powerpc: Work around gcc's -fno-omit-frame-pointer bug

This bug is causing random crashes
(http://bugzilla.kernel.org/show_bug.cgi?id=11414).

-fno-omit-frame-pointer is only needed on powerpc when -pg is also
supplied, and there is a gcc bug that causes incorrect code generation
on 32-bit powerpc when -fno-omit-frame-pointer is used---it uses stack
locations below the stack pointer, which is not allowed by the ABI
because those locations can and sometimes do get corrupted by an
interrupt.

This ensures that CONFIG_FRAME_POINTER is only selected by ftrace.
When CONFIG_FTRACE is enabled we also pass -mno-sched-epilog to work
around the gcc codegen bug.

Patch based on work by:
	Andreas Schwab <schwab@suse.de>
	Segher Boessenkool <segher@kernel.crashing.org>

Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

3 files changed, 10 insertions, 4 deletions

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 9155c9312c1e..c6be19e9ceae 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -116,6 +116,11 @@ ifeq ($(CONFIG_6xx),y)
 KBUILD_CFLAGS           += -mcpu=powerpc
 endif
 
+# Work around a gcc code-gen bug with -fno-omit-frame-pointer.
+ifeq ($(CONFIG_FTRACE),y)
+KBUILD_CFLAGS           += -mno-sched-epilog
+endif
+
 cpu-as-$(CONFIG_4xx)            += -Wa,-m405
 cpu-as-$(CONFIG_6xx)            += -Wa,-maltivec
 cpu-as-$(CONFIG_POWER4)         += -Wa,-maltivec
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 64f5948ebc9d..946daea780f1 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -14,12 +14,13 @@ endif
 
 ifdef CONFIG_FTRACE
 # Do not trace early boot code
-CFLAGS_REMOVE_cputable.o = -pg
-CFLAGS_REMOVE_prom_init.o = -pg
+CFLAGS_REMOVE_cputable.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_prom_init.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_btext.o = -pg -mno-sched-epilog
 
 ifdef CONFIG_DYNAMIC_FTRACE
 # dynamic ftrace setup.
-CFLAGS_REMOVE_ftrace.o = -pg
+CFLAGS_REMOVE_ftrace.o = -pg -mno-sched-epilog
 endif
 
 endif
diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
index 58ecdd72630f..be60d64be7ad 100644
--- a/arch/powerpc/platforms/powermac/Makefile
+++ b/arch/powerpc/platforms/powermac/Makefile
@@ -2,7 +2,7 @@ CFLAGS_bootx_init.o  		+= -fPIC
 
 ifdef CONFIG_FTRACE
 # Do not trace early boot code
-CFLAGS_REMOVE_bootx_init.o = -pg
+CFLAGS_REMOVE_bootx_init.o = -pg -mno-sched-epilog
 endif
 
 obj-y                           += pic.o setup.o time.o feature.o pci.o \