Re: What is the purpose of _dl_starting_up and why is it removed for HAVE_INLINED_SYSCALLS?

[Roland McGrath <roland at hack dot frob dot com>]

See elf/dl-writev.h.  sysdeps/unix/sysv/linux/dl-writev.h overrides that.
At the time of the cited changes, that file didn't exist and the code was
inlined in _dl_debug_vdprintf (elf/dl-misc.c) where it used _dl_starting_up
if [!HAVE_INLINED_SYSCALLS && RTLD_PRIVATE_ERRNO].

Hurd configurations still use elf/dl-writev.h and do not define
HAVE_INLINED_SYSCALLS, but they also set RTLD_PRIVATE_ERRNO to 0.  So for
_dl_writev, we could perhaps drop the use of _dl_starting_up and just have
an #error for the #if RTLD_PRIVATE_ERRNO case.  (Then new configurations
that set RTLD_PRIVATE_ERRNO to 1 would be obliged to provide their own
dl-writev.h, as Linux configurations do.)

Essentially HAVE_INLINED_SYSCALLS is being used as a proxy for identifying
Linux configurations.  That makes vague sense for the _dl_writev use
because _dl_starting_up is used there only in non-Linux configurations.
Obviously that does not make it a clean way to operate.

The other use of _dl_starting_up is to set __libc_multiple_libcs.  That use
handles it being an undefined weak symbol and that's the case for Linux
configurations.  The Fedora patch might affect what value
__libc_multiple_libcs gets under different conditions.  I'm not at all sure
off hand.  Though I recall the basic issue that necessitated the
__libc_multiple_libcs logic, I don't recall the exact details of when or
whether it should be set (i.e. both the value to give it and the chronology
in a process when it should get that value).


Thanks,
Roland