Re: [GIT PULL] headers_check fixes

Sam Ravnborg
2009-06-07T07:13:57Z

On Sat, Jun 06, 2009 at 10:47:11PM +0100, Russell King wrote:
> Right, below is a patch to unifdef.c which allows it to work out if
> an #if expression always evaluates true or false for symbols which
> are being undefined/always defined.
>
> The patch is slightly more complicated than I'd hoped because unifdef
> needs to see lines fully evaluated - doing otherwise causes it to
> mark the line as "dirty" and copy it over no matter what.
>
> What follows this email is the diff of what effect it has on the
> headers copied over - as can be seen, all resulting changes are of
> net benefit.

Result is great - thanks for implmenting this!
I have applied the following (no code changes, only a few more
details in the changelog).

Sam

commit 3a8a10760f9626856848ae815e9436a2e04a4082
Author: Russell King <rmk+lkml@arm.linux.org.uk>
Date: Sat Jun 6 22:47:11 2009 +0100

kbuild: fix headers_exports with boolean expression

When we had code like this in a header unifdef failed to
deduct that the expression was always false - and we had code exported
that was not intended for userspace.

#if defined(__KERNEL__) && !defined(__ASSEMBLY__)
int a;
#endif

This commit implment support in unidef which allows it to work out if
an #if expression always evaluates true or false for symbols which
are being undefined/always defined.

The patch is slightly more complicated than I'd hoped because unifdef
needs to see lines fully evaluated - doing otherwise causes it to
mark the line as "dirty" and copy it over no matter what.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

diff --git a/scripts/unifdef.c b/scripts/unifdef.c
index 05a31a6..30d459f 100644
--- a/scripts/unifdef.c
+++ b/scripts/unifdef.c
@@ -678,8 +678,10 @@ eval_unary(const struct ops *ops, int *valp, const char **cpp)
if (*cp == '!') {
debug("eval%d !", ops - eval_ops);
cp++;
- if (eval_unary(ops, valp, &cp) == LT_IF)
+ if (eval_unary(ops, valp, &cp) == LT_IF) {
+ *cpp = cp;
return (LT_IF);
+ }
*valp = !*valp;
} else if (*cp == '(') {
cp++;
@@ -700,13 +702,16 @@ eval_unary(const struct ops *ops, int *valp, const char **cpp)
return (LT_IF);
cp = skipcomment(cp);
sym = findsym(cp);
- if (sym < 0)
- return (LT_IF);
- *valp = (value[sym] != NULL);
cp = skipsym(cp);
cp = skipcomment(cp);
if (*cp++ != ')')
return (LT_IF);
+ if (sym >= 0)
+ *valp = (value[sym] != NULL);
+ else {
+ *cpp = cp;
+ return (LT_IF);
+ }
keepthis = false;
} else if (!endsym(*cp)) {
debug("eval%d symbol", ops - eval_ops);
@@ -741,11 +746,11 @@ eval_table(const struct ops *ops, int *valp, const char **cpp)
const struct op *op;
const char *cp;
int val;
+ Linetype lhs, rhs;

debug("eval%d", ops - eval_ops);
cp = *cpp;
- if (ops->inner(ops+1, valp, &cp) == LT_IF)
- return (LT_IF);
+ lhs = ops->inner(ops+1, valp, &cp);
for (;;) {
cp = skipcomment(cp);
for (op = ops->op; op->str != NULL; op++)
@@ -755,14 +760,32 @@ eval_table(const struct ops *ops, int *valp, const char **cpp)
break;
cp += strlen(op->str);
debug("eval%d %s", ops - eval_ops, op->str);
- if (ops->inner(ops+1, &val, &cp) == LT_IF)
- return (LT_IF);
- *valp = op->fn(*valp, val);
+ rhs = ops->inner(ops+1, &val, &cp);
+ if (op->fn == op_and && (lhs == LT_FALSE || rhs == LT_FALSE)) {
+ debug("eval%d: and always false", ops - eval_ops);
+ if (lhs == LT_IF)
+ *valp = val;
+ lhs = LT_FALSE;
+ continue;
+ }
+ if (op->fn == op_or && (lhs == LT_TRUE || rhs == LT_TRUE)) {
+ debug("eval%d: or always true", ops - eval_ops);
+ if (lhs == LT_IF)
+ *valp = val;
+ lhs = LT_TRUE;
+ continue;
+ }
+ if (rhs == LT_IF)
+ lhs = LT_IF;
+ if (lhs != LT_IF)
+ *valp = op->fn(*valp, val);
}

*cpp = cp;
debug("eval%d = %d", ops - eval_ops, *valp);
- return (*valp ? LT_TRUE : LT_FALSE);
+ if (lhs != LT_IF)
+ lhs = (*valp ? LT_TRUE : LT_FALSE);
+ return lhs;
}

/*
@@ -773,12 +796,15 @@ eval_table(const struct ops *ops, int *valp, const char **cpp)
static Linetype
ifeval(const char **cpp)
{
+ const char *cp = *cpp;
int ret;
int val;

debug("eval %s", *cpp);
keepthis = killconsts ? false : true;
- ret = eval_table(eval_ops, &val, cpp);
+ ret = eval_table(eval_ops, &val, &cp);
+ if (ret != LT_IF)
+ *cpp = cp;
debug("eval = %d", val);
return (keepthis ? LT_IF : ret);
}