[llvm-branch-commits] [llvm] 72e75ca - [MC][ELF] Allow STT_SECTION referencing SHF_MERGE on REL targets

[Fangrui Song via llvm-branch-commits]

Author: Fangrui Song
Date: 2020-12-20T18:37:14-08:00
New Revision: 72e75ca343c6ff927a2242efee3f4640943eedd6

URL: https://github.com/llvm/llvm-project/commit/72e75ca343c6ff927a2242efee3f4640943eedd6
DIFF: https://github.com/llvm/llvm-project/commit/72e75ca343c6ff927a2242efee3f4640943eedd6.diff

LOG: [MC][ELF] Allow STT_SECTION referencing SHF_MERGE on REL targets

This relands D64327 with a more specific workaround for R_386_GOTOFF
(gold<2.34 bug https://sourceware.org/bugzilla/show_bug.cgi?id=16794)

.debug_info has quite a few .debug_str relocations (R_386_32/R_ARM_ABS32).
The original workaround was too general and introduced too many .L symbols
used just as relocation targets.

>From the original review:

  ... it reduced the size of a big ARM-32 debug image by 33%. It contained ~68M
  of relocations symbols out of total ~71M symbols (96% of symbols table was
  generated for relocations with symbol).

Added: 
    

Modified: 
    llvm/lib/MC/ELFObjectWriter.cpp
    llvm/test/MC/ELF/basic-elf-32.s
    llvm/test/MC/ELF/compression.s
    llvm/test/MC/ELF/relocation-386.s
    llvm/test/MC/Mips/elf-relsym.s
    llvm/test/MC/Mips/xgot.s

Removed: 
    


################################################################################
diff  --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 10c61fc8b453..9cf29ba0a232 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -1395,9 +1395,10 @@ bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
       if (C != 0)
         return true;
 
-      // It looks like gold has a bug (http://sourceware.org/PR16794) and can
-      // only handle section relocations to mergeable sections if using RELA.
-      if (!hasRelocationAddend())
+      // gold<2.34 incorrectly ignored the addend for R_386_GOTOFF (9)
+      // (http://sourceware.org/PR16794).
+      if (TargetObjectWriter->getEMachine() == ELF::EM_386 &&
+          Type == ELF::R_386_GOTOFF)
         return true;
     }
 

diff  --git a/llvm/test/MC/ELF/basic-elf-32.s b/llvm/test/MC/ELF/basic-elf-32.s
index effc363d1c6c..eb1ed23b2784 100644
--- a/llvm/test/MC/ELF/basic-elf-32.s
+++ b/llvm/test/MC/ELF/basic-elf-32.s
@@ -46,9 +46,9 @@ main:                                   # @main
 
 // CHECK: Relocations [
 // CHECK:   Section {{.*}} .rel.text {
-// CHECK:     0x6  R_386_32   .L.str1
+// CHECK:     0x6  R_386_32   .rodata.str1.1
 // CHECK:     0xB  R_386_PC32 puts
-// CHECK:     0x12 R_386_32   .L.str2
+// CHECK:     0x12 R_386_32   .rodata.str1.1
 // CHECK:     0x17 R_386_PC32 puts
 // CHECK:   }
 // CHECK: ]

diff  --git a/llvm/test/MC/ELF/compression.s b/llvm/test/MC/ELF/compression.s
index 93a77b3fcbdb..9bc5c0ecc699 100644
--- a/llvm/test/MC/ELF/compression.s
+++ b/llvm/test/MC/ELF/compression.s
@@ -38,7 +38,7 @@
 
 // In x86 32 bit named symbols are used for temporary symbols in merge
 // sections, so make sure we handle symbols inside compressed sections
-// 386-SYMBOLS-GNU: Name: .Linfo_string0
+// 386-SYMBOLS-GNU: Name: .zdebug_str
 // 386-SYMBOLS-GNU-NOT: }
 // 386-SYMBOLS-GNU: Section: .zdebug_str
 
@@ -73,7 +73,7 @@
 // ZLIB-STYLE-FLAGS32-NEXT: AddressAlignment: 4
 // ZLIB-STYLE-FLAGS64-NEXT: AddressAlignment: 8
 
-// 386-SYMBOLS-ZLIB: Name: .Linfo_string0
+// 386-SYMBOLS-ZLIB: Name: .debug_str
 // 386-SYMBOLS-ZLIB-NOT: }
 // 386-SYMBOLS-ZLIB: Section: .debug_str
 

diff  --git a/llvm/test/MC/ELF/relocation-386.s b/llvm/test/MC/ELF/relocation-386.s
index b1428c9b2b8a..e49b25a25ce5 100644
--- a/llvm/test/MC/ELF/relocation-386.s
+++ b/llvm/test/MC/ELF/relocation-386.s
@@ -8,7 +8,10 @@
 // I386: Format: elf32-i386
 // CHECK:      Relocations [
 // CHECK-NEXT:   Section {{.*}} .rel.text {
-// CHECK-NEXT:     0x2          R_386_GOTOFF     .Lfoo
+/// Do not use STT_SECTION symbol for R_386_GOTOFF to work around a gold<2.34 bug
+/// https://sourceware.org/bugzilla/show_bug.cgi?id=16794
+// I386-NEXT:      0x2          R_386_GOTOFF     .Lfoo
+// IAMCU-NEXT:     0x2          R_386_GOTOFF     .rodata.str1.1
 // CHECK-NEXT:     0x{{[^ ]+}}  R_386_PLT32      bar2
 // CHECK-NEXT:     0x{{[^ ]+}}  R_386_GOTPC      _GLOBAL_OFFSET_TABLE_
 // Relocation 3 (bar3 at GOTOFF) is done with symbol 7 (bss)

diff  --git a/llvm/test/MC/Mips/elf-relsym.s b/llvm/test/MC/Mips/elf-relsym.s
index b8c2f89e82e6..d19b4e3c4820 100644
--- a/llvm/test/MC/Mips/elf-relsym.s
+++ b/llvm/test/MC/Mips/elf-relsym.s
@@ -4,16 +4,10 @@
 
 // CHECK: Symbols [
 // CHECK:   Symbol {
-// CHECK:     Name: $.str
+// CHECK:     Name: .rodata.cst8
 // CHECK:   }
 // CHECK:   Symbol {
-// CHECK:     Name: $.str1
-// CHECK:   }
-// CHECK:   Symbol {
-// CHECK:     Name: $CPI0_0
-// CHECK:   }
-// CHECK:   Symbol {
-// CHECK:     Name: $CPI0_1
+// CHECK:     Name: .rodata.str1.1
 // CHECK:   }
 // CHECK: ]
 

diff  --git a/llvm/test/MC/Mips/xgot.s b/llvm/test/MC/Mips/xgot.s
index 100d25e67223..0c29582d681c 100644
--- a/llvm/test/MC/Mips/xgot.s
+++ b/llvm/test/MC/Mips/xgot.s
@@ -10,8 +10,8 @@
 // CHECK:   0x1C R_MIPS_GOT_LO16 ext_1
 // CHECK:   0x24 R_MIPS_CALL_HI16 printf
 // CHECK:   0x30 R_MIPS_CALL_LO16 printf
-// CHECK:   0x2C R_MIPS_GOT16 $.str
-// CHECK:   0x38 R_MIPS_LO16 $.str
+// CHECK:   0x2C R_MIPS_GOT16 .rodata.str1.1
+// CHECK:   0x38 R_MIPS_LO16 .rodata.str1.1
 // CHECK: ]
 
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