linux-kernel - Re: [PATCH] riscv: elf: add .riscv.attributes parsing

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Message-ID: <1c0412a7-7544-9398-c4fa-657b7ea59b94@rivosinc.com>
Date:   Thu, 12 Jan 2023 12:22:10 -0800
From:   Vineet Gupta <vineetg@...osinc.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        palmer@...osinc.com, Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Kees Cook <keescook@...omium.org>, Guo Ren <guoren@...nel.org>,
        Greentime Hu <greentime.hu@...ive.com>,
        Conor Dooley <conor.dooley@...rochip.com>, linux@...osinc.com,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] riscv: elf: add .riscv.attributes parsing



On 1/11/23 08:53, Eric W. Biederman wrote:
> Vineet Gupta <vineetg@...osinc.com> writes:
>
>> This implements the elf loader hook to parse RV specific
>> .riscv.attributes section. This section is inserted by compilers
>> (gcc/llvm) with build related information such as -march organized as
>> tag/value attribute pairs.
>>
>> It identifies the various attribute tags (and corresponding values) as
>> currently specified in the psABI specification.
>>
>> This patch only implements the elf parsing mechanics, leaving out the
>> recording/usage of the attributes to subsequent patches.
> Why does the kernel care?
>
> Unless I am mistaken the kind of information you are describing is
> typically dealt with by the dynamic linker, rather than the kernel.
>
> As a general strategy I think it is smart to leave as much to
> userspace and the dynamic linker and possible intead of asking
> the kernel's elf loader to care.

That is true in general. But in some cases we might have to do stuff 
before kick starting usermode such as setting up a shadow stack with 
special permissions etc.

> That allows more rapid
> prototyping and reduces the impact of parsing bugs.