From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Palmer Dabbelt <palmer@dabbelt.com>
Cc: aou@eecs.berkeley.edu, alex@ghiti.fr, linux-mm@kvack.org,
mpe@ellerman.id.au, Anup Patel <Anup.Patel@wdc.com>,
linux-kernel@vger.kernel.org, Atish Patra <Atish.Patra@wdc.com>,
paulus@samba.org, zong.li@sifive.com,
Paul Walmsley <paul.walmsley@sifive.com>,
linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v5 1/4] riscv: Move kernel mapping to vmalloc zone
Date: Wed, 22 Jul 2020 12:21:16 +1000 [thread overview]
Message-ID: <bb461dde0df3eaf0bed949eebf0657b227431bb3.camel@kernel.crashing.org> (raw)
In-Reply-To: <mhng-cd9a74ea-2edf-47e4-aade-b090f1a069f1@palmerdabbelt-glaptop1>
On Tue, 2020-07-21 at 16:48 -0700, Palmer Dabbelt wrote:
> > Why ? Branch distance limits ? You can't use trampolines ?
>
> Nothing fundamental, it's just that we don't have a large code model in the C
> compiler. As a result all the global symbols are resolved as 32-bit
> PC-relative accesses. We could fix this with a fast large code model, but then
> the kernel would need to relax global symbol references in modules and we don't
> even do that for the simple code models we have now. FWIW, some of the
> proposed large code models are essentially just split-PLT/GOT and therefor
> don't require relaxation, but at that point we're essentially PIC until we
> have more that 2GiB of kernel text -- and even then, we keep all the
> performance issues.
My memory might be out of date but I *think* we do it on powerpc
without going to a large code model, but just having the in-kernel
linker insert trampolines.
Cheers,
Ben.
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next prev parent reply other threads:[~2020-07-22 2:22 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-07 7:59 [PATCH v5 0/4] vmalloc kernel mapping and relocatable kernel Alexandre Ghiti
2020-06-07 7:59 ` [PATCH v5 1/4] riscv: Move kernel mapping to vmalloc zone Alexandre Ghiti
2020-06-11 21:34 ` Atish Patra
2020-06-12 12:30 ` Alex Ghiti
2020-07-09 5:05 ` Palmer Dabbelt
2020-07-09 8:15 ` Zong Li
2020-07-09 11:11 ` Alex Ghiti
2020-07-21 18:36 ` Alex Ghiti
2020-07-21 19:05 ` Palmer Dabbelt
2020-07-21 23:12 ` Benjamin Herrenschmidt
2020-07-21 23:48 ` Palmer Dabbelt
2020-07-22 2:21 ` Benjamin Herrenschmidt [this message]
2020-07-22 4:50 ` Michael Ellerman
2020-07-22 5:46 ` Palmer Dabbelt
2020-07-22 9:43 ` Arnd Bergmann
2020-07-22 19:52 ` Palmer Dabbelt
2020-07-22 20:22 ` Arnd Bergmann
2020-07-22 21:05 ` Atish Patra
2020-07-24 7:20 ` Arnd Bergmann
2020-07-23 5:32 ` Alex Ghiti
2020-07-21 23:11 ` Benjamin Herrenschmidt
2020-07-21 23:36 ` Palmer Dabbelt
2020-07-23 5:36 ` Alex Ghiti
2020-07-23 5:21 ` Alex Ghiti
2020-07-23 22:33 ` Benjamin Herrenschmidt
2020-07-24 8:14 ` Arnd Bergmann
2020-06-07 7:59 ` [PATCH v5 2/4] riscv: Introduce CONFIG_RELOCATABLE Alexandre Ghiti
2020-06-10 14:10 ` Jerome Forissier
2020-06-11 19:43 ` Alex Ghiti
2020-06-07 7:59 ` [PATCH v5 3/4] powerpc: Move script to check relocations at compile time in scripts/ Alexandre Ghiti
2020-06-07 7:59 ` [PATCH v5 4/4] riscv: Check relocations at compile time Alexandre Ghiti
2020-07-08 4:21 ` [PATCH v5 0/4] vmalloc kernel mapping and relocatable kernel Alex Ghiti
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