linux-kernel - Re: [PATCH] scripts/gdb/linux/symbols.py: address changes to module_sect

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Message-ID: <0849b8a0-e1b7-4486-a376-43403e52dd1f@mandelbit.com>
Date: Fri, 21 Feb 2025 21:33:14 +0100
From: Antonio Quartulli <antonio@...delbit.com>
To: Jan Kiszka <jan.kiszka@...mens.com>, kbingham@...nel.org
Cc: linux-kernel@...r.kernel.org, Thomas Weißschuh
 <linux@...ssschuh.net>
Subject: Re: [PATCH] scripts/gdb/linux/symbols.py: address changes to
 module_sect_attrs

On 21/02/2025 17:52, Jan Kiszka wrote:
> On 21.02.25 14:03, Antonio Quartulli wrote:
>> When loading symbols from kernel modules we used to iterate
>> from 0 to module_sect_attrs::nsections, in order to
>> retrieve their name and address.
>>
>> However module_sect_attrs::nsections has been removed from
>> the struct by a previous commit.
>>
>> Re-arrange the iteration by accessing all items in
>> module_sect_attrs::grp::bin_attrs[] until NULL is found
>> (it's a NULL terminated array).
>>
>> At the same time the symbol address cannot be extracted
>> from module_sect_attrs::attrs[]::address anymore because
>> it has also been deleted. Fetch it from
>> module_sect_attrs::grp::bin_attrs[]::private as described
>> in 4b2c11e4aaf7.
>>
>> Fixes: d8959b947a8d ("module: sysfs: Drop member 'module_sect_attrs::nsections'")
>> Fixes: 4b2c11e4aaf7 ("module: sysfs: Drop member 'module_sect_attr::address'")
>> Cc: Thomas Weißschuh <linux@...ssschuh.net>
>> Signed-off-by: Antonio Quartulli <antonio@...delbit.com>
>> ---
>>   scripts/gdb/linux/symbols.py | 13 +++++++++----
>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/scripts/gdb/linux/symbols.py b/scripts/gdb/linux/symbols.py
>> index f6c1b063775a..610a3dd3c7b4 100644
>> --- a/scripts/gdb/linux/symbols.py
>> +++ b/scripts/gdb/linux/symbols.py
>> @@ -15,6 +15,7 @@ import gdb
>>   import os
>>   import re
>>   
>> +from itertools import count
>>   from linux import modules, utils, constants
>>   
>>   
>> @@ -95,10 +96,14 @@ lx-symbols command."""
>>           except gdb.error:
>>               return str(module_addr)
>>   
>> -        attrs = sect_attrs['attrs']
>> -        section_name_to_address = {
>> -            attrs[n]['battr']['attr']['name'].string(): attrs[n]['address']
>> -            for n in range(int(sect_attrs['nsections']))}
>> +        section_name_to_address = {}
>> +        for i in count():
>> +            # this is a NULL terminated array
>> +            if sect_attrs['grp']['bin_attrs'][i] == 0x0:
>> +                break
>> +
>> +            attr = sect_attrs['grp']['bin_attrs'][i].dereference()
>> +            section_name_to_address[attr['attr']['name']] = attr['private']
> 
> You dropped that .string() from the name - I don't remember the details
> anymore but we have it all around when picking up strings from C
> structures. Was there a particular reason to do that?

Ouch. That was not intentional and my test did not explode, therefore I 
assumed the code was correct.

I presume it may explode if 'name' is changed into something not a 
string. In this case .string() would throw an exception and block the 
execution.

I will send v2 shortly with .string().

> 
>>   
>>           textaddr = section_name_to_address.get(".text", module_addr)
>>           args = []
> 
> Thanks for picking up this task so quickly!

Well, I needed gdb to break into ovpn.ko :-)

Cheers,

-- 
Antonio Quartulli

CEO and Co-Founder
Mandelbit Srl
https://www.mandelbit.com