Problem - Kevin Tafuro

The mlock( ) system call on Unix imposes an additional limitation over VirtualLock( )
on Window: the process making the call must have superuser privileges. In addition,
when fork( ) is used by a process that has locked memory, the copy of the memory in
the newly created process will not be locked. In other words, child processes do not
inherit memory locks.
13.4 Using Variable Arguments Properly
Problem
You need a way to protect a function that accepts a variable number of arguments
from reading more arguments than were passed to the function.
Solution
Our solution for dealing with a variable number of arguments is actually two solutions.
The interface for both solutions is identical, however. Instead of calling va_
arg( ), you should call spc_next_varg( ), listed later in this section. Note, however,
that the signature for the two functions is different. The code:
my_int_arg = va_arg(ap, int);
becomes:
spc_next_varg(ap, int, my_int_arg);
The biggest difference from using variable argument functions is how you need to
make the calls when using this solution. If you can guarantee that your code will be
compiled only by GCC and will always be running on an x86 processor (or another
processor to which you can port the first solution), you can make calls to the function
using spc_next_varg( ) in the normal way. Otherwise, you will need to use the
VARARG_CALL_x macros, where x is the number of arguments that you will be passing
to the function, including both fixed and variable.
#include
#include
#if defined(__GNUC__) && defined(i386)
/* NOTE: This is valid only using GCC on an x86 machine */
#define spc_next_varg(ap, type, var) \
do { \
unsigned int __frame; \
__frame = *(unsigned int *)__builtin_frame_address(0); \
if ((unsigned int)(ap) = = __frame - 16) { \
fprintf(stderr, "spc_next_varg( ) called too many times!\n"); \
abort( ); \
} \
(var) = va_arg((ap), (type)); \
Using Variable Arguments Properly | 709
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