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rustllvm: Use .init_array rather than .ctors - #71234

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May 9, 2020
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rustllvm: Use .init_array rather than .ctors#71234
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@maurer

@maurermaurer commented Apr 17, 2020

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LLVM TargetMachines default to using the (now-legacy) .ctors
representation of init functions. Mixing .ctors and .init_array
representations can cause issues when linking with lld.

This happens in practice for:

  • Our profiling runtime which is currently implicitly built with
    .init_array since it is built by clang, which sets this field.
  • External C/C++ code that may be linked into the same process.

Fixes: #71233

@rust-highfive

rust-highfive commented Apr 17, 2020

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r? @cuviper

(rust_highfive has picked a reviewer for you, use r? to override)

@rust-highfiverust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Apr 17, 2020
@cuviper

cuviper commented Apr 17, 2020

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We've been talking about compatibility on #71233 -- let's get a real CI build that I can actually test on an old x86_64-unknown-linux-gnu system, at least.

@bors try

You also mentioned the possibility of a Target option for this. I think we probably do want that, as well as a -Z option for manual control, similar to -Zplt, -Zrelro-level, etc. We can default to .init_array if compatibility is broad enough, but still have a way to fall back, just like Clang 10 is still offering -fno-use-init-array.

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bors commented Apr 17, 2020

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⌛ Trying commit 1d84563f375a5977ffa8eb640aa80a84959b4bf1 with merge b87bd037d8b09eee9115142adb1d61112cb4865c...

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bors commented Apr 17, 2020

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⌛ Trying commit 1d84563f375a5977ffa8eb640aa80a84959b4bf1 with merge ab42f00561856008c3af29d224b26c802e4563d2...

@cuviper

cuviper commented Apr 17, 2020

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Sorry about that -- I didn't see bors responding, and now I got it twice... oh well.

@Dylan-DPC-zz

Dylan-DPC-zz commented Apr 17, 2020

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@bors try

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bors commented Apr 17, 2020

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⌛ Trying commit 1d84563f375a5977ffa8eb640aa80a84959b4bf1 with merge 04ec1be6a7a65dd0304d2b35993ae7daf7abbc13...

@maurer

maurer commented Apr 17, 2020

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I added in -Z use-ctors and a TargetOptions field to govern .ctors use as requested, defaulting to .init_array usage.

@petrochenkovpetrochenkov self-assigned this Apr 18, 2020
petrochenkov
petrochenkov reviewed Apr 18, 2020
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Comment threadsrc/librustc_session/options.rs Outdated
Comment threadsrc/librustc_codegen_llvm/back/write.rs Outdated
@petrochenkovpetrochenkov added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 18, 2020
@maurer

maurer commented Apr 19, 2020

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I've made the requested changes.

@petrochenkovpetrochenkov removed their assignment Apr 19, 2020
@petrochenkovpetrochenkov added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 19, 2020
@bors

bors commented Apr 22, 2020

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☔ The latest upstream changes (presumably #71374) made this pull request unmergeable. Please resolve the merge conflicts.

@nnethercote

nnethercote commented Apr 23, 2020

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When you rebase over #71374 please make sure you preserve the new alphabetical order. Also, it looks like you haven't updated the tests, please see the new comment at the top of DebuggingOptions.

@maurer

maurer commented Apr 29, 2020

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I've rebased the patch and added the test entry nnethercote asked for.

cuviper
cuviper reviewed Apr 29, 2020
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Comment threadsrc/librustc_target/spec/mod.rs Outdated
@maurer
Use .init_array rather than .ctors
0e7d5be
LLVM TargetMachines default to using the (now-legacy) .ctors
representation of init functions. Mixing .ctors and .init_array
representations can cause issues when linking with lld.
This happens in practice for:
* Our profiling runtime which is currently implicitly built with
.init_array since it is built by clang, which sets this field.
* External C/C++ code that may be linked into the same process.
To support legacy systems which may use .ctors, targets may now specify
that they use .ctors via the use_ctors attribute which defaults to
false.
For debugging and manual control, -Z use-ctors-section=yes/no will allow
manual override.
Fixes: rust-lang#71233
@cuviper

cuviper commented May 5, 2020

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The patch looks OK, but I'd like a second opinion on making this change -- maybe @joshtriplett?

@joshtriplett

joshtriplett commented May 7, 2020

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This seems reasonable to me; we should certainly use .init_array. However, lld really does need to handle the mix of .ctors and .init_array; that's not a Rust-specific issue.

@cuviper

cuviper commented May 9, 2020

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@bors r+

@bors

bors commented May 9, 2020

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📌 Commit 0e7d5be has been approved by cuviper

@borsbors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 9, 2020
@RalfJungRalfJung mentioned this pull request May 9, 2020
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bors added a commit to rust-lang-ci/rust that referenced this pull request May 9, 2020
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Auto merge ofrust-lang#72041- RalfJung:rollup-xivrvy2, r=RalfJung
bad3bf6
Rollup of 5 pull requests
Successful merges:
- rust-lang#69406 (upgrade chalk and use chalk-solve/chalk-ir/chalk-rust-ir)
- rust-lang#71185 (Move tests from `test/run-fail` to UI)
- rust-lang#71234 (rustllvm: Use .init_array rather than .ctors)
- rust-lang#71508 (Simplify the `tcx.alloc_map` API)
- rust-lang#71555 (Remove ast::{Ident, Name} reexports.)
Failed merges:
r? @ghost
@bors
bors merged commit ce05553 into rust-lang:masterMay 9, 2020
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