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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>
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2 changed files with 8 additions and 1 deletions
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@ -7,6 +7,7 @@ lib-y = cacheflush.o checksum.o cpumask.o delay.o uaccess.o \
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strchr_$(BITS).o strlen_$(BITS).o
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ifeq ($(CONFIG_TILEGX),y)
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CFLAGS_REMOVE_memcpy_user_64.o = -fno-omit-frame-pointer
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lib-y += memcpy_user_64.o
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else
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lib-y += atomic_32.o atomic_asm_32.o memcpy_tile64.o
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@ -14,7 +14,13 @@
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* Do memcpy(), but trap and return "n" when a load or store faults.
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*
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* Note: this idiom only works when memcpy() compiles to a leaf function.
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* If "sp" is updated during memcpy, the "jrp lr" will be incorrect.
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* Here leaf function not only means it does not have calls, but also
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* requires no stack operations (sp, stack frame pointer) and no
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* use of callee-saved registers, else "jrp lr" will be incorrect since
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* unwinding stack frame is bypassed. Since memcpy() is not complex so
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* these conditions are satisfied here, but we need to be careful when
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* modifying this file. This is not a clean solution but is the best
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* one so far.
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*
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* Also note that we are capturing "n" from the containing scope here.
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*/
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