[PATCH v2 0/4] riscv: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

[Palmer Dabbelt]

On Tue, 20 Jun 2023 17:13:17 PDT (-0700), Palmer Dabbelt wrote:
> On Tue, 20 Jun 2023 14:08:33 PDT (-0700), Palmer Dabbelt wrote:
>> On Tue, 20 Jun 2023 13:47:07 PDT (-0700), ndesaulniers at google.com wrote:
>>> On Tue, Jun 20, 2023 at 4:41 PM Palmer Dabbelt <palmer at dabbelt.com> wrote:
>>>>
>>>> On Tue, 20 Jun 2023 13:32:32 PDT (-0700), ndesaulniers at google.com wrote:
>>>> > On Tue, Jun 20, 2023 at 4:13 PM Conor Dooley <conor at kernel.org> wrote:
>>>> >>
>>>> >> On Tue, Jun 20, 2023 at 04:05:55PM -0400, Nick Desaulniers wrote:
>>>> >> > On Mon, Jun 19, 2023 at 6:06 PM Palmer Dabbelt <palmer at dabbelt.com> wrote:
>>>> >> > > On Thu, 15 Jun 2023 06:54:33 PDT (-0700), Palmer Dabbelt wrote:
>>>> >> > > > On Wed, 14 Jun 2023 09:25:49 PDT (-0700), jszhang at kernel.org wrote:
>>>> >> > > >> On Wed, Jun 14, 2023 at 07:49:17AM -0700, Palmer Dabbelt wrote:
>>>> >> > > >>> On Tue, 23 May 2023 09:54:58 PDT (-0700), jszhang at kernel.org wrote:
>>>> >>
>>>> >> > > >> Commit 3b90b09af5be ("riscv: Fix orphan section warnings caused by
>>>> >> > > >> kernel/pi") touches vmlinux.lds.S, so to make the merge easy, this
>>>> >> > > >> series is based on 6.4-rc2.
>>>> >> > > >
>>>> >> > > > Thanks.
>>>> >> > >
>>>> >> > > Sorry to be so slow here, but I think this is causing LLD to hang on
>>>> >> > > allmodconfig.  I'm still getting to the bottom of it, there's a few
>>>> >> > > other things I have in flight still.
>>>> >> >
>>>> >> > Confirmed with v3 on mainline (linux-next is pretty red at the moment).
>>>> >> > https://lore.kernel.org/linux-riscv/20230517082936.37563-1-falcon@tinylab.org/
>>>> >>
>>>> >> Just FYI Nick, there's been some concurrent work here from different
>>>> >> people working on the same thing & the v3 you linked (from Zhangjin) was
>>>> >> superseded by this v2 (from Jisheng).
>>>> >
>>>> > Ah! I've been testing the deprecated patch set, sorry I just looked on
>>>> > lore for "dead code" on riscv-linux and grabbed the first thread,
>>>> > without noticing the difference in authors or new version numbers for
>>>> > distinct series. ok, nevermind my noise.  I'll follow up with the
>>>> > correct patch set, sorry!
>>>>
>>>> Ya, I hadn't even noticed the v3 because I pretty much only look at
>>>> patchwork these days.  Like we talked about in IRC, I'm going to go test
>>>> the merge of this one and see what's up -- I've got it staged at
>>>> <https://git.kernel.org/pub/scm/linux/kernel/git/palmer/linux.git/commit/?h=for-next&id=1bd2963b21758a773206a1cb67c93e7a8ae8a195>,
>>>> though that won't be a stable hash if it's actually broken...
>>>
>>> Ok, https://lore.kernel.org/linux-riscv/20230523165502.2592-1-jszhang@kernel.org/
>>> built for me.  If you're seeing a hang, please let me know what
>>> version of LLD you're using and I'll build that tag from source to see
>>> if I can reproduce, then bisect if so.
>>>
>>> $ ARCH=riscv LLVM=1 /usr/bin/time -v make -j128 allmodconfig vmlinux
>>> ...
>>>         Elapsed (wall clock) time (h:mm:ss or m:ss): 2:35.68
>>> ...
>>>
>>> Tested-by: Nick Desaulniers <ndesaulniers at google.com> # build
>>
>> OK, it triggered enough of a rebuild that it might take a bit for
>> anything to filter out.
>
> I'm on LLVM 16.0.2
>
>     $ git describe
>     llvmorg-16.0.2
>     $ git log | head -n1
>     commit 18ddebe1a1a9bde349441631365f0472e9693520
>
> that seems to hang for me -- or at least run for an hour without
> completing, so I assume it's hung.  I'm not wed to 16.0.2, it just
> happens to be the last time I bumped the toolchain.  I'm moving to
> 16.0.5 to see if that changes anything.

That also takes at least an hour to link.  I tried running on LLVM trunk 
from last night

    $ git log | head -n1
    commit 5e9173c43a9b97c8614e36d6f754317f731e71e9

and that completed.  Just as a curiosity I tried to re-spin it to see 
how long it takes, and it's been running for 23 minutes so far.

So I'm no longer actually sure there's a hang, just something slow.  
That's even more of a grey area, but I think it's sane to call a 1-hour 
link time a regression -- unless it's expected that this is just very 
slow to link?

>
>>
>> Thanks!
>>
>>>
>>>>
>>>> >
>>>> >>
>>>> >> Cheers,
>>>> >> Conor.
>>>> >
>>>> >
>>>> >
>>>> > --
>>>> > Thanks,
>>>> > ~Nick Desaulniers
>>>
>>>
>>>
>>> --
>>> Thanks,
>>> ~Nick Desaulniers