[So, things fell on the floor, a while back.]
On 05/25/2017 11:17 AM, Stas Sergeev wrote:
> 24.05.2017 14:09, Michael Kerrisk (man-pages) пишет:
>> One could do this I suppose, but I read POSIX differently from
>> you and, more importantly, SS_ONSTACK breaks portability on
>> numerous other systems and is a no-op on Linux. So, the Linux man
>> page really should warn against its use in the strongest terms.
> So how about instead of the strongest terms towards
> the code's author, just explain that SS_ONSTACK is a
> bit-value on some/many OSes, and as such, 0 is a
> valid value to enable sas on them, plus all the other
> values would give EINVAL?
> No strongest terms will help w/o an explanation,
> because people will keep looking for something that
> suits as a missing SS_ENABLE.
Fair enough. I've removed the statement in the manual page
about "confusion". By now the page says:
BUGS
In the lead up to the release of the Linux 2.4 kernel, a change
was made to allow sigaltstack() to accept SS_ONSTACK in
ss.ss_flags, which results in behavior that is the same as when
ss_flags is 0 (i.e., the inclusion of SS_ONSTACK in ss.ss_flags is
a no-op). On other implementations, and according to POSIX.1,
SS_ONSTACK appears only as a reported flag in old_ss.ss_flags. On
Linux, there is no need ever to specify this flag in ss.ss_flags,
and indeed doing so should be avoided on portability grounds: var‐
ious other systems give an error if SS_ONSTACK is specified in
ss.ss_flags.
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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