[PATCH 6/6] gdb: print backtrace for internal error/warning

[Simon Marchi]

On 2021-08-19 5:49 a.m., Andrew Burgess wrote:
> This commit builds on previous work to allow GDB to print a backtrace
> of itself when GDB encounters an internal-error or internal-warning.
> 
> There's not many places where we call internal_warning, and I guess in
> most cases the user would probably continue their debug session.  And
> so, in order to avoid cluttering up the output, by default, printing
> of a backtrace is off for internal-warnings.
> 
> In contrast, printing of a backtrace is on by default for
> internal-errors, as I figure that in most cases hitting an
> internal-error is going to be the end of the debug session.
> 
> Whether a backtrace is printed or not can be controlled with the new
> settings:
> 
>   maintenance set internal-error backtrace on|off
>   maintenance show internal-error backtrace
> 
>   maintenance set internal-warning backtrace on|off
>   maintenance show internal-warning backtrace
> 
> Here is an example of what an internal-error now looks like with the
> backtrace included:
> 
>   (gdb) maintenance internal-error blah
>   ../../src.dev-3/gdb/maint.c:82: internal-error: blah
>   A problem internal to GDB has been detected,
>   further debugging may prove unreliable.
>   ----- Backtrace -----
>   0x5c61ca gdb_internal_backtrace_1
>   	../../src.dev-3/gdb/bt-utils.c:123
>   0x5c626d _Z22gdb_internal_backtracev
>   	../../src.dev-3/gdb/bt-utils.c:165
>   0xe33237 internal_vproblem
>   	../../src.dev-3/gdb/utils.c:393
>   0xe33539 _Z15internal_verrorPKciS0_P13__va_list_tag
>   	../../src.dev-3/gdb/utils.c:470
>   0x1549652 _Z14internal_errorPKciS0_z
>   	../../src.dev-3/gdbsupport/errors.cc:55
>   0x9c7982 maintenance_internal_error
>   	../../src.dev-3/gdb/maint.c:82
>   0x636f57 do_simple_func
>   	../../src.dev-3/gdb/cli/cli-decode.c:97
>    .... snip, lots more backtrace lines ....
>   ---------------------
>   ../../src.dev-3/gdb/maint.c:82: internal-error: blah
>   A problem internal to GDB has been detected,
>   further debugging may prove unreliable.
>   Quit this debugging session? (y or n) y
> 
>   This is a bug, please report it.  For instructions, see:
>   <https://www.gnu.org/software/gdb/bugs/>.
> 
>   ../../src.dev-3/gdb/maint.c:82: internal-error: blah
>   A problem internal to GDB has been detected,
>   further debugging may prove unreliable.
>   Create a core file of GDB? (y or n) n
> 
> My hope is that this backtrace might make it slightly easier to
> diagnose GDB issues if all that is provided is the console output, I
> find that we frequently get reports of an assert being hit that is
> located in pretty generic code (frame.c, value.c, etc) and it is not
> always obvious how we might have arrived at the assert.

Thanks for doing this, I think it will be very useful.

Simon