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Message-ID: <mhng-e4c58f1b-2015-48b1-88ae-dbb9db72643f@palmer-ri-x1c9>
Date: Thu, 02 Jun 2022 18:34:41 -0700 (PDT)
From: Palmer Dabbelt <palmer@...belt.com>
To: nathan@...nel.org
CC: Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
ndesaulniers@...gle.com, heiko@...ech.de,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
llvm@...ts.linux.dev, patches@...ts.linux.dev, nathan@...nel.org,
lkp@...el.com
Subject: Re: [PATCH] riscv: Move alternative length validation into subsection
On Mon, 16 May 2022 14:45:21 PDT (-0700), nathan@...nel.org wrote:
> After commit 49b290e430d3 ("riscv: prevent compressed instructions in
> alternatives"), builds with LLVM's integrated assembler fail:
>
> In file included from arch/riscv/mm/init.c:10:
> In file included from ./include/linux/mm.h:29:
> In file included from ./include/linux/pgtable.h:6:
> In file included from ./arch/riscv/include/asm/pgtable.h:108:
> ./arch/riscv/include/asm/tlbflush.h:23:2: error: expected assembly-time absolute expression
> ALT_FLUSH_TLB_PAGE(__asm__ __volatile__ ("sfence.vma %0" : : "r" (addr) : "memory"));
> ^
> ./arch/riscv/include/asm/errata_list.h:33:5: note: expanded from macro 'ALT_FLUSH_TLB_PAGE'
> asm(ALTERNATIVE("sfence.vma %0", "sfence.vma", SIFIVE_VENDOR_ID, \
> ^
> ./arch/riscv/include/asm/alternative-macros.h:187:2: note: expanded from macro 'ALTERNATIVE'
> _ALTERNATIVE_CFG(old_content, new_content, vendor_id, errata_id, CONFIG_k)
> ^
> ./arch/riscv/include/asm/alternative-macros.h:113:2: note: expanded from macro '_ALTERNATIVE_CFG'
> __ALTERNATIVE_CFG(old_c, new_c, vendor_id, errata_id, IS_ENABLED(CONFIG_k))
> ^
> ./arch/riscv/include/asm/alternative-macros.h:110:2: note: expanded from macro '__ALTERNATIVE_CFG'
> ALT_NEW_CONTENT(vendor_id, errata_id, enable, new_c)
> ^
> ./arch/riscv/include/asm/alternative-macros.h:99:3: note: expanded from macro 'ALT_NEW_CONTENT'
> ".org . - (889b - 888b) + (887b - 886b)\n" \
> ^
> <inline asm>:26:6: note: instantiated into assembly here
> .org . - (889b - 888b) + (887b - 886b)
> ^
>
> This error happens because LLVM's integrated assembler has a one-pass
> design, which means it cannot figure out the instruction lengths when
> the .org directive is outside of the subsection that contains the
> instructions, which was changed by the .option directives added by the
> above change.
>
> Move the .org directives before the .previous directive so that these
> directives are always within the same subsection, which resolves the
> failures and does not introduce any new issues with GNU as. This was
> done for arm64 in commit 966a0acce2fc ("arm64/alternatives: move length
> validation inside the subsection") and commit 22315a2296f4 ("arm64:
> alternatives: Move length validation in alternative_{insn, endif}").
>
> While there is no error from the assembly versions of the macro, they
> appear to have the same problem so just make the same change there as
> well so that there are no problems in the future.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1640
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
> arch/riscv/include/asm/alternative-macros.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/alternative-macros.h b/arch/riscv/include/asm/alternative-macros.h
> index e13b1f6bb400..ec2f3f1b836f 100644
> --- a/arch/riscv/include/asm/alternative-macros.h
> +++ b/arch/riscv/include/asm/alternative-macros.h
> @@ -27,9 +27,9 @@
> \new_c
> .option pop
> 889 :
> - .previous
> .org . - (889b - 888b) + (887b - 886b)
> .org . - (887b - 886b) + (889b - 888b)
> + .previous
> .endif
> .endm
>
> @@ -94,9 +94,9 @@
> new_c "\n" \
> ".option pop\n" \
> "889 :\n" \
> - ".previous\n" \
> ".org . - (887b - 886b) + (889b - 888b)\n" \
> ".org . - (889b - 888b) + (887b - 886b)\n" \
> + ".previous\n" \
> ".endif\n"
>
> #define __ALTERNATIVE_CFG(old_c, new_c, vendor_id, errata_id, enable) \
>
> base-commit: 93c0651617a62a69717299f1464dda798af8bebb
Thanks, this in on for-next (still for 5.19). I'm going to CC stable so
it'll get backported, as it seems pretty harmless.
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