Re: Test for pthread_rwlock_init() always passes, regardless

[Sevan Janiyan]

On 08/11/2023 09:58, Bruno Haible wrote:
> According to our function database
> https://git.savannah.gnu.org/gitweb/?p=gnulib/maint-tools.git;a=tree;f=platforms/various-symlists;h=959af7a410a8416f4b183793ac2dae7e1063024f;hb=HEAD
> the function does exist in Mac OS X 10.3, 10.4, and 10.5. In 10.5
> they added an alias pthread_rwlock_init$UNIX2003, but that is not
> relevant for the autoconf test.

You're right, I was mixing two things up.
> > Compiling the test case with 'cc -Wall -O2 -lpthread' by hand results in
> > Bus Error
> What do you mean? You get a Bus Error already at compile time, i.e.
> the compiler or linker crashes?
>
> Or do you get a Bus Error by running that test program? I.e. as if
> we had an AC_RUN_IFELSE instead of AC_LINK_IFELSE in the above test?

I get a Bus Error when I try to run the program. Mentioned it because it 
doesn't happen on newer macOS versions but that could because the 
compiler is smarter?

> > Otherwise things fail during compilation because it's
> > expecting an implementation from the host.
> > test-pthread.c:33: error: ‘PTHREAD_RWLOCK_INITIALIZER’ undeclared here
> > (not in a function).
> Ah, but that is a different problem. What you report here is that
> no macro PTHREAD_RWLOCK_INITIALIZER is defined in Mac OS X 10.4,
> while it exists in 10.5:
>    #define PTHREAD_RWLOCK_INITIALIZER {_PTHREAD_RWLOCK_SIG_init, {0}}
>
> It looks like lib/glthread/lock.h does better efforts at handling the
> lack of PTHREAD_RWLOCK_INITIALIZER than lib/pthread.in.h. What is the
> result if you change lib/pthread.in.h?

The patch passes that error and then fails in compiling test-lock.c 
because _PTHREAD_RWLOCK_SIG_init is not defined.
test-lock.c:234: error: ‘_PTHREAD_RWLOCK_SIG_init’ undeclared here (not 
in a function)

On 10.5 & newer, _PTHREAD_RWLOCK_SIG_init is defined as
#define _PTHREAD_RWLOCK_SIG_init    0x2DA8B3B4
in pthread_impl.h.

Looking into the libc source for 10.4.11 PPC [1]
It's defined with a comment in pthread_internals.h that indicates to me 
that there may be some issue with the implementation on 10.4? (they 
reached UNIX certification in 10.5)
#define _PTHREAD_RWLOCK_SIG_init        0x2DA8B3B4  /* [almost] ~'RWLK' */


Sevan
[1] 
https://github.com/apple-oss-distributions/Libc/blob/d07313eeff7c6402e25133c65d3fa66f2a64f688/pthreads/pthread_internals.h#L288