[ELF] - Ignore non-absolute R_386_GOTPC relocation in debug sections.

This is for PR34852.

GCC 8.0 or earlier have a bug that it emits R_386_GOTPC relocations
against _GLOBAL_OFFSET_TABLE for .debug_info. The bug seems to have
been fixed in 2017: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82630,
but we do not want LLD to report errors for such inputs.
In this patch we ignore such relocations.

Differential revision: https://reviews.llvm.org/D38625

llvm-svn: 316761

lld/ELF/InputSection.cpp

@@ -668,6 +668,13 @@ void InputSection::relocateNonAlloc(uint8_t *Buf, ArrayRef<RelTy> Rels) {
     if (Expr == R_NONE)
       continue;
     if (Expr != R_ABS) {
+      // GCC 8.0 or earlier have a bug that it emits R_386_GOTPC relocations
+      // against _GLOBAL_OFFSET_TABLE for .debug_info. The bug seems to have
+      // been fixed in 2017: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82630,
+      // but we need to keep this bug-compatible code for a while.
+      if (Config->EMachine == EM_386 && Type == R_386_GOTPC)
+        continue;
+
       error(this->getLocation<ELFT>(Offset) + ": has non-ABS relocation " +
             toString(Type) + " against symbol '" + toString(Sym) + "'");
       return;

lld/test/ELF/i386-debug-noabs.test

@@ -0,0 +1,33 @@
+# REQUIRES: x86
+
+# RUN: yaml2obj %s -o %t.o
+# RUN: ld.lld %t.o -o %t.exe
+
+## This is for https://bugs.llvm.org//show_bug.cgi?id=34852. GCC 8.0 or
+## earlier have a bug which creates non-absolute R_386_GOTPC relocations
+## in non-allocated sections. It is illegal, but we want to make sure that
+## lld skips them instead of reporting errors.
+
+--- !ELF
+FileHeader:      
+  Class:           ELFCLASS32
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_386
+Sections:        
+  - Name:            .debug_info
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         0000000000000000
+  - Name:            .rel.debug_info
+    Type:            SHT_REL
+    Link:            .symtab
+    AddressAlign:    0x0000000000000004
+    Info:            .debug_info
+    Relocations:     
+      - Offset:          0x000000000000041F
+        Symbol:          _GLOBAL_OFFSET_TABLE_
+        Type:            R_386_GOTPC
+Symbols:
+  Global:
+    - Name:            _GLOBAL_OFFSET_TABLE_