powerpc: Save Come-From Address Register (CFAR) in exception frame

Recent 64-bit server processors (POWER6 and POWER7) have a "Come-From
Address Register" (CFAR), that records the address of the most recent
branch or rfid (return from interrupt) instruction for debugging purposes.

This saves the value of the CFAR in the exception entry code and stores
it in the exception frame.  We also make xmon print the CFAR value in
its register dump code.

Rather than extend the pt_regs struct at this time, we steal the orig_gpr3
field, which is only used for system calls, and use it for the CFAR value
for all exceptions/interrupts other than system calls.  This means we
don't save the CFAR on system calls, which is not a great problem since
system calls tend not to happen unexpectedly, and also avoids adding the
overhead of reading the CFAR to the system call entry path.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index 65c13c48db43..74126765106a 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -92,9 +92,9 @@ struct paca_struct {
          * Now, starting in cacheline 2, the exception save areas
          */
         /* used for most interrupts/exceptions */
-        u64 exgen[10] __attribute__((aligned(0x80)));
-        u64 exmc[10];           /* used for machine checks */
-        u64 exslb[10];          /* used for SLB/segment table misses
+        u64 exgen[11] __attribute__((aligned(0x80)));
+        u64 exmc[11];           /* used for machine checks */
+        u64 exslb[11];          /* used for SLB/segment table misses
                                  * on the linear mapping */
         /* SLB related definitions */
         u16 vmalloc_sllp;