Re: GCC options for kernel live-patching (Was: Add a new option to control inlining only on static functions)

["Martin Liška" <mliska@suse.cz>]

On 10/2/18 3:28 PM, Qing Zhao wrote:
> 
>> On Oct 2, 2018, at 3:33 AM, Martin Jambor <mjambor@suse.cz> wrote:
>>
>> Hi,
>>
>> my apologies for being terse, I'm in a meeting.
>>
>> On Mon, Oct 01 2018, Qing Zhao wrote:
>>> Hi, Martin,
>>>
>>> I have studied a little more on
>>>
>>> https://github.com/marxin/kgraft-analysis-tool/blob/master/README.md <https://github.com/marxin/kgraft-analysis-tool/blob/master/README.md>
>>>
>>> in the Section “Usages”, from the example, we can see:
>>>
>>> the tool will report a list of affected functions for a function that will be patched.
>>> In this list, it includes all callers of the patched function, and the cloned functions from the patched function due to ipa const-propogation or ipa sra. 
>>>
>>> My question:
>>>
>>> what’s the current action to handle the cloned functions from the
>>> patched function due to ipa const-proposation or ipa sra, etc?
>>
>> If we want to patch an inlined, cloned, or IPA-SRAed function, we also
>> patch all of its callers.
> 
> take the example from the link:
> 
> $ gcc /home/marxin/Programming/linux/aesni-intel_glue.i -O2 -fdump-ipa-clones -c
> $ ./kgraft-ipa-analysis.py aesni-intel_glue.i.000i.ipa-clones
> 
> [..skipped..]
> Function: fls64/63 (./arch/x86/include/asm/bitops.h:479:90)
>   inlining to: __ilog2_u64/132 (include/linux/log2.h:40:5)
>     inlining to: ablkcipher_request_alloc/1639 (include/linux/crypto.h:979:82)
>       constprop: ablkcipher_request_alloc.constprop.8/3198 (include/linux/crypto.h:979:82)
>     inlining to: helper_rfc4106_decrypt/3007 (arch/x86/crypto/aesni-intel_glue.c:1016:12)
>     inlining to: helper_rfc4106_encrypt/3006 (arch/x86/crypto/aesni-intel_glue.c:939:12)
> 
>   Affected functions: 5
>     __ilog2_u64/132 (include/linux/log2.h:40:5)
>     ablkcipher_request_alloc/1639 (include/linux/crypto.h:979:82)
>     ablkcipher_request_alloc.constprop.8/3198 (include/linux/crypto.h:979:82)
>     helper_rfc4106_decrypt/3007 (arch/x86/crypto/aesni-intel_glue.c:1016:12)
>     helper_rfc4106_encrypt/3006 (arch/x86/crypto/aesni-intel_glue.c:939:12)
> [..skipped..]
> 
> 
> if we want to patch the function “fls64/63”,  what else functions we need to patch, too? my guess is:

Hi.

Yes, 'Affected functions' is exactly the list of functions you want to patch.

> 
> **all the callers:
> __ilog2_u64/132
> ablkcipher_request_alloc/1639
> helper_rfc4106_decrypt/3007
> helper_rfc4106_encrypt/3006 
> **and:
> ablkcipher_request_alloc.constprop.8/3198
> is the above correct?
> 
> how to generate patch for ablkcipher_request_alloc.constprop.8/3198? since it’s not a function in the source code?

Well, it's a 'static inline' function in a header file thus the function will be inlined in all usages.
In this particular case there's no such caller function, so you're fine.

Martin

> 
> Qing
> 
>>
>>>
>>> since those cloned functions are NOT in the source code level, how to generate the patches for the cloned functions? how to guarantee that after 
>>> the patched function is changed, the same ipa const-propogation or ipa
>>> sra will still happened?
>>
>> You don't.
>>
>> Martin
>>
>>>
>