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>

diff --git a/arch/arm/kernel/kprobes-test.c b/arch/arm/kernel/kprobes-test.c
index 6e60a34..3796399 100644 (file)
--- a/arch/arm/kernel/kprobes-test.c
+++ b/arch/arm/kernel/kprobes-test.c
@@ -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

diff --git a/arch/arm/kernel/kprobes-test.h b/arch/arm/kernel/kprobes-test.h
index e28a869..eecc90a 100644 (file)
--- a/arch/arm/kernel/kprobes-test.h
+++ b/arch/arm/kernel/kprobes-test.h
@@ -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"   \