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

[Simon Marchi <simon.marchi@polymtl.ca>]

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.

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,

Simon