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Re: musl - and menchmarking libc
On Wed, 5 Sep 2012, Rich Felker wrote:
> I'm talking about -D_FILE_OFFSET_BITS=64, not -D_LARGEFILE64_SOURCE.
> The former is advertised by glibc as one of the POSIX compilation
> environments, one that provides _POSIX_V6_ILP32_OFFBIG, and it's the
> only compilation environment provided that any modern application
> should be using on a 32-bit machine. However, it's not actually a
> POSIX conforming environment since you can't reliably use these
> interfaces without including the headers that do the redirection
> (you'll instead call the 32-bit versions with the wrong prototypes,
> thus invoking UB), and since even when you do include the headers, you
> will pull in external symbol name pollution in the namespace reserved
> for the application.
So this static library would be for listing in the output of "getconf
POSIX_V6_ILP32_OFFBIG_LIBS"? I suppose that makes sense, though I'd limit
it strictly to the functions for which it's needed for POSIX conformance
(that is, the affected functions that are defined by POSIX and whose
POSIX-defined prototypes only include standard C types and not typedefs
from system headers) since I think it's an undesirable burden to support
declaring library functions yourself beyond the cases where the standards
require it.
I think this should have a separate bug from 14106 (depending on 14106).
With GCC 4.5 or later, another approach is for the compiler options from
"getconf POSIX_V6_ILP32_OFFBIG_CFLAGS" to include "-include
/usr/include/file-offset-bits-64.h" where the header file-offset-bits-64.h
contains a sequence of "#pragma redefine_extname" calls to rename the
functions in question without declaring them. That way you don't need the
static library and the calls go straight to the __*64 functions. (GCC 4.5
was the version that made #pragma redefine_extname available for all
targets.)
--
Joseph S. Myers
joseph@codesourcery.com