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Problem Report 1140 Details
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Problem Report Number 1140 Submitter's Classification Test Suite problem State Resolved Resolution Rejected (REJ) Problem Resolution ID REJ.X.0342 Raised 1970-01-01 08:00 Updated 2003-03-13 08:00 Published null Product Standard Internationalised System Calls and Libraries Extended (UNIX 95) Certification Program The Open Brand certification program Test Suite VSU version 4.0.2 Test Identification base/mmap 17 18 19 21 22 23 Problem Summary PG4U.00130 This IR claims that the test fails on due to type conversion on 64 bit machines and that MAP_FAILED should be returned instead of (void *)-1. Problem Text
We believe that the tests are in error because they make implicit
assumptions about an implementation. Specifically, the test of the
return value from mmap() via an equality test for -1.
The POSIX.1-1996 standard (12.2.1.3 Returns) explicitly states that:
"... it shall return a value MAP_FAILED...".
Further, we realize that this is a change from previous POSIX.1 versions.
The POSIX.1-1996 rational (Page 538, lines 7477-7481) states that the
intention for the change was due to ambiguities in the C standard regarding
casting of void* types.
The ANSI C standard explicitly states in the section defining Cast operators
(note: the section numbers vary depending on which version you examine):
"An arbitrary integer may be converted to a pointer. The results is
implementation-defined(*)".
"(*) The mapping functions for converting a pointer to an integer or an
integer to a pointer are intended to be consistent with the addressing
structure of the execution environment."
For specific information, a detailed explanation concerning our
implementation is included below.
We believe that the tests need to be modified to adhere to the current
POSIX.1-1996 standard. We believe that this is easily done by replacing
all occurances of -1 with MAP_FAILED for mmap() error checking conditions.
Alternately, we provide an additional solution proposal below...
The following are the technical specifics of this problem.
The following lines (taken from the test-program supplied)
>
> if ((result = mmap(0, pgsz, PROT_READ, MAP_SHARED, fd, 0)) != (void *)-1)
> {
> printf("ERROR: mmap() did not return -1\n");
> printf("Expected :-1 Received: %p\n", result);
> return;
> }
>
are okay ONLY if we are building a 32-bit binary. This is because when
mmap() fails, the value returned by mmap() is the maximum 32-bit address.
result = 0xffffffff (32-bit address)
and when -1 is typecast to (void *) we get
(void *)-1 = 0xffffffff (32-bit pointer)
Therefore the comparison made in the test-program works for the 32-bit case.
However if the test-program is compiled to be a 64-bit binary, upon the
failure of mmap() we will get the following case:
result = 0xffffffffffffffff (64-bit address)
But now when we typecast -1 to (void *) we have
(void *)-1 = 0x00000000ffffffff (64-bit pointer)
It is no surprise that the comparison is failing. This seems to be the result
of the fact that the compiler is not sign-extending the 32-bit negative number
(-1 here) when typecasting it to a pointer (which is actually correct).
A better way to test for the success/failure status of the mmap() would be
to use the following check (which works for both 32-bit and 64-bit binaries):
if ((result = mmap(0, pgsz, PROT_READ, MAP_SHARED, fd, 0)) != (void *)-1L) {
...
}
Or better yet, the constant MAP_FAILED, prescribed by POSIX could be used.
This constant is defined as follows:
define MAP_FAILED (void *)-1L
and therefore we can test for the success of an mmap() as follows:
if( ( result = mmap(.....) ) == MAP_FAILED ) {
/* failure */
}
else {
/* success */
}
Test Output
TEST CASE: mmap
TEST PURPOSE #17
EBADF in errno and return -1 on a call to void
*mmap(void *addr, size_t len, int prot, int flags, int
fildes, off_t off) when fildes is not a valid file
descriptor.
PREP: Obtain the system page size by call to
sysconf(_SC_PAGESIZE)
PREP: Establish signal handlers for SIGSEGV and SIGBUS
PREP: Open a file and initialize it
PREP: Allocate memory for buffer
PREP: Now set proper permissions and re-open file
PREP: Create a closed file descriptor
TEST: Return -1 when file descriptor is not valid
ERROR: mmap() did not return -1
Expected :-1 Received: ffffffffffffffff
17 FAIL
TEST PURPOSE #18
EACCES in errno and return -1 on a call to void
*mmap(void *addr, size_t len, int prot, int flags, int
fildes, off_t off) when fildes is not open for reading.
PREP: Obtain the system page size by call to
sysconf(_SC_PAGESIZE)
PREP: Establish signal handlers for SIGSEGV and SIGBUS
PREP: Open a file and initialize it
PREP: Allocate memory for buffer
PREP: Now set proper permissions and re-open file
TEST: Return -1 when file descriptor is not open
for reading
ERROR: mmap() did not return -1
Expected :-1 Received: ffffffffffffffff
18 FAIL
TEST PURPOSE #19
EACCES in errno and return -1 on a call to void
*mmap(void *addr, size_t len, int prot, int flags, int
fildes, off_t off) when fildes is not open for writing
and PROT_WRITE is specified for a MAP_SHARED operation.
PREP: Obtain the system page size by call to
sysconf(_SC_PAGESIZE)
PREP: Establish signal handlers for SIGSEGV and SIGBUS
PREP: Open a file and initialize it
PREP: Allocate memory for buffer
PREP: Now set proper permissions and re-open file
TEST: Return -1 when file descriptor not open for
writing & PROT_WRITE is specified for a
MAP_SHARED operation
ERROR: mmap() did not return -1
Expected :-1 Received: ffffffffffffffff
19 FAIL
TEST PURPOSE #21
EINVAL in errno and return -1 on a call to void
*mmap(void *addr, size_t len, int prot, int flags, int
fildes, off_t off) when addr is not a multiple of the
page size returned by sysconf(_SC_PAGESIZE) and
MAP_FIXED is specified.
PREP: Obtain the system page size by call to
sysconf(_SC_PAGESIZE)
PREP: Establish signal handlers for SIGSEGV and SIGBUS
PREP: Open a file and initialize it
PREP: Allocate memory for buffer
PREP: Now set proper permissions and re-open file
PREP: Find a fixed address not aligned to page boundary
TEST: Return -1 when MAP_FIXED is set and the map
address is not multiple of page size
ERROR: mmap() did not return -1
Expected :-1 Received: 0xffffffffffffffff
21 FAIL
TEST PURPOSE #22
EINVAL in errno and return -1 on a call to void
*mmap(void *addr, size_t len, int prot, int flags, int
fildes, off_t off) when off is not a multiple of the
page size returned by sysconf(_SC_PAGESIZE).
PREP: Obtain the system page size by call to
sysconf(_SC_PAGESIZE)
PREP: Establish signal handlers for SIGSEGV and SIGBUS
PREP: Open a file and initialize it
PREP: Allocate memory for buffer
PREP: Now set proper permissions and re-open file
TEST: Return -1 when file offset is half the page size
ERROR: mmap() did not return -1
Expected :-1 Received: ffffffffffffffff
22 FAIL
TEST PURPOSE #23
EINVAL in errno and return -1 on a call to void
*mmap(void *addr, size_t len, int prot, int flags, int
fildes, off_t off) when flags does not contain either
MAP_PRIVATE or MAP_SHARED.
PREP: Obtain the system page size by call to
sysconf(_SC_PAGESIZE)
PREP: Establish signal handlers for SIGSEGV and SIGBUS
PREP: Open a file and initialize it
PREP: Allocate memory for buffer
PREP: Now set proper permissions and re-open file
TEST: Return -1 when neither MAP_SHARED nor
MAP_PRIVATE are set in flags
ERROR: mmap() did not return -1
Expected :-1 Received: ffffffffffffffff
23 UNRESOLVED
SECTION: Headers
TEST CASE: mmap
TEST PURPOSE #17,18,19,21,22,23
ERROR: mmap() did not return -1
Expected :-1 Received: ffffffffffffffff
Review Information
Review Type TSMA Review Start Date null Completed null Status Complete Review Recommendation No Resolution Given Review Response
We recommend this request be refused.
The journal output is from tests related to XSH4.2, which is testing the
following statement from the RETURN VALUE section of mmap():
Upon successful completion, mmap() returns the address at
which the mapping was placed (pa). Otherwise, it returns a
value of -1 and sets errno to indicate the error.
The mmap() function is defined to return a pointer to void, so (void
*)-1 is the proper value expected. The standard does not specify a
long integer constant (-1L) for the return value. The IUT does not
return (void *)-1, so the test properly fails as expected.
The references to MAP_FAILED are not meaningful, since this symbol is
not defined for XSH4.2. However, MAP_FAILED is defined in XSH5 and
tested for in the indicator of compliance for that specification.
Note: VSU 4.0.2 is no longer valid for branding. The submitter should
be using a more recent version of the test suite for testing.
Note: POSIX.1-1996 is not a normative reference for XSH4.2. The submitter
should be referencing POSIX.1-1990, which is normative.
Review Type SA Review Start Date null Completed null Status Complete Review Resolution No Resolution Given Review Conclusion
The tests are correct as written for the XSH 4 Version 2
specification.
However, this should be forwarded to the Base WG for consideration,
regarding the issue of whether the XSH4.2 requirements should be waived
in this case in favour of the XSH5 requirements which would thus permit
this 64-bit implementation.
Review Type Expert Group Review Start Date null Completed null Status Complete Review Resolution No Resolution Given Review Conclusion
The XSH4V2 specification states that mmap returns -1
cast to a (void *). This is not an LP64 issue.
The waiver should be refused.
Review Type SA Review Start Date null Completed null Status Complete Review Resolution Rejected (REJ) Review Conclusion
This request is refused.
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