Bug fix in commit for printing the function return value for non-triv…

…ial values

The recent commit:

  commit a0eda3d
  Author: Carl Love <[email protected]>
  Date:   Mon Nov 14 16:22:37 2022 -0500

    PowerPC, fix support for printing the function return value for non-trivial values.

Is generating a segmentation fault on x86_64-linux.

  segfault:
  ...
  PASS: gdb.asm/asm-source.exp: info source asmsrc1.s
  ERROR: GDB process no longer exists
  UNRESOLVED: gdb.asm/asm-source.exp: finish from foo3
  ...

  Reproduced on command line:
  ...
  $ gdb -q -batch -x outputs/gdb.asm/asm-source/gdb.in.1
  ...

  The problem seems to be that:
  ...
  Thread 1 "gdb" received signal SIGSEGV, Segmentation fault.
  0x000000000043de7a in symbol::type (this=0x0) at
  .../gdb_versions/devel/src/gdb/symtab.h:1287
  1287        return m_type;
  ...
  because:
  ...
  (gdb) up
  #1  0x0000000000852d94 in finish_command (arg=0x0, from_tty=0)
     at .../gdb_versions/devel/src/gdb/infcmd.c:1887
  1887        = check_typedef (sm->function->type ()->target_type ());
  (gdb) p sm->function
  $1 = (symbol *) 0x0

The code is not checking if sm->function is NULL.  If sm->function is NULL
the check for the return buffer should be skipped.

gdb/infcmd.c

@@ -1877,26 +1877,28 @@ finish_command (const char *arg, int from_tty)
   /* Find the function we will return from.  */
   frame_info_ptr callee_frame = get_selected_frame (NULL);
   sm->function = find_pc_function (get_frame_pc (callee_frame));
+  sm->return_buf = 0;    /* Initialize buffer address is not available.  */
 
   /* Determine the return convention.  If it is RETURN_VALUE_STRUCT_CONVENTION,
      attempt to determine the address of the return buffer.  */
-  enum return_value_convention return_value;
-  struct gdbarch *gdbarch = get_frame_arch (callee_frame);
+  if (sm->function != NULL)
+    {
+      enum return_value_convention return_value;
+      struct gdbarch *gdbarch = get_frame_arch (callee_frame);
 
-  struct type * val_type
-    = check_typedef (sm->function->type ()->target_type ());
+      struct type * val_type
+	= check_typedef (sm->function->type ()->target_type ());
 
-  return_value = gdbarch_return_value (gdbarch,
-				       read_var_value (sm->function, NULL,
-						       callee_frame),
-				       val_type, NULL, NULL, NULL);
+      return_value = gdbarch_return_value (gdbarch,
+					   read_var_value (sm->function, NULL,
+							   callee_frame),
+					   val_type, NULL, NULL, NULL);
 
-  if (return_value == RETURN_VALUE_STRUCT_CONVENTION
-      && val_type->code () != TYPE_CODE_VOID)
-    sm->return_buf = gdbarch_get_return_buf_addr (gdbarch, val_type,
-						  callee_frame);
-  else
-    sm->return_buf = 0;
+      if (return_value == RETURN_VALUE_STRUCT_CONVENTION
+	  && val_type->code () != TYPE_CODE_VOID)
+	sm->return_buf = gdbarch_get_return_buf_addr (gdbarch, val_type,
+						      callee_frame);
+    }
 
   /* Print info on the selected frame, including level number but not
      source.  */