glibc 2.21 - Master is frozen solid at -26 degC.

[David Miller]

From: Roland McGrath <roland@hack.frob.com>
Date: Wed, 28 Jan 2015 11:08:12 -0800 (PST)

>> nptl-init.c: In function  sighandler_setxid :
>> nptl-init.c:242:1: error: optimization may eliminate reads and/or writes to register variables [-Werror=volatile-register-var]
>> nptl-init.c:242:1: error: optimization may eliminate reads and/or writes to register variables [-Werror=volatile-register-var]
>> 
>> I get these all over the NPTL code, and every instance points to the
>> function's declaration rather than at any code within the function, which
>> makes tracking down what it's unhappy about not so easy.
>> 
>> I'll keep digging into this.
> 
> In the GCC source, that message is only for global register variables
> declared as volatile AFAIK.  I expect it's for the __thread_self global in
> sysdeps/sparc/nptl/tls.h but there is no volatile there, so I don't know
> how it would come about.

It's happening indirectly via typeof(), for example in sighandler_setxid() we
have:

  if (atomic_decrement_val (&__xidcmd->cntr) == 0)

'cntr' is volatile, and then to get the types right the non-v9 32-bit sparc
macros for atomics do things like:

  register __typeof (*(mem)) __acev_tmp __asm ("%g6");			      \
  register __typeof (mem) __acev_mem __asm ("%g1") = (mem);		      \
  register __typeof (*(mem)) __acev_oldval __asm ("%g5");		      \

and that's where the warnings come from.  I fixed it just like MIPS did
by using a union.

This has allowed me to start working on the semaphore bits.