[llvm] [AArch64] Fix Arm64EC mangling with C++ symbols using MD5 mangling. (PR #160963)
Eli Friedman via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 6 13:26:20 PDT 2025
https://github.com/efriedma-quic updated https://github.com/llvm/llvm-project/pull/160963
>From 2c52aafb42e5d43d96974bd0ec58de4c9b29cab3 Mon Sep 17 00:00:00 2001
From: Eli Friedman <efriedma at quicinc.com>
Date: Fri, 26 Sep 2025 15:36:33 -0700
Subject: [PATCH] [AArch64] Fix Arm64EC mangling with C++ symbols using MD5
mangling.
In addition to the usual mangling formats, MSVC uses a special mangling
format for very long symbols: instead of actually emitting the mangled
name, it hashes the name, and uses the hash as the symbol. This doesn't
match any of the usual forms, so it needs special handling.
Fixes a crash/link error when using such symbols.
(Unrelated to this patch, there's something weird about the way MSVC
handles these symbols in Arm64EC mode: it looks like MSVC isn't
computing a different hash compared to x64 MSVC, and clang. I think
this is bug. Noting this here in case someone wants to compare MSVC vs.
clang output.)
---
llvm/lib/IR/Mangler.cpp | 17 ++++++++
.../CodeGen/AArch64/arm64ec-exit-thunks.ll | 42 +++++++++++++++++++
llvm/unittests/IR/ManglerTest.cpp | 3 ++
3 files changed, 62 insertions(+)
diff --git a/llvm/lib/IR/Mangler.cpp b/llvm/lib/IR/Mangler.cpp
index ca6a4804087ac..55c825d272a2f 100644
--- a/llvm/lib/IR/Mangler.cpp
+++ b/llvm/lib/IR/Mangler.cpp
@@ -307,6 +307,19 @@ std::optional<std::string> llvm::getArm64ECMangledFunctionName(StringRef Name) {
if (Name.contains("$$h"))
return std::nullopt;
+ // Handle MD5 mangled names, which use a slightly different rule from
+ // other C++ manglings.
+ //
+ // A non-Arm64EC function:
+ //
+ // ??@aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@
+ //
+ // An Arm64EC function:
+ //
+ // ??@aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@$$h@
+ if (Name.starts_with("??@") && Name.ends_with("@"))
+ return (Name + "$$h@").str();
+
// Ask the demangler where we should insert "$$h".
auto InsertIdx = getArm64ECInsertionPointInMangledName(Name);
if (!InsertIdx)
@@ -324,6 +337,10 @@ llvm::getArm64ECDemangledFunctionName(StringRef Name) {
if (Name[0] != '?')
return std::nullopt;
+ // MD5 mangled name; see comment in getArm64ECMangledFunctionName.
+ if (Name.starts_with("??@") && Name.ends_with("@$$h@"))
+ return Name.drop_back(4).str();
+
// Drop the ARM64EC "$$h" tag.
std::pair<StringRef, StringRef> Pair = Name.split("$$h");
if (Pair.second.empty())
diff --git a/llvm/test/CodeGen/AArch64/arm64ec-exit-thunks.ll b/llvm/test/CodeGen/AArch64/arm64ec-exit-thunks.ll
index f829227a47cd7..dc352244deeef 100644
--- a/llvm/test/CodeGen/AArch64/arm64ec-exit-thunks.ll
+++ b/llvm/test/CodeGen/AArch64/arm64ec-exit-thunks.ll
@@ -563,6 +563,41 @@ declare <8 x i16> @large_vector(<8 x i16> %0) nounwind;
; CHECK-NEXT: .seh_endfunclet
; CHECK-NEXT: .seh_endproc
+declare void @"??@md5mangleaaaaaaaaaaaaaaaaaaaaaaa@"()
+; CHECK-LABEL: .def "??$exit_thunk at md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@";
+; CHECK-NEXT: .scl 2;
+; CHECK-NEXT: .type 32;
+; CHECK-NEXT: .endef
+; CHECK-NEXT: .section .wowthk$aa,"xr",discard,"??$exit_thunk at md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@"
+; CHECK-NEXT: .globl "??$exit_thunk at md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@" // -- Begin function ??$exit_thunk at md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@
+; CHECK-NEXT: .p2align 2
+; CHECK-NEXT: "??$exit_thunk at md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@": // @"??$exit_thunk at md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@"
+; CHECK-NEXT: .weak_anti_dep "??@md5mangleaaaaaaaaaaaaaaaaaaaaaaa@"
+; CHECK-NEXT: "??@md5mangleaaaaaaaaaaaaaaaaaaaaaaa@" = "??@md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@"
+; CHECK-NEXT: .weak_anti_dep "??@md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@"
+; CHECK-NEXT: "??@md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@" = "??$exit_thunk at md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@"
+; CHECK-NEXT: .seh_proc "??$exit_thunk at md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@"
+; CHECK-NEXT: // %bb.0:
+; CHECK-NEXT: str x30, [sp, #-16]! // 8-byte Folded Spill
+; CHECK-NEXT: .seh_save_reg_x x30, 16
+; CHECK-NEXT: .seh_endprologue
+; CHECK-NEXT: adrp x8, __os_arm64x_check_icall
+; CHECK-NEXT: adrp x11, "??@md5mangleaaaaaaaaaaaaaaaaaaaaaaa@"
+; CHECK-NEXT: add x11, x11, :lo12:"??@md5mangleaaaaaaaaaaaaaaaaaaaaaaa@"
+; CHECK-NEXT: ldr x8, [x8, :lo12:__os_arm64x_check_icall]
+; CHECK-NEXT: adrp x10, $iexit_thunk$cdecl$v$v
+; CHECK-NEXT: add x10, x10, :lo12:$iexit_thunk$cdecl$v$v
+; CHECK-NEXT: blr x8
+; CHECK-NEXT: .seh_startepilogue
+; CHECK-NEXT: ldr x30, [sp], #16 // 8-byte Folded Reload
+; CHECK-NEXT: .seh_save_reg_x x30, 16
+; CHECK-NEXT: .seh_endepilogue
+; CHECK-NEXT: br x11
+; CHECK-NEXT: .seh_endfunclet
+; CHECK-NEXT: .seh_endproc
+
+
+
; CHECK-LABEL: .section .hybmp$x,"yi"
; CHECK-NEXT: .symidx "#func_caller"
; CHECK-NEXT: .symidx $ientry_thunk$cdecl$v$v
@@ -633,6 +668,12 @@ declare <8 x i16> @large_vector(<8 x i16> %0) nounwind;
; CHECK-NEXT: .symidx "#large_vector$exit_thunk"
; CHECK-NEXT: .symidx large_vector
; CHECK-NEXT: .word 0
+; CHECK-NEXT: .symidx "??@md5mangleaaaaaaaaaaaaaaaaaaaaaaa@"
+; CHECK-NEXT: .symidx $iexit_thunk$cdecl$v$v
+; CHECK-NEXT: .word 4
+; CHECK-NEXT: .symidx "??$exit_thunk at md5mangleaaaaaaaaaaaaaaaaaaaaaaa@$$h@"
+; CHECK-NEXT: .symidx "??@md5mangleaaaaaaaaaaaaaaaaaaaaaaa@"
+; CHECK-NEXT: .word 0
define void @func_caller() nounwind {
call void @no_op()
@@ -649,5 +690,6 @@ define void @func_caller() nounwind {
call %T2 @simple_struct(%T1 { i16 0 }, %T2 { i32 0, float 0.0 }, %T3 { i64 0, double 0.0 }, %T4 { i64 0, double 0.0, i8 0 })
call <4 x i8> @small_vector(<4 x i8> <i8 0, i8 0, i8 0, i8 0>)
call <8 x i16> @large_vector(<8 x i16> <i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0>)
+ call void @"??@md5mangleaaaaaaaaaaaaaaaaaaaaaaa@"()
ret void
}
diff --git a/llvm/unittests/IR/ManglerTest.cpp b/llvm/unittests/IR/ManglerTest.cpp
index bced6ff10b45d..bb0b3edd966e8 100644
--- a/llvm/unittests/IR/ManglerTest.cpp
+++ b/llvm/unittests/IR/ManglerTest.cpp
@@ -243,6 +243,9 @@ TEST(ManglerTest, Arm64EC) {
// public: int __cdecl Wrapper<struct A>::GetValue(struct WW<struct
// A>::Z)const
"?GetValue@?$Wrapper at UA@@@@$$hQEBAHUZ@?$WW at UA@@@@@Z",
+
+ // MD5 symbol
+ "??@aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@$$h@",
};
for (const auto &Arm64ECName : Arm64ECNames) {
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