[DebugInfo] Do not dump header field for pre-DWARF5 address tables.

[ikudrin]

Summary

As there is no header in pre-DWARF5 address tables, and we fill the class data members with some artificial values, we should not dump them as that might be misleading.

[jhenderson]

I'm okay with this, but might be worth waiting for the opinion of others.

[probinson]

What do GNU tools report for a v4 .debug_addr section? Intuitively I'd want to see something that says what's going on, rather than have it look like we just forgot to print the header.

[dblaikie]

In D74195#1864283, @probinson wrote:

What do GNU tools report for a v4 .debug_addr section? Intuitively I'd want to see something that says what's going on, rather than have it look like we just forgot to print the header.

There's not much else to print, really - much like other pre-v4 sections with no separators (eg: debug_ranges) it's a flat list of things, from all the different contributions.

I'm pretty sure pre-v5 we didn't even print the "Addrs: [ ... ]" wrapper, it was ".debug_addr contents: " then lines of "<offset> <address>" pairs & that was it, maybe?

But yeah, fair question as to what binutils/GNU tools do in case there's some inspiration.

[ikudrin]

The output of readelf looks like this:

Contents of the .debug_addr section:

  For compilation unit at offset 0x0:
	Index	Address
	0:	00000000 
	1:	00000010 
	2:	00000018

As far as I remember the internals of GNU utilities, they parse .debug_info first and use references from there to parse other sections.

[ikudrin]

@probinson, @dblaikie, are you OK with this patch, or you still have any concerns?

[dblaikie]

Fine by me - thanks!

[probinson]

So the nonstandard .debug_addr section is identified by having a reference from a v4 .debug_info section... I guess there's no better way.
Yes, LGTM

llvm/lib/DebugInfo/DWARF/DWARFDebugAddr.cpp

for (uint32_t I = 0; I < AddrCount; ++I)
     else
       Addrs.push_back(Data.getU64(OffsetPtr));
   return Error::success();
 }
 
 void DWARFDebugAddrTable::dump(raw_ostream &OS, DIDumpOptions DumpOpts) const {
   if (DumpOpts.Verbose)
     OS << format("0x%8.8" PRIx32 ": ", HeaderOffset);
-  OS << format("Addr Section: length = 0x%8.8" PRIx32
+  if (HeaderData.Length)
+    OS << format("Address table header: length = 0x%8.8" PRIx32
                  ", version = 0x%4.4" PRIx16 ", "
                  "addr_size = 0x%2.2" PRIx8 ", seg_size = 0x%2.2" PRIx8 "\n",
                  HeaderData.Length, HeaderData.Version, HeaderData.AddrSize,
                  HeaderData.SegSize);
 
   if (Addrs.size() > 0) {
     const char *AddrFmt = (HeaderData.AddrSize == 4) ? "0x%8.8" PRIx64 "\n"
                                                      : "0x%16.16" PRIx64 "\n";
     OS << "Addrs: [\n";
     for (uint64_t Addr : Addrs)
       OS << format(AddrFmt, Addr);
     OS << "]\n";

llvm/test/DebugInfo/X86/debug_addr.ll

 ; DWARF4-NOT: Compile Unit
 ; DWARF4: DW_TAG_compile_unit
 ; DWARF4-NOT: DW_TAG_{{.*}}
 ; DWARF4: DW_AT_GNU_dwo_name{{.*}}test.dwo
 ; DWARF4: DW_AT_GNU_addr_base{{.*}}0x00000000
 ; DWARF4: DW_TAG_GNU_call_site
 ; DWARF4:   DW_AT_low_pc [DW_FORM_GNU_addr_index] (indexed (00000002) address = 0x0000000000000018 ".text")
 ; DWARF4: .debug_addr contents:
-; DWARF4-NEXT: 0x00000000: Addr Section: length = 0x00000000, version = 0x0004, addr_size = 0x04, seg_size = 0x00
 ; DWARF4-NEXT: Addrs: [
 ; DWARF4-NEXT: 0x00000000
 ; DWARF4-NEXT: 0x00000010
 ; DWARF4-NEXT: 0x00000018
 ; DWARF4-NEXT: ]
 
 ; DWARF5: .debug_info contents:
 ; DWARF5: Compile Unit:{{.*}}version = 0x0005
 ; DWARF5-NOT: Compile Unit
 ; DWARF5: DW_TAG_skeleton_unit
 ; DWARF5-NOT: DW_TAG_{{.*}}
 ; DWARF5: DW_AT_dwo_name{{.*}}test.dwo
 ; DWARF5: DW_AT_addr_base{{.*}}0x00000008
 ; DWARF5: DW_AT_low_pc [DW_FORM_addrx] (indexed (00000000) address = 0x0000000000000000 ".text")
 ; DWARF5: DW_AT_call_return_pc [DW_FORM_addrx] (indexed (00000002) address = 0x0000000000000018 ".text")
 ; DWARF5: .debug_addr contents:
-; DWARF5-NEXT: 0x00000000: Addr Section: length = 0x00000010, version = 0x0005, addr_size = 0x04, seg_size = 0x00
+; DWARF5-NEXT: 0x00000000: Address table header: length = 0x00000010, version = 0x0005, addr_size = 0x04, seg_size = 0x00
 ; DWARF5-NEXT: Addrs: [
 ; DWARF5-NEXT: 0x00000000
 ; DWARF5-NEXT: 0x00000010
 ; DWARF5-NEXT: 0x00000018
 ; DWARF5-NEXT: ]
 
 ; ModuleID = './test.c'
 source_filename = "./test.c"

llvm/test/tools/llvm-dwarfdump/X86/debug_addr_dwarf4.s

 # RUN: llvm-mc %s -filetype obj -triple i386-pc-linux -o %t.o
 # RUN: llvm-dwarfdump --debug-addr %t.o | FileCheck %s
 
 # CHECK: .debug_addr contents
-# CHECK-NEXT:     length = 0x00000000, version = 0x0004, addr_size = 0x04, seg_size = 0x00
 # CHECK-NEXT:     Addrs: [
 # CHECK-NEXT:     0x00000000
 # CHECK-NEXT:     0x00000001
 
   .section  .debug_abbrev,"",@progbits
   .byte 1                       # Abbreviation Code
   .section  .debug_info,"",@progbits
 .Lcu_begin0:
   .long 7                       # Length of Unit
   .short  4                     # DWARF version number
   .long .debug_abbrev           # Offset Into Abbrev. Section
   .byte 4                       # Address Size (in bytes)
   .section  .debug_addr,"",@progbits
   .long 0x00000000
   .long 0x00000001