ucontext.h or sys/ucontext.h

 

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Minor technical issue.

Regarding platforms/unix/vm/include_ucontext.h

Solaris has a #include <sys/ucontext.h> so the build was working,
but some versions adhere to the "Single Unix Specification v2" (SUS v2).

According to some info (I'm no expert in this) this is Solaris 7/8

           SUSv2        superset of SUS extended      Solaris 7
                        to support POSIX.1b-1993,
                        POSIX.1c-1996, and ISO/IEC
                        9899 (C Standard)
                        Amendment 1

Now that standard speficies that you can #include <ucontext.h>
instead of #include <sys/ucontext.h>

Also see
https://pubs.opengroup.org/onlinepubs/7908799/xsh/ucontext.h.html

I've added a small #ifdef __sun fix to use #include <ucontext.h> in the
Solaris case.

Alternatively perhaps the configure script could check for the
existence of the <ucontext.h> header file ...

Unfortunately the #include's that the program issues,
does have obviously major impact on the behaviour of the VM.

Another issue one of the fixes I submitted in the sunos branch is

or was :

  # include <sys/file.h> /* FASYNC or ioctl FIOASYNC will be issued  */

in the file platforms/unix/vm/aio.c

The issue there (completely unrelated to the ucontext.h issue) is that
that header file determines how the code in aio.c works

Because in aio.c there is code

#if defined(O_ASYNC)
#elif defined(FASYNC)
#elif defined(FIOASYNC)

great care about the configuration of header files (#include) is needed.

Perhaps also in the case of aio.c this could be dealt with in the configure
script.

The configure script could also in that case try to figure out what
the correct #include is, but it has major impact of course on the
behavior of the VM ...

David Stes

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Hi Stes
Thanks for pointing that out.

Meanwhile I found this: https://github.com/torproject/tor/blob/master/m4/pc_from_ucontext.m4
which suggests that simply using <ucontext.h> is not the best idea, funnily enough because of
OSX (which is the only SUSv2 Unix I've ever used...)

We could use an updated version (https://github.com/gperftools/gperftools/blob/master/m4/pc_from_ucontext.m4)
and derive this information automatically.

what do you all think?


Sorry, I have no Idea about that one.

Best regards
        -Tobias

 
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The issue on aio.c is totally unrelated, it's just something I wrote,
because it is also related to platform-dependent #include files,
and the big impact they can have.

Regarding the <ucontext.h> issue, it is not a big deal.

I think the files

sqUnixMain.c:#include "include_ucontext.h"

and

sqUnixVMProfile.c:#include "include_ucontext.h"

they both #include a local header file include_ucontext.h

which is doing something like:

#ifdef __OpenBSD__
# include <sys/signal.h>
#else
# include <sys/ucontext.h>
#endif

The code that is including <sys/ucontext.h> is working on Solaris,
but not entirely correct.

It depends on how the Solaris system is setup, I see that the Solaris
docs say that you have to #include <ucontext.h>

Whether <sys/ucontext.h> or <ucontext.h> it seems a little bit like
a Byzantine discussion on the sex of angels, and it seems
something that for the last 23 years (since 1997) or so caused some
discussion, as some SUS or POSIX standard committee said that the header was
#include <ucontext.h> and the de-facto standard is not following them.

Basically in the Solaris case #include <ucontext.h> is including
<sys/ucontext.h>

However I submit a minor change for the <ucontext.h> in the __sun case.

This has no impact on any other platform,
and in fact I don't think anything should be changed for other platforms.

However hopefully my pull request for the __sun change is accepted !

David

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