[PATCH] D82828: [ELF] Don't resolve a relocation in .debug_line referencing an ICF folded symbol to the tombstone value

[Fangrui Song via Phabricator via llvm-commits]

MaskRay updated this revision to Diff 274508.
MaskRay added a comment.

Address comments


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D82828/new/

https://reviews.llvm.org/D82828

Files:
  lld/ELF/InputSection.cpp
  lld/test/ELF/debug-dead-reloc-icf.s


Index: lld/test/ELF/debug-dead-reloc-icf.s
===================================================================
--- lld/test/ELF/debug-dead-reloc-icf.s
+++ lld/test/ELF/debug-dead-reloc-icf.s
@@ -10,6 +10,9 @@
 
 # CHECK:      Contents of section .debug_info:
 # CHECK-NEXT:  0000 {{[0-9a-f]+}}000 00000000 ffffffff ffffffff
+# CHECK:      Contents of section .debug_line:
+# CHECK-NEXT:  0000 [[ADDR:[0-9a-f]+]] 00000000
+# CHECK-SAME:                                   [[ADDR]] 00000000
 
 .globl _start
 _start:
@@ -22,3 +25,11 @@
 .section .debug_info
   .quad .text+8
   .quad .text.1+8
+
+## .debug_line contributions associated with folded-in functions will describe
+## different lines to the canonical function. Leaving a tombstone value would
+## prevent users from setting breakpoints on the folded-in functions.
+## Instead resolve the relocation to the folded .text.1 to .text
+.section .debug_line
+  .quad .text
+  .quad .text.1
Index: lld/ELF/InputSection.cpp
===================================================================
--- lld/ELF/InputSection.cpp
+++ lld/ELF/InputSection.cpp
@@ -856,6 +856,7 @@
   const bool isDebug = isDebugSection(*this);
   const bool isDebugLocOrRanges =
       isDebug && (name == ".debug_loc" || name == ".debug_ranges");
+  const bool isDebugLine = isDebug && name == ".debug_line";
 
   for (const RelTy &rel : rels) {
     RelType type = rel.getType(config->isMips64EL);
@@ -926,12 +927,15 @@
       // If the referenced symbol is discarded (made Undefined), or the
       // section defining the referenced symbol is garbage collected,
       // sym.getOutputSection() is nullptr. `ds->section->repl != ds->section`
-      // catches the ICF folded case.
+      // catches the ICF folded case. However, resolving a relocation in
+      // .debug_line to -1 would stop debugger users from setting breakpoints on
+      // the folded-in function, So exclude .debug_line.
       //
       // For pre-DWARF-v5 .debug_loc and .debug_ranges, -1 is a reserved value
       // (base address selection entry), so -2 is used.
       auto *ds = dyn_cast<Defined>(&sym);
-      if (!sym.getOutputSection() || (ds && ds->section->repl != ds->section)) {
+      if (!sym.getOutputSection() ||
+          (ds && ds->section->repl != ds->section && !isDebugLine)) {
         target->relocateNoSym(bufLoc, type,
                               isDebugLocOrRanges ? UINT64_MAX - 1 : UINT64_MAX);
         continue;


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