This needs more comment, I'll try to add them in a separate patch.
With the recent changes in utrace API utrace_control(UTRACE_SINGLESTEP)
postpones enable_step() to utrace_resume() stage. The tracee can pass
tracehook_report_syscall_exit() without TIF_SINGLESTEP, this breaks
the send_sigtrap() logic.
Change ptrace_resume_action() to set UTRACE_EVENT(SYSCALL_EXIT) in
PTRACE_SINGLESTEP/PTRACE_SINGLEBLOCK case, change report_syscall_exit()
to check ctx->resume to detect this case. To synthesize the trap we
set ctx->signr = SIGTRAP and provoke UTRACE_SIGNAL_REPORT, like
ptrace_resume() does.
Roland, we already discussed this a bit and I agree, this is not optimal.
We need some changes in utrace, but currently it has a lot of problems
and it is not clear yet what utrace should do. Let's fix the code now,
once we find a better solution we can revert this change.
With this patch "make check" passes all tests again (to clarify, except
some tests which upstream doesn't pass too), including this one:
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
#include <errno.h>
#include <sys/wait.h>
#include <sys/ptrace.h>
#include <assert.h>
#include <sys/user.h>
#include <sys/debugreg.h>
#include <sys/syscall.h>
#define WEVENT(s) ((s & 0xFF0000) >> 16)
static int verbose;
#define d_printf(fmt, ...) do { if (verbose) printf(fmt,
##__VA_ARGS__); } while (0)
static struct user_regs_struct regs;
static void resume(int pid, int req, int ck_stat)
{
int stat;
assert(0 == ptrace(req, pid, 0, 0));
assert(waitpid(pid, &stat, __WALL) == pid);
//d_printf("===> %06X\n %06X\n", ck_stat, stat);
assert(stat == ck_stat);
assert(0 == ptrace(PTRACE_GETREGS, pid, NULL, ®s));
}
int main(int argc, const char *argv[])
{
int pid, child, stat;
long rip, nxt_rip;
if (getpid() == __NR_getppid) {
printf("sorry, restart\n");
return 0;
}
verbose = argc > 1;
pid = fork();
if (!pid) {
assert(0 == ptrace(PTRACE_TRACEME, 0,0,0));
kill(getpid(), SIGSTOP);
// 1: SYSCALL + SYSCALL + STEP
getppid();
// 2: SYSCALL + STEP
getppid();
// 3: STEP
getppid();
// 4: SYSCALL + STEP
if (!fork()) exit(73);
// STEPs only
if (!fork()) exit(73);
assert(0);
}
assert(wait(&stat) == pid);
assert(WIFSTOPPED(stat) && WSTOPSIG(stat) == SIGSTOP);
assert(0 == ptrace(PTRACE_SETOPTIONS, pid, 0,
PTRACE_O_TRACESYSGOOD |
PTRACE_O_TRACEFORK));
//-----------------------------------------------------------------------------
d_printf("1: syscall enter\n");
resume(pid, PTRACE_SYSCALL, 0x857F);
assert(regs.orig_rax == __NR_getppid);
assert(regs.rax == -ENOSYS);
rip = regs.rip;
d_printf("1: syscall leave\n");
resume(pid, PTRACE_SYSCALL, 0x857F);
assert(regs.orig_rax == __NR_getppid);
assert(regs.rax == getpid());
assert(regs.rip == rip);
d_printf("1: singlestep\n");
resume(pid, PTRACE_SINGLESTEP, 0x57F);
assert((long)regs.orig_rax < 0);
assert(regs.rax == getpid());
assert(regs.rip != rip);
d_printf("1: singlestep\n");
resume(pid, PTRACE_SINGLESTEP, 0x57F);
assert(regs.rip != rip);
//--------------------------------------------------------------------------------
d_printf("2: stop before syscall insn\n");
do {
resume(pid, PTRACE_SINGLESTEP, 0x57F);
} while (regs.rip != rip - 2);
assert(regs.rax == __NR_getppid);
d_printf("2: syscall enter\n");
resume(pid, PTRACE_SYSCALL, 0x857F);
assert(regs.orig_rax == __NR_getppid);
assert(regs.rax == -ENOSYS);
assert(regs.rip == rip);
d_printf("2: singlestep\n");
resume(pid, PTRACE_SINGLESTEP, 0x57F);
assert(regs.orig_rax == __NR_getppid);
assert(regs.rax == getpid());
assert(regs.rip == rip);
d_printf("2: singlestep\n");
resume(pid, PTRACE_SINGLESTEP, 0x57F);
assert(regs.rip != rip);
//--------------------------------------------------------------------------------
d_printf("3: stop before syscall insn\n");
do {
resume(pid, PTRACE_SINGLESTEP, 0x57F);
} while (regs.rip != rip - 2);
assert(regs.rax == __NR_getppid);
d_printf("3: step over syscall\n");
resume(pid, PTRACE_SINGLESTEP, 0x57F);
assert(regs.orig_rax == __NR_getppid);
assert(regs.rax == getpid());
assert(regs.rip == rip);
d_printf("3: step over syscall\n");
resume(pid, PTRACE_SINGLESTEP, 0x57F);
assert(regs.rip != rip);
//----------------------------------------------------------------------------------
d_printf("4: syscall enter\n");
resume(pid, PTRACE_SYSCALL, 0x857F);
assert(regs.orig_rax == __NR_clone);
assert(regs.rax == -ENOSYS);
rip = regs.rip;
child = waitpid (-1, &stat, WNOHANG);
assert(child == 0);
d_printf("4: step\n");
resume(pid, PTRACE_SINGLESTEP, 0x057F | (PTRACE_EVENT_FORK <<
16));
assert(regs.orig_rax == __NR_clone);
//assert(regs.rax == -ENOSYS);
assert(regs.rip == rip);
child = waitpid (-1, &stat, __WALL);
assert(child > 0 && child != pid);
d_printf("4: step\n");
resume(pid, PTRACE_SINGLESTEP, 0x057F);
assert(regs.orig_rax == __NR_clone);
assert(regs.rax == child);
assert(regs.rip == rip);
d_printf("4: provoke SIGCHLD\n");
kill(child, SIGKILL);
assert(child == waitpid (-1, &stat, __WALL));
assert(stat = SIGKILL);
d_printf("4: step\n");
resume(pid, PTRACE_SINGLESTEP, 0x7F | (SIGCHLD << 8));
assert(regs.rip == rip);
d_printf("4: SIGTERM + STEP\n");
kill(pid, SIGTERM);
resume(pid, PTRACE_SINGLESTEP, 0x7F | (SIGTERM << 8));
assert(regs.rip == rip);
d_printf("4: step\n");
resume(pid, PTRACE_SINGLESTEP, 0x057F);
assert(regs.rip != rip);
nxt_rip = regs.rip;
//---------------------------------------------------------------------------
d_printf("5: stop before syscall insn\n");
do {
resume(pid, PTRACE_SINGLESTEP, 0x57F);
} while (regs.rip != rip - 2);
assert(regs.rax == __NR_clone);
d_printf("5: step\n");
resume(pid, PTRACE_SINGLESTEP, 0x057F | (PTRACE_EVENT_FORK <<
16));
assert(regs.orig_rax == __NR_clone);
//assert(regs.rax == -ENOSYS);
assert(regs.rip == rip);
child = waitpid (-1, &stat, __WALL);
assert(child > 0 && child != pid);
d_printf("5: step\n");
resume(pid, PTRACE_SINGLESTEP, 0x057F);
assert(regs.orig_rax == __NR_clone);
assert(regs.rax == child);
assert(regs.rip == rip);
d_printf("5: step\n");
resume(pid, PTRACE_SINGLESTEP, 0x057F);
assert(regs.rip == nxt_rip);
kill(child, SIGKILL);
assert(child == waitpid (-1, &stat, __WALL));
assert(stat = SIGKILL);
d_printf("5: step\n");
resume(pid, PTRACE_CONT, 0x7F | (SIGCHLD << 8));
assert(regs.rip == nxt_rip);
d_printf("5: step\n");
resume(pid, PTRACE_SINGLESTEP, 0x057F);
assert(regs.rip != nxt_rip);
//----------------------------------------------------------------------------
kill(pid, SIGKILL);
return 0;
}
---
kernel/ptrace.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
--- UTRACE-PTRACE/kernel/ptrace.c~133_SYSCALL_EXIT_TRAP 2009-11-16
00:04:22.000000000 +0100
+++ UTRACE-PTRACE/kernel/ptrace.c 2009-11-16 16:59:48.000000000 +0100
@@ -436,8 +436,16 @@ static u32 ptrace_report_syscall_exit(en
if (ptrace_event_pending(ctx))
return UTRACE_STOP;
- set_syscall_code(ctx, PTRACE_EVENT_SYSCALL_EXIT);
+ if (ctx->resume != UTRACE_RESUME) {
+ WARN_ON(ctx->resume != UTRACE_BLOCKSTEP &&
+ ctx->resume != UTRACE_SINGLESTEP);
+ ctx->resume = UTRACE_RESUME;
+
+ ctx->signr = SIGTRAP;
+ return UTRACE_INTERRUPT;
+ }
+ set_syscall_code(ctx, PTRACE_EVENT_SYSCALL_EXIT);
return UTRACE_STOP;
}
@@ -879,6 +887,7 @@ static int ptrace_resume_action(struct t
if (unlikely(!arch_has_block_step()))
return -EIO;
action = UTRACE_BLOCKSTEP;
+ events |= UTRACE_EVENT(SYSCALL_EXIT);
break;
#endif
@@ -887,6 +896,7 @@ static int ptrace_resume_action(struct t
if (unlikely(!arch_has_single_step()))
return -EIO;
action = UTRACE_SINGLESTEP;
+ events |= UTRACE_EVENT(SYSCALL_EXIT);
break;
#endif
