systemtap fails to instrument kernel modules on ARM

[Da Zheng]

On 08/11/11 13:52, William Cohen wrote:
> On 08/11/2011 03:02 PM, Da Zheng wrote:
>> Hello,
>>
>> I tried to instrument the some function in the kernel module, but failed.
>> I have a script called squashfs.stp:
>> probe module("squashfs").function("squashfs_read_data") {
>>          printf("%s, squashfs_read_data: length: %d, srclength: %d, blocksize: %d\n",
>>                  execname(), $length, $srclength, $sb->s_blocksize)
>> }
>>
>> When I cross compile the script, I got the following error:
>>
>> $ stap --vp 01 -a arm -r /build/tegra2_seaboard/tmp/portage/sys-kernel/chromeos-kernel-9999/work/chromeos-kernel-9999/build/tegra2_seaboard/ -p 4 -B CROSS_COMPILE=armv7a-cros-linux-gnueabi- -k squashfs.stp -m squashfs --all-modules
>> semantic error: no match while resolving probe point module("squashfs").function("squashfs_read_data")
>> Pass 2: analyzed script: 0 probe(s), 0 function(s), 0 embed(s), 0 global(s) using 51668virt/21632res/2132shr kb, in 0usr/40sys/36real ms.
>> Pass 2: analysis failed.  Try again with another '--vp 01' option.
>>
>> I see Cohen reported a bug of instrumenting a kernel module on ARM, but it seems the error message is a little bit different.
>> I wonder if the error was caused because stap can't find the module, as all kernel modules aren't in the standard path and aren't in /build/tegra2_seaboard/tmp/portage/sys-kernel/chromeos-kernel-9999/work/chromeos-kernel-9999/build/tegra2_seaboard/ either.
>>
>> Thanks,
>> Da
>
> Another thing to check is to check whether squashfs is being built as a module. Look at your .config for your kernel. If it the following it is being compiled in:
>
> CONFIG_SQUASHFS=y
>
> If is a module that would be:
>
> CONFIG_SQUASHFS=m
>
> If squashfs is being compiled into the kernel and you will want to use kernel.function("squashfs").function("..."). You can write the code to allow either like the following:
>
> probe kernel.function("squashfs_read_data")!,
>    module("squashfs").function("squashfs_read_data") {
>          printf("%s, squashfs_read_data: length: %d, srclength: %d, blocksize: %d\n",
>                  execname(), $length, $srclength, $sb->s_blocksize)
> }
I'm pretty sure squashfs is built as a module as I can find it in 
lib/module/2.6.38

I'll look into it with gdb later. I have piles of tasks to do :)

Thanks,
Da