[lld-macho] Fix invalid DWARF with --icf=safe_thunks

lld/MachO/SyntheticSections.cpp

@@ -1229,6 +1229,16 @@ void SymtabSection::emitStabs() {
       if (defined->isAbsolute())
         continue;
 
+      // Never generate a STABS entry for a symbol that has been ICF'ed using a
+      // thunk, just as we do for fully ICF'ed functions. Otherwise, we end up
+      // generating invalid DWARF as dsymutil will assume the entire function
+      // body is at that location, when, in reality, only the thunk is
+      // present. This will end up causing overlapping DWARF entries.
+      // TODO: Find an implementation that works in combination with
+      // `--keep-icf-stabs`.
+      if (defined->identicalCodeFoldingKind == Symbol::ICFFoldKind::Thunk)
+        continue;
+
       // Constant-folded symbols go in the executable's symbol table, but don't
       // get a stabs entry unless --keep-icf-stabs flag is specified
       if (!config->keepICFStabs &&

lld/test/MachO/icf-safe-thunks-dwarf.ll

@@ -0,0 +1,115 @@
+; REQUIRES: aarch64
+
+;;; Build the
+; RUN: rm -rf %t; mkdir %t
+; RUN: llc -filetype=obj %s -O3 -o %t/icf-obj-safe-thunks-dwarf.o -enable-machine-outliner=never -mtriple arm64-apple-macos -addrsig
+; RUN: %lld -arch arm64 -lSystem --icf=safe_thunks -dylib -o %t/icf-safe-dwarf.dylib %t/icf-obj-safe-thunks-dwarf.o
+
+;;; Check that we generate valid dSYM
+; RUN: dsymutil %t/icf-safe-dwarf.dylib -o %t/icf-safe.dSYM
+; RUN: llvm-dwarfdump --verify %t/icf-safe.dSYM | FileCheck %s --check-prefix=VERIFY-DSYM
+; VERIFY-DSYM: No errors.
+
+;;; Check that we don't generate STABS entries (N_FUN) for ICF'ed function thunks
+; RUN: dsymutil -s %t/icf-safe-dwarf.dylib | FileCheck %s --check-prefix=VERIFY-STABS
+; VERIFY-STABS-NOT:  N_FUN{{.*}}_func_B
+; VERIFY-STABS-NOT:  N_FUN{{.*}}_func_C
+
+;;; Check that we do generate STABS entries (N_FUN) for non-ICF'ed functions
+; VERIFY-STABS:  N_FUN{{.*}}_func_A
+; VERIFY-STABS:  N_FUN{{.*}}_take_func_addr
+
+
+; ModuleID = 'icf-safe-thunks-dwarf.cpp'
+source_filename = "icf-safe-thunks-dwarf.cpp"
+target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128-Fn32"
+target triple = "arm64-apple-macosx11.0.0"
+
+; Function Attrs: mustprogress noinline nounwind optnone ssp uwtable(sync)
+define i32 @func_A() #0 !dbg !13 {
+entry:
+  ret i32 1
+}
+
+; Function Attrs: mustprogress noinline nounwind optnone ssp uwtable(sync)
+define i32 @func_B() #0 !dbg !18 {
+entry:
+  ret i32 1
+}
+
+; Function Attrs: mustprogress noinline nounwind optnone ssp uwtable(sync)
+define i32 @func_C() #0 !dbg !20 {
+entry:
+  ret i32 1
+}
+
+; Function Attrs: mustprogress noinline nounwind optnone ssp uwtable(sync)
+define i64 @take_func_addr() #0 !dbg !22 {
+entry:
+  %val = alloca i64, align 8
+  store i64 0, ptr %val, align 8
+  %0 = load i64, ptr %val, align 8
+  %add = add i64 %0, ptrtoint (ptr @func_A to i64)
+  store i64 %add, ptr %val, align 8
+  %1 = load i64, ptr %val, align 8
+  %add1 = add i64 %1, ptrtoint (ptr @func_B to i64)
+  store i64 %add1, ptr %val, align 8
+  %2 = load i64, ptr %val, align 8
+  %add2 = add i64 %2, ptrtoint (ptr @func_C to i64)
+  store i64 %add2, ptr %val, align 8
+  %3 = load i64, ptr %val, align 8
+  ret i64 %3
+}
+
+attributes #0 = { noinline nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!6, !7, !8, !9, !10, !11}
+!llvm.ident = !{!12}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 20.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: Apple, sysroot: "/")
+!1 = !DIFile(filename: "icf-safe-thunks-dwarf.cpp", directory: "/tmp/test")
+!6 = !{i32 7, !"Dwarf Version", i32 4}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{i32 1, !"wchar_size", i32 4}
+!9 = !{i32 8, !"PIC Level", i32 2}
+!10 = !{i32 7, !"uwtable", i32 1}
+!11 = !{i32 7, !"frame-pointer", i32 1}
+!12 = !{!"clang version 20.0.0"}
+!13 = distinct !DISubprogram(name: "func_A", scope: !1, file: !1, line: 4, type: !14, scopeLine: 4, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!14 = !DISubroutineType(types: !15)
+!15 = !{}
+!18 = distinct !DISubprogram(name: "func_B", scope: !1, file: !1, line: 5, type: !14, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!20 = distinct !DISubprogram(name: "func_C", scope: !1, file: !1, line: 6, type: !14, scopeLine: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!22 = distinct !DISubprogram(name: "take_func_addr", scope: !1, file: !1, line: 8, type: !14, scopeLine: 8, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+
+
+
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;;;;;;;;;;;;; Generate the above LLVM IR with the below script ;;;;;;;;;;;;;;;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; #!/bin/bash
+; set -ex
+; TOOLCHAIN_BIN="llvm-project/build/Debug/bin"
+;
+; # Create icf-safe-thunks-dwarf.cpp file
+; cat > icf-safe-thunks-dwarf.cpp <<EOF
+; #define ATTR __attribute__((noinline)) extern "C"
+; typedef unsigned long long ULL;
+;
+; ATTR int func_A() { return 1; }
+; ATTR int func_B() { return 1; }
+; ATTR int func_C() { return 1; }
+;
+; ATTR ULL take_func_addr() {
+;     ULL val = 0;
+;     val += (ULL)(void*)func_A;
+;     val += (ULL)(void*)func_B;
+;     val += (ULL)(void*)func_C;
+;     return val;
+; }
+; EOF
+;
+; $TOOLCHAIN_BIN/clang -target arm64-apple-macos11.0 -S -emit-llvm -g \
+;                      icf-safe-thunks-dwarf.cpp