Hi;
On 08/01/2018 13:08, Conrad Meyer wrote:
Hi,
Response inline.
On Mon, Jan 8, 2018 at 7:41 AM, Pedro F. Giffuni <[email protected]> wrote:
Author: pfg
Date: Mon Jan 8 15:41:48 2018
New Revision: 327697
URL: https://svnweb.freebsd.org/changeset/base/327697
Log:
malloc(9): drop the __result_use_check attribute for the kernel allocator.
The __result_use_check attribute was brought to the kernel malloc in
r281203 for consistency with the userland malloc.
For the case of the M_WAITOK flag, the kernel malloc(), realloc(), and
reallocf() cannot return NULL so in that case the __result_use_check
attribute makes no sense.
We don't have any way of conditionalizing such attributes so just drop it.
Could we conditionalize the attribute using two different names and a
macro that inspected the (typically) constant flags argument?
Something like this:
#define malloc(s, t, f) \
(__builtin_constant_p(f) && (f & M_WAITOK) != 0) ?
_malloc_waitok(s, t, f) : _malloc(s, t, f)
void *_malloc(...) __malloc_like __alloc_size(1);
void *_malloc_waitok(...) __malloc_like __result_use_check __alloc_size(1);
The two names would just be aliases, or one could invoke the other as
an inline function.
That would work but I completely misunderstood the GCC attribute.
Quoting the GCC documentation:
____
warn_unused_result
The warn_unused_result attribute causes a warning to be emitted if a
caller of the function with this attribute does not use its return
value. This is useful for functions where not checking the result is
either a security problem or always a bug, such as realloc.
____
Retrospectively, our attribute is badly named but it was very difficult
to come up with a good name.
Pedro.
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