[glibc/maskray/lld] powerpc: Use scv instruction on clone when available

[glibc/maskray/lld] powerpc: Use scv instruction on clone when available

[Fangrui Song]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=41f013cef24884604c303435dd1915be2ea5c0e0

commit 41f013cef24884604c303435dd1915be2ea5c0e0
Author: Matheus Castanho <msc@linux.ibm.com>
Date:   Thu Dec 3 14:15:28 2020 -0300

    powerpc: Use scv instruction on clone when available
    
    clone already uses r31 to temporarily save input arguments before doing the
    syscall, so we use a different register to read from the TCB. We can also avoid
    allocating another stack frame, which is not needed since we can simply extend
    the usage of the red zone.
    
    Tested-by: Lucas A. M. Magalhães <lamm@linux.ibm.com>
    Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>

Diff:
---
 sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S | 33 ++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S b/sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S
index fc496fa671..247e0de68c 100644
--- a/sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S
+++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S
@@ -38,9 +38,11 @@ ENTRY (__clone)
 	beq-	cr0,L(badargs)
 
 	/* Save some regs in the "red zone".  */
+	std	r28,-32(r1)
 	std	r29,-24(r1)
 	std	r30,-16(r1)
 	std	r31,-8(r1)
+	cfi_offset(r28,-32)
 	cfi_offset(r29,-24)
 	cfi_offset(r30,-16)
 	cfi_offset(r31,-8)
@@ -69,11 +71,26 @@ ENTRY (__clone)
 
 	/* Do the call.  */
 	li 	r0,SYS_ify(clone)
-	DO_CALL_SC
+	CHECK_SCV_SUPPORT r28 0f
+	/* This is equivalent to DO_CALL_SCV, but we cannot use the macro here
+	because it uses CFI directives and we just called cfi_endproc.  */
+	mflr 	r9
+	std 	r9,FRAME_LR_SAVE(r1)
+	scv 	0
+	ld 	r9,FRAME_LR_SAVE(r1)
+	mtlr 	r9
+
+	/* Check for child process.  */
+	/* When using scv, error is indicated by negative r3.  */
+	cmpdi	cr1,r3,0
+	b 1f
+0:      DO_CALL_SC
 
 	/* Check for child process.  */
+	/* With sc, error is indicated by cr0.SO.  */
 	cmpdi	cr1,r3,0
 	crandc	cr1*4+eq,cr1*4+eq,cr0*4+so
+1:
 	bne-	cr1,L(parent)		/* The '-' is to minimise the race.  */
 
 	std	r2,FRAME_TOC_SAVE(r1)
@@ -95,19 +112,29 @@ L(badargs):
 	TAIL_CALL_SYSCALL_ERROR
 
 L(parent):
+	/* Check if scv is available. */
+	cmpdi cr1,r28,0
+
 	/* Parent.  Restore registers & return.  */
+	cfi_offset(r28,-32)
 	cfi_offset(r29,-24)
 	cfi_offset(r30,-16)
 	cfi_offset(r31,-8)
+	ld	r28,-32(r1)
 	ld	r29,-24(r1)
 	ld	r30,-16(r1)
 	ld	r31,-8(r1)
+	cfi_restore(r28)
 	cfi_restore(r29)
 	cfi_restore(r30)
 	cfi_restore(r31)
 
-	RET_SC
-	TAIL_CALL_SYSCALL_ERROR
+	beq cr1,0f
+	RET_SCV
+	b 1f
+0:	RET_SC
+1:	TAIL_CALL_SYSCALL_ERROR
+
 
 END (__clone)