powerpc: Avoid link stack corruption in misc asm functions

bl;mflr is used at several places to get code position.

Use bcl 20,31,+4 instead of bl in order to preserve link stack.

See commit c974809a ("powerpc/vdso: Avoid link stack corruption
in __get_datapage()") for details.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c6eabb4fb6c156f75d56dcbcc6f243e5ac0fba42.1629791763.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/misc.S

@@ -29,7 +29,7 @@ _GLOBAL(reloc_offset)
 	li	r3, 0
 _GLOBAL(add_reloc_offset)
 	mflr	r0
-	bl	1f
+	bcl	20,31,$+4
 1:	mflr	r5
 	PPC_LL	r4,(2f-1b)(r5)
 	subf	r5,r4,r5

arch/powerpc/kernel/misc_32.S

@@ -67,7 +67,7 @@ _GLOBAL(reloc_got2)
 	srwi.	r8,r8,2
 	beqlr
 	mtctr	r8
-	bl	1f
+	bcl	20,31,$+4
 1:	mflr	r0
 	lis	r4,1b@ha
 	addi	r4,r4,1b@l

arch/powerpc/kernel/misc_64.S

@@ -255,7 +255,7 @@ _GLOBAL(scom970_write)
  * Physical (hardware) cpu id should be in r3.
  */
 _GLOBAL(kexec_wait)
-	bl	1f
+	bcl	20,31,$+4
 1:	mflr	r5
 	addi	r5,r5,kexec_flag-1b
 

arch/powerpc/kernel/reloc_32.S

@@ -30,7 +30,7 @@ R_PPC_RELATIVE = 22
 _GLOBAL(relocate)
 
 	mflr	r0		/* Save our LR */
-	bl	0f		/* Find our current runtime address */
+	bcl	20,31,$+4	/* Find our current runtime address */
 0:	mflr	r12		/* Make it accessible */
 	mtlr	r0
 

arch/powerpc/kexec/relocate_32.S

@@ -93,7 +93,7 @@ wmmucr:
 	 * Invalidate all the TLB entries except the current entry
 	 * where we are running from
 	 */
-	bl	0f				/* Find our address */
+	bcl	20,31,$+4			/* Find our address */
 0:	mflr	r5				/* Make it accessible */
 	tlbsx	r23,0,r5			/* Find entry we are in */
 	li	r4,0				/* Start at TLB entry 0 */
@@ -158,7 +158,7 @@ write_out:
 	/* Switch to other address space in MSR */
 	insrwi	r9, r7, 1, 26		/* Set MSR[IS] = r7 */
 
-	bl	1f
+	bcl	20,31,$+4
 1:	mflr	r8
 	addi	r8, r8, (2f-1b)		/* Find the target offset */
 
@@ -202,7 +202,7 @@ next_tlb:
 	li	r9,0
 	insrwi	r9, r7, 1, 26			/* Set MSR[IS] = r7 */
 
-	bl	1f
+	bcl	20,31,$+4
 1:	mflr	r8
 	and	r8, r8, r11			/* Get our offset within page */
 	addi	r8, r8, (2f-1b)
@@ -240,7 +240,7 @@ setup_map_47x:
 	sync
 
 	/* Find the entry we are running from */
-	bl	2f
+	bcl	20,31,$+4
 2:	mflr	r23
 	tlbsx	r23, 0, r23
 	tlbre	r24, r23, 0			/* TLB Word 0 */
@@ -296,7 +296,7 @@ clear_utlb_entry:
 	/* Update the msr to the new TS */
 	insrwi	r5, r7, 1, 26
 
-	bl	1f
+	bcl	20,31,$+4
 1:	mflr	r6
 	addi	r6, r6, (2f-1b)
 
@@ -355,7 +355,7 @@ write_utlb:
 	/* Defaults to 256M */
 	lis	r10, 0x1000
 
-	bl	1f
+	bcl	20,31,$+4
 1:	mflr	r4
 	addi	r4, r4, (2f-1b)			/* virtual address  of 2f */