After commit 2decad92f473 ("arm64: mte: Ensure TIF_MTE_ASYNC_FAULT is
set atomically"), LLVM's integrated assembler fails to build entry.S:
<instantiation>:5:7: error: expected assembly-time absolute expression
.org . - (664b-663b) + (662b-661b)
^
<instantiation>:6:7: error: expected assembly-time absolute expression
.org . - (662b-661b) + (664b-663b)
^
The root cause is LLVM's assembler has a one-pass design, meaning it
cannot figure out these instruction lengths when the .org directive is
outside of the subsection that they are in, which was changed by the
.arch_extension directive added in the above commit.
Apply the same fix from commit 966a0acce2fc ("arm64/alternatives: move
length validation inside the subsection") to the alternative_endif
macro, shuffling the .org directives so that the length validation
happen will always happen in the same subsections. alternative_insn has
not shown any issue yet but it appears that it could have the same issue
in the future so just preemptively change it.
Cc: [email protected]
Fixes: f7b93d42945c ("arm64/alternatives: use subsections for replacement sequences")
Link: https://github.com/ClangBuiltLinux/linux/issues/1347
Signed-off-by: Nathan Chancellor <[email protected]>
---
Apologies if my explanation or terminology is off, I am only now getting
more familiar with assembly.
arch/arm64/include/asm/alternative-macros.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/include/asm/alternative-macros.h b/arch/arm64/include/asm/alternative-macros.h
index 5df500dcc627..8a078fc662ac 100644
--- a/arch/arm64/include/asm/alternative-macros.h
+++ b/arch/arm64/include/asm/alternative-macros.h
@@ -97,9 +97,9 @@
.popsection
.subsection 1
663: \insn2
-664: .previous
- .org . - (664b-663b) + (662b-661b)
+664: .org . - (664b-663b) + (662b-661b)
.org . - (662b-661b) + (664b-663b)
+ .previous
.endif
.endm
@@ -169,11 +169,11 @@
*/
.macro alternative_endif
664:
+ .org . - (664b-663b) + (662b-661b)
+ .org . - (662b-661b) + (664b-663b)
.if .Lasm_alt_mode==0
.previous
.endif
- .org . - (664b-663b) + (662b-661b)
- .org . - (662b-661b) + (664b-663b)
.endm
/*
base-commit: 738fa58ee1328481d1d7889e7c430b3401c571b9
--
2.31.1.272.g89b43f80a5
Hi Nathan,
On Tue, Apr 13, 2021 at 5:09 PM Nathan Chancellor <[email protected]> wrote:
>
> After commit 2decad92f473 ("arm64: mte: Ensure TIF_MTE_ASYNC_FAULT is
> set atomically"), LLVM's integrated assembler fails to build entry.S:
>
> <instantiation>:5:7: error: expected assembly-time absolute expression
> .org . - (664b-663b) + (662b-661b)
> ^
> <instantiation>:6:7: error: expected assembly-time absolute expression
> .org . - (662b-661b) + (664b-663b)
> ^
>
> The root cause is LLVM's assembler has a one-pass design, meaning it
> cannot figure out these instruction lengths when the .org directive is
> outside of the subsection that they are in, which was changed by the
> .arch_extension directive added in the above commit.
>
> Apply the same fix from commit 966a0acce2fc ("arm64/alternatives: move
> length validation inside the subsection") to the alternative_endif
> macro, shuffling the .org directives so that the length validation
> happen will always happen in the same subsections. alternative_insn has
> not shown any issue yet but it appears that it could have the same issue
> in the future so just preemptively change it.
>
> Cc: [email protected]
> Fixes: f7b93d42945c ("arm64/alternatives: use subsections for replacement sequences")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1347
> Signed-off-by: Nathan Chancellor <[email protected]>
> ---
>
> Apologies if my explanation or terminology is off, I am only now getting
> more familiar with assembly.
>
> arch/arm64/include/asm/alternative-macros.h | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/alternative-macros.h b/arch/arm64/include/asm/alternative-macros.h
> index 5df500dcc627..8a078fc662ac 100644
> --- a/arch/arm64/include/asm/alternative-macros.h
> +++ b/arch/arm64/include/asm/alternative-macros.h
> @@ -97,9 +97,9 @@
> .popsection
> .subsection 1
> 663: \insn2
> -664: .previous
> - .org . - (664b-663b) + (662b-661b)
> +664: .org . - (664b-663b) + (662b-661b)
> .org . - (662b-661b) + (664b-663b)
> + .previous
> .endif
> .endm
>
> @@ -169,11 +169,11 @@
> */
> .macro alternative_endif
> 664:
> + .org . - (664b-663b) + (662b-661b)
> + .org . - (662b-661b) + (664b-663b)
> .if .Lasm_alt_mode==0
> .previous
> .endif
> - .org . - (664b-663b) + (662b-661b)
> - .org . - (662b-661b) + (664b-663b)
> .endm
>
> /*
Thank you for fixing these!
The patch looks correct to me, next-20210413 builds with LLVM_IAS=1
after I applied it, and defconfig built with both Clang and gcc boots
normally. Please feel free to add:
Reviewed-by: Sami Tolvanen <[email protected]>
Tested-by: Sami Tolvanen <[email protected]>
Sami
On Tue, Apr 13, 2021 at 5:09 PM Nathan Chancellor <[email protected]> wrote:
>
> After commit 2decad92f473 ("arm64: mte: Ensure TIF_MTE_ASYNC_FAULT is
> set atomically"), LLVM's integrated assembler fails to build entry.S:
>
> <instantiation>:5:7: error: expected assembly-time absolute expression
> .org . - (664b-663b) + (662b-661b)
> ^
> <instantiation>:6:7: error: expected assembly-time absolute expression
> .org . - (662b-661b) + (664b-663b)
> ^
>
> The root cause is LLVM's assembler has a one-pass design, meaning it
> cannot figure out these instruction lengths when the .org directive is
> outside of the subsection that they are in, which was changed by the
> .arch_extension directive added in the above commit.
>
> Apply the same fix from commit 966a0acce2fc ("arm64/alternatives: move
> length validation inside the subsection") to the alternative_endif
> macro, shuffling the .org directives so that the length validation
> happen will always happen in the same subsections. alternative_insn has
> not shown any issue yet but it appears that it could have the same issue
> in the future so just preemptively change it.
Thanks Nathan.
Reviewed-by: Nick Desaulniers <[email protected]>
Tested-by: Nick Desaulniers <[email protected]>
I did some additional disassembly comparison. In case we ever need it
again, I'll copy it below for posterity.
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu make LLVM=1 LLVM_IAS=1
-j72 O=/tmp/a defconfig all
$ b4 am https://lore.kernel.org/lkml/[email protected]/
-o - | git am -3
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu make LLVM=1 LLVM_IAS=1
-j72 O=/tmp/b defconfig all
$ for f in $(find /tmp/a/arch/arm64 -name \*.o); do llvm-objdump -dr
$f > $f.txt; done
$ for f in $(find /tmp/b/arch/arm64 -name \*.o); do llvm-objdump -dr
$f > $f.txt; done
$ for f in $(find /tmp/a/arch/arm64 -name \*.o); do diff -u $f.txt
$(echo $f.txt|sed 's/a/b/'); done | less
For no difference. You can check more sections than .text by changing
`-d` to `-D` for llvm-objdump, though you're going to get a lot of
noise related to changes in .strtab and relocations referring to debug
info (.debug_str). But if I drop your patch, rebuild, and recompare,
I see the same differences.
>
> Cc: [email protected]
> Fixes: f7b93d42945c ("arm64/alternatives: use subsections for replacement sequences")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1347
> Signed-off-by: Nathan Chancellor <[email protected]>
> ---
>
> Apologies if my explanation or terminology is off, I am only now getting
> more familiar with assembly.
>
> arch/arm64/include/asm/alternative-macros.h | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/alternative-macros.h b/arch/arm64/include/asm/alternative-macros.h
> index 5df500dcc627..8a078fc662ac 100644
> --- a/arch/arm64/include/asm/alternative-macros.h
> +++ b/arch/arm64/include/asm/alternative-macros.h
> @@ -97,9 +97,9 @@
> .popsection
> .subsection 1
> 663: \insn2
> -664: .previous
> - .org . - (664b-663b) + (662b-661b)
> +664: .org . - (664b-663b) + (662b-661b)
> .org . - (662b-661b) + (664b-663b)
> + .previous
> .endif
> .endm
>
> @@ -169,11 +169,11 @@
> */
> .macro alternative_endif
> 664:
> + .org . - (664b-663b) + (662b-661b)
> + .org . - (662b-661b) + (664b-663b)
> .if .Lasm_alt_mode==0
> .previous
> .endif
> - .org . - (664b-663b) + (662b-661b)
> - .org . - (662b-661b) + (664b-663b)
> .endm
>
> /*
>
> base-commit: 738fa58ee1328481d1d7889e7c430b3401c571b9
> --
> 2.31.1.272.g89b43f80a5
>
--
Thanks,
~Nick Desaulniers
Hi Nathan,
On Tue, Apr 13, 2021 at 05:08:04PM -0700, Nathan Chancellor wrote:
> After commit 2decad92f473 ("arm64: mte: Ensure TIF_MTE_ASYNC_FAULT is
> set atomically"), LLVM's integrated assembler fails to build entry.S:
>
> <instantiation>:5:7: error: expected assembly-time absolute expression
> .org . - (664b-663b) + (662b-661b)
> ^
> <instantiation>:6:7: error: expected assembly-time absolute expression
> .org . - (662b-661b) + (664b-663b)
> ^
I tried the latest Linus' tree and linux-next (defconfig) with this
commit in and I can't get your build error. I used both clang-10 from
Debian stable and clang-11 from Debian sid. So, which clang version did
you use or which kernel config options?
--
Catalin
On Thu, Apr 15, 2021 at 10:17:43AM +0100, Catalin Marinas wrote:
> Hi Nathan,
>
> On Tue, Apr 13, 2021 at 05:08:04PM -0700, Nathan Chancellor wrote:
> > After commit 2decad92f473 ("arm64: mte: Ensure TIF_MTE_ASYNC_FAULT is
> > set atomically"), LLVM's integrated assembler fails to build entry.S:
> >
> > <instantiation>:5:7: error: expected assembly-time absolute expression
> > .org . - (664b-663b) + (662b-661b)
> > ^
> > <instantiation>:6:7: error: expected assembly-time absolute expression
> > .org . - (662b-661b) + (664b-663b)
> > ^
>
> I tried the latest Linus' tree and linux-next (defconfig) with this
> commit in and I can't get your build error. I used both clang-10 from
> Debian stable and clang-11 from Debian sid. So, which clang version did
> you use or which kernel config options?
>
> --
> Catalin
>
Hi Catalin,
Interesting, this reproduces for me with LLVM 12 or newer with just
defconfig.
$ make -j"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- LLVM=1 LLVM_IAS=1 defconfig arch/arm64/kernel/entry.o
https://github.com/ClangBuiltLinux/continuous-integration2/runs/2350258778?check_suite_focus=true
Cheers,
Nathan
On Thu, Apr 15, 2021 at 06:25:57AM -0700, Nathan Chancellor wrote:
> On Thu, Apr 15, 2021 at 10:17:43AM +0100, Catalin Marinas wrote:
> > On Tue, Apr 13, 2021 at 05:08:04PM -0700, Nathan Chancellor wrote:
> > > After commit 2decad92f473 ("arm64: mte: Ensure TIF_MTE_ASYNC_FAULT is
> > > set atomically"), LLVM's integrated assembler fails to build entry.S:
> > >
> > > <instantiation>:5:7: error: expected assembly-time absolute expression
> > > .org . - (664b-663b) + (662b-661b)
> > > ^
> > > <instantiation>:6:7: error: expected assembly-time absolute expression
> > > .org . - (662b-661b) + (664b-663b)
> > > ^
> >
> > I tried the latest Linus' tree and linux-next (defconfig) with this
> > commit in and I can't get your build error. I used both clang-10 from
> > Debian stable and clang-11 from Debian sid. So, which clang version did
> > you use or which kernel config options?
>
> Interesting, this reproduces for me with LLVM 12 or newer with just
> defconfig.
It fails for me as well with clang-12. Do you happen to know why it
works fine with previous clang versions?
--
Catalin
On Thu, Apr 15, 2021 at 7:02 AM Catalin Marinas <[email protected]> wrote:
>
> On Thu, Apr 15, 2021 at 06:25:57AM -0700, Nathan Chancellor wrote:
> > On Thu, Apr 15, 2021 at 10:17:43AM +0100, Catalin Marinas wrote:
> > > On Tue, Apr 13, 2021 at 05:08:04PM -0700, Nathan Chancellor wrote:
> > > > After commit 2decad92f473 ("arm64: mte: Ensure TIF_MTE_ASYNC_FAULT is
> > > > set atomically"), LLVM's integrated assembler fails to build entry.S:
> > > >
> > > > <instantiation>:5:7: error: expected assembly-time absolute expression
> > > > .org . - (664b-663b) + (662b-661b)
> > > > ^
> > > > <instantiation>:6:7: error: expected assembly-time absolute expression
> > > > .org . - (662b-661b) + (664b-663b)
> > > > ^
> > >
> > > I tried the latest Linus' tree and linux-next (defconfig) with this
> > > commit in and I can't get your build error. I used both clang-10 from
> > > Debian stable and clang-11 from Debian sid. So, which clang version did
> > > you use or which kernel config options?
> >
> > Interesting, this reproduces for me with LLVM 12 or newer with just
> > defconfig.
>
> It fails for me as well with clang-12. Do you happen to know why it
> works fine with previous clang versions?
It looks like CONFIG_ARM64_AS_HAS_MTE is not set when we use the
integrated assembler with LLVM 11, and the code that breaks later
versions is gated behind CONFIG_ARM64_MTE.
Sami
On Thu, Apr 15, 2021 at 08:50:25AM -0700, Sami Tolvanen wrote:
> On Thu, Apr 15, 2021 at 7:02 AM Catalin Marinas <[email protected]> wrote:
> >
> > On Thu, Apr 15, 2021 at 06:25:57AM -0700, Nathan Chancellor wrote:
> > > On Thu, Apr 15, 2021 at 10:17:43AM +0100, Catalin Marinas wrote:
> > > > On Tue, Apr 13, 2021 at 05:08:04PM -0700, Nathan Chancellor wrote:
> > > > > After commit 2decad92f473 ("arm64: mte: Ensure TIF_MTE_ASYNC_FAULT is
> > > > > set atomically"), LLVM's integrated assembler fails to build entry.S:
> > > > >
> > > > > <instantiation>:5:7: error: expected assembly-time absolute expression
> > > > > .org . - (664b-663b) + (662b-661b)
> > > > > ^
> > > > > <instantiation>:6:7: error: expected assembly-time absolute expression
> > > > > .org . - (662b-661b) + (664b-663b)
> > > > > ^
> > > >
> > > > I tried the latest Linus' tree and linux-next (defconfig) with this
> > > > commit in and I can't get your build error. I used both clang-10 from
> > > > Debian stable and clang-11 from Debian sid. So, which clang version did
> > > > you use or which kernel config options?
> > >
> > > Interesting, this reproduces for me with LLVM 12 or newer with just
> > > defconfig.
> >
> > It fails for me as well with clang-12. Do you happen to know why it
> > works fine with previous clang versions?
>
> It looks like CONFIG_ARM64_AS_HAS_MTE is not set when we use the
> integrated assembler with LLVM 11, and the code that breaks later
> versions is gated behind CONFIG_ARM64_MTE.
That explains it, thanks.
--
Catalin
On Tue, 13 Apr 2021 17:08:04 -0700, Nathan Chancellor wrote:
> After commit 2decad92f473 ("arm64: mte: Ensure TIF_MTE_ASYNC_FAULT is
> set atomically"), LLVM's integrated assembler fails to build entry.S:
>
> <instantiation>:5:7: error: expected assembly-time absolute expression
> .org . - (664b-663b) + (662b-661b)
> ^
> <instantiation>:6:7: error: expected assembly-time absolute expression
> .org . - (662b-661b) + (664b-663b)
> ^
>
> [...]
Applied to arm64 (for-next/fixes), thanks!
[1/1] arm64: alternatives: Move length validation in alternative_{insn, endif}
https://git.kernel.org/arm64/c/22315a2296f4
--
Catalin