Messages in this thread Patch in this message | | | From | Tejun Heo <> | Subject | [PATCH 14/17] ptrace: make group stop state visible via PTRACE_GETSIGINFO | Date | Mon, 30 May 2011 01:12:37 +0200 |
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If tracee is SEIZED, PTRACE_EVENT_STOP trap is used for group stop; however, there currently is no way to find out which signal initiated the group stop or if the group stop is still in effect.
This patch updates ptrace_do_notify() such that it reports group stop information via si.si_signo and si.si_pt_flags - both are stored in siginfo on trap. Note that it's only available if tracee was seized.
This doesn't address notification and tracer has to repeatedly put the tracee into trap and poll the flag. Later patches will deal with notification and trap transition.
Test program follows.
#define PTRACE_SEIZE 0x4206 #define PTRACE_INTERRUPT 0x4207
#define PTRACE_SEIZE_DEVEL 0x80000000
static const struct timespec ts1s = { .tv_sec = 1 };
int main(int argc, char **argv) { pid_t tracee, tracer; int i;
tracee = fork(); if (!tracee) while (1) nanosleep(&ts1s, NULL);
tracer = fork(); if (!tracer) { int last_stopped = 0, stopped; siginfo_t si;
ptrace(PTRACE_SEIZE, tracee, NULL, (void *)(unsigned long)PTRACE_SEIZE_DEVEL); repeat: ptrace(PTRACE_INTERRUPT, tracee, NULL, NULL); waitid(P_PID, tracee, NULL, WSTOPPED);
ptrace(PTRACE_GETSIGINFO, tracee, NULL, &si); if (si.si_code) { stopped = !!si.si_status; if (stopped != last_stopped) printf("tracer: stopped=%d signo=%d\n", stopped, si.si_signo); last_stopped = stopped; ptrace(PTRACE_CONT, tracee, NULL, NULL); } else { printf("tracer: SIG %d\n", si.si_signo); ptrace(PTRACE_CONT, tracee, NULL, (void *)(unsigned long)si.si_signo); } goto repeat; }
for (i = 0; i < 3; i++) { nanosleep(&ts1s, NULL); printf("mother: SIGSTOP\n"); kill(tracee, SIGSTOP); nanosleep(&ts1s, NULL); printf("mother: SIGCONT\n"); kill(tracee, SIGCONT); } nanosleep(&ts1s, NULL);
kill(tracer, SIGKILL); kill(tracee, SIGKILL); return 0; }
Tracer delivers signal, resumes group stop, induces INTERRUPT traps and reports group stop state change in busy loop. Mother sends SIGSTOP or CONT to tracee on each second. Note that si_pt_flags and flag testing are replaced with si_status testing. si_status occupies the same offset as si_pt_flags and PTRACE_SI_STOPPED is the only flag defined, so I took a dirty short cut.
# ./test-stopped mother: SIGSTOP tracer: SIG 19 tracer: stopped=1 signo=19 mother: SIGCONT tracer: stopped=0 signo=5 tracer: SIG 18 mother: SIGSTOP tracer: SIG 19 tracer: stopped=1 signo=19 mother: SIGCONT tracer: stopped=0 signo=5 tracer: SIG 18 mother: SIGSTOP tracer: SIG 19 tracer: stopped=1 signo=19 mother: SIGCONT tracer: SIG 18 tracer: stopped=0 signo=5
-v2: Local variable sig defined inside if() block it's used in as suggested by Oleg.
-v3: siginfo is filled in on trap rather than on PTRACE_GETSIGINFO as suggested by Oleg.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> --- include/linux/ptrace.h | 3 +++ kernel/signal.c | 8 ++++++++ 2 files changed, 11 insertions(+), 0 deletions(-)
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h index ad754d1..f16a63f 100644 --- a/include/linux/ptrace.h +++ b/include/linux/ptrace.h @@ -73,6 +73,9 @@ #define PTRACE_EVENT_EXIT 6 #define PTRACE_EVENT_STOP 7 +/* flags in siginfo.si_pt_flags from PTRACE_GETSIGINFO */ +#define PTRACE_SI_STOPPED 0x00000001 /* tracee is job control stopped */ + #include <asm/ptrace.h> #ifdef __KERNEL__ diff --git a/kernel/signal.c b/kernel/signal.c index 3f131be..c6ebdfe 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1875,6 +1875,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info) static void ptrace_do_notify(int exit_code, int why) { + struct signal_struct *sig = current->signal; siginfo_t info; BUG_ON((exit_code & (0x7f | ~0xffff)) != SIGTRAP); @@ -1885,6 +1886,13 @@ static void ptrace_do_notify(int exit_code, int why) info.si_pid = task_pid_vnr(current); info.si_uid = current_uid(); + if ((current->ptrace & PT_SEIZED) && + (sig->group_stop_count || sig->flags & SIGNAL_STOP_STOPPED)) { + info.si_pt_flags |= PTRACE_SI_STOPPED; + info.si_signo = current->jobctl & JOBCTL_STOP_SIGMASK; + WARN_ON_ONCE(!info.si_signo); + } + /* Let the debugger run. */ ptrace_stop(exit_code, why, 1, &info); } -- 1.7.5.2
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