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>

1 files changed, 37 insertions, 11 deletions

diff --git a/scripts/unifdef.c b/scripts/unifdef.c
index 05a31a6c7e1..30d459fb070 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);
 }