asmlinkage_protect replaces prevent_tail_call

The prevent_tail_call() macro works around the problem of the compiler
clobbering argument words on the stack, which for asmlinkage functions
is the caller's (user's) struct pt_regs.  The tail/sibling-call
optimization is not the only way that the compiler can decide to use
stack argument words as scratch space, which we have to prevent.
Other optimizations can do it too.

Until we have new compiler support to make "asmlinkage" binding on the
compiler's own use of the stack argument frame, we have work around all
the manifestations of this issue that crop up.

More cases seem to be prevented by also keeping the incoming argument
variables live at the end of the function.  This makes their original
stack slots attractive places to leave those variables, so the compiler
tends not clobber them for something else.  It's still no guarantee, but
it handles some observed cases that prevent_tail_call() did not.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 13 insertions, 13 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 53872bf993fa..073005b1cfb2 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1608,7 +1608,7 @@ asmlinkage long sys_waitid(int which, pid_t upid,
 	put_pid(pid);
 
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(5, ret, which, upid, infop, options, ru);
 	return ret;
 }
 
@@ -1640,7 +1640,7 @@ asmlinkage long sys_wait4(pid_t upid, int __user *stat_addr,
 	put_pid(pid);
 
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(4, ret, upid, stat_addr, options, ru);
 	return ret;
 }
 
diff --git a/kernel/uid16.c b/kernel/uid16.c
index dd308ba4e03b..3e41c1673e2f 100644
--- a/kernel/uid16.c
+++ b/kernel/uid16.c
@@ -21,7 +21,7 @@ asmlinkage long sys_chown16(const char __user * filename, old_uid_t user, old_gi
 {
 	long ret = sys_chown(filename, low2highuid(user), low2highgid(group));
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(3, ret, filename, user, group);
 	return ret;
 }
 
@@ -29,7 +29,7 @@ asmlinkage long sys_lchown16(const char __user * filename, old_uid_t user, old_g
 {
 	long ret = sys_lchown(filename, low2highuid(user), low2highgid(group));
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(3, ret, filename, user, group);
 	return ret;
 }
 
@@ -37,7 +37,7 @@ asmlinkage long sys_fchown16(unsigned int fd, old_uid_t user, old_gid_t group)
 {
 	long ret = sys_fchown(fd, low2highuid(user), low2highgid(group));
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(3, ret, fd, user, group);
 	return ret;
 }
 
@@ -45,7 +45,7 @@ asmlinkage long sys_setregid16(old_gid_t rgid, old_gid_t egid)
 {
 	long ret = sys_setregid(low2highgid(rgid), low2highgid(egid));
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(2, ret, rgid, egid);
 	return ret;
 }
 
@@ -53,7 +53,7 @@ asmlinkage long sys_setgid16(old_gid_t gid)
 {
 	long ret = sys_setgid(low2highgid(gid));
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(1, ret, gid);
 	return ret;
 }
 
@@ -61,7 +61,7 @@ asmlinkage long sys_setreuid16(old_uid_t ruid, old_uid_t euid)
 {
 	long ret = sys_setreuid(low2highuid(ruid), low2highuid(euid));
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(2, ret, ruid, euid);
 	return ret;
 }
 
@@ -69,7 +69,7 @@ asmlinkage long sys_setuid16(old_uid_t uid)
 {
 	long ret = sys_setuid(low2highuid(uid));
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(1, ret, uid);
 	return ret;
 }
 
@@ -78,7 +78,7 @@ asmlinkage long sys_setresuid16(old_uid_t ruid, old_uid_t euid, old_uid_t suid)
 	long ret = sys_setresuid(low2highuid(ruid), low2highuid(euid),
 				 low2highuid(suid));
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(3, ret, ruid, euid, suid);
 	return ret;
 }
 
@@ -98,7 +98,7 @@ asmlinkage long sys_setresgid16(old_gid_t rgid, old_gid_t egid, old_gid_t sgid)
 	long ret = sys_setresgid(low2highgid(rgid), low2highgid(egid),
 				 low2highgid(sgid));
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(3, ret, rgid, egid, sgid);
 	return ret;
 }
 
@@ -117,7 +117,7 @@ asmlinkage long sys_setfsuid16(old_uid_t uid)
 {
 	long ret = sys_setfsuid(low2highuid(uid));
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(1, ret, uid);
 	return ret;
 }
 
@@ -125,7 +125,7 @@ asmlinkage long sys_setfsgid16(old_gid_t gid)
 {
 	long ret = sys_setfsgid(low2highgid(gid));
 	/* avoid REGPARM breakage on x86: */
-	prevent_tail_call(ret);
+	asmlinkage_protect(1, ret, gid);
 	return ret;
 }