arm64: Make CPU_BIG_ENDIAN depend on !LD_IS_LLD
PATCH 1/1 arm64: Make CPU_BIG_ENDIAN depend on !LD_IS_LLD
Similar to commit 28187dc8ebd9 ("ARM: 9025/1: Kconfig: CPU_BIG_ENDIAN depends on !LD_IS_LLD"), ld.lld does not support aarch64 big endian, leading to the following build error when CONFIG_CPU_BIG_ENDIAN is selected:
ld.lld: error: unknown emulation: aarch64linuxb
There are not currently plans to implement big endian support for aarch64 in ld.lld but if it should be supported in the future, this symbol can depend on the version that first supports it. In the meantime, prevent this symbol from being selected to avoid these type of build errors.
While we are here, the indentation of this symbol used spaces since its introduction in commit a872013d6d03 ("arm64: kconfig: allow CPU_BIG_ENDIAN to be selected"). Change it to tabs to be consistent with kernel coding style.
--- arch/arm64/Kconfig | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
arch/arm64/Kconfig +3 -2
@@ -952,8 +952,9 @@ choice that is selected here. config CPU_BIG_ENDIAN - bool "Build big-endian kernel" - help + bool "Build big-endian kernel" + depends on !LD_IS_LLD + help Say Y if you plan on running a kernel with a big-endian userspace. config CPU_LITTLE_ENDIAN
base-commit: 88bb507a74ea7d75fa49edd421eaa710a7d80598
Signature · 1 line
2.30.0
Quoted 7 lines · Nathan Chancellor
Similar to commit
28187dc8ebd9("ARM: 9025/1:Kconfig:CPU_BIG_ENDIANdepends on !LD_IS_LLD"), ld.lld does not support aarch64 big endian, leading to the following build error whenCONFIG_CPU_BIG_ENDIANis selected:ld.lld: error: unknown emulation: aarch64linuxb
While this is the original error message I reported, I think it would be better to explain that lld actually does support linking big-endian kernels but they don't boot, for unknown reasons.
I can send a patch to address the build error and mark big-endian as "depends on !LD_IS_LLD || COMPILE_TEST" to reflect that and help with randconfig testing.
Arnd
Quoted 7 lines · Arnd Bergmann
Quoted 6 lines · Nathan Chancellor
Similar to commit
28187dc8ebd9("ARM: 9025/1:Kconfig:CPU_BIG_ENDIANdepends on !LD_IS_LLD"), ld.lld does not support aarch64 big endian, leading to the following build error whenCONFIG_CPU_BIG_ENDIANis selected:
Quoted 5 lines
Quoted 1 line
ld.lld: error: unknown emulation: aarch64linuxb
While this is the original error message I reported, I think it would be better to explain that lld actually does support linking big-endian kernels but they don't boot, for unknown reasons.
That statement seems to contradict what Peter Smith says:
https://github.com/ClangBuiltLinux/linux/issues/1288#issuecomment-770693582
https://reviews.llvm.org/D58655#1410282
Quoted 3 lines
I can send a patch to address the build error and mark big-endian as "depends on !LD_IS_LLD ||
COMPILE_TEST" to reflect that and help with randconfig testing.
I have no strong opinion on handling this though.
Cheers,
Nathan
_______________________________________________
linux-arm-kernel mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Quoted 14 lines · Nathan Chancellor
Quoted 7 lines · Arnd Bergmann
Quoted 6 lines · Nathan Chancellor
Similar to commit
28187dc8ebd9("ARM: 9025/1:Kconfig:CPU_BIG_ENDIANdepends on !LD_IS_LLD"), ld.lld does not support aarch64 big endian, leading to the following build error whenCONFIG_CPU_BIG_ENDIANis selected:Quoted 5 lines
Quoted 1 line
ld.lld: error: unknown emulation: aarch64linuxb
While this is the original error message I reported, I think it would be better to explain that lld actually does support linking big-endian kernels but they don't boot, for unknown reasons.
Quoted 5 lines
That statement seems to contradict what Peter Smith says:
https://github.com/ClangBuiltLinux/linux/issues/1288#issuecomment-770693582
Right, adding Peter to Cc for clarification. Peter, what I can tell from experiments is that lld behaves just you describe it should, and (aside from the command like flag handling) like ld.bfd, so I'm not sure if there are any known deficiencies or just minor bugs when dealing with the kernel.
FWIW, I have now built a big-endian musl C library and a helloworld binary, which I linked with ld.lld and successfully tested using qemu-aarch64_be-static
Arnd
Quoted 5 lines
Quoted 3 lines
I can send a patch to address the build error and mark big-endian as "depends on !LD_IS_LLD ||
COMPILE_TEST" to reflect that and help with randconfig testing.I have no strong opinion on handling this though.
Quoted 36 lines
-----Original Message-----
From: Arnd Bergmann <[email protected]>
Sent: 02 February 2021 20:44
To: Nathan Chancellor <[email protected]>
Cc: Catalin Marinas <[email protected]>; Will Deacon <[email protected]>; Linux ARM <[email protected]>; linux- [email protected]; Nick Desaulniers <[email protected]>; clang-built-linux <[email protected]>; Arnd Bergmann <[email protected]>; Peter Smith <[email protected]>
Subject: Re: [PATCH] arm64: MakeCPU_BIG_ENDIANdepend on !LD_IS_LLDQuoted 2 lines · Nathan Chancellor
Quoted 1 line · Arnd Bergmann
On Tue, Feb 2, 2021 at 3:25 AM Nathan Chancellor <[email protected]>
Quoted 18 lines · wrote:
Quoted 7 lines
Quoted 7 lines
Similar to commit
28187dc8ebd9("ARM: 9025/1:Kconfig:CPU_BIG_ENDIANdepends on !LD_IS_LLD"), ld.lld does not support aarch64 big endian, leading to the following build error whenCONFIG_CPU_BIG_ENDIANis
selected:Quoted 5 lines
Quoted 1 line
ld.lld: error: unknown emulation: aarch64linuxb
While this is the original error message I reported, I think it would be better to explain that lld actually does support linking big-endian kernels but they don't boot, for unknown reasons.
That statement seems to contradict what Peter Smith says:
https://github.com/ClangBuiltLinux/linux/issues/1288#issuecomment-7706
93582
Quoted 7 lines
Quoted 1 line
Right, adding Peter to Cc for clarification. Peter, what I can tell from experiments is that lld behaves just you describe it should, and (aside from the command like flag handling) like ld.bfd, so I'm not sure if there are any known deficiencies or just minor bugs when dealing with the kernel.
If an emulation (-m) is present then current LLD maps all known Arm and AArch emulations to little endian
https://github.com/llvm/llvm-project/blob/main/lld/ELF/Driver.cpp#L147
In this case we'll get an error message with a big-endian object. ld.lld: error: be.o is incompatible with aarch64linux
If there are no emulations present then LLD will auto-detect big-endian from the first object file.
https://github.com/llvm/llvm-project/blob/main/lld/ELF/Driver.cpp#L1467
This will switch the generic LLD write functions to write big-endian. This will mean that any write to instructions will need to use explicit write32le and any data relocations will need to use write32/write64 as appropriate and not use the explicit le versions. The relocations for instructions look to be using explicit le writes as we'd want them to. I've spotted at least one case of using write64le for what looks like data
https://github.com/llvm/llvm-project/blob/main/lld/ELF/Arch/AArch64.cpp#L198
I've not know anyone try LLD on big-endian before so there are no known deficiencies. I expect that without an active search and tests there will be some problems. I think every write will need looking at, if it is to instructions it needs to explicitly use le, if to data (that could be either little or big endian) it must not force little endian.
Peter
Quoted 11 lines
FWIW, I have now built a big-endian musl C library and a helloworld binary, which I linked with ld.lld and successfully tested using qemu-aarch64_be- static
Arnd
Quoted 5 lines
Quoted 3 lines
I can send a patch to address the build error and mark big-endian as "depends on !LD_IS_LLD ||
COMPILE_TEST" to reflect that and help with randconfig testing.I have no strong opinion on handling this though.
Quoted 18 lines · Nathan Chancellor
Similar to commit
28187dc8ebd9("ARM: 9025/1:Kconfig:CPU_BIG_ENDIANdepends on !LD_IS_LLD"), ld.lld does not support aarch64 big endian, leading to the following build error whenCONFIG_CPU_BIG_ENDIANis selected:ld.lld: error: unknown emulation: aarch64linuxb
There are not currently plans to implement big endian support for aarch64 in ld.lld but if it should be supported in the future, this symbol can depend on the version that first supports it. In the meantime, prevent this symbol from being selected to avoid these type of build errors.
While we are here, the indentation of this symbol used spaces since its introduction in commit
a872013d6d03("arm64: kconfig: allowCPU_BIG_ENDIANto be selected"). Change it to tabs to be consistent with kernel coding style.
Quoted 4 lines
Fangrui has pushed proper aarch64linuxb and elf64-bigaarch64 for ld.lld:
https://reviews.llvm.org/D96211
https://reviews.llvm.org/D96188
This patch is needed for OUTPUT_FORMAT in the vDSO to work properly:
https://reviews.llvm.org/D96214
Once these are all merged into LLVM 13, I will update this to be:
depends on !LD_IS_LLD || LLD_VERSION >= 130000
Cheers,
Nathan
Quoted 30 lines
--- arch/arm64/Kconfig | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)arch/arm64/Kconfig +3
-2@@ -952,8 +952,9 @@ choice that is selected here. config CPU_BIG_ENDIAN - bool "Build big-endian kernel" - help + bool "Build big-endian kernel" + depends on !LD_IS_LLD + help Say Y if you plan on running a kernel with a big-endian userspace. config CPU_LITTLE_ENDIANbase-commit:
88bb507a74ea7d75fa49edd421eaa710a7d80598Signature · 7 lines
2.30.0 _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
PATCH v2 1/1 arm64: Make CPU_BIG_ENDIAN depend on ld.bfd or ld.lld 13.0.0+
In reply to Nathan ChancellorSimilar to commit 28187dc8ebd9 ("ARM: 9025/1: Kconfig: CPU_BIG_ENDIAN depends on !LD_IS_LLD"), ld.lld prior to 13.0.0 does not properly support aarch64 big endian, leading to the following build error when CONFIG_CPU_BIG_ENDIAN is selected:
ld.lld: error: unknown emulation: aarch64linuxb
This has been resolved in LLVM 13. To avoid errors like this, only allow CONFIG_CPU_BIG_ENDIAN to be selected if using ld.bfd or ld.lld 13.0.0 and newer.
While we are here, the indentation of this symbol used spaces since its introduction in commit a872013d6d03 ("arm64: kconfig: allow CPU_BIG_ENDIAN to be selected"). Change it to tabs to be consistent with kernel coding style.
---
v1 -> v2:
* Conditionally disable CONFIG_CPU_BIG_ENDIAN for older versions of ld.lld now that proper support has been added to ld.lld 13+ (thanks to the quick work of Fangrui Song).
arch/arm64/Kconfig | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
arch/arm64/Kconfig +3 -2
@@ -952,8 +952,9 @@ choice that is selected here. config CPU_BIG_ENDIAN - bool "Build big-endian kernel" - help + bool "Build big-endian kernel" + depends on !LD_IS_LLD || LLD_VERSION >= 130000 + help Say Y if you plan on running a kernel with a big-endian userspace. config CPU_LITTLE_ENDIAN
base-commit: 92bf22614b21a2706f4993b278017e437f7785b3
Signature · 1 line
2.30.1
Re: [PATCH v2] arm64: Make CPU_BIG_ENDIAN depend on ld.bfd or ld.lld 13.0.0+
Quoted 17 lines · Nathan Chancellor
Similar to commit
28187dc8ebd9("ARM: 9025/1:Kconfig:CPU_BIG_ENDIANdepends on !LD_IS_LLD"), ld.lld prior to 13.0.0 does not properly support aarch64 big endian, leading to the following build error whenCONFIG_CPU_BIG_ENDIANis selected:ld.lld: error: unknown emulation: aarch64linuxb
This has been resolved in LLVM 13. To avoid errors like this, only allow
CONFIG_CPU_BIG_ENDIANto be selected if using ld.bfd or ld.lld 13.0.0 and newer.While we are here, the indentation of this symbol used spaces since its introduction in commit
a872013d6d03("arm64: kconfig: allowCPU_BIG_ENDIANto be selected"). Change it to tabs to be consistent with kernel coding style.
Quoted 6 lines
Reported-by Arnd Bergmann <[email protected]>Signed-off-by Nathan Chancellor <[email protected]>
LGTM, thanks for implementing BE support for aarch64 in LLD, Fangrui! (And Nathan for the kernel patch+testing)
Quoted 32 lines
---
v1 -> v2:
* Conditionally disable
CONFIG_CPU_BIG_ENDIANfor older versions of ld.lld now that proper support has been added to ld.lld 13+ (thanks to the quick work of Fangrui Song).arch/arm64/Kconfig | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)arch/arm64/Kconfig +3
-2@@ -952,8 +952,9 @@ choice that is selected here. config CPU_BIG_ENDIAN - bool "Build big-endian kernel" - help + bool "Build big-endian kernel" + depends on !LD_IS_LLD || LLD_VERSION >= 130000 + help Say Y if you plan on running a kernel with a big-endian userspace. config CPU_LITTLE_ENDIANbase-commit:
92bf22614b21a2706f4993b278017e437f7785b3--
2.30.1
Signature · 7 lines
Thanks, ~Nick Desaulniers _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Re: [PATCH v2] arm64: Make CPU_BIG_ENDIAN depend on ld.bfd or ld.lld 13.0.0+
In reply to Nathan ChancellorQuoted 8 lines · Nathan Chancellor
Similar to commit
28187dc8ebd9("ARM: 9025/1:Kconfig:CPU_BIG_ENDIANdepends on !LD_IS_LLD"), ld.lld prior to 13.0.0 does not properly support aarch64 big endian, leading to the following build error whenCONFIG_CPU_BIG_ENDIANis selected:ld.lld: error: unknown emulation: aarch64linuxb
[...]
Applied to arm64 (for-next/misc), thanks!
[1/1] arm64: Make CPU_BIG_ENDIAN depend on ld.bfd or ld.lld 13.0.0+
https://git.kernel.org/arm64/c/e9c6deee00e9
Cheers,
Signature · 10 lines
Will https://fixes.arm64.dev https://next.arm64.dev https://will.arm64.dev _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel