[LLD][COFF] Generate redirection metadata for custom ARM64EC export thunks.

lld/COFF/Writer.cpp

@@ -2062,6 +2062,24 @@ void Writer::createECChunks() {
     if (auto thunk = dyn_cast<ECExportThunkChunk>(sym->getChunk())) {
       hexpthkSec->addChunk(thunk);
       exportThunks.push_back({thunk, thunk->target});
+    } else if (auto def = dyn_cast<DefinedRegular>(sym)) {
+      // Allow section chunk to be treated as an export thunk if it looks like
+      // one.
+      SectionChunk *chunk = def->getChunk();
+      if (!chunk->live || chunk->getMachine() != AMD64)
+        continue;
+      assert(sym->getName().starts_with("EXP+"));
+      StringRef targetName = sym->getName().substr(strlen("EXP+"));
+      // If EXP+#foo is an export thunk of a hybrid patchable function,
+      // we should use the #foo$hp_target symbol as the redirection target.
+      // First, try to look up the $hp_target symbol. If it can't be found,
+      // assume it's a regular function and look for #foo instead.
+      Symbol *targetSym = ctx.symtab.find((targetName + "$hp_target").str());
+      if (!targetSym)
+        targetSym = ctx.symtab.find(targetName);
+      Defined *t = dyn_cast_or_null<Defined>(targetSym);
+      if (t && isArm64EC(t->getChunk()->getMachine()))
+        exportThunks.push_back({chunk, t});
     }
   }
 

lld/test/COFF/arm64ec-cust-export-thunk.s

@@ -0,0 +1,82 @@
+# REQUIRES: aarch64, x86
+# RUN: split-file %s %t.dir && cd %t.dir
+
+# Test that metadata is generated when a custom export thunk is supplied.
+
+# RUN: llvm-mc -filetype=obj -triple=arm64ec-windows func.s -o func.obj
+# RUN: llvm-mc -filetype=obj -triple=arm64ec-windows hp-func.s -o hp-func.obj
+# RUN: llvm-mc -filetype=obj -triple=x86_64-windows thunk.s -o thunk.obj
+# RUN: llvm-mc -filetype=obj -triple=arm64ec-windows %S/Inputs/loadconfig-arm64ec.s -o loadconfig-arm64ec.obj
+
+# RUN: lld-link -out:out.dll -machine:arm64ec func.obj thunk.obj loadconfig-arm64ec.obj -dll -noentry "-export:#func,EXPORTAS,func"
+
+# RUN: llvm-objdump -d out.dll | FileCheck --check-prefixes=DISASM,DISASM-EXP %s
+# DISASM:      Disassembly of section .text:
+# DISASM-EMPTY:
+# DISASM-NEXT: 0000000180001000 <.text>:
+# DISASM-NEXT: 180001000: 52800040     mov     w0, #0x2                // =2
+# DISASM-NEXT: 180001004: d65f03c0     ret
+# DISASM-NEXT:                 ...
+# DISASM-EXP-EMPTY:
+# DISASM-EXP-NEXT: 0000000180002000 <func>:
+# DISASM-NEXT: 180002000: b8 03 00 00 00               movl    $0x3, %eax
+# DISASM-NEXT: 180002005: c3                           retq
+
+# RUN: llvm-objdump -p out.dll | FileCheck --check-prefix=EXPORT %s
+# EXPORT:      Ordinal      RVA  Name
+# EXPORT-NEXT:       1   0x2000  func
+
+# RUN: llvm-readobj --coff-load-config out.dll | FileCheck --check-prefix=CHPE %s
+# CHPE:       CodeMap [
+# CHPE-NEXT:    0x1000 - 0x1008  ARM64EC
+# CHPE-NEXT:    0x2000 - 0x2006  X64
+# CHPE-NEXT:  ]
+# CHPE-NEXT:  CodeRangesToEntryPoints [
+# CHPE-NEXT:    0x2000 - 0x2006 -> 0x2000
+# CHPE-NEXT:  ]
+# CHPE-NEXT:  RedirectionMetadata [
+# CHPE-NEXT:    0x2000 -> 0x1000
+# CHPE-NEXT:  ]
+
+# RUN: lld-link -out:out2.dll -machine:arm64ec hp-func.obj thunk.obj loadconfig-arm64ec.obj -dll -noentry
+# RUN: llvm-objdump -d out2.dll | FileCheck --check-prefix=DISASM %s
+# RUN: llvm-readobj --coff-load-config out2.dll | FileCheck --check-prefix=CHPE %s
+
+#--- func.s
+    .globl "#func"
+    .p2align 2, 0x0
+"#func":
+    mov w0, #2
+    ret
+
+#--- hp-func.s
+    .section .text,"xr",discard,"#func$hp_target"
+    .globl "#func$hp_target"
+    .p2align 2, 0x0
+"#func$hp_target":
+    mov w0, #2
+    ret
+
+    .def "EXP+#func"
+    .scl 2
+    .type 32
+    .endef
+    .weak func
+.set func, "EXP+#func"
+    .weak "#func"
+.set "#func", "#func$hp_target"
+
+    .data
+    .rva func
+
+#--- thunk.s
+    .def "EXP+#func"
+    .scl 2
+    .type 32
+    .endef
+    .section .wowthk$aa,"xr",discard,"EXP+#func"
+    .globl "EXP+#func"
+    .p2align 2, 0x0
+"EXP+#func":
+    movl $3, %eax
+    retq