Re: [PATCH 1/4] Add sniffer for Cygwin x86_64 core dumps

[Jon Turney <jon.turney@dronecode.org.uk>]

On 20/08/2020 23:20, Simon Marchi wrote:
> On 2020-08-12 3:18 p.m., Jon Turney wrote:
>> Similarly to existing i386_cygwin_core_osabi_sniffer()
>>
>> gdb/ChangeLog:
>>
>> 2020-07-01  Jon Turney  <jon.turney@dronecode.org.uk>
>>
>> 	* amd64-windows-tdep.c (amd64_cygwin_core_osabi_sniffer): New.
>> 	(_initialize_amd64_windows_tdep): Register amd64_cygwin_core_osabi_sniffer.
> 
> Hi Jon,
> 
> I am trying to test this using these steps:

Wow.  Thanks for testing.

> 1. Write a dummy C program that just sleeps in Cygwin, compile it (gcc test.c -g3 -O0) and run it
> 2. Run "dumper" on it

The "dumper" currently shipping in x86_64 Cygwin is utterly broken. (See 
[1] et seq.).

If you use "dumper" from the latest snapshot [2], you may have more success

[1] 
https://cygwin.com/git/?p=newlib-cygwin.git;a=commitdiff;h=7dd1b08836e8a7bb37d330995096540afce152a0;hp=38f88601469f4a6ab7cf42e1f076775c99eb17f2
[2] https://cygwin.com/snapshots/

> 3. Load it in GDB (back on my amd64 Linux host)
> 
> I get this in step 3:
> 
> $ ./gdb --data-directory=data-directory -nx -q ~/a.exe
> Reading symbols from /home/simark/a.exe...
> (gdb) core ~/core.core
> BFD: BFD (GNU Binutils) 2.35.50.20200820 internal error, aborting at /home/simark/src/binutils-gdb/bfd/bfd.c:1311 in _bfd_doprnt_scan
> 
> BFD: Please report this bug.
> 
> This happens while BFD encounters an error and tries to print this format string:
> 
>    "%pB: win32pstatus NOTE_INFO_MODULE of size %lu is too small to contain a name of size %zu"
> 
> _bfd_doprnt_scan aborts because it doesn't like the z length modifier:
> 
> (top-gdb) p ptr[-1]
> $2 = 122 'z'
> 
> So there are two issues here:
> 
> 1. The actual error, the note being too small for the name.  If I go up in
>     elfcore_grok_win32pstatus, the name_size doesn't make sense:
> 
>     (top-gdb) p name_size
>     $9 = 4194304
> 
>     whereas the note size makes sense:
> 
>     (top-gdb) p note->descsz
>     $10 = 1276

This should be resolved by using a fixed "dumper".

> 2. The internal error from trying to print that error message

Clearly, I shouldn't be using '%zu' here, so I'll make a patch to fix 
that (once I work out what I should be using :) )