Eliminate many SCNO_IS_VALID checks

By adding tcp->s_ent pointer tot syscall table entry,
we can replace sysent[tcp->scno] references by tcp->s_ent.
More importantly, we may ensure that tcp->s_ent is always valid,
regardless of tcp->scno value. This allows us to drop
SCNO_IS_VALID(tcp->scno) checks before we access syscall
table entry.

We can optimize (qual_flags[tcp->scno] & QUAL_foo) checks
with a similar technique.

Resulting code shrink:
   text    data     bss     dec     hex filename
 245975     700   19072  265747   40e13 strace.t3/strace
 245703     700   19072  265475   40d03 strace.t4/strace

* count.c (count_syscall): Use cheaper SCNO_IN_RANGE() check.
* defs.h: Add "int qual_flg" and "const struct sysent *s_ent"
to struct tcb. Remove "int u_nargs" from it.
Add UNDEFINED_SCNO constant which will mark undefined scnos
in tcp->qual_flg.
* pathtrace.c (pathtrace_match): Drop SCNO_IS_VALID check.
Use tcp->s_ent instead of sysent[tcp->scno].
* process.c (sys_prctl): Use tcp->s_ent->nargs instead of tcp->u_nargs.
(sys_waitid): Likewise.
* strace.c (init): Add compile-time check that DEFAULT_QUAL_FLAGS
constant is consistent with init code.
* syscall.c (decode_socket_subcall): Use tcp->s_ent->nargs
instead of tcp->u_nargs. Set tcp->qual_flg and tcp->s_ent.
(decode_ipc_subcall): Likewise.
(printargs): Use tcp->s_ent->nargs instead of tcp->u_nargs.
(printargs_lu): Likewise.
(printargs_ld): Likewise.
(get_scno): [MIPS,ALPHA] Use cheaper SCNO_IN_RANGE() check.
If !SCNO_IS_VALID, set tcp->s_ent and tcp->qual_flg to default values.
(internal_fork): Use tcp->s_ent instead of sysent[tcp->scno].
(syscall_fixup_for_fork_exec): Remove SCNO_IS_VALID check.
Use tcp->s_ent instead of sysent[tcp->scno].
(get_syscall_args): Likewise.
(get_error): Drop SCNO_IS_VALID check where it is redundant.
(dumpio): Drop SCNO_IS_VALID check where it is redundant.
Use tcp->s_ent instead of sysent[tcp->scno].
(trace_syscall_entering): Use (tcp->qual_flg & UNDEFINED_SCNO) instead
of SCNO_IS_VALID check. Use tcp->s_ent instead of sysent[tcp->scno].
Drop SCNO_IS_VALID check where it is redundant.
Print undefined syscall name with undefined_scno_name(tcp).
(trace_syscall_exiting): Likewise.
* util.c (setbpt): Use tcp->s_ent instead of sysent[tcp->scno].

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

1 files changed, 3 insertions, 3 deletions

diff --git a/util.c b/util.c
index f0d024d..4c22c5f 100644
--- a/util.c
+++ b/util.c
@@ -1332,8 +1332,8 @@ setbpt(struct tcb *tcp)
 			}
 	}
 
-	if (sysent[tcp->scno].sys_func == sys_fork ||
-	    sysent[tcp->scno].sys_func == sys_vfork) {
+	if (tcp->s_ent->sys_func == sys_fork ||
+	    tcp->s_ent->sys_func == sys_vfork) {
 		if (arg_setup(tcp, &state) < 0
 		    || get_arg0(tcp, &state, &tcp->inst[0]) < 0
 		    || get_arg1(tcp, &state, &tcp->inst[1]) < 0
@@ -1349,7 +1349,7 @@ setbpt(struct tcb *tcp)
 		return 0;
 	}
 
-	if (sysent[tcp->scno].sys_func == sys_clone) {
+	if (tcp->s_ent->sys_func == sys_clone) {
 		/* ia64 calls directly `clone (CLONE_VFORK | CLONE_VM)'
 		   contrary to x86 vfork above.  Even on x86 we turn the
 		   vfork semantics into plain fork - each application must not