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Speed up x86 by avoiding EAX read on syscall entry

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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>
This commit is contained in:
Denys Vlasenko 2011-08-24 16:59:23 +02:00
parent 77a7459536
commit 18beb98fad
1 changed files with 26 additions and 14 deletions
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40
syscall.c
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@ -1307,7 +1307,11 @@ 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)
@ -1468,22 +1472,30 @@ 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)