gh-149202: Don't use -fno-omit-frame-pointer on ppc64le

[vstinner]

The power ABI specification requires that compilers maintain a back chain by default, so unwinding already works without a dedicated frame pointer. Don't use -fno-omit-frame-pointer on ppc64le.

• Issue: Implement PEP 831 – Frame Pointers Everywhere: Enabling System-Level Observability for Python #149202

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Documentation build overview

📚 cpython-previews | 🛠️ Build #32580775 | 📁 Comparing ea140bb against main (612140e)

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1 file changed

±using/configure.html

[vstinner]

This PR implements @stratakis' suggestions: #149409 (comment). Extract:

Adding however -fno-omit-frame-pointer forces the compiler to reserve r31 for it adding extra overhead with no benefits.

cc @stratakis@encukou@pablogsal@Fidget-Spinner@savannahostrowski

[vstinner]

I tested this change manually on Linux ppc64le:

• ./configure (gcc -O3): OPT=-DNDEBUG -g -O3 -Wall in Makefile
• ./configure --with-pydebug (gcc -Og): OPT=-g -Og -Wall in Makefile

test_frame_pointer_unwind pass successfully.

[pablogsal]

Thanks Victor!

[vstinner]

!buildbot PPC64LE

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🤖 New build scheduled with the buildbot fleet by @vstinner for commit ea140bb 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F149485%2Fmerge

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• PPC64LE Fedora Rawhide Clang Installed PR
• PPC64LE Fedora Stable Refleaks PR
• PPC64LE Fedora Rawhide LTO PR
• PPC64LE Fedora Stable PR
• PPC64LE Fedora Stable LTO + PGO PR
• PPC64LE CentOS9 LTO + PGO PR
• PPC64LE Fedora Stable LTO PR
• PPC64LE Fedora Rawhide NoGIL PR
• PPC64LE Fedora Rawhide Refleaks PR
• PPC64LE Fedora Stable Clang Installed PR
• PPC64LE Fedora Rawhide LTO + PGO PR
• PPC64LE CentOS9 PR
• PPC64LE RHEL8 LTO PR
• PPC64LE RHEL8 PR
• PPC64LE CentOS9 Refleaks PR