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fix type of semctl variadic argument

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per POSIX, the variadic argument has type union semun, which may
contain a pointer or int; the type read depends on the command being
issued. this allows the userspace part of the implementation to be
type-correct without requiring special-casing for different commands.
the kernel always expects to receive the argument interpreted as
unsigned long (or equivalently, a pointer), and does its own handling
of extracting the int portion from the representation, as needed.

this change fixes two possible issues: most immediately, reading the
argument as a (signed) long and passing it to the syscall would
perform incorrect sign-extension of pointers on the upcoming x32
target. the other possible issue is that some archs may use different
(user-space) argument-passing convention for unions, preventing va_arg
from correctly obtaining the argument when the type long (or even
unsigned long or void *) is passed to it.
This commit is contained in:
Rich Felker
2014-01-08 16:12:47 -05:00
parent 131871a3d8
commit 289294220f
1 changed files with 10 additions and 4 deletions
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14
src/ipc/semctl.c
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@ -3,16 +3,22 @@
#include "syscall.h"
#include "ipc.h"
struct semun {
int val;
struct semid_ds *buf;
unsigned short *array;
};
int semctl(int id, int num, int cmd, ...)
{
long arg;
struct semun arg;
va_list ap;
va_start(ap, cmd);
arg = va_arg(ap, long);
arg = va_arg(ap, struct semun);
va_end(ap);
#ifdef SYS_semctl
return syscall(SYS_semctl, id, num, cmd | IPC_64, arg);
return syscall(SYS_semctl, id, num, cmd | IPC_64, arg.buf);
#else
return syscall(SYS_ipc, IPCOP_semctl, id, num, cmd | IPC_64, &arg);
return syscall(SYS_ipc, IPCOP_semctl, id, num, cmd | IPC_64, &arg.buf);
#endif
}