path: root/src/ipc/semctl.c
diff options
authorRich Felker <>2014-01-08 16:12:47 -0500
committerRich Felker <>2014-01-08 16:12:47 -0500
commit289294220f278a291452332da8f45cf756f57fe5 (patch)
tree289eae9f5bda95245159a8ce5e35fb328a0efe12 /src/ipc/semctl.c
parent131871a3d846369fd925d3f8edb692edbad77e4d (diff)
fix type of semctl variadic argument
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.
Diffstat (limited to 'src/ipc/semctl.c')
1 files changed, 10 insertions, 4 deletions
diff --git a/src/ipc/semctl.c b/src/ipc/semctl.c
index 274e2cf3..49927e2e 100644
--- a/src/ipc/semctl.c
+++ b/src/ipc/semctl.c
@@ -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);
#ifdef SYS_semctl
- return syscall(SYS_semctl, id, num, cmd | IPC_64, arg);
+ return syscall(SYS_semctl, id, num, cmd | IPC_64, arg.buf);
- 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);