move the __this_cpu register to r16, reserve r13-r15

There have been several bugs between Linux and OPAL caused by both
using r13 for their primary per-CPU data address. This patch moves
OPAL to use r16 for this, and prevents the compiler from touching
r13-r15 (r14,r15 allow Linux to use additional fixed registers in
future).

This helps code to be a little more robust, and may make crashes
in OPAL (or debugging with pdbg or in simulators) easier to debug by
having easy access to the PACA.

Later, if we allow interrupts (other than non-maskable) to be taken when
running in skiboot, Linux's interrupt return handler does not restore
r13 if the interrupt was taken in PR=0 state, which would corrupt the
skiboot r13 register, so this allows for the possibility, although it
will have to become a formal OPAL ABI requirement if we rely on it.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[oliver: x86_64 has an r13, but not an r16 so the tests broke]
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>

wip: fix __this_cpu() in the test cases

2 files changed, 22 insertions, 22 deletions

diff --git a/asm/head.S b/asm/head.S
index 96ab2c4..3c0ce23 100644
--- a/asm/head.S
+++ b/asm/head.S
@@ -25,7 +25,7 @@
 	addi	stack_reg,stack_reg,EMERGENCY_CPU_STACKS_OFFSET@l;
 
 #define GET_CPU()							\
-	clrrdi	%r13,%r1,STACK_SHIFT
+	clrrdi	%r16,%r1,STACK_SHIFT
 
 #define SAVE_GPR(reg,sp)	std %r##reg,STACK_GPR##reg(sp)
 #define REST_GPR(reg,sp)	ld %r##reg,STACK_GPR##reg(sp)
@@ -403,7 +403,7 @@ boot_entry:
 	 * before relocation so we need to keep track of its location to wake
 	 * them up.
 	 */
-	mr	%r15,%r30
+	mr	%r18,%r30
 
 	/* Check if we need to copy ourselves up and update %r30 to
 	 * be our new offset
@@ -449,7 +449,7 @@ boot_entry:
 
 	/* Tell secondaries to move to second stage (relocated) spin loop */
 	LOAD_IMM32(%r3, boot_flag - __head)
-	add	%r3,%r3,%r15
+	add	%r3,%r3,%r18
 	li	%r0,1
 	stw	%r0,0(%r3)
 
@@ -464,18 +464,18 @@ boot_entry:
 	addi	%r3,%r3,8
 	bdnz	1b
 
-	/* Get our per-cpu pointer into r13 */
+	/* Get our per-cpu pointer into r16 */
 	GET_CPU()
 
 #ifdef STACK_CHECK_ENABLED
 	/* Initialize stack bottom mark to 0, it will be updated in C code */
 	li	%r0,0
-	std	%r0,CPUTHREAD_STACK_BOT_MARK(%r13)
+	std	%r0,CPUTHREAD_STACK_BOT_MARK(%r16)
 #endif
 	/* Initialize the stack guard */
 	LOAD_IMM64(%r3,STACK_CHECK_GUARD_BASE);
 	xor	%r3,%r3,%r31
-	std	%r3,0(%r13)
+	std	%r3,0(%r16)
 
 	/* Jump to C */
 	mr	%r3,%r27
@@ -536,7 +536,7 @@ secondary_not_found:
 	b	.
 
 call_relocate:
-	mflr	%r14
+	mflr	%r17
 	LOAD_IMM32(%r4,__dynamic_start - __head)
 	LOAD_IMM32(%r5,__rela_dyn_start - __head)
 	add	%r4,%r4,%r30
@@ -545,7 +545,7 @@ call_relocate:
 	bl	relocate
 	cmpwi	%r3,0
 	bne	1f
-	mtlr	%r14
+	mtlr	%r17
 	blr
 1:	/* Fatal relocate failure */
 	attn
@@ -592,12 +592,12 @@ reset_wakeup:
 	/* Get PIR */
 	mfspr	%r31,SPR_PIR
 
-	/* Get that CPU stack base and use it to restore r13 */
+	/* Get that CPU stack base and use it to restore r16 */
 	GET_STACK(%r1,%r31)
 	GET_CPU()
 
 	/* Restore original stack pointer */
-	ld	%r1,CPUTHREAD_SAVE_R1(%r13)
+	ld	%r1,CPUTHREAD_SAVE_R1(%r16)
 
 	/* Restore more stuff */
 	lwz	%r4,STACK_CR(%r1)
@@ -655,7 +655,7 @@ reset_fast_reboot_wakeup:
 	/* Get PIR */
 	mfspr	%r31,SPR_PIR
 
-	/* Get that CPU stack base and use it to restore r13 */
+	/* Get that CPU stack base and use it to restore r16 */
 	GET_STACK(%r1,%r31)
 	GET_CPU()
 
@@ -923,17 +923,17 @@ opal_entry:
 	std	%r9,STACK_GPR9(%r1)
 	std	%r10,STACK_GPR10(%r1)
 
-	/* Save Token (r0), LR and r13 */
+	/* Save Token (r0), LR and r16 */
 	mflr	%r12
 	std	%r0,STACK_GPR0(%r1)
-	std	%r13,STACK_GPR13(%r1)
+	std	%r16,STACK_GPR16(%r1)
 	std	%r12,STACK_LR(%r1)
 
 	/* Get the CPU thread */
 	GET_CPU()
 
 	/* Store token in CPU thread */
-	std	%r0,CPUTHREAD_CUR_TOKEN(%r13)
+	std	%r0,CPUTHREAD_CUR_TOKEN(%r16)
 
 	/* Mark the stack frame */
 	li	%r12,STACK_ENTRY_OPAL_API
@@ -975,14 +975,14 @@ opal_entry:
 	bl	opal_exit_check /* r3 is preserved */
 
 	/*
-	 * Restore r1 and r13 before decrementing in_opal_call.
-	 * Move per-cpu pointer to volatile r12, restore lr, r1, r13.
+	 * Restore r1 and r16 before decrementing in_opal_call.
+	 * Move per-cpu pointer to volatile r12, restore lr, r1, r16.
 	 */
 .Lreturn:
 	ld	%r12,STACK_LR(%r1)
 	mtlr	%r12
-	mr	%r12,%r13
-	ld	%r13,STACK_GPR13(%r1)
+	mr	%r12,%r16
+	ld	%r16,STACK_GPR16(%r1)
 	ld	%r1,STACK_GPR1(%r1)
 .Lreject:
 	sync 	/* release barrier vs quiescing */
diff --git a/asm/misc.S b/asm/misc.S
index 9290663..e2b1989 100644
--- a/asm/misc.S
+++ b/asm/misc.S
@@ -214,7 +214,7 @@ enter_p8_pm_state:
 	bl	pm_save_regs
 
 	/* Save stack pointer in struct cpu_thread */
-	std	%r1,CPUTHREAD_SAVE_R1(%r13)
+	std	%r1,CPUTHREAD_SAVE_R1(%r16)
 
 	/* Winkle or nap ? */
 	cmpli	%cr0,0,%r3,0
@@ -222,7 +222,7 @@ enter_p8_pm_state:
 
 	/* nap sequence */
 	ptesync
-0:	ld	%r0,CPUTHREAD_SAVE_R1(%r13)
+0:	ld	%r0,CPUTHREAD_SAVE_R1(%r16)
 	cmpd	cr0,%r0,%r0
 	bne	0b
 	PPC_INST_NAP
@@ -230,7 +230,7 @@ enter_p8_pm_state:
 
 	/* rvwinkle sequence */
 1:	ptesync
-0:	ld	%r0,CPUTHREAD_SAVE_R1(%r13)
+0:	ld	%r0,CPUTHREAD_SAVE_R1(%r16)
 	cmpd	cr0,%r0,%r0
 	bne	0b
 	PPC_INST_RVWINKLE
@@ -251,7 +251,7 @@ enter_p9_pm_state:
 	bl	pm_save_regs
 
 	/* Save stack pointer in struct cpu_thread */
-	std	%r1,CPUTHREAD_SAVE_R1(%r13)
+	std	%r1,CPUTHREAD_SAVE_R1(%r16)
 
 	mtspr	SPR_PSSCR,%r3
 	PPC_INST_STOP