On Ubuntu 10.04.1, with
"uname -a" outputting "Linux hostname 2.6.32-25-generic #44-Ubuntu SMP Fri Sep 17 20:26:08 UTC 2010 i686 GNU/Linux"
"gcc --version" outputting "gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3"

On hg revision 7965 of the py3k branch, I get the following compile-time warnings:

/mnt/data/src/py3k/Modules/_posixsubprocess.c: In function ‘child_exec’:
/mnt/data/src/py3k/Modules/_posixsubprocess.c:152: warning: ignoring return value of ‘write’, declared with attribute warn_unused_result
/mnt/data/src/py3k/Modules/_posixsubprocess.c:158: warning: ignoring return value of ‘write’, declared with attribute warn_unused_result
/mnt/data/src/py3k/Modules/_posixsubprocess.c:159: warning: ignoring return value of ‘write’, declared with attribute warn_unused_result
/mnt/data/src/py3k/Modules/_posixsubprocess.c:163: warning: ignoring return value of ‘write’, declared with attribute warn_unused_result
/mnt/data/src/py3k/Modules/_posixsubprocess.c:164: warning: ignoring return value of ‘write’, declared with attribute warn_unused_result

/mnt/data/src/py3k/Modules/socketmodule.c: In function ‘socket_gethostbyname_ex’:
/mnt/data/src/py3k/Modules/socketmodule.c:3282: warning: dereferencing pointer ‘sa’ does break strict-aliasing rules
/mnt/data/src/py3k/Modules/socketmodule.c:3280: note: initialized from here
/mnt/data/src/py3k/Modules/socketmodule.c: In function ‘socket_gethostbyaddr’:
/mnt/data/src/py3k/Modules/socketmodule.c:3339: warning: dereferencing pointer ‘sa’ does break strict-aliasing rules
/mnt/data/src/py3k/Modules/socketmodule.c:3309: note: initialized from here

/mnt/data/src/py3k/Modules/_multiprocessing/multiprocessing.c: In function ‘multiprocessing_sendfd’:
/mnt/data/src/py3k/Modules/_multiprocessing/multiprocessing.c:125: warning: dereferencing type-punned pointer will break strict-aliasing rules
/mnt/data/src/py3k/Modules/_multiprocessing/multiprocessing.c: In function ‘multiprocessing_recvfd’:
/mnt/data/src/py3k/Modules/_multiprocessing/multiprocessing.c:168: warning: dereferencing type-punned pointer will break strict-aliasing rules

/mnt/data/src/py3k/Modules/_ctypes/libffi/src/closures.c: In function ‘dlmmap_locked’:
/mnt/data/src/py3k/Modules/_ctypes/libffi/src/closures.c:416: warning: ignoring return value of ‘ftruncate’, declared with attribute warn_unused_result
/mnt/data/src/py3k/Modules/_ctypes/libffi/src/closures.c:428: warning: ignoring return value of ‘ftruncate’, declared with attribute warn_unused_result
/mnt/data/src/py3k/Modules/_ctypes/libffi/src/dlmalloc.c: In function ‘mmap_resize’:
/mnt/data/src/py3k/Modules/_ctypes/libffi/src/dlmalloc.c:3193: warning: implicit declaration of function ‘mremap’
/mnt/data/src/py3k/Modules/_ctypes/libffi/src/dlmalloc.c: In function ‘sys_trim’:
/mnt/data/src/py3k/Modules/_ctypes/libffi/src/dlmalloc.c:3612: warning: comparison between pointer and integer