[Bug gdb/20287] X32 and "gdb_static_assert (sizeof (nat_siginfo_t) == sizeof (siginfo_t))"

["palves at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=20287

--- Comment #30 from Pedro Alves <palves at redhat dot com> ---
OK, so PTRACE_GETSIGINFO returns a x32 siginfo_t object when the ptracer is a
x32 process.

So the correct fix is indeed to make nat_siginfo_t match the x32 siginfo, when
gdb is built as an x32 program.

However, it doesn't look like it's just the padding that is wrong.  We have
this:

 /* For native 64-bit, clock_t in _sigchld is 64bit aligned at 4 bytes.  */
 typedef long __attribute__ ((__aligned__ (4))) nat_clock_t;

However, /usr/include/bits/siginfo.h has:

 # if defined __x86_64__ && __WORDSIZE == 32
 /* si_utime and si_stime must be 4 byte aligned for x32 to match the
    kernel.  We align siginfo_t to 8 bytes so that si_utime and si_stime
    are actually aligned to 8 bytes since their offsets are multiple of
    8 bytes.  */
 typedef __clock_t __attribute__ ((__aligned__ (4))) __sigchld_clock_t;
 #  define __SI_ALIGNMENT __attribute__ ((__aligned__ (8)))
 # else
 typedef __clock_t __sigchld_clock_t;
 #  define __SI_ALIGNMENT
 # endif

So we're currently forcing 4-byte alignment on clock_t, when it should only be
so for x32, not 64-bit?

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