From: Matheus Castanho <msc@linux.ibm.com>
Date: Thu, 3 Dec 2020 17:15:28 +0000 (-0300)
Subject: powerpc: Use scv instruction on clone when available
X-Git-Tag: glibc-2.33~116
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=41f013cef24884604c303435dd1915be2ea5c0e0;p=thirdparty%2Fglibc.git

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 --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S b/sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S
index fc496fa6713..247e0de68ce 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)