[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, 96 insertions, 71 deletions

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 2e99ae41723c..8fed9538f188 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -200,8 +200,6 @@ _GLOBAL(DoSyscall)
         bl      do_show_syscall
 #endif /* SHOW_SYSCALLS */
         rlwinm  r10,r1,0,0,(31-THREAD_SHIFT)    /* current_thread_info() */
-        li      r11,0
-        stb     r11,TI_SC_NOERR(r10)
         lwz     r11,TI_FLAGS(r10)
         andi.   r11,r11,_TIF_SYSCALL_T_OR_A
         bne-    syscall_dotrace
@@ -222,25 +220,21 @@ ret_from_syscall:
         bl      do_show_syscall_exit
 #endif
         mr      r6,r3
-        li      r11,-_LAST_ERRNO
-        cmplw   0,r3,r11
         rlwinm  r12,r1,0,0,(31-THREAD_SHIFT)    /* current_thread_info() */
-        blt+    30f
-        lbz     r11,TI_SC_NOERR(r12)
-        cmpwi   r11,0
-        bne     30f
-        neg     r3,r3
-        lwz     r10,_CCR(r1)    /* Set SO bit in CR */
-        oris    r10,r10,0x1000
-        stw     r10,_CCR(r1)
-
         /* disable interrupts so current_thread_info()->flags can't change */
-30:     LOAD_MSR_KERNEL(r10,MSR_KERNEL) /* doesn't include MSR_EE */
+        LOAD_MSR_KERNEL(r10,MSR_KERNEL) /* doesn't include MSR_EE */
         SYNC
         MTMSRD(r10)
         lwz     r9,TI_FLAGS(r12)
-        andi.   r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SIGPENDING|_TIF_NEED_RESCHED)
+        li      r8,-_LAST_ERRNO
+        andi.   r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SIGPENDING|_TIF_NEED_RESCHED|_TIF_RESTOREALL)
         bne-    syscall_exit_work
+        cmplw   0,r3,r8
+        blt+    syscall_exit_cont
+        lwz     r11,_CCR(r1)                    /* Load CR */
+        neg     r3,r3
+        oris    r11,r11,0x1000  /* Set SO bit in CR */
+        stw     r11,_CCR(r1)
 syscall_exit_cont:
 #if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
         /* If the process has its own DBCR0 value, load it up.  The single
@@ -292,46 +286,113 @@ syscall_dotrace:
         b       syscall_dotrace_cont
 
 syscall_exit_work:
-        stw     r6,RESULT(r1)   /* Save result */
+        andi.   r0,r9,_TIF_RESTOREALL
+        bne-    2f
+        cmplw   0,r3,r8
+        blt+    1f
+        andi.   r0,r9,_TIF_NOERROR
+        bne-    1f
+        lwz     r11,_CCR(r1)                    /* Load CR */
+        neg     r3,r3
+        oris    r11,r11,0x1000  /* Set SO bit in CR */
+        stw     r11,_CCR(r1)
+
+1:      stw     r6,RESULT(r1)   /* Save result */
         stw     r3,GPR3(r1)     /* Update return value */
-        andi.   r0,r9,_TIF_SYSCALL_T_OR_A
-        beq     5f
-        ori     r10,r10,MSR_EE
-        SYNC
-        MTMSRD(r10)             /* re-enable interrupts */
+2:      andi.   r0,r9,(_TIF_PERSYSCALL_MASK)
+        beq     4f
+
+        /* Clear per-syscall TIF flags if any are set, but _leave_
+        _TIF_SAVE_NVGPRS set in r9 since we haven't dealt with that
+        yet.  */
+
+        li      r11,_TIF_PERSYSCALL_MASK
+        addi    r12,r12,TI_FLAGS
+3:      lwarx   r8,0,r12
+        andc    r8,r8,r11
+#ifdef CONFIG_IBM405_ERR77
+        dcbt    0,r12
+#endif
+        stwcx.  r8,0,r12
+        bne-    3b
+        subi    r12,r12,TI_FLAGS
+        
+4:      /* Anything which requires enabling interrupts? */
+        andi.   r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SINGLESTEP|_TIF_SAVE_NVGPRS)
+        beq     7f
+
+        /* Save NVGPRS if they're not saved already */
         lwz     r4,_TRAP(r1)
         andi.   r4,r4,1
-        beq     4f
+        beq     5f
         SAVE_NVGPRS(r1)
         li      r4,0xc00
         stw     r4,_TRAP(r1)
-4:
+
+        /* Re-enable interrupts */
+5:      ori     r10,r10,MSR_EE
+        SYNC
+        MTMSRD(r10)
+
+        andi.   r0,r9,_TIF_SAVE_NVGPRS
+        bne     save_user_nvgprs
+
+save_user_nvgprs_cont:
+        andi.   r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SINGLESTEP)
+        beq     7f
+
         addi    r3,r1,STACK_FRAME_OVERHEAD
         bl      do_syscall_trace_leave
         REST_NVGPRS(r1)
-2:
-        lwz     r3,GPR3(r1)
+
+6:      lwz     r3,GPR3(r1)
         LOAD_MSR_KERNEL(r10,MSR_KERNEL) /* doesn't include MSR_EE */
         SYNC
         MTMSRD(r10)             /* disable interrupts again */
         rlwinm  r12,r1,0,0,(31-THREAD_SHIFT)    /* current_thread_info() */
         lwz     r9,TI_FLAGS(r12)
-5:
+7:
         andi.   r0,r9,_TIF_NEED_RESCHED
-        bne     1f
+        bne     8f
         lwz     r5,_MSR(r1)
         andi.   r5,r5,MSR_PR
-        beq     syscall_exit_cont
+        beq     ret_from_except
         andi.   r0,r9,_TIF_SIGPENDING
-        beq     syscall_exit_cont
+        beq     ret_from_except
         b       do_user_signal
-1:
+8:
         ori     r10,r10,MSR_EE
         SYNC
         MTMSRD(r10)             /* re-enable interrupts */
         bl      schedule
-        b       2b
+        b       6b
+
+save_user_nvgprs:
+        ld      r8,TI_SIGFRAME(r12)
+
+.macro savewords start, end
+  1:    stw \start,4*(\start)(r8)
+        .section __ex_table,"a"
+        .align  2
+        .long   1b,save_user_nvgprs_fault
+        .previous
+        .if \end - \start
+        savewords "(\start+1)",\end
+        .endif
+.endm   
+        savewords 14,31
+        b       save_user_nvgprs_cont
+
+        
+save_user_nvgprs_fault:
+        li      r3,11           /* SIGSEGV */
+        ld      r4,TI_TASK(r12)
+        bl      force_sigsegv
 
+        rlwinm  r12,r1,0,0,(31-THREAD_SHIFT)    /* current_thread_info() */
+        ld      r9,TI_FLAGS(r12)
+        b       save_user_nvgprs_cont
+        
 #ifdef SHOW_SYSCALLS
 do_show_syscall:
 #ifdef SHOW_SYSCALLS_TASK
@@ -401,28 +462,10 @@ show_syscalls_task:
 #endif /* SHOW_SYSCALLS */
 
 /*
- * The sigsuspend and rt_sigsuspend system calls can call do_signal
- * and thus put the process into the stopped state where we might
- * want to examine its user state with ptrace.  Therefore we need
- * to save all the nonvolatile registers (r13 - r31) before calling
- * the C code.
+ * The fork/clone functions need to copy the full register set into
+ * the child process. Therefore we need to save all the nonvolatile
+ * registers (r13 - r31) before calling the C code.
  */
-        .globl  ppc_sigsuspend
-ppc_sigsuspend:
-        SAVE_NVGPRS(r1)
-        lwz     r0,_TRAP(r1)
-        rlwinm  r0,r0,0,0,30            /* clear LSB to indicate full */
-        stw     r0,_TRAP(r1)            /* register set saved */
-        b       sys_sigsuspend
-
-        .globl  ppc_rt_sigsuspend
-ppc_rt_sigsuspend:
-        SAVE_NVGPRS(r1)
-        lwz     r0,_TRAP(r1)
-        rlwinm  r0,r0,0,0,30
-        stw     r0,_TRAP(r1)
-        b       sys_rt_sigsuspend
-
         .globl  ppc_fork
 ppc_fork:
         SAVE_NVGPRS(r1)
@@ -447,14 +490,6 @@ ppc_clone:
         stw     r0,_TRAP(r1)            /* register set saved */
         b       sys_clone
 
-        .globl  ppc_swapcontext
-ppc_swapcontext:
-        SAVE_NVGPRS(r1)
-        lwz     r0,_TRAP(r1)
-        rlwinm  r0,r0,0,0,30            /* clear LSB to indicate full */
-        stw     r0,_TRAP(r1)            /* register set saved */
-        b       sys_swapcontext
-
 /*
  * Top-level page fault handling.
  * This is in assembler because if do_page_fault tells us that
@@ -626,16 +661,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_601)
         .long   ret_from_except
 #endif
 
-        .globl  sigreturn_exit
-sigreturn_exit:
-        subi    r1,r3,STACK_FRAME_OVERHEAD
-        rlwinm  r12,r1,0,0,(31-THREAD_SHIFT)    /* current_thread_info() */
-        lwz     r9,TI_FLAGS(r12)
-        andi.   r0,r9,_TIF_SYSCALL_T_OR_A
-        beq+    ret_from_except_full
-        bl      do_syscall_trace_leave
-        /* fall through */
-
         .globl  ret_from_except_full
 ret_from_except_full:
         REST_NVGPRS(r1)
@@ -658,7 +683,7 @@ user_exc_return:		/* r10 contains MSR_KERNEL here */
         /* Check current_thread_info()->flags */
         rlwinm  r9,r1,0,0,(31-THREAD_SHIFT)
         lwz     r9,TI_FLAGS(r9)
-        andi.   r0,r9,(_TIF_SIGPENDING|_TIF_NEED_RESCHED)
+        andi.   r0,r9,(_TIF_SIGPENDING|_TIF_NEED_RESCHED|_TIF_RESTOREALL)
         bne     do_work
 
 restore_user: