[PATCH] i386: fix singlestep through an int80 syscall
Chuck Ebbert [Thu, 23 Mar 2006 10:59:48 +0000 (02:59 -0800)]
Using PTRACE_SINGLESTEP on a child that does an int80 syscall misses the
SIGTRAP that should be delivered upon syscall exit.  Fix that by setting
TIF_SINGLESTEP when entering the kernel via int80 with TF set.

/* Test whether singlestep through an int80 syscall works.
 */
#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <asm/user.h>

static int child, status;
static struct user_regs_struct regs;

static void do_child()
{
ptrace(PTRACE_TRACEME, 0, 0, 0);
kill(getpid(), SIGUSR1);
asm ("int $0x80" : : "a" (20)); /* getpid */
}

static void do_parent()
{
unsigned long eip, expected = 0;
again:
waitpid(child, &status, 0);
if (WIFEXITED(status) || WIFSIGNALED(status))
return;

if (WIFSTOPPED(status)) {
ptrace(PTRACE_GETREGS, child, 0, &regs);
eip = regs.eip;
if (expected)
fprintf(stderr, "child stop @ %08x, expected %08x %s\n",
eip, expected,
eip == expected ? "" : " <== ERROR");

if (*(unsigned short *)eip == 0x80cd) {
fprintf(stderr, "int 0x80 at %08x\n", (unsigned int)eip);
expected = eip + 2;
} else
expected = 0;

ptrace(PTRACE_SINGLESTEP, child, NULL, NULL);
}
goto again;
}

int main(int argc, char * const argv[])
{
child = fork();
if (child)
do_parent();
else
do_child();
return 0;
}

Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/entry.S

index 4d70472..cfc683f 100644 (file)
@@ -226,6 +226,10 @@ ENTRY(system_call)
        pushl %eax                      # save orig_eax
        SAVE_ALL
        GET_THREAD_INFO(%ebp)
+       testl $TF_MASK,EFLAGS(%esp)
+       jz no_singlestep
+       orl $_TIF_SINGLESTEP,TI_flags(%ebp)
+no_singlestep:
                                        # system call tracing in operation / emulation
        /* Note, _TIF_SECCOMP is bit number 8, and so it needs testw and not testb */
        testw $(_TIF_SYSCALL_EMU|_TIF_SYSCALL_TRACE|_TIF_SECCOMP|_TIF_SYSCALL_AUDIT),TI_flags(%ebp)