[PATCH 2.6.21-rc1] Extend print_symbol capability

[PATCH 2.6.21-rc1] Extend print_symbol capability

[Robert Peterson]

Today's print_symbol function dumps a kernel symbol with printk.
This patch extends the functionality of kallsyms.c so that the symbol
lookup function may be used without the printk.  This is
useful for modules that want to dump symbols elsewhere, for
example, to debugfs.  I intend to use the new function call in the
GFS2 file system (which will be a separate patch).

Signed-off-by: Robert Peterson <rpeterso@redhat.com>
---
 include/linux/kallsyms.h |   10 ++++++++++
 kernel/kallsyms.c        |   21 ++++++++++++++-------
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index 1cebcbc..a54afe5 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -7,6 +7,8 @@
 
 
 #define KSYM_NAME_LEN 127
+#define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s]") + KSYM_NAME_LEN + \
+                        2*(BITS_PER_LONG*3/10) + MODULE_NAME_LEN + 1)
 
 #ifdef CONFIG_KALLSYMS
 /* Lookup the address for a symbol. Returns 0 if not found. */
@@ -22,6 +24,9 @@ const char *kallsyms_lookup(unsigned long addr,
                            unsigned long *offset,
                            char **modname, char *namebuf);
 
+/* Look up a kernel symbol and return it in a text buffer. */
+extern void lookup_symbol(unsigned long addr, char *buffer);
+
 /* Replace "%s" in format with address, if found */
 extern void __print_symbol(const char *fmt, unsigned long address);
 
@@ -47,6 +52,11 @@ static inline const char *kallsyms_lookup(unsigned 
long addr,
        return NULL;
 }
 
+static inline void lookup_symbol(unsigned long addr, char *buffer)
+{
+       return NULL;
+}
+
 /* Stupid that this does nothing, but I didn't create this mess. */
 #define __print_symbol(fmt, addr)
 #endif /*CONFIG_KALLSYMS*/
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 6f294ff..a5fedf5 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -267,20 +267,17 @@ const char *kallsyms_lookup(unsigned long addr,
        return NULL;
 }
 
-/* Replace "%s" in format with address, or returns -errno. */
-void __print_symbol(const char *fmt, unsigned long address)
+/* Look up a kernel symbol and return it in a text buffer. */
+void lookup_symbol(unsigned long addr, char *buffer)
 {
        char *modname;
        const char *name;
        unsigned long offset, size;
        char namebuf[KSYM_NAME_LEN+1];
-       char buffer[sizeof("%s+%#lx/%#lx [%s]") + KSYM_NAME_LEN +
-                   2*(BITS_PER_LONG*3/10) + MODULE_NAME_LEN + 1];
-
-       name = kallsyms_lookup(address, &size, &offset, &modname, namebuf);
 
+       name = kallsyms_lookup(addr, &size, &offset, &modname, namebuf);
        if (!name)
-               sprintf(buffer, "0x%lx", address);
+               sprintf(buffer, "0x%lx", addr);
        else {
                if (modname)
                        sprintf(buffer, "%s+%#lx/%#lx [%s]", name, offset,
@@ -288,6 +285,15 @@ void __print_symbol(const char *fmt, unsigned long 
address)
                else
                        sprintf(buffer, "%s+%#lx/%#lx", name, offset, size);
        }
+}
+
+/* Replace "%s" in format with address, or returns -errno. */
+void __print_symbol(const char *fmt, unsigned long address)
+{
+       char buffer[KSYM_SYMBOL_LEN];
+
+       lookup_symbol(address, buffer);
+
        printk(fmt, buffer);
 }
 
@@ -452,3 +458,4 @@ static int __init kallsyms_init(void)
 __initcall(kallsyms_init);
 
 EXPORT_SYMBOL(__print_symbol);
+EXPORT_SYMBOL(lookup_symbol);

Re: [PATCH 2.6.21-rc1] Extend print_symbol capability

[Paulo Marques]

Robert Peterson wrote:
> [...]
> #define KSYM_NAME_LEN 127
> +#define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s]") + KSYM_NAME_LEN + \
> +                        2*(BITS_PER_LONG*3/10) + MODULE_NAME_LEN + 1)
> 
> #ifdef CONFIG_KALLSYMS
> /* Lookup the address for a symbol. Returns 0 if not found. */
> @@ -22,6 +24,9 @@ const char *kallsyms_lookup(unsigned long addr,
>                            unsigned long *offset,
>                            char **modname, char *namebuf);
> 
> +/* Look up a kernel symbol and return it in a text buffer. */
> +extern void lookup_symbol(unsigned long addr, char *buffer);

I don't like this name much :(

We already have kallsyms_lookup and kallsyms_lookup_name. The name of 
this function should imply that it will print the formatted result into 
the buffer, not just lookup a symbol.

Maybe "__sprint_symbol", and change the interface to 
"__sprint_symbol(char *buffer, unsigned long addr)"?

> +
> /* Replace "%s" in format with address, if found */
> extern void __print_symbol(const char *fmt, unsigned long address);
> 
> @@ -47,6 +52,11 @@ static inline const char *kallsyms_lookup(unsigned 
> long addr,
>        return NULL;
> }
> 
> +static inline void lookup_symbol(unsigned long addr, char *buffer)
> +{
> +       return NULL;
> +}

Returning NULL in a function returning "void" doesn't seem right :P

Maybe it should be something like this instead:
{
	*buffer = '\0';
}

> [...]

Anyway, the change looks useful, so thanks for the patch :)

-- 
Paulo Marques - www.grupopie.com

"Very funny Scotty. Now beam up my clothes."

Re: [PATCH 2.6.21-rc1] Extend print_symbol capability

[Robert Peterson]

Paulo Marques wrote:
> I don't like this name much :(
>
> We already have kallsyms_lookup and kallsyms_lookup_name. The name of 
> this function should imply that it will print the formatted result 
> into the buffer, not just lookup a symbol.
>
> Maybe "__sprint_symbol", and change the interface to 
> "__sprint_symbol(char *buffer, unsigned long addr)"?
I'm not sure I like the leading __.  In the print_symbol case, I think 
the function
was given a leading __ so that code referencing print_symbol would use the
macro which formulates the call into __print_symbol.  I don't mind 
sprint_symbol
though.  Since Andrew Morton included the patch, I'll defer to his judgment.
>> +static inline void lookup_symbol(unsigned long addr, char *buffer)
>> +{
>> +       return NULL;
>> +}
> Returning NULL in a function returning "void" doesn't seem right :P
You're right.  This should just be a simple "return;".  My bad.  Good catch.
Since Andrew Morton has already included this patch, I'll let him
make this change if he sees fit.

Regards,

Bob Peterson
Red Hat Cluster Suite