Re: [PATCH 1/2] Use -fno-asynchronous-unwind-tables if C program is compiled without debug info on x86

[Pedro Alves <palves@redhat.com>]

On 04/22/2016 03:23 PM, Yao Qi wrote:

> I want to focus on handling unavailable memory in frame unwinder, so I
> cannot do all of them above.  What I can do are:
> 
>  1. Name some unwinders, such as dwarf unwinders, prologue unwinders,
>  sigtramp unwinders, stub unwinders, etc.  Other unwinders are nameless.
>  2. Add a new maint command "maint set/show preferred-unwinder".  This
>  command tell GDB to prefer a unwinder during frame unwinding.  If the
>  unwinder can't be applied to the frame (sniffer fails), it is not chosen.

Instead of a name, maybe a frame-unwinder-class enum, based on 
https://sourceware.org/bugzilla/show_bug.cgi?id=19288#c13

~~~~~~~~~~~~~~~
- The "Accurate unwinders"

  These would be the DWARF / x64 SEH based ones.

- JIT unwinders 

  Python/Guile unwind API unwinders, and also the C JIT-reader
  API unwinder, in jit.c.

- Fallback prologue unwinders
~~~~~~~~~~~~~~~

Then it could be "required" instead of "preferred", which would
catch problems with the unwinder's sniffer as well.

>  3. Prefer different unwinders (dwarf vs. prologue) in the different
>  runs of gdb.trace tests, like
> 
>  foreach_with_prefix unwinder { "dwarf" "prologue" } {
>    gdb_test "maint set preferred-unwinder $unwinder"
>    gdb_test "tfind start"
>    .....
>    gdb_test "tfind stop"
>  }
> 
>  so that the PR 19947 can be reproduced.  I'll stop here.
> 
>  What I don't plan to do in the short term are:
> 
>  - Write a case, let GDB single-step through its body, including
>    prologue, epilogue and its callees, and check "bt" can show the
>    frames correctly with different unwinders.
>  - Single-step through dynamic symbol resolution / plt, prefer "dwarf"
>    unwinder, and check "bt" can show the frames correctly.
> 
> Is it OK to you?
> 

Yes, that sounds good to me.

Thanks,
Pedro Alves