[llvm] 7650a01 - [DWARF5][COFF] Emit section-relative .debug_line_str relocations (#83773)

[via llvm-commits]

Author: timoh-ba
Date: 2024-03-21T17:30:10+02:00
New Revision: 7650a01927b8488b1d6d0930109e78c695193faf

URL: https://github.com/llvm/llvm-project/commit/7650a01927b8488b1d6d0930109e78c695193faf
DIFF: https://github.com/llvm/llvm-project/commit/7650a01927b8488b1d6d0930109e78c695193faf.diff

LOG: [DWARF5][COFF] Emit section-relative .debug_line_str relocations (#83773)

Dwarf 5 allows separating filenames from .debug_line into a separate
.debug_line_str section. The strings are referenced relative to the
start of the .debug_line_str section. Previously, on COFF, the
relocation information instead caused offsets to be relocated to the
base address of the COFF-File. This lead  to wrong offsets in linked
COFF (PE) files which caused the debugger to be unable to find the
correct source files.

This patch fixes this problem by making the offsets relative to the
start of the .debug_line_str section instead. There should be no
changes for ELF-Files as everything seems to be working there.

A test is also added to ensure that the correct relocation entries are
emitted.

Added: 
    llvm/test/MC/COFF/dwarf5lineinfo.s

Modified: 
    llvm/lib/MC/MCDwarf.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/MC/MCDwarf.cpp b/llvm/lib/MC/MCDwarf.cpp
index d0face9140de66..2ee0c3eb27b92e 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -360,7 +360,12 @@ void MCDwarfLineStr::emitRef(MCStreamer *MCOS, StringRef Path) {
   size_t Offset = addString(Path);
   if (UseRelocs) {
     MCContext &Ctx = MCOS->getContext();
-    MCOS->emitValue(makeStartPlusIntExpr(Ctx, *LineStrLabel, Offset), RefSize);
+    if (Ctx.getAsmInfo()->needsDwarfSectionOffsetDirective()) {
+      MCOS->emitCOFFSecRel32(LineStrLabel, Offset);
+    } else {
+      MCOS->emitValue(makeStartPlusIntExpr(Ctx, *LineStrLabel, Offset),
+                      RefSize);
+    }
   } else
     MCOS->emitIntValue(Offset, RefSize);
 }

diff  --git a/llvm/test/MC/COFF/dwarf5lineinfo.s b/llvm/test/MC/COFF/dwarf5lineinfo.s
new file mode 100644
index 00000000000000..f0789feb208508
--- /dev/null
+++ b/llvm/test/MC/COFF/dwarf5lineinfo.s
@@ -0,0 +1,13 @@
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-windows-gnu %s -o - | llvm-readobj -r  - | FileCheck %s
+
+// CHECK: Relocations [
+// CHECK:  Section (4) .debug_line {
+// CHECK:    0x22 IMAGE_REL_AMD64_SECREL .debug_line_str (8)
+// CHECK:    0x2C IMAGE_REL_AMD64_SECREL .debug_line_str (8)
+// CHECK:    0x36 IMAGE_REL_AMD64_ADDR64 .text (0)
+// CHECK:  }
+
+main:
+	.file	0 "/" "test.c"
+	.loc	0 1 0
+	retq