Should NBPG be unconditionally undefined to avoid references to PAGE_SIZE?

[Stephen M. Kenton]

This is probably a better place to discuss this than bug-binutils. I am 
trying to make it easier for people to build cross-compile tool chains 
for all 20+ targets supported by the Linux kernel, using the currently 
released versions of binutils, glibc, gcc and the kernel. When I build 
binutils for alpha as part of a cross-compile tool chain everything is 
fine because (host != target) in bfd/configure and thus COREFILE= 
COREFLAG= TRAD_HEADER= are not set so trad-core.c is not built. When I 
use that tool chain to build a Canadian cross to install in the sysroot, 
however, binutils fails to build because NBPG is set to PAGE_SIZE in 
<sys/user.h> in bfd/trad-core.c. It would be easy enough to patch that 
header, but I really think things should build out-of-the-box. This same 
problem can be found in bugzilla for m68k, so others have tripped over 
it too.

As shown below, glibc-2.6.1 still defines NBPG to PAGE_SIZE in many 
cases. In reality, PAGE_SIZE is not a constant value for some 
processors. For this reason it has been removed from the exported kernel 
headers.  The obvious change is to use getpagesize() instead. This 
should get fixed in glibc at some point, but as of now, including 
<sys/user.h> in bfd/trad-core.c can set NBPG to PAGE_SIZE which causes a 
build failure with some configs. The undef statement show with <---- got 
things building for me again with binutils-2.18.50. Is there some reason 
this is not unconditional now that PAGE_SIZE has gone away in the kernel 
headers?  From a code correctness point of view I don't see how always 
using getpagesize() is not better than relying on a possibly flakey 
definition of NBPG from elsewhere, for any modern kernel or glibc 
versions. Should something similar make it into a suitable central place 
in the next release of binutils so no target by target fixups are 
required and it will build more consistently regardless of the version 
the libc headers? Obviously not a problem to distro users, but a big 
help to the roll-your-own cross-compiler crowd.

Thanks - Steve


--- From bfd/trad-core.c ---
#include <signal.h>
 
#include <sys/user.h>           /* After a.out.h  */
#undef NBPG /* Do not let <sys/user.h> set this to PAGE_SIZE */ 
<--------------------------
 
#ifdef TRAD_HEADER
#include TRAD_HEADER
#endif
 
#ifndef NBPG
# define NBPG getpagesize()
#endif

--- From glibc-2.6.1 for multiple Linux ports ---
find . -name user.h -exec grep PAGE_SIZE {} \;  -print
#define NBPG                   PAGE_SIZE /* XXX 4096 maybe? */
./sparc64-linux/usr/include/asm-sparc64/user.h
#define NBPG                    PAGE_SIZE
./m32r-linux/usr/include/asm/user.h
#define NBPG PAGE_SIZE
./s390-linux/usr/include/asm/user.h
#define NBPG                    PAGE_SIZE
./sh64-linux/usr/include/asm/user.h
#define NBPG PAGE_SIZE
./bfin-linux-uclibc/usr/include/asm/user.h
#define NBPG                    PAGE_SIZE
./cris-linux/usr/include/asm/user.h
#define NBPG                    PAGE_SIZE
./avr-linux/usr/include/asm/user.h
#define NBPG                    PAGE_SIZE
./frv-linux/usr/include/asm/user.h
#define NBPG PAGE_SIZE
./x86_64-linux/usr/include/asm-x86_64/user.h
#define NBPG PAGE_SIZE
./x86_64-linux/usr/include/asm-i386/user.h
#define NBPG                    PAGE_SIZE
./alpha-linux/usr/include/asm/user.h
#define NBPG                    PAGE_SIZE
./alpha-linux/usr/include/sys/user.h
#define NBPG                    PAGE_SIZE
./sh-linux/usr/include/asm/user.h
#define NBPG PAGE_SIZE
./i386-linux/usr/include/asm/user.h
#define NBPG                    PAGE_SIZE
./ia64-linux/usr/include/asm/user.h
#define NBPG PAGE_SIZE
./h8300-elf/usr/include/asm/user.h
#define NBPG PAGE_SIZE
./arm-linux/usr/include/asm/user.h