[CodeGen][ARM64EC] Define hybrid_patchable EXP thunk symbol as a function.

[cjacek]

This is needed for MSVC link.exe to generate redirection metadata for hybrid patchable thunks.

I noticed this while working on LLD support for this. Redirection metadata is a part of CHPE metadata generated by the linker. It's undocumented, but I briefly documented my findings here. Its logic seems to be separate from generating thunks themselves in the linker. While for export thunks any unresolved EXP+... symbol is sufficient, redirection metadata logic is more strict and, according to my experiments, function symbol type is important and enough to make it work.

There is a different logic for exported symbols, those already work fine with hybrid patchable functions, but for a different reason. I think that in practice that metadata is not actually needed for functions that are not exported. Call checkers don't need it, it's probably mostly used for auxiliary IAT handling. If that's right, then this fix won't change much in practice. But since it's undocumented, I can't be sure so I think it's better to just get it right and make sure that generated metadata matches what would be seen with MSVC.

[llvmbot]

@llvm/pr-subscribers-backend-aarch64

Author: Jacek Caban (cjacek)

Changes

This is needed for MSVC link.exe to generate redirection metadata for hybrid patchable thunks.

I noticed this while working on LLD support for this. Redirection metadata is a part of CHPE metadata generated by the linker. It's undocumented, but I briefly documented my findings here. Its logic seems to be separate from generating thunks themselves in the linker. While for export thunks any unresolved EXP+... symbol is sufficient, redirection metadata logic is more strict and, according to my experiments, function symbol type is important and enough to make it work.

There is a different logic for exported symbols, those already work fine with hybrid patchable functions, but for a different reason. I think that in practice that metadata is not actually needed for functions that are not exported. Call checkers don't need it, it's probably mostly used for auxiliary IAT handling. If that's right, then this fix won't change much in practice. But since it's undocumented, I can't be sure so I think it's better to just get it right and make sure that generated metadata matches what would be seen with MSVC.

---

Full diff: https://github.com/llvm/llvm-project/pull/102898.diff

2 Files Affected:

• (modified) llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp (+7)
• (modified) llvm/test/CodeGen/AArch64/arm64ec-hybrid-patchable.ll (+20-4)

diff --git a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
index 0391d518324315..b8f9b58a216446 100644
--- a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
+++ b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
@@ -1310,6 +1310,13 @@ void AArch64AsmPrinter::emitGlobalAlias(const Module &M,
       StringRef ExpStr = cast<MDString>(Node->getOperand(0))->getString();
       MCSymbol *ExpSym = MMI->getContext().getOrCreateSymbol(ExpStr);
       MCSymbol *Sym = MMI->getContext().getOrCreateSymbol(GA.getName());
+
+      OutStreamer->beginCOFFSymbolDef(ExpSym);
+      OutStreamer->emitCOFFSymbolStorageClass(COFF::IMAGE_SYM_CLASS_EXTERNAL);
+      OutStreamer->emitCOFFSymbolType(COFF::IMAGE_SYM_DTYPE_FUNCTION
+                                      << COFF::SCT_COMPLEX_TYPE_SHIFT);
+      OutStreamer->endCOFFSymbolDef();
+
       OutStreamer->beginCOFFSymbolDef(Sym);
       OutStreamer->emitCOFFSymbolStorageClass(COFF::IMAGE_SYM_CLASS_EXTERNAL);
       OutStreamer->emitCOFFSymbolType(COFF::IMAGE_SYM_DTYPE_FUNCTION
diff --git a/llvm/test/CodeGen/AArch64/arm64ec-hybrid-patchable.ll b/llvm/test/CodeGen/AArch64/arm64ec-hybrid-patchable.ll
index 64fb5b36b2c623..1ed6a273338abb 100644
--- a/llvm/test/CodeGen/AArch64/arm64ec-hybrid-patchable.ll
+++ b/llvm/test/CodeGen/AArch64/arm64ec-hybrid-patchable.ll
@@ -240,6 +240,10 @@ define dso_local void @caller() nounwind {
 ; CHECK-NEXT:      .section        .drectve,"yni"
 ; CHECK-NEXT:      .ascii  " /EXPORT:exp"
 
+; CHECK-NEXT:      .def    "EXP+#func";
+; CHECK-NEXT:      .scl    2;
+; CHECK-NEXT:      .type   32;
+; CHECK-NEXT:      .endef
 ; CHECK-NEXT:      .def    func;
 ; CHECK-NEXT:      .scl    2;
 ; CHECK-NEXT:      .type   32;
@@ -252,6 +256,10 @@ define dso_local void @caller() nounwind {
 ; CHECK-NEXT:      .type   32;
 ; CHECK-NEXT:      .endef
 ; CHECK-NEXT:  .set "#func", "#func$hybpatch_thunk"{{$}}
+; CHECK-NEXT:      .def    "EXP+#has_varargs";
+; CHECK-NEXT:      .scl    2;
+; CHECK-NEXT:      .type   32;
+; CHECK-NEXT:      .endef
 ; CHECK-NEXT:      .def    has_varargs;
 ; CHECK-NEXT:      .scl    2;
 ; CHECK-NEXT:      .type   32;
@@ -264,6 +272,10 @@ define dso_local void @caller() nounwind {
 ; CHECK-NEXT:      .type   32;
 ; CHECK-NEXT:      .endef
 ; CHECK-NEXT:  .set "#has_varargs", "#has_varargs$hybpatch_thunk"
+; CHECK-NEXT:      .def    "EXP+#has_sret";
+; CHECK-NEXT:      .scl    2;
+; CHECK-NEXT:      .type   32;
+; CHECK-NEXT:      .endef
 ; CHECK-NEXT:      .def    has_sret;
 ; CHECK-NEXT:      .scl    2;
 ; CHECK-NEXT:      .type   32;
@@ -276,6 +288,10 @@ define dso_local void @caller() nounwind {
 ; CHECK-NEXT:      .type   32;
 ; CHECK-NEXT:      .endef
 ; CHECK-NEXT:  .set "#has_sret", "#has_sret$hybpatch_thunk"
+; CHECK-NEXT:      .def    "EXP+#exp";
+; CHECK-NEXT:      .scl    2;
+; CHECK-NEXT:      .type   32;
+; CHECK-NEXT:      .endef
 ; CHECK-NEXT:      .def    exp;
 ; CHECK-NEXT:      .scl    2;
 ; CHECK-NEXT:      .type   32;
@@ -295,18 +311,18 @@ define dso_local void @caller() nounwind {
 ; SYM:      [78](sec 20)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 #exp$hybpatch_thunk
 ; SYM:      [110](sec  0)(fl 0x00)(ty   0)(scl  69) (nx 1) 0x00000000 func
 ; SYM-NEXT: AUX indx 112 srch 3
-; SYM-NEXT: [112](sec  0)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000 EXP+#func
+; SYM-NEXT: [112](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 EXP+#func
 ; SYM:      [116](sec  0)(fl 0x00)(ty   0)(scl  69) (nx 1) 0x00000000 #func
 ; SYM-NEXT: AUX indx 53 srch 3
 ; SYM:      [122](sec  0)(fl 0x00)(ty   0)(scl  69) (nx 1) 0x00000000 has_varargs
 ; SYM-NEXT: AUX indx 124 srch 3
-; SYM-NEXT: [124](sec  0)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000 EXP+#has_varargs
+; SYM-NEXT: [124](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 EXP+#has_varargs
 ; SYM-NEXT: [125](sec  0)(fl 0x00)(ty   0)(scl  69) (nx 1) 0x00000000 has_sret
 ; SYM-NEXT: AUX indx 127 srch 3
-; SYM-NEXT: [127](sec  0)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000 EXP+#has_sret
+; SYM-NEXT: [127](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 EXP+#has_sret
 ; SYM-NEXT: [128](sec  0)(fl 0x00)(ty   0)(scl  69) (nx 1) 0x00000000 exp
 ; SYM-NEXT: AUX indx 130 srch 3
-; SYM-NEXT: [130](sec  0)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000 EXP+#exp
+; SYM-NEXT: [130](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 EXP+#exp
 ; SYM-NEXT: [131](sec  0)(fl 0x00)(ty   0)(scl  69) (nx 1) 0x00000000 #has_varargs
 ; SYM-NEXT: AUX indx 58 srch 3
 ; SYM-NEXT: [133](sec  0)(fl 0x00)(ty   0)(scl  69) (nx 1) 0x00000000 #has_sret

[efriedma-quic]

LGTM

[cjacek]

/cherry-pick d550ada

[llvmbot]

/pull-request #103048