[all-commits] [llvm/llvm-project] 976a04: [SystemZ][z/OS] Keep weak references weak (#226840)

[MMS IT GmbH via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 976a04b549b3e91e51eb7676d86caa8c34a63571
      https://github.com/llvm/llvm-project/commit/976a04b549b3e91e51eb7676d86caa8c34a63571
  Author: MMS IT GmbH <info at mms-it.ch>
  Date:   2026-09-29 (Tue, 29 Sep 2026)

  Changed paths:
    M llvm/include/llvm/MC/MCGOFFAttributes.h
    M llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
    M llvm/lib/MC/GOFFObjectWriter.cpp
    M llvm/lib/MC/MCObjectFileInfo.cpp
    M llvm/lib/MC/MCSymbolGOFF.cpp
    M llvm/lib/Target/SystemZ/SystemZXPLINKAsmPrinter.cpp
    A llvm/test/CodeGen/SystemZ/zos-extern-weak.ll

  Log Message:
  -----------
  [SystemZ][z/OS] Keep weak references weak (#226840)

Fixes #226835.

An `extern_weak` reference must stay unresolved without an error when
the symbol does not exist. On z/OS two kinds of references were always
strong:

- Taking the address of an external function goes through the indirect
symbol `<name>@indirect` (ADA slot `MO_ADA_INDIRECT_FUNC_DESC`). It
never got the weak attribute of the function symbol. The weak attribute
is already set on the function symbol when the ADA is emitted, because
`AsmPrinter::doFinalization` emits the weak references before
`emitEndOfAsmFile`. So the indirect symbol now becomes a weak reference
too.
- An external data reference is a part reference (PR). `GOFF::PRAttr`
had no binding strength, and the PR constructor in `GOFFObjectWriter`
did not set it. `PRAttr` gets a `BindingStrength` field, and
`defineExtern` passes the strength of the symbol.

Without this change, a C program with `extern int wv
__attribute__((weak));` and `extern void wf(void)
__attribute__((weak));` that takes `&wv` and `wf` fails to bind on z/OS
3.1 (IEW2456E for `wv` and `wf`). With the change it binds, and at run
time both addresses are null, as on other targets.

Tests: new `zos-extern-weak.ll` checks `WXTRN wf at indirect` in the HLASM
output and the binding strength of the ER and PR symbols in the object
file. `llvm-lit test/CodeGen/SystemZ test/MC/SystemZ test/MC/GOFF`
passes (1304 passed, 19 unsupported). Without the fix, both checks of
the new test fail.

Found while porting Free Pascal to z/OS (`weakexternal`).

Assisted-by: Claude Code (Anthropic)

🤖 Generated with [Claude Code](https://claude.com/claude-code)



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