On Mon, 2011-08-22 at 12:21 +0200, Denys Vlasenko wrote:
> 4. Another speedup: on x86, EAX read on syscall entry is also not
> necessary if we know that post-execve SIGTRAP is disabled by
> PTRACE_O_TRACEEXEC ptrace option. This patch (a) moves EAX retrieval
> from syscall_fixup to get_scno_on_sysexit, and (b) perform EAX retrieval
> in syscall_fixup only if we are in syscall entry and PTRACE_O_TRACEEXEC
> option is not on.
diff -d -urpN strace.3/syscall.c strace.4/syscall.c
--- strace.3/syscall.c 2011-08-22 03:37:40.306072274 +0200
+++ strace.4/syscall.c 2011-08-22 04:01:28.851814943 +0200
@@ -1309,7 +1309,11 @@ get_scno_on_sysexit(struct tcb *tcp)
return -1;
# elif defined(BFIN)
# elif defined (I386)
+ if (upeek(tcp, 4*EAX, &eax) < 0)
+ return -1;
# elif defined (X86_64)
+ if (upeek(tcp, 8*RAX, &rax) < 0)
+ return -1;
# elif defined(IA64)
# define IA64_PSR_IS ((long)1 << 34)
if (upeek(tcp, PT_CR_IPSR, &psr) >= 0)
@@ -1470,22 +1474,30 @@ syscall_fixup(struct tcb *tcp)
#ifdef LINUX
/* A common case of "not a syscall entry" is post-execve SIGTRAP */
#if defined (I386)
- if (upeek(tcp, 4*EAX, &eax) < 0)
- return -1;
- if (eax != -ENOSYS && entering(tcp)) {
- if (debug)
- fprintf(stderr, "not a syscall entry (eax = %ld)\n",
eax);
- return 0;
+ /* With PTRACE_O_TRACEEXEC, post-execve SIGTRAP is disabled.
+ * Every extra ptrace call is expensive, so check EAX
+ * on syscall entry only if PTRACE_O_TRACEEXEC is not enabled:
+ */
+ if (entering(tcp) && !(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 (upeek(tcp, 8*RAX, &rax) < 0)
- return -1;
- if (current_personality == 1)
- rax = (long int)(int)rax; /* sign extend from 32 bits */
- if (rax != -ENOSYS && entering(tcp)) {
- if (debug)
- fprintf(stderr, "not a syscall entry (rax = %ld)\n",
rax);
- return 0;
+ if (entering(tcp) && !(ptrace_setoptions & PTRACE_O_TRACEEXEC)) {
+ if (upeek(tcp, 8*RAX, &rax) < 0)
+ return -1;
+ if (current_personality == 1)
+ rax = (long int)(int)rax; /* sign extend from 32 bits */
+ if (rax != -ENOSYS && entering(tcp)) {
+ if (debug)
+ fprintf(stderr, "not a syscall entry (rax =
%ld)\n", rax);
+ return 0;
+ }
}
#elif defined (S390) || defined (S390X)
if (upeek(tcp, PT_GPR2, &gpr2) < 0)
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