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

[Mathieu Desnoyers]

* Avik Sil (avik.sil at linaro.org) wrote:
> 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

Hi Avik,

Instead of modifying all those wrappers individually, can you create a
wrapper/kallsyms.h and create a wrapper for kallsyms_lookup_name ? This
way, the ifdef for the ARM special-case would only appear once.

Thanks!

Mathieu

> 
> 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
> 
> 
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> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com