release/18.x: [Codegen][X86] Fix /HOTPATCH with clang-cl and inline asm (#87639) #88388
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@aganea What do you think about merging this PR to the release branch? |
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@llvm/pr-subscribers-backend-x86 Author: None (llvmbot) ChangesBackport ec1af63 Requested by: @aganea Full diff: https://github.com/llvm/llvm-project/pull/88388.diff 2 Files Affected:
diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 58ebe023cd61ec..7ce0aa22b99795 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -959,8 +959,10 @@ void X86AsmPrinter::LowerPATCHABLE_OP(const MachineInstr &MI,
SmallString<256> Code;
unsigned MinSize = MI.getOperand(0).getImm();
- if (NextMI != MI.getParent()->end()) {
+ if (NextMI != MI.getParent()->end() && !NextMI->isInlineAsm()) {
// Lower the next MachineInstr to find its byte size.
+ // If the next instruction is inline assembly, we skip lowering it for now,
+ // and assume we should always generate NOPs.
MCInst MCI;
MCIL.Lower(&*NextMI, MCI);
diff --git a/llvm/test/CodeGen/X86/patchable-prologue.ll b/llvm/test/CodeGen/X86/patchable-prologue.ll
index 71a392845fdea3..43761e3d1e1eb9 100644
--- a/llvm/test/CodeGen/X86/patchable-prologue.ll
+++ b/llvm/test/CodeGen/X86/patchable-prologue.ll
@@ -193,3 +193,20 @@ do.body: ; preds = %do.body, %entry
do.end: ; preds = %do.body
ret void
}
+
+
+; Test that inline asm is properly hotpatched. We currently don't examine the
+; asm instruction when printing it, thus we always emit patching NOPs.
+
+; 64: inline_asm:
+; 64-NEXT: # %bb.0:
+; 64-NEXT: xchgw %ax, %ax # encoding: [0x66,0x90]
+; 64-NEXT: #APP
+; 64-NEXT: int3 # encoding: [0xcc]
+; 64-NEXT: #NO_APP
+
+define dso_local void @inline_asm() "patchable-function"="prologue-short-redirect" {
+entry:
+ call void asm sideeffect "int3", "~{dirflag},~{fpsr},~{flags}"()
+ ret void
+}
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aganea
approved these changes
Apr 11, 2024
There was a problem hiding this comment.
It think this should be good to go, but ideally I'd like someone else to sign off please. @phoebewang @KanRobert @sylvain-audi
I think it's safe and good to go too. |
This fixes an edge case where functions starting with inline assembly would assert while trying to lower that inline asm instruction. After this PR, for now we always add a no-op (xchgw in this case) without considering the size of the next inline asm instruction. We might want to revisit this in the future. This fixes Unreal Engine 5.3.2 compilation with clang-cl and /HOTPATCH. Should close llvm#56234 (cherry picked from commit ec1af63)
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Hi @aganea (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. |
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Backport ec1af63
Requested by: @aganea