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, 2 deletions

diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
index a3e1a9e96a7f..4efbfb3f3254 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h
@@ -180,6 +180,7 @@ extern const char *powerpc_base_platform;
 
 
 #define CPU_FTR_HVMODE_206              LONG_ASM_CONST(0x0000000800000000)
+#define CPU_FTR_CFAR                    LONG_ASM_CONST(0x0000001000000000)
 #define CPU_FTR_IABR                    LONG_ASM_CONST(0x0000002000000000)
 #define CPU_FTR_MMCRA                   LONG_ASM_CONST(0x0000004000000000)
 #define CPU_FTR_CTRL                    LONG_ASM_CONST(0x0000008000000000)
@@ -412,7 +413,7 @@ extern const char *powerpc_base_platform;
             CPU_FTR_COHERENT_ICACHE | \
             CPU_FTR_PURR | CPU_FTR_SPURR | CPU_FTR_REAL_LE | \
             CPU_FTR_DSCR | CPU_FTR_UNALIGNED_LD_STD | \
-            CPU_FTR_STCX_CHECKS_ADDRESS | CPU_FTR_POPCNTB)
+            CPU_FTR_STCX_CHECKS_ADDRESS | CPU_FTR_POPCNTB | CPU_FTR_CFAR)
 #define CPU_FTRS_POWER7 (CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \
             CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | CPU_FTR_HVMODE_206 |\
             CPU_FTR_MMCRA | CPU_FTR_SMT | \
@@ -420,7 +421,7 @@ extern const char *powerpc_base_platform;
             CPU_FTR_PURR | CPU_FTR_SPURR | CPU_FTR_REAL_LE | \
             CPU_FTR_DSCR | CPU_FTR_SAO  | CPU_FTR_ASYM_SMT | \
             CPU_FTR_STCX_CHECKS_ADDRESS | CPU_FTR_POPCNTB | CPU_FTR_POPCNTD | \
-            CPU_FTR_ICSWX)
+            CPU_FTR_ICSWX | CPU_FTR_CFAR)
 #define CPU_FTRS_CELL   (CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \
             CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | \
             CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \