Revision 455bd4c430b0c0a361f38e8658a0d6cb469942b5 authored by Ivan Djelic on 06 March 2013, 19:09:27 UTC, committed by Russell King on 07 March 2013, 16:14:22 UTC
Recent GCC versions (e.g. GCC-4.7.2) perform optimizations based on
assumptions about the implementation of memset and similar functions.
The current ARM optimized memset code does not return the value of
its first argument, as is usually expected from standard implementations.
For instance in the following function:
void debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter)
{
memset(waiter, MUTEX_DEBUG_INIT, sizeof(*waiter));
waiter->magic = waiter;
INIT_LIST_HEAD(&waiter->list);
}
compiled as:
800554d0 <debug_mutex_lock_common>:
800554d0: e92d4008 push {r3, lr}
800554d4: e1a00001 mov r0, r1
800554d8: e3a02010 mov r2, #16 ; 0x10
800554dc: e3a01011 mov r1, #17 ; 0x11
800554e0: eb04426e bl 80165ea0 <memset>
800554e4: e1a03000 mov r3, r0
800554e8: e583000c str r0, [r3, #12]
800554ec: e5830000 str r0, [r3]
800554f0: e5830004 str r0, [r3, #4]
800554f4: e8bd8008 pop {r3, pc}
GCC assumes memset returns the value of pointer 'waiter' in register r0; causing
register/memory corruptions.
This patch fixes the return value of the assembly version of memset.
It adds a 'mov' instruction and merges an additional load+store into
existing load/store instructions.
For ease of review, here is a breakdown of the patch into 4 simple steps:
Step 1
======
Perform the following substitutions:
ip -> r8, then
r0 -> ip,
and insert 'mov ip, r0' as the first statement of the function.
At this point, we have a memset() implementation returning the proper result,
but corrupting r8 on some paths (the ones that were using ip).
Step 2
======
Make sure r8 is saved and restored when (! CALGN(1)+0) == 1:
save r8:
- str lr, [sp, #-4]!
+ stmfd sp!, {r8, lr}
and restore r8 on both exit paths:
- ldmeqfd sp!, {pc} @ Now <64 bytes to go.
+ ldmeqfd sp!, {r8, pc} @ Now <64 bytes to go.
(...)
tst r2, #16
stmneia ip!, {r1, r3, r8, lr}
- ldr lr, [sp], #4
+ ldmfd sp!, {r8, lr}
Step 3
======
Make sure r8 is saved and restored when (! CALGN(1)+0) == 0:
save r8:
- stmfd sp!, {r4-r7, lr}
+ stmfd sp!, {r4-r8, lr}
and restore r8 on both exit paths:
bgt 3b
- ldmeqfd sp!, {r4-r7, pc}
+ ldmeqfd sp!, {r4-r8, pc}
(...)
tst r2, #16
stmneia ip!, {r4-r7}
- ldmfd sp!, {r4-r7, lr}
+ ldmfd sp!, {r4-r8, lr}
Step 4
======
Rewrite register list "r4-r7, r8" as "r4-r8".
Signed-off-by: Ivan Djelic <ivan.djelic@parrot.com>
Reviewed-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Dirk Behme <dirk.behme@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
1 parent 44d6b1f
mount.h
#include <linux/mount.h>
#include <linux/seq_file.h>
#include <linux/poll.h>
struct mnt_namespace {
atomic_t count;
unsigned int proc_inum;
struct mount * root;
struct list_head list;
struct user_namespace *user_ns;
u64 seq; /* Sequence number to prevent loops */
wait_queue_head_t poll;
int event;
};
struct mnt_pcp {
int mnt_count;
int mnt_writers;
};
struct mount {
struct list_head mnt_hash;
struct mount *mnt_parent;
struct dentry *mnt_mountpoint;
struct vfsmount mnt;
#ifdef CONFIG_SMP
struct mnt_pcp __percpu *mnt_pcp;
#else
int mnt_count;
int mnt_writers;
#endif
struct list_head mnt_mounts; /* list of children, anchored here */
struct list_head mnt_child; /* and going through their mnt_child */
struct list_head mnt_instance; /* mount instance on sb->s_mounts */
const char *mnt_devname; /* Name of device e.g. /dev/dsk/hda1 */
struct list_head mnt_list;
struct list_head mnt_expire; /* link in fs-specific expiry list */
struct list_head mnt_share; /* circular list of shared mounts */
struct list_head mnt_slave_list;/* list of slave mounts */
struct list_head mnt_slave; /* slave list entry */
struct mount *mnt_master; /* slave is on master->mnt_slave_list */
struct mnt_namespace *mnt_ns; /* containing namespace */
#ifdef CONFIG_FSNOTIFY
struct hlist_head mnt_fsnotify_marks;
__u32 mnt_fsnotify_mask;
#endif
int mnt_id; /* mount identifier */
int mnt_group_id; /* peer group identifier */
int mnt_expiry_mark; /* true if marked for expiry */
int mnt_pinned;
int mnt_ghosts;
};
#define MNT_NS_INTERNAL ERR_PTR(-EINVAL) /* distinct from any mnt_namespace */
static inline struct mount *real_mount(struct vfsmount *mnt)
{
return container_of(mnt, struct mount, mnt);
}
static inline int mnt_has_parent(struct mount *mnt)
{
return mnt != mnt->mnt_parent;
}
static inline int is_mounted(struct vfsmount *mnt)
{
/* neither detached nor internal? */
return !IS_ERR_OR_NULL(real_mount(mnt));
}
extern struct mount *__lookup_mnt(struct vfsmount *, struct dentry *, int);
static inline void get_mnt_ns(struct mnt_namespace *ns)
{
atomic_inc(&ns->count);
}
struct proc_mounts {
struct seq_file m;
struct mnt_namespace *ns;
struct path root;
int (*show)(struct seq_file *, struct vfsmount *);
};
#define proc_mounts(p) (container_of((p), struct proc_mounts, m))
extern const struct seq_operations mounts_op;
Computing file changes ...
