[AArch64] Restrict .variant_pcs directive to ELF targets

[MacDue]

Directive was implemented in c87bd2d to support lazy binding and is emitted for vector PCS functions. It's specific to ELF but is currently emitted for all binary formats and crashing on non-ELF targets.

Fixes #138260

Co-authored-by: Cullen Rhodes cullen.rhodes@arm.com

[llvmbot]

@llvm/pr-subscribers-backend-aarch64

Author: Benjamin Maxwell (MacDue)

Changes

This was causing crashes on Mach-O targets as we don't construct a TargetStreamer for that object format. Other uses of the TargetStreamer (TS) appear to be limited to ELF and COFF platforms (where it is none null, so don't need changing).

---

Full diff: https://github.com/llvm/llvm-project/pull/138924.diff

2 Files Affected:

• (modified) llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp (+2-1)
• (modified) llvm/test/CodeGen/AArch64/variant-pcs.ll (+3)

diff --git a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
index 870df4c387ca4..1166a78bf1088 100644
--- a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
+++ b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
@@ -1372,7 +1372,8 @@ void AArch64AsmPrinter::emitFunctionEntryLabel() {
       MF->getInfo<AArch64FunctionInfo>()->isSVECC()) {
     auto *TS =
         static_cast<AArch64TargetStreamer *>(OutStreamer->getTargetStreamer());
-    TS->emitDirectiveVariantPCS(CurrentFnSym);
+    if (TS)
+      TS->emitDirectiveVariantPCS(CurrentFnSym);
   }
 
   AsmPrinter::emitFunctionEntryLabel();
diff --git a/llvm/test/CodeGen/AArch64/variant-pcs.ll b/llvm/test/CodeGen/AArch64/variant-pcs.ll
index 49c504177358e..0c995b5b0e8ef 100644
--- a/llvm/test/CodeGen/AArch64/variant-pcs.ll
+++ b/llvm/test/CodeGen/AArch64/variant-pcs.ll
@@ -2,6 +2,9 @@
 ; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sve -filetype=obj -o - %s \
 ; RUN:   | llvm-readobj --symbols - | FileCheck %s --check-prefix=CHECK-OBJ
 
+; Check we don't crash when using a Mach-O object format.
+; RUN: llc -mtriple=arm64-apple-macosx15.0.0 -mattr=+sve -filetype=obj -o /dev/null %s
+
 define i32 @base_pcs() {
 ; CHECK-ASM-LABEL: base_pcs:
 ; CHECK-ASM-NOT: .variant_pcs

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[sdesmalen-arm]

Looking at this again, I think we should only emit the variant PCS attribute when the target's triple is ELF (TM.getTargetTriple().isOSBinFormatELF()) because this is specifically an ELF attribute. This means you can remove this condition, because for ELF targets it should never return a nullptr.

[gbossu]

Curious: Why is it that the Mach-O format does not get a TargetStreamer? Does it really need no target-specific support?

[MacDue]

Curious: Why is it that the Mach-O format does not get a TargetStreamer? Does it really need no target-specific support?

Presumably not, there's currently only ELF and Windows COFF TargetStreamers. The ELF one does not add much (seems like mainly a few attributes) and the Windows one seems to only handle various unwinding instructions. I guess Mach-O handles these differently (though I don't know the details here).