false on WASM, forcing the GC to use the
  decommit+commit fallback (memset to zero) rather than relying on
  madvise, which is a no-op on emscripten.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @dotnet/gc
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR separates WebAssembly-specific GC OS interface behavior from the shared Unix implementation by introducing a dedicated gcenv.wasm.cpp, and adjusts the PAL virtual memory implementation on WASM to avoid relying on Emscripten’s incomplete mmap/munmap support.

Changes:

• Added a dedicated WASM GCToOSInterface implementation (gcenv.wasm.cpp) and CMake wiring for building it.
• Routed WASM GC builds to the new gc/wasm directory and removed WASM-specific #ifdef paths from gcenv.unix.cpp.
• Updated PAL virtual memory reserve/release on WASM to use posix_memalign/free instead of mmap/munmap.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/coreclr/pal/src/map/virtual.cpp	Switches WASM reserve/release behavior to posix_memalign/free and adjusts related error/cleanup paths.
src/coreclr/gc/wasm/gcenv.wasm.cpp	New WASM-specific GC OS interface implementation (virtual memory, CPU/NUMA stubs, memory stats).
src/coreclr/gc/wasm/CMakeLists.txt	Adds build definition for the WASM GC PAL object library.
src/coreclr/gc/unix/gcenv.unix.cpp	Removes WASM-specific branches and fixes nanosleep EINTR retry logic.
src/coreclr/gc/CMakeLists.txt	Routes WASM builds to gc/wasm instead of gc/unix.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated no new comments.

[janvorli]

LGTM, thank you!

[pavelsavara]

/ba-g unrelated CI fail

[pavelsavara]

Fixes#121036
Fixes#117813
Fixes#118943

Summary

This PR adds a dedicated WASM implementation of the GC's OS abstraction layer
(GCToOSInterface) and updates the GC and PAL to handle the fact that on WASM
there is no virtual memory: pages cannot be reserved without committing,
partial unmaps don't return memory to the engine, and MAP_FIXED / madvise
are not supported.

The previous approach reused gcenv.unix.cpp with #ifdef TARGET_WASM patches
and overloaded use_large_pages_p to mean "decommit is a no-op". This change
splits those concerns:

• A new gc/wasm/gcenv.cpp replaces gc/unix/gcenv.unix.cpp on WASM and
  implements VirtualReserve / VirtualCommit / VirtualDecommit /
  VirtualRelease on top of posix_memalign / free. WASM-specific patches
  in gcenv.unix.cpp are removed.
• A new GC flag never_decommit_p replaces every "is decommit a no-op" check
  that was previously expressed as use_large_pages_p. It is set on WASM
  unconditionally and on other platforms whenever use_large_pages_p is set.
• gc/CMakeLists.txt now selects gc/wasm for WASM targets while still
  including unix/configure.cmake to generate config.gc.h.
• The PAL's virtual.cpp is similarly cleaned up to use posix_memalign /
  free on WASM and to zero memory on MEM_DECOMMIT, so the next
  VirtualCommit (a no-op on WASM) sees zeroed memory.
• A new minipal_getpagesize abstraction is introduced. On WASM it returns a
  compile-time constant of 16 KB (the GC's page granularity, distinct from the
  64 KB memory.grow granularity that getpagesize() reports). On Windows it
  returns the 4 KB constant inline. On other POSIX systems it caches
  getpagesize() once per process. CoreCLR PAL callers are updated to use it.

Why a separate never_decommit_p

On large pages, decommit is a no-op because the OS pre-commits the entire
range. On WASM, decommit is a no-op because there is no way to give linear
memory back to the engine. The two cases share the same set of GC code paths
that must be skipped or modified (decommit_ephemeral_segment_pages,
decommit_step, decommit_region, decommit_heap_segment_pages,
decommit_heap_segment, distribute_free_regions tail-decommit,
reset_memory, virtual_commit, virtual_decommit assert), but they have
nothing else in common. Reusing use_large_pages_p on WASM was misleading and
made it easy to forget large-pages-only behavior (e.g., pre-touch). The new
flag captures only the "decommit is a no-op" semantics; non-WASM behavior is
unchanged because never_decommit_p == use_large_pages_p everywhere except
WASM.

Why minipal_getpagesize

The GC needs the OS page size to be a compile-time constant on WASM (16 KB)
so that alignment math folds. getpagesize() on emscripten returns 64 KB
(the memory.grow granularity), which is too coarse for GC alignment and
thresholds. Centralizing this in minipal lets PAL and GC agree on a single
value and avoids #ifdefs at every call site.

Notes

• VirtualReserveAndCommitLargePages on WASM falls through to the regular
  reserve/commit path; the GC does not request large pages on WASM.
• posix_memalign may return either freshly grown linear memory (zeroed by
  the WASM spec) or a recycled block from emscripten's allocator free list.
  We always memset to zero on reserve and on decommit so callers can rely
  on the standard "memory starts zeroed" contract.
• VirtualReset returns false on WASM, forcing the GC to use the
  decommit+commit fallback (memset to zero) rather than relying on
  madvise, which is a no-op on emscripten.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @dotnet/gc
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR separates WebAssembly-specific GC OS interface behavior from the shared Unix implementation by introducing a dedicated gcenv.wasm.cpp, and adjusts the PAL virtual memory implementation on WASM to avoid relying on Emscripten’s incomplete mmap/munmap support.

Changes:

• Added a dedicated WASM GCToOSInterface implementation (gcenv.wasm.cpp) and CMake wiring for building it.
• Routed WASM GC builds to the new gc/wasm directory and removed WASM-specific #ifdef paths from gcenv.unix.cpp.
• Updated PAL virtual memory reserve/release on WASM to use posix_memalign/free instead of mmap/munmap.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/coreclr/pal/src/map/virtual.cpp	Switches WASM reserve/release behavior to posix_memalign/free and adjusts related error/cleanup paths.
src/coreclr/gc/wasm/gcenv.wasm.cpp	New WASM-specific GC OS interface implementation (virtual memory, CPU/NUMA stubs, memory stats).
src/coreclr/gc/wasm/CMakeLists.txt	Adds build definition for the WASM GC PAL object library.
src/coreclr/gc/unix/gcenv.unix.cpp	Removes WASM-specific branches and fixes nanosleep EINTR retry logic.
src/coreclr/gc/CMakeLists.txt	Routes WASM builds to gc/wasm instead of gc/unix.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated no new comments.

[janvorli]

LGTM, thank you!

[pavelsavara]

/ba-g unrelated CI fail

[pavelsavara]

Fixes#121036
Fixes#117813
Fixes#118943

Summary

This PR adds a dedicated WASM implementation of the GC's OS abstraction layer
(GCToOSInterface) and updates the GC and PAL to handle the fact that on WASM
there is no virtual memory: pages cannot be reserved without committing,
partial unmaps don't return memory to the engine, and MAP_FIXED / madvise
are not supported.

The previous approach reused gcenv.unix.cpp with #ifdef TARGET_WASM patches
and overloaded use_large_pages_p to mean "decommit is a no-op". This change
splits those concerns:

• A new gc/wasm/gcenv.cpp replaces gc/unix/gcenv.unix.cpp on WASM and
  implements VirtualReserve / VirtualCommit / VirtualDecommit /
  VirtualRelease on top of posix_memalign / free. WASM-specific patches
  in gcenv.unix.cpp are removed.
• A new GC flag never_decommit_p replaces every "is decommit a no-op" check
  that was previously expressed as use_large_pages_p. It is set on WASM
  unconditionally and on other platforms whenever use_large_pages_p is set.
• gc/CMakeLists.txt now selects gc/wasm for WASM targets while still
  including unix/configure.cmake to generate config.gc.h.
• The PAL's virtual.cpp is similarly cleaned up to use posix_memalign /
  free on WASM and to zero memory on MEM_DECOMMIT, so the next
  VirtualCommit (a no-op on WASM) sees zeroed memory.
• A new minipal_getpagesize abstraction is introduced. On WASM it returns a
  compile-time constant of 16 KB (the GC's page granularity, distinct from the
  64 KB memory.grow granularity that getpagesize() reports). On Windows it
  returns the 4 KB constant inline. On other POSIX systems it caches
  getpagesize() once per process. CoreCLR PAL callers are updated to use it.

Why a separate never_decommit_p

On large pages, decommit is a no-op because the OS pre-commits the entire
range. On WASM, decommit is a no-op because there is no way to give linear
memory back to the engine. The two cases share the same set of GC code paths
that must be skipped or modified (decommit_ephemeral_segment_pages,
decommit_step, decommit_region, decommit_heap_segment_pages,
decommit_heap_segment, distribute_free_regions tail-decommit,
reset_memory, virtual_commit, virtual_decommit assert), but they have
nothing else in common. Reusing use_large_pages_p on WASM was misleading and
made it easy to forget large-pages-only behavior (e.g., pre-touch). The new
flag captures only the "decommit is a no-op" semantics; non-WASM behavior is
unchanged because never_decommit_p == use_large_pages_p everywhere except
WASM.

Why minipal_getpagesize

The GC needs the OS page size to be a compile-time constant on WASM (16 KB)
so that alignment math folds. getpagesize() on emscripten returns 64 KB
(the memory.grow granularity), which is too coarse for GC alignment and
thresholds. Centralizing this in minipal lets PAL and GC agree on a single
value and avoids #ifdefs at every call site.

Notes

• VirtualReserveAndCommitLargePages on WASM falls through to the regular
  reserve/commit path; the GC does not request large pages on WASM.
• posix_memalign may return either freshly grown linear memory (zeroed by
  the WASM spec) or a recycled block from emscripten's allocator free list.
  We always memset to zero on reserve and on decommit so callers can rely
  on the standard "memory starts zeroed" contract.
• VirtualReset returns false on WASM, forcing the GC to use the
  decommit+commit fallback (memset to zero) rather than relying on
  madvise, which is a no-op on emscripten.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @dotnet/gc
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR separates WebAssembly-specific GC OS interface behavior from the shared Unix implementation by introducing a dedicated gcenv.wasm.cpp, and adjusts the PAL virtual memory implementation on WASM to avoid relying on Emscripten’s incomplete mmap/munmap support.

Changes:

• Added a dedicated WASM GCToOSInterface implementation (gcenv.wasm.cpp) and CMake wiring for building it.
• Routed WASM GC builds to the new gc/wasm directory and removed WASM-specific #ifdef paths from gcenv.unix.cpp.
• Updated PAL virtual memory reserve/release on WASM to use posix_memalign/free instead of mmap/munmap.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/coreclr/pal/src/map/virtual.cpp	Switches WASM reserve/release behavior to posix_memalign/free and adjusts related error/cleanup paths.
src/coreclr/gc/wasm/gcenv.wasm.cpp	New WASM-specific GC OS interface implementation (virtual memory, CPU/NUMA stubs, memory stats).
src/coreclr/gc/wasm/CMakeLists.txt	Adds build definition for the WASM GC PAL object library.
src/coreclr/gc/unix/gcenv.unix.cpp	Removes WASM-specific branches and fixes nanosleep EINTR retry logic.
src/coreclr/gc/CMakeLists.txt	Routes WASM builds to gc/wasm instead of gc/unix.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated no new comments.

[janvorli]

LGTM, thank you!

[pavelsavara]

/ba-g unrelated CI fail

[pavelsavara]

Fixes#121036
Fixes#117813
Fixes#118943

Summary

This PR adds a dedicated WASM implementation of the GC's OS abstraction layer
(GCToOSInterface) and updates the GC and PAL to handle the fact that on WASM
there is no virtual memory: pages cannot be reserved without committing,
partial unmaps don't return memory to the engine, and MAP_FIXED / madvise
are not supported.

The previous approach reused gcenv.unix.cpp with #ifdef TARGET_WASM patches
and overloaded use_large_pages_p to mean "decommit is a no-op". This change
splits those concerns:

• A new gc/wasm/gcenv.cpp replaces gc/unix/gcenv.unix.cpp on WASM and
  implements VirtualReserve / VirtualCommit / VirtualDecommit /
  VirtualRelease on top of posix_memalign / free. WASM-specific patches
  in gcenv.unix.cpp are removed.
• A new GC flag never_decommit_p replaces every "is decommit a no-op" check
  that was previously expressed as use_large_pages_p. It is set on WASM
  unconditionally and on other platforms whenever use_large_pages_p is set.
• gc/CMakeLists.txt now selects gc/wasm for WASM targets while still
  including unix/configure.cmake to generate config.gc.h.
• The PAL's virtual.cpp is similarly cleaned up to use posix_memalign /
  free on WASM and to zero memory on MEM_DECOMMIT, so the next
  VirtualCommit (a no-op on WASM) sees zeroed memory.
• A new minipal_getpagesize abstraction is introduced. On WASM it returns a
  compile-time constant of 16 KB (the GC's page granularity, distinct from the
  64 KB memory.grow granularity that getpagesize() reports). On Windows it
  returns the 4 KB constant inline. On other POSIX systems it caches
  getpagesize() once per process. CoreCLR PAL callers are updated to use it.

Why a separate never_decommit_p

On large pages, decommit is a no-op because the OS pre-commits the entire
range. On WASM, decommit is a no-op because there is no way to give linear
memory back to the engine. The two cases share the same set of GC code paths
that must be skipped or modified (decommit_ephemeral_segment_pages,
decommit_step, decommit_region, decommit_heap_segment_pages,
decommit_heap_segment, distribute_free_regions tail-decommit,
reset_memory, virtual_commit, virtual_decommit assert), but they have
nothing else in common. Reusing use_large_pages_p on WASM was misleading and
made it easy to forget large-pages-only behavior (e.g., pre-touch). The new
flag captures only the "decommit is a no-op" semantics; non-WASM behavior is
unchanged because never_decommit_p == use_large_pages_p everywhere except
WASM.

Why minipal_getpagesize

The GC needs the OS page size to be a compile-time constant on WASM (16 KB)
so that alignment math folds. getpagesize() on emscripten returns 64 KB
(the memory.grow granularity), which is too coarse for GC alignment and
thresholds. Centralizing this in minipal lets PAL and GC agree on a single
value and avoids #ifdefs at every call site.

Notes

• VirtualReserveAndCommitLargePages on WASM falls through to the regular
  reserve/commit path; the GC does not request large pages on WASM.
• posix_memalign may return either freshly grown linear memory (zeroed by
  the WASM spec) or a recycled block from emscripten's allocator free list.
  We always memset to zero on reserve and on decommit so callers can rely
  on the standard "memory starts zeroed" contract.
• VirtualReset returns false on WASM, forcing the GC to use the
  decommit+commit fallback (memset to zero) rather than relying on
  madvise, which is a no-op on emscripten.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @dotnet/gc
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR separates WebAssembly-specific GC OS interface behavior from the shared Unix implementation by introducing a dedicated gcenv.wasm.cpp, and adjusts the PAL virtual memory implementation on WASM to avoid relying on Emscripten’s incomplete mmap/munmap support.

Changes:

• Added a dedicated WASM GCToOSInterface implementation (gcenv.wasm.cpp) and CMake wiring for building it.
• Routed WASM GC builds to the new gc/wasm directory and removed WASM-specific #ifdef paths from gcenv.unix.cpp.
• Updated PAL virtual memory reserve/release on WASM to use posix_memalign/free instead of mmap/munmap.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/coreclr/pal/src/map/virtual.cpp	Switches WASM reserve/release behavior to posix_memalign/free and adjusts related error/cleanup paths.
src/coreclr/gc/wasm/gcenv.wasm.cpp	New WASM-specific GC OS interface implementation (virtual memory, CPU/NUMA stubs, memory stats).
src/coreclr/gc/wasm/CMakeLists.txt	Adds build definition for the WASM GC PAL object library.
src/coreclr/gc/unix/gcenv.unix.cpp	Removes WASM-specific branches and fixes nanosleep EINTR retry logic.
src/coreclr/gc/CMakeLists.txt	Routes WASM builds to gc/wasm instead of gc/unix.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated no new comments.

[janvorli]

LGTM, thank you!

[pavelsavara]

/ba-g unrelated CI fail