[ltt-dev] [PATCH] ARM: Set bit 0 for thumb mode in kallsyms_lookup_name returned address

[Avik Sil]

This patch fixes the undefined instruction oops due to execution
of thumb-2 code in ARM mode. The zero bit in the symbol address
returned by kallsyms_lookup_name is not set, leading to switching
to ARM mode that generates oops while executing thumb-2 code. For
detailed discussion, see [1].
[1] http://lists.casi.polymtl.ca/pipermail/ltt-dev/2011-September/005176.html

Signed-off-by: Avik Sil <avik.sil at linaro.org>
---
 lttng-context-prio.c |   11 ++++++++++-
 wrapper/ftrace.h     |   28 ++++++++++++++++++++++------
 wrapper/splice.c     |   14 ++++++++++++--
 wrapper/vmalloc.h    |   14 +++++++++++---
 4 files changed, 55 insertions(+), 12 deletions(-)

diff --git a/lttng-context-prio.c b/lttng-context-prio.c
index ad1c42f..5e8c0d2 100644
--- a/lttng-context-prio.c
+++ b/lttng-context-prio.c
@@ -20,7 +20,16 @@ int (*wrapper_task_prio_sym)(struct task_struct *t);
 
 int wrapper_task_prio_init(void)
 {
-	wrapper_task_prio_sym = (void *) kallsyms_lookup_name("task_prio");
+        unsigned long addr;
+
+        addr = kallsyms_lookup_name("task_prio");
+#ifdef CONFIG_ARM 
+#ifdef CONFIG_THUMB2_KERNEL
+        if (addr)
+                addr |= 1; /* set bit 0 in address for thumb mode */
+#endif
+#endif
+        wrapper_task_prio_sym = (void *) addr;
 	if (!wrapper_task_prio_sym) {
 		printk(KERN_WARNING "LTTng: task_prio symbol lookup failed.\n");
 		return -EINVAL;
diff --git a/wrapper/ftrace.h b/wrapper/ftrace.h
index 9c18cc5..d79aa5e 100644
--- a/wrapper/ftrace.h
+++ b/wrapper/ftrace.h
@@ -21,10 +21,18 @@ static inline
 int wrapper_register_ftrace_function_probe(char *glob,
 		struct ftrace_probe_ops *ops, void *data)
 {
-	int (*register_ftrace_function_probe_sym)(char *glob,
-			struct ftrace_probe_ops *ops, void *data);
+        unsigned long addr;
+        int (*register_ftrace_function_probe_sym)(char *glob,
+                        struct ftrace_probe_ops *ops, void *data);
 
-	register_ftrace_function_probe_sym = (void *) kallsyms_lookup_name("register_ftrace_function_probe");
+        addr = kallsyms_lookup_name("register_ftrace_function_probe");
+#ifdef CONFIG_ARM 
+#ifdef CONFIG_THUMB2_KERNEL
+        if (addr)
+                addr |= 1; /* set bit 0 in address for thumb mode */
+#endif
+#endif
+        register_ftrace_function_probe_sym = (void *) addr;
 	if (register_ftrace_function_probe_sym) {
 		return register_ftrace_function_probe_sym(glob, ops, data);
 	} else {
@@ -37,10 +45,18 @@ static inline
 void wrapper_unregister_ftrace_function_probe(char *glob,
 		struct ftrace_probe_ops *ops, void *data)
 {
-	void (*unregister_ftrace_function_probe_sym)(char *glob,
-			struct ftrace_probe_ops *ops, void *data);
+        unsigned long addr;
+        void (*unregister_ftrace_function_probe_sym)(char *glob,
+                        struct ftrace_probe_ops *ops, void *data);
 
-	unregister_ftrace_function_probe_sym = (void *) kallsyms_lookup_name("unregister_ftrace_function_probe");
+        addr = kallsyms_lookup_name("unregister_ftrace_function_probe");
+#ifdef CONFIG_ARM 
+#ifdef CONFIG_THUMB2_KERNEL
+        if (addr)
+                addr |= 1; /* set bit 0 in address for thumb mode */
+#endif
+#endif
+        unregister_ftrace_function_probe_sym = (void *) addr;
 	if (unregister_ftrace_function_probe_sym) {
 		unregister_ftrace_function_probe_sym(glob, ops, data);
 	} else {
diff --git a/wrapper/splice.c b/wrapper/splice.c
index edc499c..c2c275b 100644
--- a/wrapper/splice.c
+++ b/wrapper/splice.c
@@ -21,8 +21,18 @@ ssize_t (*splice_to_pipe_sym)(struct pipe_inode_info *pipe,
 ssize_t wrapper_splice_to_pipe(struct pipe_inode_info *pipe,
 			       struct splice_pipe_desc *spd)
 {
-	if (!splice_to_pipe_sym)
-		splice_to_pipe_sym = (void *) kallsyms_lookup_name("splice_to_pipe");
+        unsigned long addr;
+
+        if (!splice_to_pipe_sym) {
+                addr = kallsyms_lookup_name("splice_to_pipe");
+#ifdef CONFIG_ARM 
+#ifdef CONFIG_THUMB2_KERNEL
+                if (addr)
+                        addr |= 1; /* set bit 0 in address for thumb mode */
+#endif
+#endif
+                splice_to_pipe_sym = (void *) addr;
+        }
 	if (splice_to_pipe_sym) {
 		return splice_to_pipe_sym(pipe, spd);
 	} else {
diff --git a/wrapper/vmalloc.h b/wrapper/vmalloc.h
index 7d87855..d512c89 100644
--- a/wrapper/vmalloc.h
+++ b/wrapper/vmalloc.h
@@ -18,9 +18,17 @@
 static inline
 void wrapper_vmalloc_sync_all(void)
 {
-	void (*vmalloc_sync_all_sym)(void);
-
-	vmalloc_sync_all_sym = (void *) kallsyms_lookup_name("vmalloc_sync_all");
+        unsigned long addr;
+        void (*vmalloc_sync_all_sym)(void);
+
+        addr = kallsyms_lookup_name("vmalloc_sync_all");
+#ifdef CONFIG_ARM 
+#ifdef CONFIG_THUMB2_KERNEL
+        if (addr)
+                addr |= 1; /* set bit 0 in address for thumb mode */
+#endif
+#endif
+        vmalloc_sync_all_sym = (void *) addr;
 	if (vmalloc_sync_all_sym) {
 		vmalloc_sync_all_sym();
 	} else {
-- 
1.7.0.4