Re: Building: alloc.c:766:1: error: negative width in bit-field `_gl_verify_error_if_negative'

[Paul Eggert]

On 02/13/2012 05:07 AM, Alan Mackenzie wrote:
> How can the compiler transform "INT_MAX <= PTRDIFF_MAX" into a message
> about bit-field widths?

That message is generated for compilers that are not known to
support C11-style static assertions
<http://gcc.gnu.org/ml/gcc-patches/2010-05/msg01188.html>.
In GCC 4.6.0 and later, verify(X) simply expands to _Static_assert(X).
Other compilers (including older GCCs) are not known to have
_Static_assert, so verify(X) expands to:

  struct { unsigned _gl_verify_error_if_negative: (X) ? 1 : -1; }

which causes a compile-time error if X is false (the desired
effect); as you've noticed, the diagnostic isn't as nice as
with GCC 4.6.0 and later.

This is implemented in lib/verify.h -- more commentary is there.

My guess is that PTRDIFF_MAX is set incorrectly in your implementation.
Emacs's 'configure' script attempts to detect that, and replace it
with a correct PTRDIFF_MAX, but perhaps we need to improve 'configure'
so that it detects the problem with your implementation.

Can you send the compressed "gcc -E ..." output of the offending
compilation, and the contents of 'config.log' and 'src/config.h' and
(if present) 'lib/stdint.h'?  That should help debug the situation.
Also, if you could determine which standard header is defining
ptrdiff_t and PTRDIFF_MAX, and what they're defined to, that might
help.