[PATCH] D59553: [LLD][ELF][DebugInfo] llvm-symbolizer shows incorrect source line info if --gc-sections used

[Alexey Lapshin via Phabricator via llvm-commits]

avl updated this revision to Diff 201495.
avl added a comment.

deleted redundant tests.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D59553/new/

https://reviews.llvm.org/D59553

Files:
  lld/ELF/InputSection.cpp
  lld/ELF/InputSection.h
  lld/test/ELF/gc-sections-debuginfo.s


Index: lld/test/ELF/gc-sections-debuginfo.s
===================================================================
--- /dev/null
+++ lld/test/ELF/gc-sections-debuginfo.s
@@ -0,0 +1,41 @@
+# REQUIRES: x86
+
+# RUN: echo '.section .text,"a"; .byte 0;  .section .debug_foo,"", at progbits; .quad .text' \
+# RUN:   | llvm-mc --filetype=obj --arch=x86-64 - -o %t
+# RUN: ld.lld %t -o %t2 --gc-sections
+# RUN: llvm-readobj --sections --section-data %t2 | FileCheck %s --check-prefixes=CHECK,CHECK64
+
+# RUN: echo '.section .text,"a"; .byte 0;  .section .debug_foo,"", at progbits; .long .text' \
+# RUN:   | llvm-mc --filetype=obj --arch=x86 - -o %t
+# RUN: ld.lld %t -o %t2 --gc-sections
+# RUN: llvm-readobj --sections --section-data %t2 | FileCheck %s --check-prefixes=CHECK,CHECK32
+
+
+# When --gc-sections is used, the linker deletes unused text sections,
+# but their debug data is left in the binary. That debug data could have relocations
+# pointing to deleted sections. Address ranges of such debug data could overlap
+# with other address ranges for correct debug data. To prevent addresses clashing 
+# it is neccessary to resolve such relocations to an address which is out of the
+# module address space. That test checks that relocations from the .debug_foo 
+# section pointing to a deleted .text section would be resolved 
+# to 0xfffffffffffffffe.
+
+# CHECK-NOT: Name: .text
+
+# CHECK:      Name: .debug_foo
+# CHECK-NEXT: Type: SHT_PROGBITS
+# CHECK-NEXT: Flags [
+# CHECK-NEXT: ]
+# CHECK-NEXT: Address:
+# CHECK-NEXT: Offset:
+# CHECK64-NEXT: Size: 8 
+# CHECK32-NEXT: Size: 4
+# CHECK-NEXT: Link:
+# CHECK-NEXT: Info:
+# CHECK-NEXT: AddressAlignment:
+# CHECK-NEXT: EntrySize:
+# CHECK-NEXT: SectionData (
+# CHECK64-NEXT:   0000: FEFFFFFF FFFFFFFF
+# CHECK32-NEXT:   0000: FEFFFFFF
+# CHECK-NEXT: )
+
Index: lld/ELF/InputSection.h
===================================================================
--- lld/ELF/InputSection.h
+++ lld/ELF/InputSection.h
@@ -73,6 +73,9 @@
 
   unsigned Bss : 1;
 
+  // True if this is a debuginfo section.
+  unsigned Debug : 1;
+
   // Set for sections that should not be folded by ICF.
   unsigned KeepUnique : 1;
 
@@ -100,7 +103,7 @@
               uint64_t Entsize, uint64_t Alignment, uint32_t Type,
               uint32_t Info, uint32_t Link)
       : Name(Name), Repl(this), SectionKind(SectionKind), Live(false),
-        Assigned(false), Bss(false), KeepUnique(false), Alignment(Alignment),
+        Assigned(false), Bss(false), Debug(false), KeepUnique(false), Alignment(Alignment),
         Flags(Flags), Entsize(Entsize), Type(Type), Link(Link), Info(Info) {}
 };
 
Index: lld/ELF/InputSection.cpp
===================================================================
--- lld/ELF/InputSection.cpp
+++ lld/ELF/InputSection.cpp
@@ -71,6 +71,7 @@
 
   NumRelocations = 0;
   AreRelocsRela = false;
+  Debug = Name.startswith(".debug") || Name.startswith(".zdebug");
 
   // The ELF spec states that a value of 0 means the section has
   // no alignment constraits.
@@ -830,8 +831,16 @@
 
     if (Sym.isTls() && !Out::TlsPhdr)
       Target->relocateOne(BufLoc, Type, 0);
-    else
+    else if (Sym.getOutputSection() || !Debug)
       Target->relocateOne(BufLoc, Type, SignExtend64<Bits>(Sym.getVA(Addend)));
+    else
+      // If the relocation points to a deleted section, e.g. due to
+      // --gc-sections, then it is neccessary to make the start offset
+      // be outside the module address range to not overlap with the module's
+      // ranges. We use UINT64_MAX-1 as maximal value of an address because
+      // UINT64_MAX has special usage in .debug_ranges.
+      // https://bugs.llvm.org/show_bug.cgi?id=41124
+      Target->relocateOne(BufLoc, Type, 0xfffffffffffffffeULL);
   }
 }
 


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