[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, 23 insertions, 36 deletions

diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 5a2eba6..c9d0275 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -76,7 +76,6 @@
  * registers from *regs.  This is what we need
  * to do when a signal has been delivered.
  */
-#define sigreturn_exit(regs)	return 0
 
 #define GP_REGS_SIZE	min(sizeof(elf_gregset_t32), sizeof(struct pt_regs32))
 #undef __SIGNAL_FRAMESIZE
@@ -156,9 +155,17 @@ static inline int save_general_regs(struct pt_regs *regs,
 	elf_greg_t64 *gregs = (elf_greg_t64 *)regs;
 	int i;
 
-	for (i = 0; i <= PT_RESULT; i ++)
+	if (!FULL_REGS(regs)) {
+		set_thread_flag(TIF_SAVE_NVGPRS);
+		current_thread_info()->nvgprs_frame = frame->mc_gregs;
+	}
+
+	for (i = 0; i <= PT_RESULT; i ++) {
+		if (i == 14 && !FULL_REGS(regs))
+			i = 32;
 		if (__put_user((unsigned int)gregs[i], &frame->mc_gregs[i]))
 			return -EFAULT;
+	}
 	return 0;
 }
 
@@ -179,8 +186,6 @@ static inline int restore_general_regs(struct pt_regs *regs,
 
 #else /* CONFIG_PPC64 */
 
-extern void sigreturn_exit(struct pt_regs *);
-
 #define GP_REGS_SIZE	min(sizeof(elf_gregset_t), sizeof(struct pt_regs))
 
 static inline int put_sigset_t(sigset_t __user *uset, sigset_t *set)
@@ -256,8 +261,10 @@ long sys_sigsuspend(old_sigset_t mask, int p2, int p3, int p4, int p6, int p7,
 	while (1) {
 		current->state = TASK_INTERRUPTIBLE;
 		schedule();
-		if (do_signal(&saveset, regs))
-			sigreturn_exit(regs);
+		if (do_signal(&saveset, regs)) {
+			set_thread_flag(TIF_RESTOREALL);
+			return 0;
+		}
 	}
 }
 
@@ -292,8 +299,10 @@ long sys_rt_sigsuspend(
 	while (1) {
 		current->state = TASK_INTERRUPTIBLE;
 		schedule();
-		if (do_signal(&saveset, regs))
-			sigreturn_exit(regs);
+		if (do_signal(&saveset, regs)) {
+			set_thread_flag(TIF_RESTOREALL);
+			return 0;
+		}
 	}
 }
 
@@ -391,9 +400,6 @@ struct rt_sigframe {
 static int save_user_regs(struct pt_regs *regs, struct mcontext __user *frame,
 		int sigret)
 {
-#ifdef CONFIG_PPC32
-	CHECK_FULL_REGS(regs);
-#endif
 	/* Make sure floating point registers are stored in regs */
 	flush_fp_to_thread(current);
 
@@ -828,12 +834,6 @@ static int handle_rt_signal(unsigned long sig, struct k_sigaction *ka,
 	regs->gpr[6] = (unsigned long) rt_sf;
 	regs->nip = (unsigned long) ka->sa.sa_handler;
 	regs->trap = 0;
-#ifdef CONFIG_PPC64
-	regs->result = 0;
-
-	if (test_thread_flag(TIF_SINGLESTEP))
-		ptrace_notify(SIGTRAP);
-#endif
 	return 1;
 
 badframe:
@@ -911,8 +911,8 @@ long sys_swapcontext(struct ucontext __user *old_ctx,
 	 */
 	if (do_setcontext(new_ctx, regs, 0))
 		do_exit(SIGSEGV);
-	sigreturn_exit(regs);
-	/* doesn't actually return back to here */
+
+	set_thread_flag(TIF_RESTOREALL);
 	return 0;
 }
 
@@ -945,12 +945,11 @@ long sys_rt_sigreturn(int r3, int r4, int r5, int r6, int r7, int r8,
 	 * nobody does any...
 	 */
 	compat_sys_sigaltstack((u32)(u64)&rt_sf->uc.uc_stack, 0, 0, 0, 0, 0, regs);
-	return (int)regs->result;
 #else
 	do_sigaltstack(&rt_sf->uc.uc_stack, NULL, regs->gpr[1]);
-	sigreturn_exit(regs);		/* doesn't return here */
-	return 0;
 #endif
+	set_thread_flag(TIF_RESTOREALL);
+	return 0;
 
  bad:
 	force_sig(SIGSEGV, current);
@@ -1041,9 +1040,7 @@ int sys_debug_setcontext(struct ucontext __user *ctx,
 	 */
 	do_sigaltstack(&ctx->uc_stack, NULL, regs->gpr[1]);
 
-	sigreturn_exit(regs);
-	/* doesn't actually return back to here */
-
+	set_thread_flag(TIF_RESTOREALL);
  out:
 	return 0;
 }
@@ -1107,12 +1104,6 @@ static int handle_signal(unsigned long sig, struct k_sigaction *ka,
 	regs->gpr[4] = (unsigned long) sc;
 	regs->nip = (unsigned long) ka->sa.sa_handler;
 	regs->trap = 0;
-#ifdef CONFIG_PPC64
-	regs->result = 0;
-
-	if (test_thread_flag(TIF_SINGLESTEP))
-		ptrace_notify(SIGTRAP);
-#endif
 
 	return 1;
 
@@ -1160,12 +1151,8 @@ long sys_sigreturn(int r3, int r4, int r5, int r6, int r7, int r8,
 	    || restore_user_regs(regs, sr, 1))
 		goto badframe;
 
-#ifdef CONFIG_PPC64
-	return (int)regs->result;
-#else
-	sigreturn_exit(regs);		/* doesn't return */
+	set_thread_flag(TIF_RESTOREALL);
 	return 0;
-#endif
 
 badframe:
 	force_sig(SIGSEGV, current);