On Thu, Aug 25, 2011 at 12:10:06PM +0200, Denys Vlasenko wrote: > 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.
Yes, use of PTRACE_GETREGS is a long awaited change.
I expect a significant reduction of ptrace() syscall invocations.
> I guess we need to add a check on startup to make sure PTRACE_GETREGS works?
PTRACE_GETREGS is quite ancient thing, it is supported even by linux-2.2.26,
so I see no need in the runtime check this time.
> --- 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;
I suppose we shouldn't hurry with this. There is a <asm/ptrace.h> where
all this stuff is defined and supported for all linux architectures.
So I think migrating from <sys/ptrace.h> to <linux/ptrace.h> is the right
way to go.
> @@ -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;
> + }
Looks like the check for !(ptrace_setoptions & PTRACE_O_TRACEEXEC) was
removed here.
> +#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)
--
ldv
pgpDYKosLZHhI.pgp
Description: PGP signature
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