Re: dlerror sets errno to ENOSYS

[Diego Nieto Cid]

Hi

The patch for thread-specific data key related functions is attached. As
discussed on IRC, the modifications were extended to __libc_setspecific
and __libc_getspecific.

It has been generated with quilt against debian source package.

On Sun, Feb 28, 2016 at 07:57:43PM +0100, Samuel Thibault wrote:
> 
> extern void *(*_cthread_init_routine) (void) __attribute__ ((weak));
> #define __libc_key_create(KEY,DEST) 
> (_cthread_init_routine?cthread_keycreate(KEY):1)
> 

A slight variation of the conditional was used:

    #define __libc_ctf_call(FUNC, ARGS, ELSE) \
      (&_cthread_init_routine && _cthread_init_routine \
        ? FUNC ARGS : ELSE)

I had to add the first condition because otherwise a segmentation
fault was triggered.

Apparently, for an unbound weak symbol to be present in a program/library
and evaluate to NULL, you have to take its address at least once (the crash
was in libdl, libc access its address during startup).
I'd really like to remove that condition. I'll accept any suggestions :)

Finally, while this fixes the case where pthread is not present, there are
still some issues when linking pthread in. For instance, if I launch gdb, add
a breakpoint in '__libc_getspecific' and run the program until that point then
the code I see using the list command is the one from the weak functions; as if
pthread were not overriding those symbols.

My attempts at inspecting how the symbols were bound, using 'LD_DEBUG=all',
have failed. glibc's loader prints some output but is eventually killed. This
also happens on the rescue shell (from netinst.iso). Below, the last few
messages printed before the program being killed:

    $ LD_DEBUG=all ls
             0:     symbol=realloc;  lookup in file=ls [0]
             0:     symbol=realloc;  lookup in 
file=/home/diego/src/debian/glibc/glibc-2.21/build-tree/hurd-i386-libc/libc.so.0.3
 [0]
             0:     binding file /lib/ld.so [0] to 
/home/diego/src/debian/glibc/glibc-2.21/build-tree/hurd-i386-libc/libc.so.0.3 
[0]: normal symbol `realloc' [GLIBC_2.2.6]
             0:     symbol=_hurd_intr_rpc_mach_msg;  lookup in file=ls [0]
             0:     symbol=_hurd_intr_rpc_mach_msg;  lookup in 
file=/home/diego/src/debian/glibc/glibc-2.21/build-tree/hurd-i386-libc/libc.so.0.3
 [0]
             0:     binding file /lib/ld.so [0] to 
/home/diego/src/debian/glibc/glibc-2.21/build-tree/hurd-i386-libc/libc.so.0.3 
[0]: normal symbol `_hurd_intr_rpc_mach_msg' [GLIBC_2.2.6]
    Killed

That's all I could research for now.

Regards,
Diego

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