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.
Link: https://github.com/ClangBuiltLinux/linux/issues/380
Link: https://github.com/ClangBuiltLinux/linux/issues/1288
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
arch/arm64/Kconfig | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
On Tue, Feb 2, 2021 at 3:25 AM Nathan Chancellor [off-list ref] wrote:
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
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
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Tue, Feb 02, 2021 at 09:04:34AM +0100, Arnd Bergmann wrote:
On Tue, Feb 2, 2021 at 3:25 AM Nathan Chancellor [off-list ref] wrote:
quoted
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
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.
I have no strong opinion on handling this though.
Cheers,
Nathan
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Tue, Feb 2, 2021 at 8:51 PM Nathan Chancellor [off-list ref] wrote:
On Tue, Feb 02, 2021 at 09:04:34AM +0100, Arnd Bergmann wrote:
quoted
On Tue, Feb 2, 2021 at 3:25 AM Nathan Chancellor [off-list ref] wrote:
quoted
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
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.
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
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.
From: Peter Smith <hidden> Date: 2021-02-03 10:09:39
-----Original Message-----
From: Arnd Bergmann <arnd@kernel.org>
Sent: 02 February 2021 20:44
To: Nathan Chancellor <nathan@kernel.org>
Cc: Catalin Marinas <Catalin.Marinas@arm.com>; Will Deacon
[off-list ref]; Linux ARM [off-list ref]; linux-
kernel@vger.kernel.org; Nick Desaulniers [off-list ref];
clang-built-linux [off-list ref]; Arnd Bergmann
[off-list ref]; Peter Smith [off-list ref]
Subject: Re: [PATCH] arm64: Make CPU_BIG_ENDIAN depend on !LD_IS_LLD
On Tue, Feb 2, 2021 at 8:51 PM Nathan Chancellor [off-list ref]
wrote:
quoted
On Tue, Feb 02, 2021 at 09:04:34AM +0100, Arnd Bergmann wrote:
quoted
On Tue, Feb 2, 2021 at 3:25 AM Nathan Chancellor [off-list ref]
wrote:
quoted
quoted
quoted
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
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.
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
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
quoted
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.
On Mon, Feb 01, 2021 at 07:24:42PM -0700, Nathan Chancellor wrote:
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.
Link: https://github.com/ClangBuiltLinux/linux/issues/380
Link: https://github.com/ClangBuiltLinux/linux/issues/1288
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Similar 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.
Link: https://github.com/ClangBuiltLinux/linux/issues/380
Link: https://github.com/ClangBuiltLinux/linux/issues/1288
Link: https://github.com/llvm/llvm-project/commit/7605a9a009b5fa3bdac07e3131c8d82f6d08feb7
Link: https://github.com/llvm/llvm-project/commit/eea34aae2e74e9b6fbdd5b95f479bc7f397bf387
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
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(-)
LGTM, thanks for implementing BE support for aarch64 in LLD, Fangrui!
(And Nathan for the kernel patch+testing)
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
quoted hunk
---
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(-)
From: Will Deacon <will@kernel.org> Date: 2021-02-09 14:37:51
On Mon, 8 Feb 2021 17:57:20 -0700, Nathan Chancellor wrote:
Similar 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
[...]