Speed up x86 by avoiding EAX read on syscall entry
on x86, EAX read on syscall entry is 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.
* syscall.c (get_scno_on_sysexit): On I386 and X86_64, read eax/rax
which contain syscall return value.
(syscall_fixup): On I386 and X86_64, read eax/rax only on syscall enter
and only if PTRACE_O_TRACEEXEC is not in effect.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/syscall.c b/syscall.c
index a6f47af..fc502bf 100644
--- a/syscall.c
+++ b/syscall.c
@@ -1307,7 +1307,11 @@
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)
@@ -1468,22 +1472,30 @@
#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)