svn commit: r354672 - head/lib/libc/secure

[Pedro Giffuni]

Hi;

On 12/11/2019 23:44, Warner Losh wrote:
>
>
> On Tue, Nov 12, 2019 at 9:20 PM Kyle Evans <kevans at freebsd.org 
> <mailto:kevans at freebsd.org>> wrote:
>
>
>
>     On Tue, Nov 12, 2019, 22:04 Pedro Giffuni <pfg at freebsd.org
>     <mailto:pfg at freebsd.org>> wrote:
>
>
>         On 12/11/2019 22:00, Kyle Evans wrote:
>>         Author: kevans
>>         Date: Wed Nov 13 03:00:32 2019
>>         New Revision: 354672
>>         URL:https://svnweb.freebsd.org/changeset/base/354672
>>
>>         Log:
>>            ssp: rework the logic to use priority=200 on clang builds
>>            
>>            The preproc logic was added at the last minute to appease GCC 4.2, and
>>            kevans@ did clearly not go back and double-check that the logic worked out
>>            for clang builds to use the new variant.
>>            
>>            It turns out that clang defines __GNUC__ == 4. Flip it around and check
>>            __clang__ as well, leaving a note to remove it later.
>>            
>         clang reports itself as GCC 4.2, the priority argument was
>         introduced in GCC 4.3.
>>            Reported by:	cem
>>
>>         Modified:
>>            head/lib/libc/secure/stack_protector.c
>>
>>         Modified: head/lib/libc/secure/stack_protector.c
>>         ==============================================================================
>>         --- head/lib/libc/secure/stack_protector.c	Wed Nov 13 02:22:00 2019	(r354671)
>>         +++ head/lib/libc/secure/stack_protector.c	Wed Nov 13 03:00:32 2019	(r354672)
>>         @@ -47,13 +47,15 @@ __FBSDID("$FreeBSD$");
>>            * they're either not usually statically linked or they simply don't do things
>>            * in constructors that would be adversely affected by their positioning with
>>            * respect to this initialization.
>>         + *
>>         + * This conditional should be removed when GCC 4.2 is removed.
>>            */
>>         -#if defined(__GNUC__) && __GNUC__ <= 4
>>         -#define	_GUARD_SETUP_CTOR_ATTR	\
>>         -    __attribute__((__constructor__, __used__));
>>         -#else
>>         +#if defined(__clang__) || (defined(__GNUC__) && __GNUC__ > 4)
>>           #define	_GUARD_SETUP_CTOR_ATTR	 \
>>               __attribute__((__constructor__ (200), __used__));
>>         +#else
>>         +#define	_GUARD_SETUP_CTOR_ATTR	\
>>         +    __attribute__((__constructor__, __used__));
>>           #endif
>>           
>>           extern int __sysctl(const int *name, u_int namelen, void *oldp,
>
>         Please fix properly. Assuming clang always supported it,
>         something like:
>
>         #if __GNUC_PREREQ__(4, 3) || __has_attribute(__constructor__)
>
>         should work
>
>         Cheers,
>
>
>     I considered something of this sort, but searching for information
>     on the priority argument in the first place was annoying enough
>     that I had too much search-fatigue to figure out when GCC actually
>     corrected this, thus assuming that GCC5 (which seemed to be an
>     all-around good release if memory serves) and later (since I
>     confirmed GCC6) was sufficient.
>
>     I'll fix it in the morning (~8 hours) if I receive no further
>     objections to address.
>
>
> Soon enough this can be removed entirely... Getting it pedantically 
> right in the mean time has little value. We don't really support gcc5 
> at the moment. gcc6 and later have good support, but anything new 
> between 4.3 and 6.0 likely is poorly tagged...
>

Well, tracking attributes on GCC versions is not easy but I did spend a 
good amount of time getting the attributes right on cdefs.h and while I 
lost the battle to get support for older GCC versions deprecated, 
getting the attributes properly defined in the GCC 4.2 vs clang vicinity 
is particularly important.

I particularly dislike the idea of leaving notes of stuff that can be 
removed when an existing compiler is gone. In this case, we can fix this 
without adding more lines of code, and that also helps in case the code 
is MFCd.

Now ... if you want to be pedantic: this code doesn't handle the case 
for non-GCC based compilers, and it probably could be done more generic 
and clean in cdefs.h where it can be reused. But I am not asking for 
that ;).

Pedro.