Messages in this thread | | | Date | Fri, 4 Aug 2006 09:00:18 -0700 | From | "Randy.Dunlap" <> | Subject | Re: [PATCH] module interface improvement for kprobes |
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On Fri, 04 Aug 2006 10:17:32 -0500 David Smith wrote:
> When inserting a kprobes probe into a loadable module, there isn't a way > for the kprobes module to get a module reference (in order to find the > base address of the module among perhaps other things). > > A kprobes probe needs the base address of the module in order to > "relocate" the addresses of probe points (since the load address of the > module can change from run to run of the kprobe). > > I've added a new function, module_get_byname(), that looks up a module > by name and returns the module reference. Note that module_get_byname() > also increments the module reference count. It does this so that the > module won't be unloaded between the time that module_get_byname() is > called and register_kprobe() is called. > > Here's an example of how it would be used from a kprobe: > > ==== > static struct module *mod = NULL; > > int init_module(void) > { > /* grab the module, making sure it won't get unloaded until > * we're done */ > const char *mod_name = "joydev"; > if (module_get_byname(mod_name, &mod) != 0) > return 1; > > /* Specify the address/offset where you want to insert > * probe. If this were a real kprobe module, we'd "relocate" > * our probe address based on the load address of the module > * we're interested in. */ > kp.addr = (kprobe_opcode_t *) mod->module_core + 0; > > /* All set to register with Kprobes */ > register_kprobe(&kp); > return 0; > } > > void cleanup_module(void) > { > if (kp.addr != NULL) > unregister_kprobe(&kp); > > /* allow the module to get unloaded, if needed */ > if (mod != NULL) > module_put(mod); > } > ==== > > I've included a patch that implements the new function. > > Signed-off-by: David Smith <dsmith@redhat.com> > --- > > diff --git a/include/linux/module.h b/include/linux/module.h > index 0dfb794..7464e29 100644 > --- a/include/linux/module.h > +++ b/include/linux/module.h > @@ -374,6 +374,8 @@ extern void __module_put_and_exit(struct > __attribute__((noreturn)); > #define module_put_and_exit(code) __module_put_and_exit(THIS_MODULE, > code); > > +long module_get_byname(const char *mod_name, struct module **mod);
Why long instead of int?
> + > #ifdef CONFIG_MODULE_UNLOAD > unsigned int module_refcount(struct module *mod); > void __symbol_put(const char *symbol); > @@ -549,6 +551,11 @@ static inline int is_exported(const char > return 0; > } > > +static inline long module_get_byname(const char *mod_name, struct > module **mod) > +{ > + return 1; > +} > + > static inline int register_module_notifier(struct notifier_block * nb) > { > /* no events will happen anyway, so this can always succeed */ > diff --git a/kernel/module.c b/kernel/module.c > index 2a19cd4..30449ce 100644 > --- a/kernel/module.c > +++ b/kernel/module.c > @@ -291,7 +291,27 @@ static struct module *find_module(const > } > return NULL; > } > + > +long module_get_byname(const char *mod_name, struct module **mod) > +{ > + *mod = NULL; > > + /* We must hold module_mutex before calling find_module(). */ > + if (mutex_lock_interruptible(&module_mutex) != 0) > + return -EINTR; > + > + *mod = find_module(mod_name); > + mutex_unlock(&module_mutex); > + if (*mod) { > + if (! strong_try_module_get(*mod)) {
no space following the '!'.
> + *mod = NULL; > + return -EINVAL; > + } > + } > + return 0; > +} > +EXPORT_SYMBOL(module_get_byname); > + > #ifdef CONFIG_SMP > /* Number of blocks used and allocated. */ > static unsigned int pcpu_num_used, pcpu_num_allocated;
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