While discussing ptrace speedup, in one email Linus said
that it's stupid that strace doesn't even use already existing
speedups, such as PTRACE_GETREGS.
I decided to give it a try.
Stracing a strace running a strace running a strace running a static binary,
before patch:
$ time ./strace -s999 -o/dev/null ./strace -s999 -o/dev/null ./strace -s999
-o/dev/null ./strace -s999 -o/dev/null ./strace ./true
execve("/bin/true", ["true"], [/* 51 vars */]) = 0
ioctl(0, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS,
{B38400 opost isig icanon echo ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS,
{B38400 opost isig icanon echo ...}) = 0
getuid32() = 0
_exit(0) = ?
+++ exited with 0 +++
real 0m33.178s
user 0m6.753s
sys 0m28.798s
After the patch:
$ time ./strace -s999 -o/dev/null ./strace -s999 -o/dev/null ./strace -s999
-o/dev/null ./strace -s999 -o/dev/null ./strace ./true
execve("/bin/true", ["true"], [/* 51 vars */]) = 0
ioctl(0, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS,
{B38400 opost isig icanon echo ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS,
{B38400 opost isig icanon echo ...}) = 0
getuid32() = 0
_exit(0) = ?
+++ exited with 0 +++
real 0m14.608s
user 0m2.959s
sys 0m12.828s
Patch follows. Please review.
I guess we need to add a check on startup to make sure PTRACE_GETREGS works?
--
vda
diff -d -urpN strace.5/syscall.c strace.6/syscall.c
--- strace.5/syscall.c 2011-08-25 10:39:36.000000000 +0200
+++ strace.6/syscall.c 2011-08-25 11:51:32.148543603 +0200
@@ -716,7 +716,28 @@ struct tcb *tcp_last = NULL;
#ifdef LINUX
# if defined (I386)
-static long eax;
+struct i386_user_regs_struct {
+ long ebx;
+ long ecx;
+ long edx;
+ long esi;
+ long edi;
+ long ebp;
+ long eax;
+ long xds;
+ long xes;
+ long xfs;
+ long xgs;
+ long orig_eax;
+ long eip;
+ long xcs;
+ long eflags;
+ long esp;
+ long xss;
+ /* Just in case we forgot a few fields and kernel would write more... */
+ long paranoia[8];
+};
+static struct i386_user_regs_struct i386_regs;
# elif defined (IA64)
long r8, r10, psr; /* TODO: make static? */
long ia32 = 0; /* not static */
@@ -895,8 +916,9 @@ get_scno(struct tcb *tcp)
if (upeek(tcp, PT_ORIG_P0, &scno))
return -1;
# elif defined (I386)
- if (upeek(tcp, 4*ORIG_EAX, &scno) < 0)
+ if (ptrace(PTRACE_GETREGS, tcp->pid, NULL, (long)&i386_regs) < 0)
return -1;
+ scno = i386_regs.orig_eax;
# elif defined (X86_64)
if (upeek(tcp, 8*ORIG_RAX, &scno) < 0)
return -1;
@@ -969,7 +991,7 @@ get_scno(struct tcb *tcp)
if (upeek(tcp, PT_CR_IPSR, &psr) >= 0)
ia32 = (psr & IA64_PSR_IS) != 0;
if (ia32) {
- if (upeek(tcp, PT_R1, &scno) < 0) /* orig eax */
+ if (upeek(tcp, PT_R1, &scno) < 0)
return -1;
} else {
if (upeek(tcp, PT_R15, &scno) < 0)
@@ -1291,21 +1313,17 @@ syscall_fixup_on_sysenter(struct tcb *tc
#ifdef LINUX
/* A common case of "not a syscall entry" is post-execve SIGTRAP */
#if defined (I386)
+ if (i386_regs.eax != -ENOSYS) {
+ if (debug)
+ fprintf(stderr, "not a syscall entry (eax = %ld)\n",
i386_regs.eax);
+ return 0;
+ }
+#elif defined (X86_64)
/* With PTRACE_O_TRACEEXEC, post-execve SIGTRAP is disabled.
- * Every extra ptrace call is expensive, so check EAX
+ * Every extra ptrace call is expensive, so check RAX
* on syscall entry only if PTRACE_O_TRACEEXEC is not enabled:
*/
if (!(ptrace_setoptions & PTRACE_O_TRACEEXEC)) {
- if (upeek(tcp, 4*EAX, &eax) < 0)
- return -1;
- if (eax != -ENOSYS) {
- if (debug)
- fprintf(stderr, "not a syscall entry (eax =
%ld)\n", eax);
- return 0;
- }
- }
-#elif defined (X86_64)
- if (!(ptrace_setoptions & PTRACE_O_TRACEEXEC)) {
if (upeek(tcp, 8*RAX, &rax) < 0)
return -1;
if (current_personality == 1)
@@ -1582,7 +1600,16 @@ syscall_enter(struct tcb *tcp)
for (i = 0; i < nargs; ++i)
if (upeek(tcp, (i < 5 ? i : i + 2)*4, &tcp->u_arg[i]) < 0)
return -1;
-# else /* Other architecture (like i386) (32bits specific) */
+# elif defined(I386)
+ (void)i;
+ (void)nargs;
+ tcp->u_arg[0] = i386_regs.ebx;
+ tcp->u_arg[1] = i386_regs.ecx;
+ tcp->u_arg[2] = i386_regs.edx;
+ tcp->u_arg[3] = i386_regs.esi;
+ tcp->u_arg[4] = i386_regs.edi;
+ tcp->u_arg[5] = i386_regs.ebp;
+# else /* Other architecture (32bits specific) */
for (i = 0; i < nargs; ++i)
if (upeek(tcp, i*4, &tcp->u_arg[i]) < 0)
return -1;
@@ -1882,7 +1909,7 @@ get_syscall_result(struct tcb *tcp)
if (upeek(tcp, PT_R0, &r0) < 0)
return -1;
# elif defined (I386)
- if (upeek(tcp, 4*EAX, &eax) < 0)
+ if (ptrace(PTRACE_GETREGS, tcp->pid, NULL, (long)&i386_regs) < 0)
return -1;
# elif defined (X86_64)
if (upeek(tcp, 8*RAX, &rax) < 0)
@@ -2053,12 +2080,12 @@ get_error(struct tcb *tcp)
tcp->u_rval = gpr2;
}
# elif defined(I386)
- if (check_errno && is_negated_errno(eax)) {
+ if (check_errno && is_negated_errno(i386_regs.eax)) {
tcp->u_rval = -1;
- u_error = -eax;
+ u_error = -i386_regs.eax;
}
else {
- tcp->u_rval = eax;
+ tcp->u_rval = i386_regs.eax;
}
# elif defined(X86_64)
if (check_errno && is_negated_errno(rax)) {
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