svn commit: r328218 - in head/sys: amd64/amd64 arm/xscale/ixp425 arm64/arm64 cam cam/ctl compat/ndis dev/aacraid dev/advansys dev/ath dev/beri/virtio dev/bnxt dev/bwn dev/ciss dev/cxgbe/crypto dev/...

[Pedro Giffuni]

Hi;


On 23/01/2018 14:08, Conrad Meyer wrote:
> Hi Pedro,
>
> On Sun, Jan 21, 2018 at 7:42 AM, Pedro F. Giffuni <pfg at freebsd.org> wrote:
>> Author: pfg
>> Date: Sun Jan 21 15:42:36 2018
>> New Revision: 328218
>> URL: https://svnweb.freebsd.org/changeset/base/328218
>>
>> Log:
>>    Revert r327828, r327949, r327953, r328016-r328026, r328041:
>>    Uses of mallocarray(9).
>>
>>    The use of mallocarray(9) has rocketed the required swap to build FreeBSD.
>>    This is likely caused by the allocation size attributes which put extra pressure
>>    on the compiler.
> I'm confused about this change.  Wouldn't it be better to remove the
> annotation/attributes from mallocarray() than to remove the protection
> against overflow?

Not in my opinion: it would be better to detect such overflows at 
compile time (or through a static analyzer) than to have late 
notification though panics. The blind use of mallocarray(9) is probably 
a mistake also: we shouldn't use it unless there is some real risk of 
overflow.

>    (If the compiler is fixed in the future to not use
> excessive memory with these attributes, they can be conditionalized on
> compiler version, of course.)

All in all, the compiler is not provably wrong: it's just using more 
swap space, which is rather inconvenient for small platforms but not 
necessarily wrong.

Pedro.