32-on-64 (x86-64) siginfo corruption

[Albert Cahalan]

The situation:  32-bit debugger, 32-bit child, 64-bit kernel

The debugger sends an RT signal to the child. (to stop it, with
a queue and siginfo so that non-debugger signals don't get lost)
To do this, the debugger uses tgkill().

Later, the debugger checks the child's siginfo_t before discarding
it. This is to be sure that the child didn't get the RT signal from
some other source. The debugger fills a siginfo_t with 0xff, then
fetches siginfo data via ptrace. The data is corrupt:

FIELD     32-ON-64   NORMAL
si_pid      -1       getpid()
si_uid    getpid()   getuid()

The "getpid" and "getuid" above are done in the debugger, not in
the child. The si_code values are SI_TKILL.

Probably the other ports with 32-on-64 support ought to verify
that this stuff works right.
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