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 needed code to return the value
RETURN_VALUE_STRUCT_CONVENTION in this case.

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.

diff --git a/gdb/ppc-sysv-tdep.c b/gdb/ppc-sysv-tdep.c
index d7f05ddc6b43c4d451ebcdc52ccf3d94017316f1..450162dd46e895af3f148cdd836e7f0fd7a18bac 100644 (file)
--- a/gdb/ppc-sysv-tdep.c
+++ b/gdb/ppc-sysv-tdep.c
@@ -2099,6 +2099,10 @@ ppc64_sysv_abi_return_value (struct gdbarch *gdbarch, struct value *function,
       return RETURN_VALUE_REGISTER_CONVENTION;
     }
 
+  if (!language_pass_by_reference (valtype).trivially_copyable
+      && valtype->code () == TYPE_CODE_STRUCT)
+    return RETURN_VALUE_STRUCT_CONVENTION;
+
   /* In the ELFv2 ABI, aggregate types of up to 16 bytes are
      returned in registers r3:r4.  */
   if (tdep->elf_abi == POWERPC_ELF_V2