Commit 41b5368f authored Nov 08, 2013 by Taras Kondratiuk Committed by Taras Kondratiuk Apr 01, 2014

ARM: kprobes-test: Workaround GAS .align bug



By default if no fill symbol is given to .align directive in a code
section it fills gap with NOPs. If previous fragment is not
instruction-aligned, additional pre-alignment is done by zero bytes
before NOPs. These zero bytes are marked as data by special symbol $d in
symbol table. Unfortunately GAS assumes that there is only code in the
code section so it "puts back" code symbol $a at the end of this
pre-alignment. So if there is some data after alignment it will be
interpreted as code and will be swapped back to LE for BE8 system during
a final linking.

If explicit fill value is given to .align, the NOP-padding code is
skipped and symbol table does not get messed-up.

So the workaround for this issue:
Use explicit fill value if data should be aligned in the code section.

Acked-by: Ben Dooks <ben.dooks@codethink.co.uk>
Acked-by: Jon Medhurst <tixy@linaro.org>
Signed-off-by: Taras Kondratiuk <taras.kondratiuk@linaro.org>

parent 3b86ee7a

arch/arm/kernel/kprobes-test.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -113,7 +113,7 @@
		* @ start of inline data...
		* .ascii "mov r0, r7" @ text title for test case
		* .byte 0
		* .align 2
		* .align 2, 0
		*
		* @ TEST_ARG_REG
		* .byte ARG_TYPE_REG

arch/arm/kernel/kprobes-test.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -115,7 +115,7 @@ struct test_arg_end {
		/* multiple strings to be concatenated. */ \
		".ascii "#title" \n\t" \
		".byte 0 \n\t" \
		".align 2 \n\t"
		".align 2, 0 \n\t"

		#define TEST_ARG_REG(reg, val) \
		".byte "__stringify(ARG_TYPE_REG)" \n\t" \