Re: [PATCH] [AArch64] Fix PR gdb/28681

[Andrew Burgess via Gdb-patches <gdb-patches@sourceware.org>]

* Luis Machado <luis.machado@linaro.org> [2022-01-04 14:22:54 -0300]:

> This is the same as commit b1718fcdd1d2a5c514f8ee504ba07fb3f42b8608, but
> fixing things for AArch64.
> 
> With the patch, gdb.cp/non-trivial-retval.exp has full passes on
> AArch64-Linux Ubuntu 20.04/18.04.
> ---
>  gdb/aarch64-tdep.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
> index 70fb66954a4..802762f303c 100644
> --- a/gdb/aarch64-tdep.c
> +++ b/gdb/aarch64-tdep.c
> @@ -2323,6 +2323,15 @@ aarch64_extract_return_value (struct type *type, struct regcache *regs,
>  	  valbuf += X_REGISTER_SIZE;
>  	}
>      }
> +  else if (!language_pass_by_reference (type).trivially_copyable)
> +    {
> +      /* If the object is a non-trivial C++ object, the result is passed as a
> +	 pointer stored in X0.  */
> +      CORE_ADDR addr;
> +
> +      regs->cooked_read (AARCH64_X0_REGNUM, &addr);
> +      read_memory (addr, valbuf, TYPE_LENGTH (type));
> +    }
>    else
>      {
>        /* For a structure or union the behaviour is as if the value had

The aarch64_extract_return_value function is called exclusively from
aarch64_return_value.

After calling this function the aarch64_return_value function returns
RETURN_VALUE_REGISTER_CONVENTION, which I don't think is correct in
the above case.

I think we should be returning one of either
RETURN_VALUE_STRUCT_CONVENTION, RETURN_VALUE_ABI_RETURNS_ADDRESS or
RETURN_VALUE_ABI_PRESERVES_ADDRESS.

I wonder if aarch64_return_in_memory should be doing more of the work
in this case?  But that's just a thought, I'm sure whatever you come
up with will be fine, so long as the return type is correct.

Thanks,
Andrew