[llvm-commits] [PATCH] Emit DWARF relocation from .debug_aranges to .debug_info for asm files.

[Alexey Samsonov]

Hi rafael,

According to DWARF standard, header of each entry set in .debug_aranges
section contains an offset into .debug_info section for the corresponging compile
unit. Typically this should be a relocation into .debug_info section, not
hard-coded zero. Otherwise the binary compiled from multiple assembler sources
will have inconsistent debug_aranges and debug_info.

http://llvm-reviews.chandlerc.com/D115

Files:
  test/MC/ELF/gen-dwarf.s
  lib/MC/MCDwarf.cpp

Index: test/MC/ELF/gen-dwarf.s
===================================================================
--- test/MC/ELF/gen-dwarf.s
+++ test/MC/ELF/gen-dwarf.s
@@ -1,8 +1,9 @@
 // RUN: llvm-mc -g -triple  i686-pc-linux-gnu %s -filetype=obj -o - | elf-dump | FileCheck %s
 
 
-// Test that on ELF the debug info has a relocation to debug_abbrev and one to
-// to debug_line.
+// Test that on ELF:
+// 1. the debug info has a relocation to debug_abbrev and one to to debug_line.
+// 2. the debug_aranges has relocations to text and debug_line.
 
 
     .text
@@ -47,6 +48,34 @@
 // CHECK:       # Section 8
 // CHECK-NEXT:  (('sh_name', 0x00000001) # '.debug_abbrev'
 
+// Section 9 is .debug_aranges
+// CHECK:       # Section 9
+// CHECK-NEXT:  (('sh_name', 0x0000001e) # '.debug_aranges'
+
+// Two relocations in .debug_aranges, one to text and one to debug_info.
+// CHECK:       # '.rel.debug_aranges'
+// CHECK:       # Relocation 0
+// CHECK-NEXT:  (('r_offset', 0x00000006)
+// CHECK-NEXT:   ('r_sym', 0x000005)
+// CHECK-NEXT:   ('r_type', 0x01)
+// CHECK-NEXT:  ),
+// CHECK-NEXT:  # Relocation 1
+// CHECK-NEXT: (('r_offset', 0x00000010)
+// CHECK-NEXT:  ('r_sym', 0x000001)
+// CHECK-NEXT:  ('r_type', 0x01)
+// CHECK-NEXT: ),
+
+// Symbol 1 is section 1 (.text)
+// CHECK:         # Symbol 1
+// CHECK-NEXT:    (('st_name', 0x00000000) # ''
+// CHECK-NEXT:     ('st_value', 0x00000000)
+// CHECK-NEXT:     ('st_size', 0x00000000)
+// CHECK-NEXT:     ('st_bind', 0x0)
+// CHECK-NEXT:     ('st_type', 0x3)
+// CHECK-NEXT:     ('st_other', 0x00)
+// CHECK-NEXT:     ('st_shndx', 0x0001)
+// CHECK-NEXT:    ),
+
 // Symbol 4 is section 4 (.debug_line)
 // CHECK:         # Symbol 4
 // CHECK-NEXT:    (('st_name', 0x00000000) # ''
@@ -58,6 +87,17 @@
 // CHECK-NEXT:     ('st_shndx', 0x0004)
 // CHECK-NEXT:    ),
 
+// Symbol 5 is section 6 (.debug_info)
+// CHECK:         # Symbol 5
+// CHECK-NEXT:    (('st_name', 0x00000000) # ''
+// CHECK-NEXT:     ('st_value', 0x00000000)
+// CHECK-NEXT:     ('st_size', 0x00000000)
+// CHECK-NEXT:     ('st_bind', 0x0)
+// CHECK-NEXT:     ('st_type', 0x3)
+// CHECK-NEXT:     ('st_other', 0x00)
+// CHECK-NEXT:     ('st_shndx', 0x0006)
+// CHECK-NEXT:    ),
+
 // Symbol 6 is section 8 (.debug_abbrev)
 // CHECK:         # Symbol 6
 // CHECK-NEXT:    (('st_name', 0x00000000) # ''
Index: lib/MC/MCDwarf.cpp
===================================================================
--- lib/MC/MCDwarf.cpp
+++ lib/MC/MCDwarf.cpp
@@ -484,7 +484,8 @@
 // .debug_aranges section.  Which contains a header and a table of pairs of
 // PointerSize'ed values for the address and size of section(s) with line table
 // entries (just the default .text in our case) and a terminating pair of zeros.
-static void EmitGenDwarfAranges(MCStreamer *MCOS) {
+static void EmitGenDwarfAranges(MCStreamer *MCOS,
+                                const MCSymbol *InfoSectionSymbol) {
   MCContext &context = MCOS->getContext();
 
   // Create a symbol at the end of the section that we are creating the dwarf
@@ -523,8 +524,11 @@
   // The 2 byte version, which is 2.
   MCOS->EmitIntValue(2, 2);
   // The 4 byte offset to the compile unit in the .debug_info from the start
-  // of the .debug_info, it is at the start of that section so this is zero.
-  MCOS->EmitIntValue(0, 4);
+  // of the .debug_info.
+  if (InfoSectionSymbol)
+    MCOS->EmitSymbolValue(InfoSectionSymbol, 4);
+  else
+    MCOS->EmitIntValue(0, 4);
   // The 1 byte size of an address.
   MCOS->EmitIntValue(AddrSize, 1);
   // The 1 byte size of a segment descriptor, we use a value of zero.
@@ -705,24 +709,30 @@
   // Create the dwarf sections in this order (.debug_line already created).
   MCContext &context = MCOS->getContext();
   const MCAsmInfo &AsmInfo = context.getAsmInfo();
+  bool CreateDwarfSectionSymbols =
+      AsmInfo.doesDwarfUseRelocationsAcrossSections();
+  if (!CreateDwarfSectionSymbols)
+    LineSectionSymbol = NULL;
+  MCSymbol *AbbrevSectionSymbol = NULL;
+  MCSymbol *InfoSectionSymbol = NULL;
   MCOS->SwitchSection(context.getObjectFileInfo()->getDwarfInfoSection());
+  if (CreateDwarfSectionSymbols) {
+    InfoSectionSymbol = context.CreateTempSymbol();
+    MCOS->EmitLabel(InfoSectionSymbol);
+  }
   MCOS->SwitchSection(context.getObjectFileInfo()->getDwarfAbbrevSection());
-  MCSymbol *AbbrevSectionSymbol;
-  if (AsmInfo.doesDwarfUseRelocationsAcrossSections()) {
+  if (CreateDwarfSectionSymbols) {
     AbbrevSectionSymbol = context.CreateTempSymbol();
     MCOS->EmitLabel(AbbrevSectionSymbol);
-  } else {
-    AbbrevSectionSymbol = NULL;
-    LineSectionSymbol = NULL;
   }
   MCOS->SwitchSection(context.getObjectFileInfo()->getDwarfARangesSection());
 
   // If there are no line table entries then do not emit any section contents.
   if (context.getMCLineSections().empty())
     return;
 
   // Output the data for .debug_aranges section.
-  EmitGenDwarfAranges(MCOS);
+  EmitGenDwarfAranges(MCOS, InfoSectionSymbol);
 
   // Output the data for .debug_abbrev section.
   EmitGenDwarfAbbrev(MCOS);
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