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[Bug ports/16191] New: PAGE_SIZE defined constant on MIPS, but size is configurable
- From: "ams at sourceware dot org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Tue, 19 Nov 2013 14:55:33 +0000
- Subject: [Bug ports/16191] New: PAGE_SIZE defined constant on MIPS, but size is configurable
- Auto-submitted: auto-generated
https://sourceware.org/bugzilla/show_bug.cgi?id=16191
Bug ID: 16191
Summary: PAGE_SIZE defined constant on MIPS, but size is
configurable
Product: glibc
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: ports
Assignee: unassigned at sourceware dot org
Reporter: ams at sourceware dot org
CC: carlos at redhat dot com, roland at gnu dot org
The sys/user.h header defines PAGE_SIZE to a constant (4096), but that figure
is not always accurate; the page size is a kernel configuration option.
#define PAGE_SHIFT 12
#define PAGE_SIZE (1UL << PAGE_SHIFT)
#define PAGE_MASK (~(PAGE_SIZE-1))
#define NBPG PAGE_SIZE
#define UPAGES 1
#define HOST_TEXT_START_ADDR (u.start_code)
#define HOST_DATA_START_ADDR (u.start_data)
#define HOST_STACK_END_ADDR (u.start_stack + u.u_ssize * NBPG)
A knock-on effect of this bug is that sysdeps/unix/sysv/linux/ifaddrs.c uses an
"optimization" when PAGE_SIZE is constant that means getifaddrs will always
fail when the real page size does not match PAGE_SIZE.
#ifdef PAGE_SIZE
/* Help the compiler optimize out the malloc call if PAGE_SIZE
is constant and smaller or equal to PTHREAD_STACK_MIN/4. */
const size_t buf_size = PAGE_SIZE;
#else
const size_t buf_size = __getpagesize ();
#endif
According to Andrew Pinski, the constant PAGE_SIZE is not appropriate on any
MIPS variant, so at least some of the above macros can be removed. Other
architectures appear to remove all of them, but it's not clear that that's
correct on MIPS.
This issue probably applied to other architectures also. Joseph Myers has
mentioned MicroBlaze.
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