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authorChris Metcalf <cmetcalf@tilera.com>2012-03-29 14:05:04 -0400
committerChris Metcalf <cmetcalf@tilera.com>2012-04-02 12:12:42 -0400
commitefb734d8ed040b053f53fd53589ed5d9c9b5cd04 (patch)
tree6f001ff457da8e8a2020f3c3ec5f7cf7c9e561ff /arch/tile/lib
parentb287f69676a34a9fc341de4d79a9c74e1959dec6 (diff)
arch/tile: make sure to build memcpy_user_64 without frame pointer
Add a comment explaining why this is important, and add a CFLAGS_REMOVE clause to the Makefile to make sure it happens. Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Diffstat (limited to 'arch/tile/lib')
-rw-r--r--arch/tile/lib/Makefile1
-rw-r--r--arch/tile/lib/memcpy_user_64.c8
2 files changed, 8 insertions, 1 deletions
diff --git a/arch/tile/lib/Makefile b/arch/tile/lib/Makefile
index 0c26086ecbef..985f59858234 100644
--- a/arch/tile/lib/Makefile
+++ b/arch/tile/lib/Makefile
@@ -7,6 +7,7 @@ lib-y = cacheflush.o checksum.o cpumask.o delay.o uaccess.o \
strchr_$(BITS).o strlen_$(BITS).o
ifeq ($(CONFIG_TILEGX),y)
+CFLAGS_REMOVE_memcpy_user_64.o = -fno-omit-frame-pointer
lib-y += memcpy_user_64.o
else
lib-y += atomic_32.o atomic_asm_32.o memcpy_tile64.o
diff --git a/arch/tile/lib/memcpy_user_64.c b/arch/tile/lib/memcpy_user_64.c
index 4763b3aff1cc..37440caa7370 100644
--- a/arch/tile/lib/memcpy_user_64.c
+++ b/arch/tile/lib/memcpy_user_64.c
@@ -14,7 +14,13 @@
* Do memcpy(), but trap and return "n" when a load or store faults.
*
* Note: this idiom only works when memcpy() compiles to a leaf function.
- * If "sp" is updated during memcpy, the "jrp lr" will be incorrect.
+ * Here leaf function not only means it does not have calls, but also
+ * requires no stack operations (sp, stack frame pointer) and no
+ * use of callee-saved registers, else "jrp lr" will be incorrect since
+ * unwinding stack frame is bypassed. Since memcpy() is not complex so
+ * these conditions are satisfied here, but we need to be careful when
+ * modifying this file. This is not a clean solution but is the best
+ * one so far.
*
* Also note that we are capturing "n" from the containing scope here.
*/