not that this is a great idea, but my read of the documentation implies that
forking in a signal handler should work.  indeed it does in glibc unless there
has been a call to malloc.  i orginally thought this might be a kernel problem
(see: http://lkml.org/lkml/2004/5/4/150) but they directed me here.  here's some
ver_linux output:
-----
Linux e.mscd.edu 2.6.10-1.766_FC3 #1 Wed Feb 9 23:06:42 EST 2005 i686 i686 i
386 GNU/Linux
 
Gnu C                  3.4.2
Gnu make               3.80
binutils               2.15.92.0.2
Linux C Library        2.3.4
Dynamic linker (ldd)   2.3.4
-----

here's the program:

-----
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#include <assert.h>

void sig_handler (int signum)
{
        int     child;
        if ((child = fork ()) == 0) exit (0);
        waitpid (child, NULL, 0);
}

int
main (int argc, char **argv)
{
        int parent = getpid();
        int child;
        struct sigaction action;
        sigemptyset (&action.sa_mask);
        action.sa_handler = sig_handler;

        /* works if the following line is commented out */
        malloc (sizeof (int));

        assert (sigaction (SIGALRM, &action, NULL) == 0);

        /*
        ** create a child that sends the signal to be caught
        */
        if ((child = fork ()) == 0)
        {
                if (kill (parent, SIGALRM) == -1) perror ("kill");
                exit (0);
        }
        waitpid (child, NULL, 0);
}

and here is a capture of an strace:
beaty@emess->Problem$ strace ./problem
execve("./problem", ["./problem"], [/* 28 vars */]) = 0
uname({sys="Linux", node="emess.mscd.edu", ...}) = 0
brk(0)                                  = 0x9360000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=124129, ...}) = 0
old_mmap(NULL, 124129, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7fcc000
close(3)                                = 0
open("/lib/tls/libc.so.6", O_RDONLY)    = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0 O\1\000"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1521612, ...}) = 0
old_mmap(NULL, 1219740, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) =
0x7fe000
mprotect(0x921000, 27804, PROT_NONE)    = 0
old_mmap(0x922000, 16384, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x123000) = 0x922000
old_mmap(0x926000, 7324, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x926000
close(3)                                = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
0xb7fcb000
mprotect(0x922000, 8192, PROT_READ)     = 0
mprotect(0xe5c000, 4096, PROT_READ)     = 0
set_thread_area({entry_number:-1 -> 6, base_addr:0xb7fcb940, limit:1048575,
seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0,
useable:1}) = 0
munmap(0xb7fcc000, 124129)              = 0
getpid()                                = 12119
brk(0)                                  = 0x9360000
brk(0x9381000)                          = 0x9381000
rt_sigaction(SIGALRM, {0x8048550, [], SA_RESTORER, 0x825a48}, NULL, 8) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0xb7fcb988) = 12120
--- SIGALRM (Alarm clock) @ 0 (0) ---
--- SIGCHLD (Child exited) @ 0 (0) ---
futex(0x925c90, FUTEX_WAIT, 2, NULL <unfinished ...>
-----

any ideas/pointers would be most appreciated.