[PATCH v6 20/25] powerpc: Change system_call_exception calling convention

[Rohan McLure]

Change system_call_exception arguments to pass a pointer to a stack frame
container caller state, as well as the original r0, which determines the
number of the syscall. This has been observed to yield improved performance
to passing them by registers, circumventing the need to allocate a stack frame.

Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>
---
V6: Split off from syscall wrapper patch.
---
 arch/powerpc/include/asm/interrupt.h |  3 +--
 arch/powerpc/kernel/entry_32.S       |  6 +++---
 arch/powerpc/kernel/interrupt_64.S   | 20 ++++++++++----------
 arch/powerpc/kernel/syscall.c        | 10 +---------
 4 files changed, 15 insertions(+), 24 deletions(-)

diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
index 8069dbc4b8d1..48eec9cd1429 100644
--- a/arch/powerpc/include/asm/interrupt.h
+++ b/arch/powerpc/include/asm/interrupt.h
@@ -665,8 +665,7 @@ static inline void interrupt_cond_local_irq_enable(struct pt_regs *regs)
 		local_irq_enable();
 }
 
-long system_call_exception(long r3, long r4, long r5, long r6, long r7, long r8,
-			   unsigned long r0, struct pt_regs *regs);
+long system_call_exception(struct pt_regs *regs, unsigned long r0);
 notrace unsigned long syscall_exit_prepare(unsigned long r3, struct pt_regs *regs, long scv);
 notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs);
 notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs);
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index e4b694cebc44..96782aa72083 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -122,9 +122,9 @@ transfer_to_syscall:
 	SAVE_NVGPRS(r1)
 	kuep_lock
 
-	/* Calling convention has r9 = orig r0, r10 = regs */
-	addi	r10,r1,STACK_FRAME_OVERHEAD
-	mr	r9,r0
+	/* Calling convention has r3 = regs, r4 = orig r0 */
+	addi	r3,r1,STACK_FRAME_OVERHEAD
+	mr	r4,r0
 	bl	system_call_exception
 
 ret_from_syscall:
diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
index 7d92a7a54727..a5dd78bdbe6d 100644
--- a/arch/powerpc/kernel/interrupt_64.S
+++ b/arch/powerpc/kernel/interrupt_64.S
@@ -70,7 +70,7 @@ _ASM_NOKPROBE_SYMBOL(system_call_vectored_\name)
 	ld	r2,PACATOC(r13)
 	mfcr	r12
 	li	r11,0
-	/* Can we avoid saving r3-r8 in common case? */
+	/* Save syscall parameters in r3-r8 */
 	SAVE_GPRS(3, 8, r1)
 	/* Zero r9-r12, this should only be required when restoring all GPRs */
 	std	r11,GPR9(r1)
@@ -87,9 +87,11 @@ _ASM_NOKPROBE_SYMBOL(system_call_vectored_\name)
 	std	r11,_TRAP(r1)
 	std	r12,_CCR(r1)
 	std	r3,ORIG_GPR3(r1)
-	addi	r10,r1,STACK_FRAME_OVERHEAD
+	/* Calling convention has r3 = regs, r4 = orig r0 */
+	addi	r3,r1,STACK_FRAME_OVERHEAD
+	mr	r4,r0
 	ld	r11,exception_marker at toc(r2)
-	std	r11,-16(r10)		/* "regshere" marker */
+	std	r11,-16(r3)		/* "regshere" marker */
 
 BEGIN_FTR_SECTION
 	HMT_MEDIUM
@@ -104,8 +106,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 	 * but this is the best we can do.
 	 */
 
-	/* Calling convention has r9 = orig r0, r10 = regs */
-	mr	r9,r0
 	bl	system_call_exception
 
 .Lsyscall_vectored_\name\()_exit:
@@ -237,7 +237,7 @@ END_BTB_FLUSH_SECTION
 	ld	r2,PACATOC(r13)
 	mfcr	r12
 	li	r11,0
-	/* Can we avoid saving r3-r8 in common case? */
+	/* Save syscall parameters in r3-r8 */
 	SAVE_GPRS(3, 8, r1)
 	/* Zero r9-r12, this should only be required when restoring all GPRs */
 	std	r11,GPR9(r1)
@@ -260,9 +260,11 @@ END_BTB_FLUSH_SECTION
 	std	r11,_TRAP(r1)
 	std	r12,_CCR(r1)
 	std	r3,ORIG_GPR3(r1)
-	addi	r10,r1,STACK_FRAME_OVERHEAD
+	/* Calling convention has r3 = regs, r4 = orig r0 */
+	addi	r3,r1,STACK_FRAME_OVERHEAD
+	mr	r4,r0
 	ld	r11,exception_marker at toc(r2)
-	std	r11,-16(r10)		/* "regshere" marker */
+	std	r11,-16(r3)		/* "regshere" marker */
 
 #ifdef CONFIG_PPC_BOOK3S
 	li	r11,1
@@ -283,8 +285,6 @@ END_BTB_FLUSH_SECTION
 	wrteei	1
 #endif
 
-	/* Calling convention has r9 = orig r0, r10 = regs */
-	mr	r9,r0
 	bl	system_call_exception
 
 .Lsyscall_exit:
diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
index 15af0ed019a7..0e9ba3efee94 100644
--- a/arch/powerpc/kernel/syscall.c
+++ b/arch/powerpc/kernel/syscall.c
@@ -13,9 +13,7 @@
 
 
 /* Has to run notrace because it is entered not completely "reconciled" */
-notrace long system_call_exception(long r3, long r4, long r5,
-				   long r6, long r7, long r8,
-				   unsigned long r0, struct pt_regs *regs)
+notrace long system_call_exception(struct pt_regs *regs, unsigned long r0)
 {
 	long ret;
 	syscall_fn f;
@@ -136,12 +134,6 @@ notrace long system_call_exception(long r3, long r4, long r5,
 		r0 = do_syscall_trace_enter(regs);
 		if (unlikely(r0 >= NR_syscalls))
 			return regs->gpr[3];
-		r3 = regs->gpr[3];
-		r4 = regs->gpr[4];
-		r5 = regs->gpr[5];
-		r6 = regs->gpr[6];
-		r7 = regs->gpr[7];
-		r8 = regs->gpr[8];
 
 	} else if (unlikely(r0 >= NR_syscalls)) {
 		if (unlikely(trap_is_unsupported_scv(regs))) {
-- 
2.34.1