Messages in this thread | | | Date | Tue, 22 Dec 2020 20:14:33 -0800 (PST) | Subject | Re: [PATCH v3 3/5] RISC-V: Align the .init.text section | From | Palmer Dabbelt <> |
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On Fri, 18 Dec 2020 00:19:09 PST (-0800), atishp@atishpatra.org wrote: > On Thu, Dec 17, 2020 at 12:33 AM Atish Patra <atishp@atishpatra.org> wrote: >> >> On Wed, Dec 16, 2020 at 10:51 PM Palmer Dabbelt <palmer@dabbelt.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@sifive.com> >> > >> Signed-off-by: Atish Patra <atish.patra@wdc.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/
Thanks!
> >> > > 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@lists.infradead.org >> > http://lists.infradead.org/mailman/listinfo/linux-riscv >> >> >> >> -- >> Regards, >> Atish
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