Re: [PATCH 1/2 ver 3] PowerPC, function ppc64_sysv_abi_return_value add missing return value convention

[Ulrich Weigand <Ulrich.Weigand@de.ibm.com>]

Carl Love <cel@us.ibm.com> wrote:

>-------------------------------
>PowerPC, function ppc64_sysv_abi_return_value add missing return value convention
>
>This patch address five testcase failures in gdb.cp/non-trivial-retval.exp.
>The following commit resulted in the five testcases failures on PowerPC.  The
>value returned by the function is being reported incorrectly.
>
>  commit b1718fcdd1d2a5c514f8ee504ba07fb3f42b8608
>  Author: Andrew Burgess <aburgess@redhat.com>
>  Date:   Mon Dec 13 16:56:16 2021 +0000
>
>      gdb: on x86-64 non-trivial C++ objects are returned in memory
>
>      Fixes PR gdb/28681.  It was observed that after using the `finish`
>      command an incorrect value was displayed in some cases.  Specifically,
>      this behaviour was observed on an x86-64 target.
>
>The function:
>
>  enum return_value_convention
>  ppc64_sysv_abi_return_value (struct gdbarch *gdbarch, struct value *function,
>                               struct type *valtype, struct regcache *regcache,
>                               gdb_byte *readbuf, const gdb_byte *writebuf)
>
>should return RETURN_VALUE_STRUCT_CONVENTION if the valtype->code() is
>TYPE_CODE_STRUCT and if the language_pass_by_reference is not
>trivially_copyable.
>
>This patch adds the need code to return the value
>RETURN_VALUE_STRUCT_CONVENTION in the case of this case.

This still has the typos Kevin pointed out.

>With this patch, the five test cases still fail but with the message "Value
>returned has type: A. Cannot determine contents".  The PowerPC ABI stores the
>address of the buffer containing the function return value in register r3 on
>entry to the function.  However, the PowerPC ABI does not guarentee that r3
>will not be modified in the function.  So when the function returns, the return
>buffer address cannot be reliably obtained from register r3.  Thus the message
>"Cannot determine contents" is appropriate in this case.

OK with the above typos fixed.

Bye,
Ulrich