Readelf section header printing alignment

Readelf section header printing alignment

[Pete Dietl]

The section headers output from readelf with the '-W' option become ugly and
unaligned when a section name is too long.
Example:

Section Headers:
  [Nr] Name              Type            Address          Off    Size
 ES Flg Lk Inf Al
  [ 0]                   NULL            0000000000000000 000000
000000 00      0   0  0
  [ 1] .text             PROGBITS        0000000000000000 000040
00000f 00  AX  0   0  1
  [ 2] .data             PROGBITS        0000000000000000 00004f
000000 00  WA  0   0  1
  [ 3] .bss              NOBITS          0000000000000000 00004f
000000 00  WA  0   0  1
  [ 4] .comment          PROGBITS        0000000000000000 00004f
00002c 01  MS  0   0  1
  [ 5] .note.GNU-stack   PROGBITS        0000000000000000 00007b
000000 00      0   0  1
  [ 6] .note.gnu.property NOTE            0000000000000000 000080
000020 00   A  0   0  8
  [ 7] .eh_frame         PROGBITS        0000000000000000 0000a0
000038 00   A  0   0  8
  [ 8] .rela.eh_frame    RELA            0000000000000000 000148
000018 18   I  9   7  8
  [ 9] .symtab           SYMTAB          0000000000000000 0000d8
000060 18     10   3  8
  [10] .strtab           STRTAB          0000000000000000 000138
00000d 00      0   0  1
  [11] .shstrtab         STRTAB          0000000000000000 000160
000067 00      0   0  1

May I submit a patch to compute the amount of space between 'Name' and 'Type'
from the longest of the section header names, or is this just a silly
formatting detail that no one cares about? :)

Thanks,
Pete

Re: Readelf section header printing alignment

[Mike Frysinger]

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On 26 Dec 2023 15:01, Pete Dietl wrote:
> The section headers output from readelf with the '-W' option become ugly and
> unaligned when a section name is too long.
> Example:
> 
> Section Headers:
>   [Nr] Name              Type            Address          Off    Size
>  ES Flg Lk Inf Al
>   [ 0]                   NULL            0000000000000000 000000
> 000000 00      0   0  0
>   [ 1] .text             PROGBITS        0000000000000000 000040
> 00000f 00  AX  0   0  1
>   [ 2] .data             PROGBITS        0000000000000000 00004f
> 000000 00  WA  0   0  1
>   [ 3] .bss              NOBITS          0000000000000000 00004f
> 000000 00  WA  0   0  1
>   [ 4] .comment          PROGBITS        0000000000000000 00004f
> 00002c 01  MS  0   0  1
>   [ 5] .note.GNU-stack   PROGBITS        0000000000000000 00007b
> 000000 00      0   0  1
>   [ 6] .note.gnu.property NOTE            0000000000000000 000080
> 000020 00   A  0   0  8
>   [ 7] .eh_frame         PROGBITS        0000000000000000 0000a0
> 000038 00   A  0   0  8
>   [ 8] .rela.eh_frame    RELA            0000000000000000 000148
> 000018 18   I  9   7  8
>   [ 9] .symtab           SYMTAB          0000000000000000 0000d8
> 000060 18     10   3  8
>   [10] .strtab           STRTAB          0000000000000000 000138
> 00000d 00      0   0  1
>   [11] .shstrtab         STRTAB          0000000000000000 000160
> 000067 00      0   0  1
> 
> May I submit a patch to compute the amount of space between 'Name' and 'Type'
> from the longest of the section header names, or is this just a silly
> formatting detail that no one cares about? :)

i think all of the cols can get unaligned if the content is bigger than the
allocated space.  i wish it would autoalign/fix itself, at least when using
the -W option.
-mike

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Re: Readelf section header printing alignment

[Nick Clifton]

Hi Pete,

> The section headers output from readelf with the '-W' option become ugly and
> unaligned when a section name is too long.

Agreed.  In hindsight it would have been better to emit the section name
as the last entry on the output line, rather than the second.

If it helps you could try using the readelf program the elfutils project
(eu-readelf) as this appear to adjust the column positions to allow for
extra long section names.  I think that this is a bad idea however as
it could end up looking very strange if just one section has an extremely
long section name.

Changing the default output layout now would be a bad idea as there
are scripts and tools out there that depend upon the current behaviour.

It would be possible however to add a new command line option which
would change the layout.  Perhaps simply --section-name-at-end ?
Although this seems a bit, hmm, hackish.  Or maybe:

   --section-listing-layout=[number,name,type,addr,off,size,flags,info,align]

Then this option could be used to just display the fields of interest
to the user, in the order that they want.  So:

   --section-listing-layout=type,size,name

would produce output like this:

   Section Headers:
     Type      Size     Name
     NULL           0
     PROGBITS  00000f  .text
     PROGBITS  000000  .data
     NOBITS    000000  .bss
     PROGBITS  00002c  .comment
     PROGBITS  000000  .note.GNU-stack
     NOTE      000020  .note.gnu.property

whereas:

  --section-listing-layout=name,size

would produce output like this:

   Section Headers:
     Name Size
       0
     .text 00000f
     .data 000000
     .bss  000000
     .comment 00002c
     .note.GNU-stack 000000
     .note.gnu.property 000020

I am just theorizing however.  I am not actually volunteering to write
the code.  But, as they say, "patches welcome"...

Cheers
   Nick

Re: Readelf section header printing alignment

[Fangrui Song]

On Fri, Jan 5, 2024 at 7:12 AM Nick Clifton <nickc@redhat.com> wrote:
>
> Hi Pete,
>
> > The section headers output from readelf with the '-W' option become ugly and
> > unaligned when a section name is too long.
>
> Agreed.  In hindsight it would have been better to emit the section name
> as the last entry on the output line, rather than the second.
>
> If it helps you could try using the readelf program the elfutils project
> (eu-readelf) as this appear to adjust the column positions to allow for
> extra long section names.  I think that this is a bad idea however as
> it could end up looking very strange if just one section has an extremely
> long section name.
>
> Changing the default output layout now would be a bad idea as there
> are scripts and tools out there that depend upon the current behaviour.
>
> It would be possible however to add a new command line option which
> would change the layout.  Perhaps simply --section-name-at-end ?
> Although this seems a bit, hmm, hackish.  Or maybe:
>
>    --section-listing-layout=[number,name,type,addr,off,size,flags,info,align]
>
> Then this option could be used to just display the fields of interest
> to the user, in the order that they want.  So:
>
>    --section-listing-layout=type,size,name
>
> would produce output like this:
>
>    Section Headers:
>      Type      Size     Name
>      NULL           0
>      PROGBITS  00000f  .text
>      PROGBITS  000000  .data
>      NOBITS    000000  .bss
>      PROGBITS  00002c  .comment
>      PROGBITS  000000  .note.GNU-stack
>      NOTE      000020  .note.gnu.property
>
> whereas:
>
>   --section-listing-layout=name,size
>
> would produce output like this:
>
>    Section Headers:
>      Name Size
>        0
>      .text 00000f
>      .data 000000
>      .bss  000000
>      .comment 00002c
>      .note.GNU-stack 000000
>      .note.gnu.property 000020
>
> I am just theorizing however.  I am not actually volunteering to write
> the code.  But, as they say, "patches welcome"...
>
> Cheers
>    Nick
>

> i think all of the cols can get unaligned if the content is bigger than the
> allocated space.  i wish it would autoalign/fix itself, at least when using
> the -W option.

Both eu-readelf and llvm-readelf simply ignore -W/--wide and do not
implement the narrow output at all.
Many folks like me always prefer -W since the narrow output for
certain features has truncated output (e.g. -s output truncates the
symbol name).

If a tool reads readelf -W output and will be broken due to readelf -W
changing the number of spaces, the tool is very likely broken dealing
with the object file in the first place.
To elaborate on what Mike mentioned, columns like (Flg,Lk,Inf,Al) have
the length problem as well... Fixing it will make the code more
complex, so perhaps we can recognize the problem and leave things
as-is...

Note: section warnings immediately follow the section row and
precomputing the column size can easily change the output, though it
probably doesn't matter.

% readelf -S a32
There are 4 section headers, starting at offset 0x54:

Section Headers:
  [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            00000000 000000 000000 00      0   0  0
readelf: Warning: [ 1]: Unexpected value (1) in info field.
  [ 1] .foo              PROGBITS        00000002 000037 000003 06  WA  4   1  5
readelf: Warning: section 1: sh_link value of 4 is larger than the
number of sections
  [ 2] .strtab           STRTAB          00000000 00003a 000001 00      0   0  1
  [ 3] .shstrtab         STRTAB          00000000 00003b 000018 00      0   0  1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
  L (link order), O (extra OS processing required), G (group), T (TLS),
  C (compressed), x (unknown), o (OS specific), E (exclude),
  D (mbind), p (processor specific)