diff mbox series

expand: 'conservative' must not bypass valid simplifications

Message ID 20190302172444.44644-1-luc.vanoostenryck@gmail.com (mailing list archive)
State Mainlined, archived
Headers show
Series expand: 'conservative' must not bypass valid simplifications | expand

Commit Message

Luc Van Oostenryck March 2, 2019, 5:24 p.m. UTC 
From: Thomas Weißschuh <thomas@t-8ch.de>

During the expansion of shifts, the variable 'conservative' is used
to inhibit any possible diagnostics (for example, because he needed
information is if the expression is a constant or not).

However, this must not inhibit the simplification of valid shift
expressions. Unfortunately, by moving the validation inside
check_shift_count(), this what was done by commit
	0b73dee01 ("big-shift: move the check into check_shift_count()").

Found through a false positive VLA detected in the Linux kernel.
The array size was computed through min() on a shifted constant value
and sparse complained about it.

Fix this by returning early (and thus avoiding possible diagnostics
*and* simplification) if 'conservative' is set only if the shift count
is invalid.

Fixes: 0b73dee0171a15800d0a4ae6225b602bf8961599
Signed-off-by: Thomas Weißschuh <thomas@t-8ch.de>
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 expand.c                     |  2 +-
 validation/simplify-binops.c | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 validation/simplify-binops.c
diff mbox series

Patch

diff --git a/expand.c b/expand.c
index e8e50b080..7936e29cb 100644
--- a/expand.c
+++ b/expand.c
@@ -197,7 +197,7 @@  static int simplify_int_binop(struct expression *expr, struct symbol *ctype)
 		return 0;
 	r = right->value;
 	if (expr->op == SPECIAL_LEFTSHIFT || expr->op == SPECIAL_RIGHTSHIFT) {
-		if (conservative)
+		if (conservative && left->type != EXPR_VALUE)
 			return 0;
 		check_shift_count(expr, right);
 	}
diff --git a/validation/simplify-binops.c b/validation/simplify-binops.c
new file mode 100644
index 000000000..e464c37ac
--- /dev/null
+++ b/validation/simplify-binops.c
@@ -0,0 +1,12 @@ 
+#define __is_constexpr(x) \
+        (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
+static void test(int x) {
+	static int b[] = {
+		[__builtin_choose_expr(__is_constexpr(1 << 1), 1, x)] = 0,
+	};
+}
+
+/*
+ * check-name: simplify-binops
+ */