[PATCH] activate context checking when context input and output values in __attribute__() are the same and different of zero

["sylvain nahas" <sylvain.nahas@googlemail.com>]

Hi,
the following patch activates context checking when context input and
output values are the same and different of zero in
__attribute__((context())), by making the parser generate a OP_CONTEXT
pseudo instruction.

Use case: specify that a function needs to be called in locked context.

Below is a sample case.
---
#define __needlock      __attribute__((context(lock,1,1)))
#define __acquire(x)	__context__(1)
#define __release(x)    __context__(-1)

static int __needlock test1(void)
{
	return 0;
}

static int __needlock test2(void)
{
	return test1(); /* OK */
}

static int test3(void)
{
        return test1(); /* should generate a warning */
}

int main(void)
{
	test1(); /* should generate a warning */
	test2(); /* should generate a warning */
	test3(); /* OK */
	__acquire();
	test1(); /* OK */
	__release();
	return -1;
}
---

I have used it on a relative big bunch of code and I believe it works well.
Thanks,

signed-off-by: Sylvain Nahas <sylvain.nahas@googlemailcom>
---
--- a/linearize.c
+++ b/linearize.c
@@ -1244,6 +1244,12 @@ static pseudo_t
linearize_call_expression(struct entrypoint *ep, struct expressi
                                out = 0;
                        }
                        context_diff = out - in;
+
+                       if( !context_diff && (in>0) ){
+                               check = 1;
+                               context_diff = in;
+                       }
+
                        if (check || context_diff) {
                                insn = alloc_instruction(OP_CONTEXT, 0);
                                insn->increment = context_diff;