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GH-115802: Remove no-plt for Linux AArch64 by diegorusso · Pull Request #148238 · python/cpython · GitHub
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GH-115802: Remove no-plt for Linux AArch64#148238

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diegorusso merged 3 commits into
python:mainfrom
diegorusso:drop-no-plt
Apr 8, 2026
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GH-115802: Remove no-plt for Linux AArch64#148238
diegorusso merged 3 commits into
python:mainfrom
diegorusso:drop-no-plt

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diegorusso commented Apr 8, 2026 •
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Removing -fno-plt makes Linux stencils use more direct call relocations and fewer GOT-indirect call sequences. On AArch64 it means CALL26 instead of adrp/ldr/blr GOT calls

This improves code size and some complexity of the JIT stencils. It reduces the amount of GOT-specific patching the JIT has to do.

bedevere-app Bot mentioned this pull request Apr 8, 2026
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diegorusso changed the title GH-115802: Remove no-plt for Linux targets GH-115802: Remove no-plt for Linux AArch64 Apr 8, 2026

diegorusso commented Apr 8, 2026 •
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I had to revert the x86-64 changes as they are more involved and require more investigation. I'm going to create a new issue for changing x86-64 Linux target: #148256

diegorusso mentioned this pull request Apr 8, 2026
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Fidget-Spinner commented Apr 8, 2026

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Do you have any numbers for this?

diegorusso commented Apr 8, 2026 •
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Do you have any numbers for this?

Relocation Before (-fno-plt) After (default) Delta
R_AARCH64_CALL26 0 368 +368
R_AARCH64_JUMP26 269 269 0
R_AARCH64_ADR_GOT_PAGE 831 461 -370
R_AARCH64_LD64_GOT_LO12_NC 829 461 -368

Before all the calls were done via GOT, now only 55% are done via the GOT and the rest using a direct bl

Hide details View details diegorusso merged commit e11315d into python:main Apr 8, 2026
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diegorusso deleted the drop-no-plt branch April 8, 2026 15:34

brandtbucher commented Apr 8, 2026

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Sorry, didn’t have a chance to look at this yet. What happens if the jump is outside the 26 bit range? The trampolines get used? Were the trampolines being used at all before?

diegorusso commented Apr 8, 2026

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Sorry, didn’t have a chance to look at this yet. What happens if the jump is outside the 26 bit range? The trampolines get used? Were the trampolines being used at all before?

Earlier no trampolines were used at all. Now if a jump is out of range, the trampoline is generated.

ljfp pushed a commit to ljfp/cpython that referenced this pull request Apr 25, 2026
pythonGH-115802: Remove no-plt for Linux AArch64 (python#148238)
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Fidget-Spinner Fidget-Spinner approved these changes
markshannon Awaiting requested review from markshannon
brandtbucher Awaiting requested review from brandtbucher brandtbucher is a code owner
savannahostrowski Awaiting requested review from savannahostrowski savannahostrowski is a code owner

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