Re: [PATCH PR gdb/22736] [aarch64] gdb crashes on a conditional breakpoint with cast return type

[Pedro Alves <palves@redhat.com>]

On 05/26/2018 02:14 AM, Simon Marchi wrote:
> On 2018-05-25 19:20, Weimin Pan wrote:
>> Don't call language_pass_by_reference() with function that has no return type.
>>
>> Only call language_pass_by_reference(), which returns whether or not an
>> additional initial argument has been given, when return_type is not NULL
>> in function aarch64_push_dummy_call().
> 
> Hi Weimin,
> 
> Since Pedro's patch that makes GDB not assume that the return type of functions without debug info is int:
> 
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=7022349d5c86bae74b49225515f42d2e221bd368
> 
> I think we will always know the return type of the function.  Either it's in the debug info or it's provided by the user.  In call_function_by_hand_dummy, if the debug info doesn't provide the return type of the function, we use the type of the user-provided cast:
> 
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gdb/infcall.c;h=cd3eedfeeb712b27234a68cf8af394558ce4f57d;hb=cd3eedfeeb712b27234a68cf8af394558ce4f57d#l870
> 
> I think the default_return_type could be passed down to gdbarch_push_dummy_call and used the same way, so that we always have a return type.

Agreed.  

Note this bug discussed earlier, and Alan had a patch too:

 https://sourceware.org/ml/gdb-patches/2018-03/msg00157.html

That was discussed just before the recent ifunc revamp, and I
wasn't exactly sure whether master still had the issue.  Also I
forgot about it.  :-P

Alan, do you recall the status of that from your end?

The issue of using the cast-to type was discussed then too:

 https://sourceware.org/ml/gdb-patches/2018-03/msg00204.html

So I wonder whether you already had a patch for that somewhere.

> 
> Also, could you add a test case for this?  I was able to create a simple C++ (not C) program made from an object file built with no debug info:
> 
> int returns_two ()
> {
>   return 2;
> }
> 
> and one built with debug info:
> 
> int returns_two();
> 
> void func()
> {
> }
> 
> int main()
> {
>   func();
>   return 0;
> }
> 
> 
> Putting this breakpoint and running crashes GDB:
> 
> (gdb) b func if (int)returns_two() == 2"
Thanks,
Pedro Alves