[lld][MachO] Prevent doubled N_SO when comp_dir and name absolute

[mysterymath]

When forming MachO STABS, this change detects if the DW_AT_name of the compile unit is already absolute (as allowed by DWARF), and if so, does not prepend DW_AT_comp_dir.

Fixes #70995

[llvmbot]

@llvm/pr-subscribers-lld-macho

@llvm/pr-subscribers-lld

Author: Daniel Thornburgh (mysterymath)

Changes

When forming MachO STABS, this change detects if the DW_AT_name of the compile unit is already absolute (as allowed by DWARF), and if so, does not prepend DW_AT_comp_dir.

Fixes #70995

---

Full diff: https://github.com/llvm/llvm-project/pull/71608.diff

2 Files Affected:

• (modified) lld/MachO/InputFiles.cpp (+4-1)
• (added) lld/test/MachO/stabs-abs-path.s (+58)

diff --git a/lld/MachO/InputFiles.cpp b/lld/MachO/InputFiles.cpp
index 09c6ea9b19b5da2..4cf38169c4bfc9a 100644
--- a/lld/MachO/InputFiles.cpp
+++ b/lld/MachO/InputFiles.cpp
@@ -1522,13 +1522,16 @@ void ObjFile::registerEhFrames(Section &ehFrameSection) {
 }
 
 std::string ObjFile::sourceFile() const {
+  const char *unitName = compileUnit->getUnitDIE().getShortName();
+  if (sys::path::is_absolute(unitName))
+    return unitName;
   SmallString<261> dir(compileUnit->getCompilationDir());
   StringRef sep = sys::path::get_separator();
   // We don't use `path::append` here because we want an empty `dir` to result
   // in an absolute path. `append` would give us a relative path for that case.
   if (!dir.endswith(sep))
     dir += sep;
-  return (dir + compileUnit->getUnitDIE().getShortName()).str();
+  return (dir + unitName).str();
 }
 
 lld::DWARFCache *ObjFile::getDwarf() {
diff --git a/lld/test/MachO/stabs-abs-path.s b/lld/test/MachO/stabs-abs-path.s
new file mode 100644
index 000000000000000..565ed1ae7715598
--- /dev/null
+++ b/lld/test/MachO/stabs-abs-path.s
@@ -0,0 +1,58 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+
+# RUN: %lld -lSystem %t.o -o %t
+# RUN: dsymutil -s %t | FileCheck %s
+
+# CHECK:      (N_SO         ) 00      0000   0000000000000000   '/foo.cpp'
+
+.text
+.globl  _main
+_main:
+Lfunc_begin0:
+  retq
+Lfunc_end0:
+
+.section  __DWARF,__debug_str,regular,debug
+  .asciz  "/foo.cpp"             ## string offset=0
+  .asciz  "/tmp"                 ## string offset=9
+.section  __DWARF,__debug_abbrev,regular,debug
+Lsection_abbrev:
+  .byte  1                       ## Abbreviation Code
+  .byte  17                      ## DW_TAG_compile_unit
+  .byte  1                       ## DW_CHILDREN_yes
+  .byte  3                       ## DW_AT_name
+  .byte  14                      ## DW_FORM_strp
+  .byte  27                      ## DW_AT_comp_dir
+  .byte  14                      ## DW_FORM_strp
+  .byte  17                      ## DW_AT_low_pc
+  .byte  1                       ## DW_FORM_addr
+  .byte  18                      ## DW_AT_high_pc
+  .byte  6                       ## DW_FORM_data4
+  .byte  0                       ## EOM(1)
+  .byte  0                       ## EOM(2)
+  .byte  0                       ## EOM(3)
+.section  __DWARF,__debug_info,regular,debug
+.set Lset0, Ldebug_info_end0-Ldebug_info_start0 ## Length of Unit
+  .long  Lset0
+Ldebug_info_start0:
+  .short  4                       ## DWARF version number
+.set Lset1, Lsection_abbrev-Lsection_abbrev ## Offset Into Abbrev. Section
+  .long  Lset1
+  .byte  8                       ## Address Size (in bytes)
+  .byte  1                       ## Abbrev [1] 0xb:0x48 DW_TAG_compile_unit
+  .long  0                       ## DW_AT_name
+  .long  9                       ## DW_AT_comp_dir
+  .quad  Lfunc_begin0            ## DW_AT_low_pc
+.set Lset3, Lfunc_end0-Lfunc_begin0     ## DW_AT_high_pc
+  .long  Lset3
+  .byte  0                       ## End Of Children Mark
+Ldebug_info_end0:
+
+.section  __DWARF,__debug_aranges,regular,debug
+ltmp1:
+  .byte 0
+
+.subsections_via_symbols
+
+

[smeenai]

LGTM, and thanks for fixing this! Will you need someone to commit this for you?

[thevinster]

-lSystem isn't needed here.

[mysterymath]

Done.

[thevinster]

Is there a need to create a new test file for this use case? This seems like this could be placed in stabs.s

[mysterymath]

I was hesitant to try to add another file there given its complexity, but I'll give it a stab.

[mysterymath]

LGTM, and thanks for fixing this! Will you need someone to commit this for you?

Nah, I've got it. Thanks though! :)