Re: [PATCH/RFC] auxv entries

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> Date: Mon, 15 Sep 2008 11:20:31 +0200 (CEST)
> From: Mark Kettenis <mark.kettenis@xs4all.nl>
> 
> > From: Thiago Jung Bauermann <bauerman@br.ibm.com>
> > Date: Sun, 14 Sep 2008 21:33:04 -0300
> > 
> > I have this in <elf.h> in ppc64-linux:
> > 
> > typedef struct
> > {
> >   uint64_t a_type;              /* Entry type */
> >   union
> >     {
> >       uint64_t a_val;           /* Integer value */
> >       /* We use to have pointer elements added here.  We cannot do that,
> >          though, since it does not work when using 32-bit definitions
> >          on 64-bit platforms and vice versa.  */
> >     } a_un;
> > } Elf64_auxv_t;
> > 
> > So default_auxv_parse seems right to me.
> 
> Hmm, so it looks like Linux doesn't follow the 64-bit PowerPC ABI
> here.  At least version 1.7 of that spec has the "standard" form of
> the struct with a_type being an int.
> 
> OpenBSD and Solaris both use the "standard" form, so I'd argue that
> Linux is the odd one out here.  I'll see if I can come up with a diff
> that overrides the standard layout for 64-bit PPC linux.
> 

Here is the promised diff.  Tested on Linux on amd64 (which doesn't
say a lot since it is little-endian).

ok?


Index: ChangeLog
from  Mark Kettenis  <kettenis@gnu.org>

	* auxv.c (default_auxv_parse): Change code to reflect standard
	auxv_t layout.
	* linux-nat.c (linux_nat_auxv_parse): New function.
	(linux_nat_add_target): Install linux_nat_auxv_parse.

Index: auxv.c
===================================================================
RCS file: /cvs/src/src/gdb/auxv.c,v
retrieving revision 1.14
diff -u -p -r1.14 auxv.c
--- auxv.c 11 Sep 2008 14:29:21 -0000 1.14
+++ auxv.c 15 Sep 2008 20:17:42 -0000
@@ -82,20 +82,22 @@ int
 default_auxv_parse (struct target_ops *ops, gdb_byte **readptr,
 		   gdb_byte *endptr, CORE_ADDR *typep, CORE_ADDR *valp)
 {
-  const int sizeof_auxv_field = gdbarch_ptr_bit (target_gdbarch)
-				/ TARGET_CHAR_BIT;
+  struct type *builtin_int = builtin_type (target_gdbarch)->builtin_int;
+  struct type *builtin_long = builtin_type (target_gdbarch)->builtin_long;
+  const int sizeof_auxv_type = TYPE_LENGTH(builtin_int);
+  const int sizeof_auxv_val = TYPE_LENGTH(builtin_long);
   gdb_byte *ptr = *readptr;
 
   if (endptr == ptr)
     return 0;
 
-  if (endptr - ptr < sizeof_auxv_field * 2)
+  if (endptr - ptr < sizeof_auxv_val * 2)
     return -1;
 
-  *typep = extract_unsigned_integer (ptr, sizeof_auxv_field);
-  ptr += sizeof_auxv_field;
-  *valp = extract_unsigned_integer (ptr, sizeof_auxv_field);
-  ptr += sizeof_auxv_field;
+  *typep = extract_unsigned_integer (ptr, sizeof_auxv_type);
+  ptr += sizeof_auxv_val;	/* Alignment.  */
+  *valp = extract_unsigned_integer (ptr, sizeof_auxv_val);
+  ptr += sizeof_auxv_val;
 
   *readptr = ptr;
   return 1;
Index: linux-nat.c
===================================================================
RCS file: /cvs/src/src/gdb/linux-nat.c,v
retrieving revision 1.102
diff -u -p -r1.102 linux-nat.c
--- linux-nat.c 8 Sep 2008 21:51:18 -0000 1.102
+++ linux-nat.c 15 Sep 2008 20:17:44 -0000
@@ -4353,6 +4353,29 @@ send_sigint_callback (struct lwp_info *l
   return 0;
 }
 
+static int
+linux_nat_auxv_parse(struct target_ops *ops, gdb_byte **readptr,
+		     gdb_byte *endptr, CORE_ADDR *typep, CORE_ADDR *valp)
+{
+  struct type *builtin_long = builtin_type (target_gdbarch)->builtin_long;
+  const int sizeof_auxv_field = TYPE_LENGTH(builtin_long);
+  gdb_byte *ptr = *readptr;
+
+  if (endptr == ptr)
+    return 0;
+
+  if (endptr - ptr < sizeof_auxv_field * 2)
+    return -1;
+
+  *typep = extract_unsigned_integer (ptr, sizeof_auxv_field);
+  ptr += sizeof_auxv_field;
+  *valp = extract_unsigned_integer (ptr, sizeof_auxv_field);
+  ptr += sizeof_auxv_field;
+
+  *readptr = ptr;
+  return 1;
+}
+
 static void
 linux_nat_stop (ptid_t ptid)
 {
@@ -4401,6 +4424,10 @@ linux_nat_add_target (struct target_ops 
   t->to_terminal_inferior = linux_nat_terminal_inferior;
   t->to_terminal_ours = linux_nat_terminal_ours;
 
+  /* The Linux folks messed up and didn't follow the ELF ABI on
+     various 64-bit architectures.  */
+  t->to_auxv_parse = linux_nat_auxv_parse;
+
   /* Methods for non-stop support.  */
   t->to_stop = linux_nat_stop;