[PATCH] syscall entry/exit revamp

This cleanup patch speeds up the null syscall path on ppc64 by about 3%,
and brings the ppc32 and ppc64 code slightly closer together.

The ppc64 code was checking current_thread_info()->flags twice in the
syscall exit path; once for TIF_SYSCALL_T_OR_A before disabling
interrupts, and then again for TIF_SIGPENDING|TIF_NEED_RESCHED etc after
disabling interrupts. Now we do the same as ppc32 -- check the flags
only once in the fast path, and re-enable interrupts if necessary in the
ptrace case.

The patch abolishes the 'syscall_noerror' member of struct thread_info
and replaces it with a TIF_NOERROR bit in the flags, which is handled in
the slow path. This shortens the syscall entry code, which no longer
needs to clear syscall_noerror.

The patch adds a TIF_SAVE_NVGPRS flag which causes the syscall exit slow
path to save the non-volatile GPRs into a signal frame. This removes the
need for the assembly wrappers around sys_sigsuspend(),
sys_rt_sigsuspend(), et al which existed solely to save those registers
in advance. It also means I don't have to add new wrappers for ppoll()
and pselect(), which is what I was supposed to be doing when I got
distracted into this...

Finally, it unifies the ppc64 and ppc32 methods of handling syscall exit
directly into a signal handler (as required by sigsuspend et al) by
introducing a TIF_RESTOREALL flag which causes _all_ the registers to be
reloaded from the pt_regs by taking the ret_from_exception path, instead
of the normal syscall exit path which stomps on the callee-saved GPRs.

It appears to pass an LTP test run on ppc64, and passes basic testing on
ppc32 too. Brief tests of ptrace functionality with strace and gdb also
appear OK. I wouldn't send it to Linus for 2.6.15 just yet though :)

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

2 files changed, 10 insertions, 4 deletions

diff --git a/include/asm-powerpc/ptrace.h b/include/asm-powerpc/ptrace.h
index 1f7ecdb0b6ce..9c550b314823 100644
--- a/include/asm-powerpc/ptrace.h
+++ b/include/asm-powerpc/ptrace.h
@@ -87,7 +87,7 @@ extern unsigned long profile_pc(struct pt_regs *regs);
 
 #define force_successful_syscall_return()   \
         do { \
-                current_thread_info()->syscall_noerror = 1; \
+                set_thread_flag(TIF_NOERROR); \
         } while(0)
 
 /*
diff --git a/include/asm-powerpc/thread_info.h b/include/asm-powerpc/thread_info.h
index e525f49bd179..ac1e80e6033e 100644
--- a/include/asm-powerpc/thread_info.h
+++ b/include/asm-powerpc/thread_info.h
@@ -37,8 +37,7 @@ struct thread_info {
         int             preempt_count;          /* 0 => preemptable,
                                                    <0 => BUG */
         struct restart_block restart_block;
-        /* set by force_successful_syscall_return */
-        unsigned char   syscall_noerror;
+        void *nvgprs_frame;
         /* low level flags - has atomic operations done on it */
         unsigned long   flags ____cacheline_aligned_in_smp;
 };
@@ -123,6 +122,9 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_SINGLESTEP          9       /* singlestepping active */
 #define TIF_MEMDIE              10
 #define TIF_SECCOMP             11      /* secure computing */
+#define TIF_RESTOREALL          12      /* Restore all regs (implies NOERROR) */
+#define TIF_SAVE_NVGPRS         13      /* Save r14-r31 in signal frame */
+#define TIF_NOERROR             14      /* Force successful syscall return */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE      (1<<TIF_SYSCALL_TRACE)
@@ -136,10 +138,14 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_SYSCALL_AUDIT      (1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SINGLESTEP         (1<<TIF_SINGLESTEP)
 #define _TIF_SECCOMP            (1<<TIF_SECCOMP)
+#define _TIF_RESTOREALL         (1<<TIF_RESTOREALL)
+#define _TIF_SAVE_NVGPRS        (1<<TIF_SAVE_NVGPRS)
+#define _TIF_NOERROR            (1<<TIF_NOERROR)
 #define _TIF_SYSCALL_T_OR_A     (_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP)
 
 #define _TIF_USER_WORK_MASK     (_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | \
-                                 _TIF_NEED_RESCHED)
+                                 _TIF_NEED_RESCHED | _TIF_RESTOREALL)
+#define _TIF_PERSYSCALL_MASK    (_TIF_RESTOREALL|_TIF_NOERROR|_TIF_SAVE_NVGPRS)
 
 #endif /* __KERNEL__ */