[llvm-dwarfdump] - Stop printing the bogus empty section name on invalid dwarf.

[grimar]

Summary

When there is no .debug_addr section for some reason,
llvm-dwarfdump would print the bogus empty section name when dumping ranges
in .debug_info:

# CHECK:       DW_AT_ranges [DW_FORM_rnglistx]   (indexed (0x0) rangelist = 0x00000004
# CHECK-NEXT:    [0x0000000000000000, 0x0000000000000001) ""
# CHECK-NEXT:    [0x0000000000000000, 0x0000000000000002) "")

That happens because of the code which uses 0 (zero) as a section index as a default value.
The code should use -1ULL instead because technically 0 is a valid zero section index
in ELF and -1ULL is a special constant used that means "no section available".

This is mostly a fix for the overall correctness/safety of the code, but a test case is provided too.

[probinson]

Are those hard tabs in the test .s file? many editors do that automatically in assembler source, but the LLVM project doesn't want hard tabs.

LGTM otherwise.

[grimar]

In D55113#1314660, @probinson wrote:

Are those hard tabs in the test .s file? many editors do that automatically in assembler source, but the LLVM project doesn't want hard tabs.

LGTM otherwise.

There were few trailing whitespaces I didn't notice. Will remove them before the commit. Thanks!

[dblaikie]

llvm/trunk/test/tools/llvm-dwarfdump/X86/no_debug_addr.s

4–11 ↗

(On Diff #176333)

Could you provide the source (& compilation commands) for this assembly in a comment here so it's easier to eyeball what the input is to this test rather than reading all the assembly?

Also, does this need 3 ranges, or would two suffice (thus creating shorter assembly that might be a little easier to understand)? Anything else you can do to simplify the test case would be great.

Actually, why are there 3 ranges here, when it looks like there are only 2 functions? (ah, I see, invalid input/DWARF as you mentioned in the description - but still, could be simpler to have 2 functions rather than 3)

[grimar]

llvm/trunk/test/tools/llvm-dwarfdump/X86/no_debug_addr.s

4–11 ↗

(On Diff #176333)

Could you provide the source (& compilation commands) for this assembly in a comment here so it's easier to eyeball what the input is to this > test rather than reading all the assembly?

I could, but found that would not be useful probably.
The idea of this test is that .debug_addr is absent. So I had to drop it manually. At the same time, test should
use both the DW_RLE_startx_length and DW_RLE_base_addressx. I had to reduce and manually edit the assembly and
particularly edited the .debug_rnglists to add the DW_RLE_base_addressx + 'DW_RLE_offset_pair' entries too.
(It was much easier than trying to find the matching c++ code for the DWARF I want to emit)

So I think the user needs to read it to understand the test anyways and having c++ code is more confusing than useful here,
because c++ code would have no so much common with the case I am testing here.

Actually, why are there 3 ranges here, when it looks like there are only 2 functions? (ah, I see, invalid input/DWARF as you mentioned
in the description - but still, could be simpler to have 2 functions rather than 3)

That is because DW_RLE_startx_length were generated from c++ file, but I edited the assembly and added the DW_RLE_base_addressx + DW_RLE_offset_pair entries manually because wanted to test the change I did for DW_RLE_base_addressx

Technically this test case needs 2 ranges in total, not 3.
I added/updated the comment and removed few excessive things from the test and posted D55261.

lib/DebugInfo/DWARF/DWARFDebugRnglists.cpp

DWARFDebugRnglist::getAbsoluteRanges(llvm::Optional<SectionedAddress> BaseAddr,
                                      DWARFUnit &U) const {
   DWARFAddressRangesVector Res;
   for (const RangeListEntry &RLE : Entries) {
     if (RLE.EntryKind == dwarf::DW_RLE_end_of_list)
       break;
     if (RLE.EntryKind == dwarf::DW_RLE_base_addressx) {
       BaseAddr = U.getAddrOffsetSectionItem(RLE.Value0);
       if (!BaseAddr)
-        BaseAddr = {RLE.Value0, 0};
+        BaseAddr = {RLE.Value0, -1ULL};
       continue;
     }
     if (RLE.EntryKind == dwarf::DW_RLE_base_address) {
       BaseAddr = {RLE.Value0, RLE.SectionIndex};
       continue;
     }
 
     DWARFAddressRange E;
case dwarf::DW_RLE_start_end:
       break;
     case dwarf::DW_RLE_start_length:
       E.LowPC = RLE.Value0;
       E.HighPC = E.LowPC + RLE.Value1;
       break;
     case dwarf::DW_RLE_startx_length: {
       auto Start = U.getAddrOffsetSectionItem(RLE.Value0);
       if (!Start)
-        Start = {0, 0};
+        Start = {0, -1ULL};
       E.SectionIndex = Start->SectionIndex;
       E.LowPC = Start->Address;
       E.HighPC = E.LowPC + RLE.Value1;
       break;
     }
     default:
       // Unsupported encodings should have been reported during extraction,
       // so we should not run into any here.

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

+# RUN: llvm-mc %s -filetype obj -triple=x86_64-pc-linux -o %t.o
+# RUN: llvm-dwarfdump -v %t.o | FileCheck %s
+
+## When .debug_addr is absent for some reason,
+## check we do not print a bogus section name.
+
+# CHECK:       DW_AT_ranges [DW_FORM_rnglistx]   (indexed (0x0) rangelist = 0x00000004
+# CHECK-NEXT:    [0x0000000000000000, 0x0000000000000001)
+# CHECK-NEXT:    [0x0000000000000000, 0x0000000000000002)
+# CHECK-NEXT:    [0x0000000000000003, 0x0000000000000004))
+
+.text
+.section .text._Z3zedv,"ax",@progbits
+.Lfunc_begin0:
+  retq
+.Lfunc_end0:
+
+.section .text.main,"ax",@progbits
+.Lfunc_begin1:
+ retq
+ retq
+.Lfunc_end1:
+
+.section .debug_str_offsets,"",@progbits
+.long 32
+.short 5
+.short 0
+.Lstr_offsets_base0:
+ .long .Linfo_string0
+ .long .Linfo_string0
+ .long .Linfo_string0
+ .long .Linfo_string0
+ .long .Linfo_string0
+ .long .Linfo_string0
+ .long .Linfo_string0
+
+.section .debug_str,"MS",@progbits,1
+.Linfo_string0:
+ .asciz "stub"
+
+.section .debug_abbrev,"",@progbits
+  .byte  1                           # Abbreviation Code
+  .byte  17                          # DW_TAG_compile_unit
+  .byte  1                           # DW_CHILDREN_yes
+  .byte  37                          # DW_AT_producer
+  .byte  37                          # DW_FORM_strx1
+  .byte  19                          # DW_AT_language
+  .byte  5                           # DW_FORM_data2
+  .byte  3                           # DW_AT_name
+  .byte  37                          # DW_FORM_strx1
+  .byte  114                         # DW_AT_str_offsets_base
+  .byte  23                          # DW_FORM_sec_offset
+  .byte  16                          # DW_AT_stmt_list
+  .byte  23                          # DW_FORM_sec_offset
+  .byte  27                          # DW_AT_comp_dir
+  .byte  37                          # DW_FORM_strx1
+  .byte  115                         # DW_AT_addr_base
+  .byte  23                          # DW_FORM_sec_offset
+  .byte  17                          # DW_AT_low_pc
+  .byte  1                           # DW_FORM_addr
+  .byte  85                          # DW_AT_ranges
+  .byte  35                          # DW_FORM_rnglistx
+  .byte  116                         # DW_AT_rnglists_base
+  .byte  23                          # DW_FORM_sec_offset
+  .byte  0                           # EOM(1)
+  .byte  0                           # EOM(2)
+  .byte  2                           # Abbreviation Code
+  .byte  46                          # DW_TAG_subprogram
+  .byte  0                           # DW_CHILDREN_no
+  .byte  17                          # DW_AT_low_pc
+  .byte  27                          # DW_FORM_addrx
+  .byte  18                          # DW_AT_high_pc
+  .byte  6                           # DW_FORM_data4
+  .byte  64                          # DW_AT_frame_base
+  .byte  24                          # DW_FORM_exprloc
+  .byte  110                         # DW_AT_linkage_name
+  .byte  37                          # DW_FORM_strx1
+  .byte  3                           # DW_AT_name
+  .byte  37                          # DW_FORM_strx1
+  .byte  58                          # DW_AT_decl_file
+  .byte  11                          # DW_FORM_data1
+  .byte  59                          # DW_AT_decl_line
+  .byte  11                          # DW_FORM_data1
+  .byte  73                          # DW_AT_type
+  .byte  19                          # DW_FORM_ref4
+  .byte  63                          # DW_AT_external
+  .byte  25                          # DW_FORM_flag_present
+  .byte  0                           # EOM(1)
+  .byte  0                           # EOM(2)
+  .byte  3                           # Abbreviation Code
+  .byte  46                          # DW_TAG_subprogram
+  .byte  0                           # DW_CHILDREN_no
+  .byte  17                          # DW_AT_low_pc
+  .byte  27                          # DW_FORM_addrx
+  .byte  18                          # DW_AT_high_pc
+  .byte  6                           # DW_FORM_data4
+  .byte  64                          # DW_AT_frame_base
+  .byte  24                          # DW_FORM_exprloc
+  .byte  3                           # DW_AT_name
+  .byte  37                          # DW_FORM_strx1
+  .byte  58                          # DW_AT_decl_file
+  .byte  11                          # DW_FORM_data1
+  .byte  59                          # DW_AT_decl_line
+  .byte  11                          # DW_FORM_data1
+  .byte  73                          # DW_AT_type
+  .byte  19                          # DW_FORM_ref4
+  .byte  63                          # DW_AT_external
+  .byte  25                          # DW_FORM_flag_present
+  .byte  0                           # EOM(1)
+  .byte  0                           # EOM(2)
+  .byte  4                           # Abbreviation Code
+  .byte  36                          # DW_TAG_base_type
+  .byte  0                           # DW_CHILDREN_no
+  .byte  3                           # DW_AT_name
+  .byte  37                          # DW_FORM_strx1
+  .byte  62                          # DW_AT_encoding
+  .byte  11                          # DW_FORM_data1
+  .byte  11                          # DW_AT_byte_size
+  .byte  11                          # DW_FORM_data1
+  .byte  0                           # EOM(1)
+  .byte  0                           # EOM(2)
+  .byte  0                           # EOM(3)
+
+.section .debug_info,"",@progbits
+.Lcu_begin0:
+  .long  75                          # Length of Unit
+  .short 5                           # DWARF version number
+  .byte  1                           # DWARF Unit Type
+  .byte  8                           # Address Size (in bytes)
+  .long  .debug_abbrev               # Offset Into Abbrev. Section
+  
+  .byte  1                           # Abbrev [1] 0xc:0x43 DW_TAG_compile_unit
+  .byte  0                           # DW_AT_producer
+  .short 4                           # DW_AT_language
+  .byte  1                           # DW_AT_name
+  .long  .Lstr_offsets_base0         # DW_AT_str_offsets_base
+  .long  0                           # DW_AT_stmt_list
+  .byte  2                           # DW_AT_comp_dir
+  .long  0                           # DW_AT_addr_base
+  .quad  0                           # DW_AT_low_pc
+  .byte  0                           # DW_AT_ranges
+  .long  .Lrnglists_table_base0      # DW_AT_rnglists_base
+
+  .byte 2                            # Abbrev [2] 0x2b:0x10 DW_TAG_subprogram
+  .byte 0                            # DW_AT_low_pc
+  .long .Lfunc_end0-.Lfunc_begin0    # DW_AT_high_pc
+  .byte 1                            # DW_AT_frame_base
+  .byte 86
+  .byte 3                            # DW_AT_linkage_name
+  .byte 4                            # DW_AT_name
+  .byte 1                            # DW_AT_decl_file
+  .byte 1                            # DW_AT_decl_line
+  .long 74                           # DW_AT_type
+                                     # DW_AT_external
+
+  .byte  3                           # Abbrev [3] 0x3b:0xf DW_TAG_subprogram
+  .byte  1                           # DW_AT_low_pc
+  .long  .Lfunc_end1-.Lfunc_begin1   # DW_AT_high_pc
+  .byte  1                           # DW_AT_frame_base
+  .byte  86
+  .byte  6                           # DW_AT_name
+  .byte  1                           # DW_AT_decl_file
+  .byte  5                           # DW_AT_decl_line
+  .long  74                          # DW_AT_type
+                                     # DW_AT_external
+
+  .byte  4                           # Abbrev [4] 0x4a:0x4 DW_TAG_base_type
+  .byte  5                           # DW_AT_name
+  .byte  5                           # DW_AT_encoding
+  .byte  4                           # DW_AT_byte_size
+  .byte  0                           # End Of Children Mark
+
+.section .debug_rnglists,"",@progbits
+.long .Ldebug_rnglist_table_end0-.Ldebug_rnglist_table_start0 # Length
+.Ldebug_rnglist_table_start0:        
+  .short 5                           # Version
+  .byte  8                           # Address size
+  .byte  0                           # Segment selector size
+  .long  1                           # Offset entry count
+.Lrnglists_table_base0:
+  .long .Ldebug_ranges0-.Lrnglists_table_base0
+.Ldebug_ranges0:
+  .byte 3                            # DW_RLE_startx_length
+  .byte 0                            #   start index
+  .uleb128 .Lfunc_end0-.Lfunc_begin0 #   length
+  .byte 3                            # DW_RLE_startx_length
+  .byte 1                            #   start index
+  .uleb128 .Lfunc_end1-.Lfunc_begin1 #   length
+  
+  .byte 1                            # DW_RLE_base_addressx
+  .byte 0                            # Base address (index 0 in .debug_addr)
+  .byte 4                            # DW_RLE_offset_pair
+  .byte 0x3                          # Start offset
+  .byte 0x4                          # End offset
+
+  .byte 0                            # DW_RLE_end_of_list
+.Ldebug_rnglist_table_end0: