x86: be careful about tailcall breakage for sys_open[at] too

Came up through a quick grep for other cases similar to the ftruncate()
one in commit 0a489cb3b6a7b277030cdbc97c2c65905db94536.

Also, add a comment, so that people who read the code understand why we
do what looks like a no-op.

(Again, this won't actually matter to any sane user, since libc will
save and restore the register gcc stomps on, but it's still wrong to
stomp on it)

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/fs/open.c b/fs/open.c
index 8279c65..53ec28c 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -332,6 +332,7 @@ out:
 asmlinkage long sys_ftruncate(unsigned int fd, unsigned long length)
 {
        long ret = do_sys_ftruncate(fd, length, 1);
+       /* avoid REGPARM breakage on x86: */
        prevent_tail_call(ret);
        return ret;
 }
@@ -346,6 +347,7 @@ asmlinkage long sys_truncate64(const char __user * path, loff_t length)
 asmlinkage long sys_ftruncate64(unsigned int fd, loff_t length)
 {
        long ret = do_sys_ftruncate(fd, length, 0);
+       /* avoid REGPARM breakage on x86: */
        prevent_tail_call(ret);
        return ret;
 }
@@ -1097,20 +1099,30 @@ long do_sys_open(int dfd, const char __user *filename, int flags, int mode)
 
 asmlinkage long sys_open(const char __user *filename, int flags, int mode)
 {
+       long ret;
+
        if (force_o_largefile())
                flags |= O_LARGEFILE;
 
-       return do_sys_open(AT_FDCWD, filename, flags, mode);
+       ret = do_sys_open(AT_FDCWD, filename, flags, mode);
+       /* avoid REGPARM breakage on x86: */
+       prevent_tail_call(ret);
+       return ret;
 }
 EXPORT_SYMBOL_GPL(sys_open);
 
 asmlinkage long sys_openat(int dfd, const char __user *filename, int flags,
                           int mode)
 {
+       long ret;
+
        if (force_o_largefile())
                flags |= O_LARGEFILE;
 
-       return do_sys_open(dfd, filename, flags, mode);
+       ret = do_sys_open(dfd, filename, flags, mode);
+       /* avoid REGPARM breakage on x86: */
+       prevent_tail_call(ret);
+       return ret;
 }
 EXPORT_SYMBOL_GPL(sys_openat);