[RFC] fixing addr2line inline info

Josh Stone jistone at redhat.com
Wed Nov 19 02:04:13 UTC 2014


Hi,

I have a simple patch attached to improve the output addr2line -fi.  The
problem I had is it failed to identify the parent function name if there
was any lexical_block in the scope hierarchy.  For example, try the
following, compiled as the attached testfile-lex-inlines.bz2:

  1 // g++ x.cpp -g -fPIC -olibx.so -shared -O3 -fvisibility=hidden
  2
  3 void foobar()
  4 {
  5   __asm__ ( "nop" ::: );
  6 }
  7
  8 void foo()
  9 {
 10   {
 11     void (*bar) () = foobar;
 12     bar();
 13   }
 14 }

$ eu-addr2line -f -i -e testfile-lex-inlines.bz2 0x690
foobar inlined at /tmp/x.cpp:12 in _Z3foov
/tmp/x.cpp:9
??
/tmp/x.cpp:12

With my patch:

$ ./src/addr2line -fi -e testfile-lex-inlines.bz2 0x690
foobar inlined at /tmp/x.cpp:12 in _Z3foov
/tmp/x.cpp:9
_Z3foov
/tmp/x.cpp:12

So the name is resolved, and I'm happier.  But, as I went to make this a
testcase, I noticed that the ":9" line isn't really correct for "foobar"
-- that's the start of "foo".

There are two candidate lines for 0x690:
 [    33] special opcode 246: address+16 = +0x690 <_Z3foov>, line+4 = 9
 [    34] special opcode 14: address+0 = +0x690 <_Z3foov>, line-4 = 5

So what happens AFAICT, the name is found with dwarf_getscopes(), which
will find the innermost address match.  The line is found with
dwfl_module_getsrc, which uses a binary search, making no guarantees if
there are multiple matches.  The bsearch happened to pick the first one
in this case.  Perhaps this should choose the last matching address to
be approximately innermost?

I also noticed that addr2line's print_dwarf_function() doesn't try to
read linkage_name, although that wouldn't matter for this foobar inline.
 It also looks like it's trying to walk up the inline / subprogram
stack, but since dwarf_getscopes chases the abstract_origin, it doesn't
have any of that.  So print_dwarf_function() returns false, and it falls
back to dwfl_module_addrname to get the outer name.

With dwarf_getscopes_die this would work, including multiple layers of
inlines, as it later does for -i.  But actually, I think having -i makes
this "inlined at ..." message redundant.  Binutils addr2line -fi doesn't
print anything like this.  Should we just kill that part?

Patch review and other thoughts appreciated...

Josh
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Call frame search table section [13] '.eh_frame_hdr':
 version:          1
 eh_frame_ptr_enc: 0x1b (sdata4 pcrel)
 fde_count_enc:    0x3 (udata4)
 table_enc:        0x3b (sdata4 datarel)
 eh_frame_ptr:     0x24 (offset: 0x6c8)
 fde_count:        3
 Table:
  0xfffffec0 (offset:  0x560) -> 0x40 fde=[    18]
  0xffffffe0 (offset:  0x680) -> 0x68 fde=[    40]
  0xfffffff0 (offset:  0x690) -> 0x80 fde=[    58]

Call frame information section [14] '.eh_frame' at offset 0x6c8:

 [     0] CIE length=20
   CIE_id:                   0
   version:                  1
   augmentation:             "zR"
   code_alignment_factor:    1
   data_alignment_factor:    -8
   return_address_register:  16
   Augmentation data:        0x1b (FDE address encoding: sdata4 pcrel)

   Program:
     def_cfa r7 (rsp) at offset 8
     offset r16 (rip) at cfa-8
     nop
     nop

 [    18] FDE length=36 cie=[     0]
   CIE_pointer:              28
   initial_location:         +0x0000000000000560 (offset: 0x560)
   address_range:            0x30 (end offset: 0x590)

   Program:
     def_cfa_offset 16
     advance_loc 6 to 0x566
     def_cfa_offset 24
     advance_loc 10 to 0x570
     def_cfa_expression 11
          [   0] breg7 8
          [   2] breg16 0
          [   4] lit15
          [   5] and
          [   6] lit11
          [   7] ge
          [   8] lit3
          [   9] shl
          [  10] plus
     nop
     nop
     nop
     nop

 [    40] FDE length=20 cie=[     0]
   CIE_pointer:              68
   initial_location:         +0x0000000000000680 <_Z6foobarv> (offset: 0x680)
   address_range:            0x2 (end offset: 0x682)

   Program:
     nop
     nop
     nop
     nop
     nop
     nop
     nop

 [    58] FDE length=20 cie=[     0]
   CIE_pointer:              92
   initial_location:         +0x0000000000000690 <_Z3foov> (offset: 0x690)
   address_range:            0x2 (end offset: 0x692)

   Program:
     nop
     nop
     nop
     nop
     nop
     nop
     nop

 [    70] Zero terminator

DWARF section [24] '.debug_aranges' at offset 0x1054:

Table at offset 0:

 Length:            44
 DWARF version:      2
 CU offset:          0
 Address size:       8
 Segment size:       0

   +0x0000000000000680 <_Z6foobarv>..+0x0000000000000691 <_Z3foov+0x1>

DWARF section [25] '.debug_info' at offset 0x1084:
 [Offset]
 Compilation unit at offset 0:
 Version: 4, Abbreviation section offset: 0, Address size: 8, Offset size: 4
 [     b]  compile_unit
           producer             (strp) "GNU C++ 4.8.3 20140911 (Red Hat 4.8.3-7) -mtune=generic -march=x86-64 -g -O3 -fPIC -fvisibility=hidden"
           language             (data1) C_plus_plus (4)
           name                 (strp) "x.cpp"
           comp_dir             (strp) "/tmp"
           low_pc               (addr) +0x0000000000000680 <_Z6foobarv>
           high_pc              (data8) 18 (+0x0000000000000692)
           stmt_list            (sec_offset) 0
 [    2d]    subprogram
             external             (flag_present) Yes
             name                 (strp) "foobar"
             decl_file            (data1) 1
             decl_line            (data1) 3
             inline               (data1) inlined (1)
 [    35]    subprogram
             abstract_origin      (ref4) [    2d]
             linkage_name         (strp) "_Z6foobarv"
             low_pc               (addr) +0x0000000000000680 <_Z6foobarv>
             high_pc              (data8) 2 (+0x0000000000000682)
             frame_base           (exprloc) 
              [   0] call_frame_cfa
             GNU_all_call_sites   (flag_present) Yes
 [    50]    subprogram
             external             (flag_present) Yes
             name                 (string) "foo"
             decl_file            (data1) 1
             decl_line            (data1) 8
             linkage_name         (strp) "_Z3foov"
             low_pc               (addr) +0x0000000000000690 <_Z3foov>
             high_pc              (data8) 2 (+0x0000000000000692)
             frame_base           (exprloc) 
              [   0] call_frame_cfa
             GNU_all_call_sites   (flag_present) Yes
             sibling              (ref4) [    b1]
 [    71]      lexical_block
               low_pc               (addr) +0x0000000000000690 <_Z3foov>
               high_pc              (data8) 2 (+0x0000000000000692)
 [    82]        variable
                 name                 (string) "bar"
                 decl_file            (data1) 1
                 decl_line            (data1) 11
                 type                 (ref4) [    b2]
                 location             (exprloc) 
                  [   0] addr +0x680 <_Z6foobarv>
                  [   9] stack_value
 [    98]        inlined_subroutine
                 abstract_origin      (ref4) [    2d]
                 low_pc               (addr) +0x0000000000000690 <_Z3foov>
                 high_pc              (data8) 2 (+0x0000000000000692)
                 call_file            (data1) 1
                 call_line            (data1) 12
 [    b1]    subroutine_type
 [    b2]    pointer_type
             byte_size            (data1) 8
             type                 (ref4) [    b1]

DWARF section [26] '.debug_abbrev' at offset 0x113d:
 [ Code]

Abbreviation section at offset 0:
 [    1] offset: 0, children: yes, tag: compile_unit
          attr: producer, form: strp, offset: 0
          attr: language, form: data1, offset: 0x2
          attr: name, form: strp, offset: 0x4
          attr: comp_dir, form: strp, offset: 0x6
          attr: low_pc, form: addr, offset: 0x8
          attr: high_pc, form: data8, offset: 0xa
          attr: stmt_list, form: sec_offset, offset: 0xc
 [    2] offset: 19, children: no, tag: subprogram
          attr: external, form: flag_present, offset: 0x13
          attr: name, form: strp, offset: 0x15
          attr: decl_file, form: data1, offset: 0x17
          attr: decl_line, form: data1, offset: 0x19
          attr: inline, form: data1, offset: 0x1b
 [    3] offset: 34, children: no, tag: subprogram
          attr: abstract_origin, form: ref4, offset: 0x22
          attr: linkage_name, form: strp, offset: 0x24
          attr: low_pc, form: addr, offset: 0x26
          attr: high_pc, form: data8, offset: 0x28
          attr: frame_base, form: exprloc, offset: 0x2a
          attr: GNU_all_call_sites, form: flag_present, offset: 0x2c
 [    4] offset: 52, children: yes, tag: subprogram
          attr: external, form: flag_present, offset: 0x34
          attr: name, form: string, offset: 0x36
          attr: decl_file, form: data1, offset: 0x38
          attr: decl_line, form: data1, offset: 0x3a
          attr: linkage_name, form: strp, offset: 0x3c
          attr: low_pc, form: addr, offset: 0x3e
          attr: high_pc, form: data8, offset: 0x40
          attr: frame_base, form: exprloc, offset: 0x42
          attr: GNU_all_call_sites, form: flag_present, offset: 0x44
          attr: sibling, form: ref4, offset: 0x47
 [    5] offset: 78, children: yes, tag: lexical_block
          attr: low_pc, form: addr, offset: 0x4e
          attr: high_pc, form: data8, offset: 0x50
 [    6] offset: 87, children: no, tag: variable
          attr: name, form: string, offset: 0x57
          attr: decl_file, form: data1, offset: 0x59
          attr: decl_line, form: data1, offset: 0x5b
          attr: type, form: ref4, offset: 0x5d
          attr: location, form: exprloc, offset: 0x5f
 [    7] offset: 102, children: no, tag: inlined_subroutine
          attr: abstract_origin, form: ref4, offset: 0x66
          attr: low_pc, form: addr, offset: 0x68
          attr: high_pc, form: data8, offset: 0x6a
          attr: call_file, form: data1, offset: 0x6c
          attr: call_line, form: data1, offset: 0x6e
 [    8] offset: 117, children: no, tag: subroutine_type
 [    9] offset: 122, children: no, tag: pointer_type
          attr: byte_size, form: data1, offset: 0x7a
          attr: type, form: ref4, offset: 0x7c

DWARF section [27] '.debug_line' at offset 0x11c1:

Table at offset 0:

 Length:                     54
 DWARF version:              2
 Prologue length:            28
 Minimum instruction length: 1
 Maximum operations per instruction: 1
 Initial value if 'is_stmt': 1
 Line base:                  -5
 Line range:                 14
 Opcode base:                13

Opcodes:
  [ 1]  0 arguments
  [ 2]  1 argument
  [ 3]  1 argument
  [ 4]  1 argument
  [ 5]  1 argument
  [ 6]  0 arguments
  [ 7]  0 arguments
  [ 8]  0 arguments
  [ 9]  1 argument
  [10]  0 arguments
  [11]  0 arguments
  [12]  1 argument

Directory table:

File name table:
 Entry Dir   Time      Size      Name
 1     0     0         0         x.cpp

Line number statements:
 [    26] extended opcode 2:  set address to +0x680 <_Z6foobarv>
 [    31] special opcode 21: address+0 = +0x680 <_Z6foobarv>, line+3 = 4
 [    32] special opcode 19: address+0 = +0x680 <_Z6foobarv>, line+1 = 5
 [    33] special opcode 246: address+16 = +0x690 <_Z3foov>, line+4 = 9
 [    34] special opcode 14: address+0 = +0x690 <_Z3foov>, line-4 = 5
 [    35] advance address by 2 to +0x692
 [    37] extended opcode 1:  end of sequence

DWARF section [28] '.debug_str' at offset 0x11fb:
 Offset  String
 [   0]  "foobar"
 [   7]  "GNU C++ 4.8.3 20140911 (Red Hat 4.8.3-7) -mtune=generic -march=x86-64 -g -O3 -fPIC -fvisibility=hidden"
 [  6e]  "/tmp"
 [  73]  "_Z6foobarv"
 [  7e]  "_Z3foov"
 [  86]  "x.cpp"


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