Issue 923315: AIX POLLNVAL definition causes problems (original) (raw)

Under AIX (5.1 at least), POLLNVAL (from sys/poll.h) is 0x8000. This causes a problem because it is stored in a (signed) short (e.g., revents):

struct pollfd { int fd; /* file descriptor or file ptr / short events; / requested events / short revents; / returned events */ };

As such, the following tests and results are given:

ashort (%hx) = 8000, ashort (%x) = ffff8000 POLLNVAL (%hx) = 8000, POLLNVAL (%x) = 8000 ashort == POLLNVAL => 0 ashort == (short)POLLNVAL => 1

Note that the 'ashort == POLLNVAL' test is 0 rather than 1 because (I believe) POLLNVAL is treated as a signed integer, the ashort value is then promoted to signed integer thus giving 0xffff8000, not 0x8000. The problem arises because IBM has chosen to use a negative short value (0x8000) in a signed short variable. Neither Linux or IRIX have this problem because they use POLLNVAL=0x20 which promotes to 0x20. This situation will cause the test_poll to fail and will certainly be a gotcha for AIX users. I have added the following code to the selectmodule.c to address the problem (mask out the upper 32 bits): -----~ line 513:selectmodule.c num = PyInt_FromLong(self->ufds[i].revents & 0xffff);

John