Optimize out PTRACE_PEEKUSER with -i

strace -i was fetching PC with a separate PEEKUSER
despite having GETREGS data:

ptrace(PTRACE_GETREGS, 22331, 0, 0x8087f00) = 0
ptrace(PTRACE_PEEKUSER, 22331, 4*EIP, [0x80dd7b7]) = 0
write(3, "[080dd7b7] ioctl(0, SNDCTL_TMR_T"..., 82) = 82
ptrace(PTRACE_SYSCALL, 22331, 0, SIG_0) = 0

Now it does this:

ptrace(PTRACE_GETREGS, 22549, 0, 0x8087ea0) = 0
write(3, "[080dd7b7] ioctl(0, SNDCTL_TMR_T"..., 82) = 82
ptrace(PTRACE_SYSCALL, 22549, 0, SIG_0) = 0

Analogous improvement in sys_sigreturn() is also implemented.

* defs.h: Declare extern struct pt_regs regs for SPARC[64] and ARM.
Declare clear_regs(), get_regs() and get_regs_error flag variable.
* strace.c (trace): Call get_regs(pid) as soon as we know the tcb
and that it is stopped.
* syscall.c (get_regs): New function. Used to fetch registers early,
just after tracee has stopped.
(printcall): Move it here from util.c. Use global regs.REG data,
if available on the arch, instead of re-fetching it.
(get_scno): Use global regs.REG data.
(get_syscall_result): Likewise.
* signal.c (sys_sigreturn): Likewise.
* util.c (printcall): Moved to syscall.c.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/strace.c b/strace.c
index 1331e38..3df3fbb 100644
--- a/strace.c
+++ b/strace.c
@@ -1933,6 +1933,10 @@ trace(void)
 			}
 		}
 
+		clear_regs();
+		if (WIFSTOPPED(status))
+			get_regs(pid);
+
 		/* Under Linux, execve changes pid to thread leader's pid,
 		 * and we see this changed pid on EVENT_EXEC and later,
 		 * execve sysexit. Leader "disappears" without exit