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Documentation now matches the implementation of the Linux time system call wrapper.

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git-svn-id: svn://svn.valgrind.org/valgrind/trunk@7919
This commit is contained in:
Bart Van Assche 2008-04-26 10:47:29 +00:00
parent 1acba43fc4
commit 8dde97e5cc
1 changed files with 21 additions and 15 deletions
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36
README_MISSING_SYSCALL_OR_IOCTL
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@ -44,38 +44,45 @@ should be familiar to many Unix programmers.
The syscall wrapper for time()
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Removing the debug printing clutter, it looks like this:
The wrapper for the time system call looks like this:
PRE(time)
PRE(sys_time)
{
/* time_t time(time_t *t); */
PRINT("time ( %p )",arg1);
if (arg1 != (UWord)NULL) {
PRE_MEM_WRITE( "time", arg1, sizeof(time_t) );
PRINT("sys_time ( %p )",ARG1);
PRE_REG_READ1(long, "time", int *, t);
if (ARG1 != 0) {
PRE_MEM_WRITE( "time(t)", ARG1, sizeof(vki_time_t) );
}
}
POST(time)
POST(sys_time)
{
if (arg1 != (UWord)NULL) {
POST_MEM_WRITE( arg1, sizeof(vki_time_t) );
if (ARG1 != 0) {
POST_MEM_WRITE( ARG1, sizeof(vki_time_t) );
}
}
The first thing we do happens before the syscall occurs, in the PRE() function:
if a non-NULL buffer is passed in as the argument, tell the tool that the
tell the tool the return type of the syscall, that the syscall has one
argument, the type of the argument and that the argument is being read from a
register:
PRE_REG_READ1(long, "time", int *, t);
Next, if a non-NULL buffer is passed in as the argument, tell the tool that the
buffer is about to be written to:
if (arg1 != (UWord)NULL) {
PRE_MEM_WRITE( "time", arg1, sizeof(vki_time_t) );
if (ARG1 != 0) {
PRE_MEM_WRITE( "time", ARG1, sizeof(vki_time_t) );
}
Finally, the really important bit, after the syscall occurs, in the POST()
function: if, and only if, the system call was successful, tell the tool that
the memory was written:
if (arg1 != (UInt)NULL) {
POST_MEM_WRITE( arg1, sizeof(vki_time_t) );
if (ARG1 != 0) {
POST_MEM_WRITE( ARG1, sizeof(vki_time_t) );
}
The POST() function won't be called if the syscall failed, so you
@ -134,8 +141,7 @@ following:
dependant ones (in syswrap-$(PLATFORM)-linux.c).
The *XY variant if it requires a PRE() and POST() function, and
the *X_ variant if it only requires a PRE()
function. The 2nd arg of these macros indicate if the syscall
could possibly block.
function.
If you find this difficult, read the wrappers for other syscalls
for ideas. A good tip is to look for the wrapper for a syscall