From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ard Biesheuvel Subject: [PATCH v3] sparse: treat function pointers as pointers to const data Date: Mon, 8 Sep 2014 08:30:03 +0200 Message-ID: <1410157803-3658-1-git-send-email-ard.biesheuvel@linaro.org> Return-path: Received: from mail-wg0-f45.google.com ([74.125.82.45]:55794 "EHLO mail-wg0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751404AbaIHGaH (ORCPT ); Mon, 8 Sep 2014 02:30:07 -0400 Received: by mail-wg0-f45.google.com with SMTP id z12so588399wgg.28 for ; Sun, 07 Sep 2014 23:30:05 -0700 (PDT) Sender: linux-sparse-owner@vger.kernel.org List-Id: linux-sparse@vger.kernel.org To: sparse@chrisli.org, linux-sparse@vger.kernel.org Cc: will.deacon@arm.com, Ard Biesheuvel This code snippet: static void bar(void const *arg) { int (*foo)(void) = arg; } produces the following warning: test.c:4:28: warning: incorrect type in initializer (different modifiers) test.c:4:28: expected int ( *foo )( ... ) test.c:4:28: got void const *arg which is caused by the fact that the function pointer 'foo' is not annotated as being a pointer to const data. However, dereferencing a function pointer does not produce an lvalue, so a function pointer points to const data by definition, and we should treat it accordingly. To avoid producing a warning on the inverse case, i.e., static void bar(void) { void *foo = bar; } we only address the case where the function pointer is the target of an assignment. Reviewed-by: Josh Triplett Signed-off-by: Ard Biesheuvel --- v3: add rationale for restriction to assignments to commit message add R-b v2: only treat function pointers as pointers to const data when they are the target of an assignment evaluate.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/evaluate.c b/evaluate.c index 66556150ddac..a5a830978bda 100644 --- a/evaluate.c +++ b/evaluate.c @@ -1359,6 +1359,15 @@ static int compatible_assignment_types(struct expression *expr, struct symbol *t typediff = "different address spaces"; goto Err; } + /* + * If this is a function pointer assignment, it is + * actually fine to assign a pointer to const data to + * it, as a function pointer points to const data + * implicitly, i.e., dereferencing it does not produce + * an lvalue. + */ + if (b1->type == SYM_FN) + mod1 |= MOD_CONST; if (mod2 & ~mod1) { typediff = "different modifiers"; goto Err; -- 1.8.3.2