In an effort to accomodate saving the critical vs. non-critical exception
state for transfer_to_handler in head_4xx.S I'd previously used r0. This
had the unfortunate side-effect of squishing the syscall number for things
like kthread_init.
Instead, I've found that r7 seems to be a reasonable alternative. However,
in order to do this, r7 needs to be saved before transfer_to_handler
rather than in it.
In an effort to keep the 4xx, 8xx, and other ports in sync, please
consider the following patch against 2.3.31:
--- linux-2.3.31/arch/ppc/kernel/head.S Thu Dec 2 14:37:34 1999
+++ linux/arch/ppc/kernel/head.S Fri Dec 10 10:00:13 1999
@@ -287,7 +287,8 @@
stw r2,GPR2(r21); \
stw r1,0(r21); \
tovirt(r1,r21); /* set new kernel sp */ \
- SAVE_4GPRS(3, r21);
+ SAVE_4GPRS(3, r21); \
+ SAVE_GPR(7, r21);
/*
* Note: code which follows this uses cr0.eq (set if from kernel),
* r21, r22 (SRR0), and r23 (SRR1).
@@ -674,7 +675,6 @@
transfer_to_handler:
stw r22,_NIP(r21)
stw r23,_MSR(r21)
- SAVE_GPR(7, r21)
SAVE_4GPRS(8, r21)
SAVE_8GPRS(12, r21)
SAVE_8GPRS(24, r21)
--- linux-2.3.31/arch/ppc/kernel/head_8xx.S Thu Oct 7 10:17:08 1999
+++ linux/arch/ppc/kernel/head_8xx.S Fri Dec 10 10:00:49 1999
@@ -197,7 +197,8 @@
stw r2,GPR2(r21); \
stw r1,0(r21); \
tovirt(r1,r21); /* set new kernel sp */ \
- SAVE_4GPRS(3, r21);
+ SAVE_4GPRS(3, r21); \
+ SAVE_GPR(7, r21);
/*
* Note: code which follows this uses cr0.eq (set if from kernel),
* r21, r22 (SRR0), and r23 (SRR1).
@@ -591,7 +592,6 @@
lis r22,MSR_POW at h
andc r23,r23,r22
stw r23,_MSR(r21)
- SAVE_GPR(7, r21)
SAVE_4GPRS(8, r21)
SAVE_8GPRS(12, r21)
SAVE_8GPRS(24, r21)
--- linux-2.3.31/arch/ppc/kernel/head_4xx.S Sat Nov 27 15:41:59 1999
+++ linux/arch/ppc/kernel/head_4xx.S Fri Dec 10 10:13:13 1999
@@ -129,7 +129,8 @@
stw r2,GPR2(r21); /* Save r2 on the stack */\
stw r1,0(r21); \
tovirt(r1,r21); /* Set-up new kernel stack pointer */\
- SAVE_4GPRS(3, r21); /* Save r3 through r6 on the stack */
+ SAVE_4GPRS(3, r21); /* Save r3 through r6 on the stack */\
+ SAVE_GPR(7, r21); /* Save r7 on the stack */
## Common exception code for standard (non-critical) exceptions.
@@ -166,7 +167,7 @@
START_EXCEPTION(n, label); \
STND_EXCEPTION_PROLOG; \
addi r3,r1,STACK_FRAME_OVERHEAD; \
- li r0,STND_EXC; \
+ li r7,STND_EXC; \
li r20,MSR_KERNEL; \
FINISH_EXCEPTION(func)
@@ -175,7 +176,7 @@
START_EXCEPTION(n, label); \
CRIT_EXCEPTION_PROLOG; \
addi r3,r1,STACK_FRAME_OVERHEAD; \
- li r0,CRIT_EXC; \
+ li r7,CRIT_EXC; \
li r20,MSR_KERNEL; \
FINISH_EXCEPTION(func)
@@ -184,7 +185,7 @@
START_EXCEPTION(n, label); \
STND_EXCEPTION_PROLOG; \
addi r3,r1,STACK_FRAME_OVERHEAD; \
- li r0,STND_EXC; \
+ li r7,STND_EXC; \
li r20,MSR_KERNEL; \
li r4,0; \
bl transfer_to_handler; \
@@ -214,7 +215,7 @@
mfspr r4,SPRN_DEAR # Grab the DEAR, save it, pass as arg2
stw r4,_DEAR(r21)
addi r3,r1,STACK_FRAME_OVERHEAD
- li r0,STND_EXC # This is a standard exception
+ li r7,STND_EXC # This is a standard exception
li r20,MSR_KERNEL
rlwimi r20,r23,0,16,16 # Copy EE bit from the saved MSR
FINISH_EXCEPTION(do_page_fault) # do_page_fault(regs, ESR, DEAR)
@@ -226,7 +227,7 @@
mr r4,r22 # Pass SRR0 as arg2
mr r5,r23 # Pass SRR1 as arg3
addi r3,r1,STACK_FRAME_OVERHEAD
- li r0,STND_EXC # This is a standard exception
+ li r7,STND_EXC # This is a standard exception
li r20,MSR_KERNEL
rlwimi r20,r23,0,16,16 # Copy EE bit from the saved MSR
FINISH_EXCEPTION(do_page_fault) # do_page_fault(regs, SRR0, SRR1)
@@ -242,7 +243,7 @@
mfspr r4,SPRN_DEAR # Grab the DEAR and save it
stw r4,_DEAR(r21)
addi r3,r1,STACK_FRAME_OVERHEAD
- li r0,STND_EXC # This is a standard exception
+ li r7,STND_EXC # This is a standard exception
li r20,MSR_KERNEL
rlwimi r20,r23,0,16,16 # Copy EE bit from the saved MSR
FINISH_EXCEPTION(AlignmentException)
@@ -252,7 +253,7 @@
START_EXCEPTION(0x0700, ProgramCheck)
STND_EXCEPTION_PROLOG
addi r3,r1,STACK_FRAME_OVERHEAD
- li r0,STND_EXC # This is a standard exception
+ li r7,STND_EXC # This is a standard exception
li r20,MSR_KERNEL
rlwimi r20,r23,0,16,16 # Copy EE bit from the saved MSR
FINISH_EXCEPTION(ProgramCheckException)
@@ -266,7 +267,7 @@
START_EXCEPTION(0x0C00, SystemCall)
STND_EXCEPTION_PROLOG
stw r3,ORIG_GPR3(r21)
- li r0,STND_EXC # This is a standard exception
+ li r7,STND_EXC # This is a standard exception
li r20,MSR_KERNEL
rlwimi r20,r23,0,16,16 # Copy EE bit from the saved MSR
FINISH_EXCEPTION(DoSyscall)
@@ -294,7 +295,7 @@
START_EXCEPTION(0x1100, DTLBMiss)
STND_EXCEPTION_PROLOG
addi r3,r1,STACK_FRAME_OVERHEAD
- li r0,STND_EXC
+ li r7,STND_EXC
li r20,MSR_KERNEL
FINISH_EXCEPTION(UnknownException)
@@ -303,7 +304,7 @@
START_EXCEPTION(0x1200, ITLBMiss)
STND_EXCEPTION_PROLOG
addi r3,r1,STACK_FRAME_OVERHEAD
- li r0,STND_EXC
+ li r7,STND_EXC
li r20,MSR_KERNEL
FINISH_EXCEPTION(UnknownException)
@@ -341,7 +342,6 @@
_GLOBAL(transfer_to_handler)
stw r22,_NIP(r21) # Save the faulting IP on the stack
stw r23,_MSR(r21) # Save the exception MSR on the stack
- SAVE_GPR(7, r21) # Save r7 on the stack
SAVE_4GPRS(8, r21) # Save r8 through r11 on the stack
SAVE_8GPRS(12, r21) # Save r12 through r19 on the stack
SAVE_8GPRS(24, r21) # Save r24 through r31 on the stack
@@ -367,7 +367,7 @@
bgt- stack_ovf # If r2 < r1 < r2 + TASK_STRUCT_SIZE
lwz r24,0(r23) # Virtual address of the handler
lwz r23,4(r23) # Handler return pointer
- cmpwi cr0,r0,STND_EXC # What type of exception is this?
+ cmpwi cr0,r7,STND_EXC # What type of exception is this?
bne 3f # It is a critical exception...
## Standard exception jump path
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