[Tcsh] tcsh and Alpine Linux: progress, anyone?

[Luke Mewburn]

Hi folks,

I've enhanced configure to search for a working sbrk(N) (HAVE_WORKING_SBRK)
based on Vlad's analysis, and changed config_f.h to force SYSMALLOC
unless HAVE_WORKING_SBRK.

The pull request is: https://github.com/tcsh-org/tcsh/pull/61

I also did some configure style cleanups first.


Note that I have NOT committed the output of autoreconf, because
I have different/older autoconf / gettext versions that the last
system that regenerated, and I wanted to avoid the diff skew.


cheers,
Luke.


On 22-11-28 14:15, Vlad Meşco wrote:
  | On Mon, 28 Nov 2022 at 12:47, Vlad Meșco <vlad.mesco at gmail.com> wrote:
  | >
  | > Le 28 novembre 2022 11:33:15 GMT+02:00, Luke Mewburn <luke at mewburn.net> a écrit :
  | > >On 22-11-26 23:41, Vlad Meșco wrote:
  | > >  | Le 26 novembre 2022 21:21:01 GMT+02:00, Christos Zoulas <christos at zoulas.com> a écrit :
  | > >  | >Alpine uses must c which is "opinionated" about things like
  | > >  | >defining a CPP symbol to differentiate itself because it claims one
  | > >  | >should not be needed because it provides a standards compliant
  | > >  | >implementation and such checks should be unnecessary:
  | > >  | >https://wiki.musl-libc.org/faq.html
  | > >  | >At the same time it uses a malloc implementation that causes
  | > >  | >problems for programs which try to use a custom allocator (replace musl's
  | > >  | >allocator):
  | > >  | >https://www.linkedin.com/pulse/testing-alternative-c-memory-allocators-pt-2-musl-mystery-gomes/
  | > >  | >https://gitlab.alpinelinux.org/alpine/aports/-/issues/12913
  | > >  | >
  | > >  |
  | > >  | My $0.02: Having to occasionally support cross platform builds
  | > >  | across a whole bunch of platforms at work, I wouldn't rely on GLIBC
  | > >  | not being defined meaning it's musl's/Alpine's  behaviour in 2022.
  | > >  | There's bionic, uclib, and probably someone out there is working on
  | > >  | a 15th standard C library, and there will be a distro using it. And
  | > >  | somewhere there will be an issue. It would be a neverending problem.
  | > >  |
  | > >  |  [...]
  | > >  |
  | > >  | You mention musl has issues with someone trying to replace the
  | > >  | allocator, surely that can be tested for? Now this is me being
  | > >  | ignorant to how autoconf works: is one able to add a custom check,
  | > >  | if such a check can be written? Then this could add a define to the
  | > >  | pile to force SYSMALLOC on in config_f.h (wishful thinking). I mean,
  | > >  | this is less of a preference and more of a necessity.
  | > >
  | > >Hi Vlad,
  | > >
  | > >If you can provide a minimal test program that we can run
  | > >to determine if the problem exists on Alpine / musl /... ,
  | > >versus not failing on more common platforms, I'm happy to work
  | > >with you to turn that into an autoconf check (since I have a
  | > >lot of experience with doing that).
  | > >
  | > >regards,
  | > >Luke.
  | >
  | > Cool!
  | >
  | > I'll go find some time.
  | >
  | > Vlad
  | 
  | Hello,
  | 
  | It turns out musl just doesn't make the sbrk syscall if you give
  | the library function anything other than 0 [1]. It's still true on their
  | HEAD.  I started off doing what tc.alloc.c/morecore() was doing:
  | 
  |     #include <unistd.h>
  | 
  |     int main(int argc, char* argv[])
  |     {
  |         void* p = sbrk(0);
  |         if(p == (void*)-1) return 1;
  |         if((long)p & 0x3ff) {
  |             p = sbrk((int) (1024 - ((long)p & 0x3ff)));
  |             if(p == (void*)-1) return 2;
  |         }
  |         p = sbrk(2048);
  |         if(p == (void*)-1) return 3;
  |         return 0;
  |     }
  | 
  | But that can be reduced to "one" line:
  | 
  |     #include <unistd.h>
  | 
  |     int main(int argc, char* arvv[])
  |     {
  |         return sbrk(2048) == (void*)-1;
  |     }
  | 
  | I've only tested on some older Alpine in WSL2 and a CentOS 7
  | machine (for sanity). This checks if sbrk() can increase; if sbrk()
  | is "read-only", then the custom allocator will not work, so tcsh
  | may as well use the system/libc malloc.
  | 
  | [1] http://git.musl-libc.org/cgit/musl/commit/src/linux/sbrk.c?id=7a995fe706e519a4f55399776ef0df9596101f93
  | 
  | Best regards,
  | Vlad