* [PATCH v3] sparse: treat function pointers as pointers to const data
@ 2014-09-08 6:30 Ard Biesheuvel
2014-10-06 14:44 ` Ard Biesheuvel
0 siblings, 1 reply; 9+ messages in thread
From: Ard Biesheuvel @ 2014-09-08 6:30 UTC (permalink / raw)
To: sparse, linux-sparse; +Cc: will.deacon, 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 <josh@joshtriplett.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
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
^ permalink raw reply related [flat|nested] 9+ messages in thread* Re: [PATCH v3] sparse: treat function pointers as pointers to const data
2014-09-08 6:30 [PATCH v3] sparse: treat function pointers as pointers to const data Ard Biesheuvel
@ 2014-10-06 14:44 ` Ard Biesheuvel
2014-10-08 18:00 ` Christopher Li
0 siblings, 1 reply; 9+ messages in thread
From: Ard Biesheuvel @ 2014-10-06 14:44 UTC (permalink / raw)
To: sparse, linux-sparse; +Cc: Will Deacon, Ard Biesheuvel
On 8 September 2014 08:30, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> 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 <josh@joshtriplett.org>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> 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
>
Ping?
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v3] sparse: treat function pointers as pointers to const data
2014-10-06 14:44 ` Ard Biesheuvel
@ 2014-10-08 18:00 ` Christopher Li
2014-10-08 18:06 ` Ard Biesheuvel
0 siblings, 1 reply; 9+ messages in thread
From: Christopher Li @ 2014-10-08 18:00 UTC (permalink / raw)
To: Ard Biesheuvel; +Cc: Linux-Sparse, Will Deacon
On Mon, Oct 6, 2014 at 10:44 PM, Ard Biesheuvel
<ard.biesheuvel@linaro.org> wrote:
>> we only address the case where the function pointer is the target of
>> an assignment.
I apply the patch in my private branch but haven't push out yet.
I just want to confirm, you didn't find this kind of assignment in the
kernel, right?
Chris
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v3] sparse: treat function pointers as pointers to const data
2014-10-08 18:00 ` Christopher Li
@ 2014-10-08 18:06 ` Ard Biesheuvel
2014-10-14 12:55 ` Ard Biesheuvel
0 siblings, 1 reply; 9+ messages in thread
From: Ard Biesheuvel @ 2014-10-08 18:06 UTC (permalink / raw)
To: Christopher Li; +Cc: Linux-Sparse, Will Deacon
On 8 October 2014 20:00, Christopher Li <sparse@chrisli.org> wrote:
> On Mon, Oct 6, 2014 at 10:44 PM, Ard Biesheuvel
> <ard.biesheuvel@linaro.org> wrote:
>>> we only address the case where the function pointer is the target of
>>> an assignment.
>
> I apply the patch in my private branch but haven't push out yet.
>
> I just want to confirm, you didn't find this kind of assignment in the
> kernel, right?
>
I noticed this patch
https://git.kernel.org/cgit/linux/kernel/git/kvmarm/kvmarm.git/commit/?h=queue&id=de56fb1923ca11f428bf557870e0faa99f38762e
and saw that it was bogus: changing the return type of the pointed-to
function to 'const int' makes no sense at all, and yet it shuts up
sparse.
With my sparse patch, that patch could have been dropped (although I
think it was merged after all)
--
Ard.
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v3] sparse: treat function pointers as pointers to const data
2014-10-08 18:06 ` Ard Biesheuvel
@ 2014-10-14 12:55 ` Ard Biesheuvel
2014-10-15 1:34 ` Christopher Li
0 siblings, 1 reply; 9+ messages in thread
From: Ard Biesheuvel @ 2014-10-14 12:55 UTC (permalink / raw)
To: Christopher Li; +Cc: Linux-Sparse, Will Deacon
On 8 October 2014 20:06, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> On 8 October 2014 20:00, Christopher Li <sparse@chrisli.org> wrote:
>> On Mon, Oct 6, 2014 at 10:44 PM, Ard Biesheuvel
>> <ard.biesheuvel@linaro.org> wrote:
>>>> we only address the case where the function pointer is the target of
>>>> an assignment.
>>
>> I apply the patch in my private branch but haven't push out yet.
>>
>> I just want to confirm, you didn't find this kind of assignment in the
>> kernel, right?
>>
>
> I noticed this patch
>
> https://git.kernel.org/cgit/linux/kernel/git/kvmarm/kvmarm.git/commit/?h=queue&id=de56fb1923ca11f428bf557870e0faa99f38762e
>
> and saw that it was bogus: changing the return type of the pointed-to
> function to 'const int' makes no sense at all, and yet it shuts up
> sparse.
>
> With my sparse patch, that patch could have been dropped (although I
> think it was merged after all)
>
Ping?
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v3] sparse: treat function pointers as pointers to const data
2014-10-14 12:55 ` Ard Biesheuvel
@ 2014-10-15 1:34 ` Christopher Li
2014-10-15 5:16 ` Ard Biesheuvel
0 siblings, 1 reply; 9+ messages in thread
From: Christopher Li @ 2014-10-15 1:34 UTC (permalink / raw)
To: Ard Biesheuvel; +Cc: Linux-Sparse, Will Deacon
On Tue, Oct 14, 2014 at 8:55 PM, Ard Biesheuvel
<ard.biesheuvel@linaro.org> wrote:
>
> Ping?
It is already applied and pushed as c1763a249aba0a40bd326c845c2a146132a02448
Chris
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v3] sparse: treat function pointers as pointers to const data
2014-10-15 1:34 ` Christopher Li
@ 2014-10-15 5:16 ` Ard Biesheuvel
2014-10-15 7:06 ` Christopher Li
0 siblings, 1 reply; 9+ messages in thread
From: Ard Biesheuvel @ 2014-10-15 5:16 UTC (permalink / raw)
To: Christopher Li; +Cc: Linux-Sparse, Will Deacon
On 15 October 2014 03:34, Christopher Li <sparse@chrisli.org> wrote:
> On Tue, Oct 14, 2014 at 8:55 PM, Ard Biesheuvel
> <ard.biesheuvel@linaro.org> wrote:
>>
>> Ping?
>
> It is already applied and pushed as c1763a249aba0a40bd326c845c2a146132a02448
>
OK, thanks!
Which upstream repo is that? I couldn't find it on
git://git.kernel.org/pub/scm/devel/sparse/sparse.git
regards,
Ard.
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2014-10-15 7:10 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2014-09-08 6:30 [PATCH v3] sparse: treat function pointers as pointers to const data Ard Biesheuvel
2014-10-06 14:44 ` Ard Biesheuvel
2014-10-08 18:00 ` Christopher Li
2014-10-08 18:06 ` Ard Biesheuvel
2014-10-14 12:55 ` Ard Biesheuvel
2014-10-15 1:34 ` Christopher Li
2014-10-15 5:16 ` Ard Biesheuvel
2014-10-15 7:06 ` Christopher Li
2014-10-15 7:10 ` Ard Biesheuvel
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