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GeezerVison is showing github.com — GH-115802: Remove no-plt for Linux AArch64 by diegorusso · Pull Request #148238 · python/cpython

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@diegorusso

@diegorusso 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.

  • Issue: Improving JIT code quality #115802

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@diegorusso
pythonGH-115802: Remove no-plt for Linux targets
ba32120
@diegorusso
diegorusso requested review from Fidget-Spinner and markshannon April 8, 2026 06:55
@diegorusso
diegorusso requested review from brandtbucher and savannahostrowski as code owners April 8, 2026 06:56
@bedevere-app bedevere-app Bot added the awaiting core review label Apr 8, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Apr 8, 2026
Improving JIT code quality #115802
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8 of 13 tasks
blurb-it Bot and others added 2 commits April 8, 2026 06:59
@blurb-it
📜🤖 Added by blurb_it.
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@diegorusso
Revert changes for Linux x86-64
6714906
@diegorusso diegorusso changed the title GH-115802: Remove no-plt for Linux targets GH-115802: Remove no-plt for Linux AArch64 Apr 8, 2026
@diegorusso

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
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@diegorusso diegorusso mentioned this pull request Apr 8, 2026
JIT: drop -fno-plt on Linux x86-64 #148256
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@Fidget-Spinner

Fidget-Spinner commented Apr 8, 2026

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Do you have any numbers for this?
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@diegorusso

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
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Fidget-Spinner
Fidget-Spinner approved these changes Apr 8, 2026
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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting core review labels Apr 8, 2026
@diegorusso
diegorusso merged commit e11315d into python:main Apr 8, 2026
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@bedevere-app bedevere-app Bot removed the awaiting merge label Apr 8, 2026
@diegorusso
diegorusso deleted the drop-no-plt branch April 8, 2026 15:34
@brandtbucher

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?
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@diegorusso

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.
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ljfp pushed a commit to ljfp/cpython that referenced this pull request Apr 25, 2026
@diegorusso @ljfp
pythonGH-115802: Remove no-plt for Linux AArch64 (python#148238)
05b7318
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Reviewers

@Fidget-Spinner Fidget-Spinner Fidget-Spinner approved these changes
@markshannon markshannon Awaiting requested review from markshannon
@brandtbucher brandtbucher Awaiting requested review from brandtbucher brandtbucher is a code owner
@savannahostrowski savannahostrowski Awaiting requested review from savannahostrowski

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3 participants

@diegorusso @Fidget-Spinner @brandtbucher
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