Re: [0/2] Inspect extra signal information

[Pedro Alves <pedro at codesourcery dot com>]

Hi Mark,

Thanks for taking a look, and for your comments.

On Monday 12 January 2009 23:24:16, Mark Kettenis wrote:

> One thing I wonder about is whether it really is a good idea to is the
> obfuscated typenames like __uid_t instead of a straight uid_t.  I
> realize that is the way the type is defined in headers, but in GDB we
> don't really have to worry about namespace pollution.

I don't really have much of an opinion here.  I didn't think of a reason
to be different, so I just cloned the types from glibc's headers.  I
can change that if you think it's important.

> The other thing I worry about is padding for these structure types
> that may be necessary on some platforms.  Does your code handle that?

I think so.  That is handled on the synthesized type itself.
There's this in linux_get_siginfo_type:

+  {
+    const int si_max_size = 128;
+    int si_pad_size;
+    int size_of_int = gdbarch_int_bit (gdbarch) / HOST_CHAR_BIT;
+
+    /* _pad */
+    if (gdbarch_ptr_bit (gdbarch) == 64)
+      si_pad_size = (si_max_size / size_of_int) - 4;
+    else
+      si_pad_size = (si_max_size / size_of_int) - 3;
+    append_composite_type_field (sifields_type, "_pad",
+                                init_vector_type (int_type, si_pad_size));
+  }

Which mimics this, in glibc's headers:

# define __SI_MAX_SIZE     128
# if __WORDSIZE == 64
#  define __SI_PAD_SIZE     ((__SI_MAX_SIZE / sizeof (int)) - 4)
# else
#  define __SI_PAD_SIZE     ((__SI_MAX_SIZE / sizeof (int)) - 3)
# endif

 struct siginfo
   {
     int si_signo;
     int si_errno;
     int si_code;
 
     union
       {
         int _pad[__SI_PAD_SIZE]; <<<


There's also this change, that allows us to add a field to
a struct with enforced alignment > 0:

 void
-append_composite_type_field (struct type *t, char *name,
-                            struct type *field)
+append_composite_type_field_aligned (struct type *t, char *name,
+                                    struct type *field, int alignment)
 {
   struct field *f;
   TYPE_NFIELDS (t) = TYPE_NFIELDS (t) + 1;
@@ -1860,12 +1860,31 @@ append_composite_type_field (struct type
     {
       TYPE_LENGTH (t) = TYPE_LENGTH (t) + TYPE_LENGTH (field);
       if (TYPE_NFIELDS (t) > 1)
-       FIELD_BITPOS (f[0]) = (FIELD_BITPOS (f[-1])
-                              + (TYPE_LENGTH (FIELD_TYPE (f[-1]))
-                                 * TARGET_CHAR_BIT));
+       {
+         FIELD_BITPOS (f[0]) = (FIELD_BITPOS (f[-1])
+                                + (TYPE_LENGTH (FIELD_TYPE (f[-1]))
+                                   * TARGET_CHAR_BIT));
+
+         if (alignment)
+           {
+             int left = FIELD_BITPOS (f[0]) % (alignment * TARGET_CHAR_BIT);
+             if (left)
+               {
+                 FIELD_BITPOS (f[0]) += left;
+                 TYPE_LENGTH (t) += left / TARGET_CHAR_BIT;
+               }
+           }
+       }
     }
 }

It is used to add the _sifields field to ``struct siginfo'' aligned to
``TYPE_LENGTH (long_type)'', with:

+  append_composite_type_field_aligned (siginfo_type,
+                                      "_sifields", sifields_type,
+                                      TYPE_LENGTH (long_type));

-- 
Pedro Alves