[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>

1 files changed, 18 insertions, 5 deletions

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 1decf2785530..5462bef898f6 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -96,8 +96,10 @@ long sys_rt_sigsuspend(sigset_t __user *unewset, size_t sigsetsize, int p3, int
         while (1) {
                 current->state = TASK_INTERRUPTIBLE;
                 schedule();
-                if (do_signal(&saveset, regs))
+                if (do_signal(&saveset, regs)) {
+                        set_thread_flag(TIF_RESTOREALL);
                         return 0;
+                }
         }
 }
 
@@ -152,6 +154,14 @@ static long setup_sigcontext(struct sigcontext __user *sc, struct pt_regs *regs,
         err |= __put_user(0, &sc->v_regs);
 #endif /* CONFIG_ALTIVEC */
         err |= __put_user(&sc->gp_regs, &sc->regs);
+        if (!FULL_REGS(regs)) {
+                /* Zero out the unsaved GPRs to avoid information
+                   leak, and set TIF_SAVE_NVGPRS to ensure that the
+                   registers do actually get saved later. */
+                memset(&regs->gpr[14], 0, 18 * sizeof(unsigned long));
+                set_thread_flag(TIF_SAVE_NVGPRS);
+                current_thread_info()->nvgprs_frame = &sc->gp_regs;
+        }
         err |= __copy_to_user(&sc->gp_regs, regs, GP_REGS_SIZE);
         err |= __copy_to_user(&sc->fp_regs, &current->thread.fpr, FP_REGS_SIZE);
         err |= __put_user(signr, &sc->signal);
@@ -340,6 +350,7 @@ int sys_swapcontext(struct ucontext __user *old_ctx,
                 do_exit(SIGSEGV);
 
         /* This returns like rt_sigreturn */
+        set_thread_flag(TIF_RESTOREALL);
         return 0;
 }
 
@@ -372,7 +383,8 @@ int sys_rt_sigreturn(unsigned long r3, unsigned long r4, unsigned long r5,
          */
         do_sigaltstack(&uc->uc_stack, NULL, regs->gpr[1]);
 
-        return regs->result;
+        set_thread_flag(TIF_RESTOREALL);
+        return 0;
 
 badframe:
 #if DEBUG_SIG
@@ -454,9 +466,6 @@ static int setup_rt_frame(int signr, struct k_sigaction *ka, siginfo_t *info,
         if (err)
                 goto badframe;
 
-        if (test_thread_flag(TIF_SINGLESTEP))
-                ptrace_notify(SIGTRAP);
-
         return 1;
 
 badframe:
@@ -502,6 +511,8 @@ static inline void syscall_restart(struct pt_regs *regs, struct k_sigaction *ka)
                  * we only get here if there is a handler, we dont restart.
                  */
                 regs->result = -EINTR;
+                regs->gpr[3] = EINTR;
+                regs->ccr |= 0x10000000;
                 break;
         case -ERESTARTSYS:
                 /* ERESTARTSYS means to restart the syscall if there is no
@@ -509,6 +520,8 @@ static inline void syscall_restart(struct pt_regs *regs, struct k_sigaction *ka)
                  */
                 if (!(ka->sa.sa_flags & SA_RESTART)) {
                         regs->result = -EINTR;
+                        regs->gpr[3] = EINTR;
+                        regs->ccr |= 0x10000000;
                         break;
                 }
                 /* fallthrough */