linux-kernel - Re: [PATCH -fixes] riscv: Fix relocatable kernels with early alternatives using -fno-pie

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Message-ID: <cf0d2d2a-c407-7b3d-a5ab-ea5c19e7b890@ghiti.fr>
Date:   Sun, 28 May 2023 15:42:59 +0200
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Conor Dooley <conor@...nel.org>,
        Alexandre Ghiti <alexghiti@...osinc.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andreas Schwab <schwab@...ux-m68k.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -fixes] riscv: Fix relocatable kernels with early
 alternatives using -fno-pie

On 28/05/2023 15:12, Conor Dooley wrote:
> On Sun, May 28, 2023 at 03:00:57PM +0200, Alexandre Ghiti wrote:
>> On Sat, May 27, 2023 at 12:02 PM Conor Dooley <conor@...nel.org> wrote:
>>> On Sat, May 27, 2023 at 11:13:18AM +0200, Alexandre Ghiti wrote:
>>>> On 26/05/2023 18:35, Conor Dooley wrote:
>>>>> On Fri, May 26, 2023 at 05:24:41PM +0100, Conor Dooley wrote:
>>>>>> On Fri, May 26, 2023 at 05:46:30PM +0200, Alexandre Ghiti wrote:
>>>>>>> Early alternatives are called with the mmu disabled, and then should not
>>>>>>> access any global symbols through the GOT since it requires relocations,
>>>>>>> relocations that we do before but *virtually*. So only use medany code
>>>>>>> model for this early code.
>>>>>>>
>>>>>>> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
>>>>>>> ---
>>>>>>>
>>>>>>> Note that I'm not very happy with this fix, I think we need to put more
>>>>>>> effort into "harmonizing" this very early code (ie before the mmu is
>>>>>>> enabled) as it is spread between different locations and compiled
>>>>>>> differently.
>>>>>> Totally & I'll happily spend the time trying to review that work.
>>>>>>
>>>>>>> I'll work on that later, but for now, this fix does what is
>>>>>>> needed to work (from my testing at least). Any Tested-by on the Unmatched
>>>>>>> and T-head boards is welcome!
>>>>>> On 6.4-rc1 & v6.4-rc1 + this patch, with CONFIG_RELOCATABLE added to my
>>>>>> config, my Nezha fails to boot. There is no output whatsoever from the
>>>>>> kernel. Turning off CONFIG_RELOCATABLE boots again.
>>>>> I don't know if this is better or worse news, but same thing happens on
>>>>> an icicle kit. What systems, other than QEMU, has the relocatable
>>>>> eries been tested with, btw?
>>>>
>>>> I tested it on the Unmatched (Andreas did too).
>>> Cool. I cracked out my unmatched and it has the same issue as the
>>> icicle. Ditto my Visionfive v2. Here's my config.
>>> https://raw.githubusercontent.com/ConchuOD/riscv-env/dev/conf/defconfig
>>>
>>> A ~default qemu virt doesn't work either. (-m 2G -smp 5)
>> I can boot with this config using:
>>
>> $ sudo ~/qemu/build/qemu-system-riscv64 -machine virt -cpu
>> rv64,sv48=off -nographic -m 2G -smp 5 -kernel
>> build_conor/arch/riscv/boot/Image -s
> Just in case, that is my normal config that I use for testing random
> stuff on LKML, I added CONFIG_RELOCATABLE in addition to that.
>
>> I noticed when trying to add this to our internal CI that I had local
>> failures that did not happen in the CI because the CI was not using
>> the same toolchain: can you give me the full .config? So that I can
>> see if the compiler added stack guards or some other things I did not
>> think of.
> https://gist.githubusercontent.com/ConchuOD/655f9cc19fb3be63f1c9da7e7e3ab717/raw/a1aad3c0d307609b2062fd3a66705166aede9f9f/.config
>
> 90% of what I test for upstream stuff uses clang, since clang appears to
> be a minority choice - but I could reproduce this with gcc-12 as well,
> using the same defconfig as linked above + CONFIG_RELOCATABLE.

Hmmm, it still works for me with both clang and gcc-9.

You don't have to do that now but is there a way I could get your 
compiled image? With the sha1 used to build it? Sorry, I don't see what 
happens, I need to get my hands dirty in some debug!

Thanks for being so quick Conor!

> Cheers,
> Conor.
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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