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arch/tile: make sure to build memcpy_user_64 without frame pointer

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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>
This commit is contained in:
Chris Metcalf 2012-03-29 14:05:04 -04:00
parent b287f69676
commit efb734d8ed
2 changed files with 8 additions and 1 deletions
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1
arch/tile/lib/Makefile
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@ -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

8
arch/tile/lib/memcpy_user_64.c
View File

@ -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.
*/