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Date: Fri, 18 Dec 2020 00:19:09 -0800 From: Atish Patra <atishp@...shpatra.org> To: Palmer Dabbelt <palmer@...belt.com> Cc: Alistair Francis <Alistair.Francis@....com>, Albert Ou <aou@...s.berkeley.edu>, Zong Li <zong.li@...ive.com>, Anup Patel <anup@...infault.org>, "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>, linux-riscv <linux-riscv@...ts.infradead.org>, Atish Patra <Atish.Patra@....com>, ren_guo@...ky.com, Paul Walmsley <paul.walmsley@...ive.com>, ojeda@...nel.org, Greentime Hu <greentime.hu@...ive.com>, Andrew Morton <akpm@...ux-foundation.org>, Michel Lespinasse <walken@...gle.com>, Ard Biesheuvel <ardb@...nel.org>, Mike Rapoport <rppt@...nel.org>, Jim Wilson <jimw@...ive.com> Subject: Re: [PATCH v3 3/5] RISC-V: Align the .init.text section On Thu, Dec 17, 2020 at 12:33 AM Atish Patra <atishp@...shpatra.org> wrote: > > On Wed, Dec 16, 2020 at 10:51 PM Palmer Dabbelt <palmer@...belt.com> wrote: > > > > On Tue, 15 Dec 2020 22:02:54 PST (-0800), Palmer Dabbelt wrote: > > > On Wed, 04 Nov 2020 16:04:37 PST (-0800), Atish Patra wrote: > > >> In order to improve kernel text protection, we need separate .init.text/ > > >> .init.data/.text in separate sections. However, RISC-V linker relaxation > > >> code is not aware of any alignment between sections. As a result, it may > > >> relax any RISCV_CALL relocations between sections to JAL without realizing > > >> that an inter section alignment may move the address farther. That may > > >> lead to a relocation truncated fit error. However, linker relaxation code > > >> is aware of the individual section alignments. > > >> > > >> The detailed discussion on this issue can be found here. > > >> https://github.com/riscv/riscv-gnu-toolchain/issues/738 > > >> > > >> Keep the .init.text section aligned so that linker relaxation will take > > >> that as a hint while relaxing inter section calls. > > >> Here are the code size changes for each section because of this change. > > >> > > >> section change in size (in bytes) > > >> .head.text +4 > > >> .text +40 > > >> .init.text +6530 > > >> .exit.text +84 > > >> > > >> The only significant increase in size happened for .init.text because > > >> all intra relocations also use 2MB alignment. > > >> > > >> Suggested-by: Jim Wilson <jimw@...ive.com> > > >> Signed-off-by: Atish Patra <atish.patra@....com> > > >> --- > > >> arch/riscv/kernel/vmlinux.lds.S | 8 +++++++- > > >> 1 file changed, 7 insertions(+), 1 deletion(-) > > >> > > >> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S > > >> index 3ffbd6cbdb86..cacd7898ba7f 100644 > > >> --- a/arch/riscv/kernel/vmlinux.lds.S > > >> +++ b/arch/riscv/kernel/vmlinux.lds.S > > >> @@ -30,7 +30,13 @@ SECTIONS > > >> . = ALIGN(PAGE_SIZE); > > >> > > >> __init_begin = .; > > >> - INIT_TEXT_SECTION(PAGE_SIZE) > > >> + __init_text_begin = .; > > >> + .init.text : AT(ADDR(.init.text) - LOAD_OFFSET) ALIGN(SECTION_ALIGN) { \ > > >> + _sinittext = .; \ > > >> + INIT_TEXT \ > > >> + _einittext = .; \ > > >> + } > > >> + > > >> . = ALIGN(8); > > >> __soc_early_init_table : { > > >> __soc_early_init_table_start = .; > > > > > > Not sure what's going on here (or why I wasn't catching it earlier), but this > > > is breaking boot on one of my test configs. I'm not getting any Linux boot > > > spew, so it's something fairly early. I'm running defconfig with > > > > > > CONFIG_PREEMPT=y > > > CONFIG_DEBUG_PREEMPT=y > > > CONFIG_PROVE_LOCKING=y > > > > > > It looks like that's been throwing a bunch of warnings for a while, but it did > > > at least used to boot. No idea what PREEMPT would have to do with this, and > > > the other two don't generally trigger issues that early in boot (or at least, > > > trigger halts that early in boot). > > > I am able to reproduce this issue but with CONFIG_PROVE_LOCKING not CONFIG_PREEMPT. With CONFIG_PREEMPT, I see a bunch of warnings around smp_processor_id but it boots even with 5.0. If CONFIG_PROVE_LOCKING is enabled, I am not able to boot using 5.0. However, 5.2.0 works fine. I am going to take a look at the issue with 5.0 and PROVE_LOCKING. The config preempt warnings are resolved by the following patch. I have tested it in Qemu. https://patchwork.kernel.org/project/linux-riscv/patch/20201116081238.44223-1-wangkefeng.wang@huawei.com/ > > > There's a bunch of other stuff that depends on this that's on for-next so I > > > don't want to just drop it, but I also don't want to break something. I'm just > > > running QEMU's virt board. > > > > > I just verified for-next on QEMU 5.2.0 for virt (RV32,64, nommu) and > sifive_u as well. > I will give it a try on unleashed tomorrow as well with the above > configs enabled. > > > > I'll take a look again tomorrow night, but if anyone has some time to look > > > that'd be great! > > > > Looks like this breaks on QEMU 5.0.0 but works on 5.2.0. > > I will take a look tomorrow to check the root cause. > > I guess technically > > that means could be considered a regression, but as we don't really have any > > scheme for which old versions of QEMU we support it's not absolute. I'd > > usually err on the side of keeping support for older platforms, but in this > > case it's probably just not worth the time so I'm going to just ignore it. > > > > _______________________________________________ > > linux-riscv mailing list > > linux-riscv@...ts.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-riscv > > > > -- > Regards, > Atish -- Regards, Atish
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