Re: [PATCH 2/2 ver 3] PowerPC, fix support for printing the function return value for non-trivial values.

[Carl Love <cel@us.ibm.com>]

Ulrich, Tom, Simon:

On Tue, 2022-11-15 at 18:05 +0000, Ulrich Weigand wrote:
> Carl Love <cel@us.ibm.com> wrote:
> 
> > +      else
> > +	sm->return_buf = 0;
> > +    }
> >   else
> > -    sm->return_buf = 0;
> > +    sm->return_buf = 0;  /* Return buffer address is not
> > available.  */
> 
> Just as a minor nit, it might be cleaner to initialize
> sm->return_buf to 0 just once up-front.
> 
> Patch is OK otherwise.
> 
> 
> Thanks,
> Ulrich

Yes, I agree, it would be best to just set sm->return_buf = 0
initially.  Then if the return buffer is available update it as needed.
That makes things a lot cleaner.

The updated patch is below.  Note, it has been tested on PowerPC and
X86_64.  It does not introduce any additional regression errors.  It
does fix the seven unresolved testcases that the initial patch
introduced and were missed by my testing of the initial patch. 

Tom, if you can verify this fix works on your system it would be
greatly appreciated.  Thanks.

                        Carl Love
---------------------------------------------------
Bug fix in commit for printing the function return value for non-trivial values

The recent commit:

  commit a0eda3df5b750ae32576a9be092b361281a41787
  Author: Carl Love <cel@us.ibm.com>
  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 | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index b71dc10370b..a72df2d6a01 100644
--- a/gdb/infcmd.c
+++ b/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.  */
-- 
2.31.1