| Message ID | 1614820544-10686-1-git-send-email-yangtiezhu@loongson.cn (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | MIPS: Add comment about CONFIG_MIPS32_O32 in loongson3_defconfig when build with Clang | expand |
On Thu, Mar 04, 2021 at 09:15:44AM +0800, Tiezhu Yang wrote: > When build kernel with Clang [1]: > > $ make CC=clang loongson3_defconfig > $ make CC=clang > > there exists the following error: > > Checking missing-syscalls for O32 > CALL scripts/checksyscalls.sh > error: ABI 'o32' is not supported on CPU 'mips64r2' > make[1]: *** [Kbuild:48: missing-syscalls] Error 1 > make: *** [arch/mips/Makefile:419: archprepare] Error 2 > > This is a known bug [2] with Clang, as Simon Atanasyan said, > "There is no plan on support O32 for MIPS64 due to lack of > resources". > > It is not a good idea to remove this config due to GCC works > well, so add comment to point out this bug and suggest the > users to remove CONFIG_MIPS32_O32=y in defconfig when build > kernel with Clang. > > [1] https://www.kernel.org/doc/html/latest/kbuild/llvm.html > [2] https://bugs.llvm.org/show_bug.cgi?id=38063 > > Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn> > --- > arch/mips/configs/loongson3_defconfig | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/mips/configs/loongson3_defconfig b/arch/mips/configs/loongson3_defconfig > index 0e79f81..cacf9dd 100644 > --- a/arch/mips/configs/loongson3_defconfig > +++ b/arch/mips/configs/loongson3_defconfig > @@ -35,6 +35,9 @@ CONFIG_NUMA=y > CONFIG_SMP=y > CONFIG_HZ_256=y > CONFIG_KEXEC=y > +# Please remove CONFIG_MIPS32_O32=y when build with Clang > +# due to "ABI 'o32' is not supported on CPU 'mips64r2'", > +# https://bugs.llvm.org/show_bug.cgi?id=38063 > CONFIG_MIPS32_O32=y > CONFIG_MIPS32_N32=y > CONFIG_VIRTUALIZATION=y > -- > 2.1.0 > I think this might be a better solution. I know that I personally never read defconfig files if a build fails. If CONFIG_MIPS32_O32 is broken with clang and the MIPS backend maintainer has said that it will not be supported due to lack of resources, then the config should not even be selectable in my opinion. Cheers, Nathan diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index d89efba3d8a4..ed35318a759d 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -3315,6 +3315,8 @@ config SYSVIPC_COMPAT config MIPS32_O32 bool "Kernel support for o32 binaries" depends on 64BIT + # https://bugs.llvm.org/show_bug.cgi?id=38063 + depends on $(success,$(CC) $(CLANG_FLAGS) -march=mips64 -o32 -c -x c /dev/null -o /dev/null) select ARCH_WANT_OLD_COMPAT_IPC select COMPAT select MIPS32_COMPAT
On 03/04/2021 10:02 AM, Nathan Chancellor wrote: > On Thu, Mar 04, 2021 at 09:15:44AM +0800, Tiezhu Yang wrote: >> When build kernel with Clang [1]: >> >> $ make CC=clang loongson3_defconfig >> $ make CC=clang [snip] > I think this might be a better solution. I know that I personally never > read defconfig files if a build fails. > > If CONFIG_MIPS32_O32 is broken with clang and the MIPS backend > maintainer has said that it will not be supported due to lack of > resources, then the config should not even be selectable in my opinion. > > Cheers, > Nathan > > diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig > index d89efba3d8a4..ed35318a759d 100644 > --- a/arch/mips/Kconfig > +++ b/arch/mips/Kconfig > @@ -3315,6 +3315,8 @@ config SYSVIPC_COMPAT > config MIPS32_O32 > bool "Kernel support for o32 binaries" > depends on 64BIT > + # https://bugs.llvm.org/show_bug.cgi?id=38063 > + depends on $(success,$(CC) $(CLANG_FLAGS) -march=mips64 -o32 -c -x c /dev/null -o /dev/null) > select ARCH_WANT_OLD_COMPAT_IPC > select COMPAT > select MIPS32_COMPAT Hi Nathan, Thank you very much for your reply and suggestion, maybe the following change is simple, clear and better? If yes, I will send v2 later. diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index 3a38d27..f6ba59f 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -3318,6 +3318,8 @@ config SYSVIPC_COMPAT config MIPS32_O32 bool "Kernel support for o32 binaries" depends on 64BIT + # https://bugs.llvm.org/show_bug.cgi?id=38063 + depends on !CC_IS_CLANG select ARCH_WANT_OLD_COMPAT_IPC select COMPAT select MIPS32_COMPAT Thanks, Tiezhu
On Thu, Mar 04, 2021 at 11:48:09AM +0800, Tiezhu Yang wrote: > On 03/04/2021 10:02 AM, Nathan Chancellor wrote: > > On Thu, Mar 04, 2021 at 09:15:44AM +0800, Tiezhu Yang wrote: > > > When build kernel with Clang [1]: > > > > > > $ make CC=clang loongson3_defconfig > > > $ make CC=clang > > [snip] > > > I think this might be a better solution. I know that I personally never > > read defconfig files if a build fails. > > > > If CONFIG_MIPS32_O32 is broken with clang and the MIPS backend > > maintainer has said that it will not be supported due to lack of > > resources, then the config should not even be selectable in my opinion. > > > > Cheers, > > Nathan > > > > diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig > > index d89efba3d8a4..ed35318a759d 100644 > > --- a/arch/mips/Kconfig > > +++ b/arch/mips/Kconfig > > @@ -3315,6 +3315,8 @@ config SYSVIPC_COMPAT > > config MIPS32_O32 > > bool "Kernel support for o32 binaries" > > depends on 64BIT > > + # https://bugs.llvm.org/show_bug.cgi?id=38063 > > + depends on $(success,$(CC) $(CLANG_FLAGS) -march=mips64 -o32 -c -x c /dev/null -o /dev/null) > > select ARCH_WANT_OLD_COMPAT_IPC > > select COMPAT > > select MIPS32_COMPAT > > Hi Nathan, > > Thank you very much for your reply and suggestion, maybe the following > change is simple, clear and better? If yes, I will send v2 later. Hi Tiezhu, I think that the change is simpler but better is subjective. I tend to prefer tests like mine so that it is not dependent on someone going "oh hey, this LLVM bug has been fixed so we can turn this config on!". Instead, the config will just turn on automatically as soon as that bug is fixed. However, in this particular case, it does not seem like that will happen unless someone steps but there have been times where an independent party will implement some change that benefits them and nobody notices for a while. Plus, I periodically grep the tree for CC_IS_CLANG to see if there are any configuration options that can be re-enabled.. Regardless, if Thomas is happy with the below change, so am I, as it will allow us to test more 64-bit MIPS configurations. I can add an ack or review at that point in time. Cheers, Nathan > diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig > index 3a38d27..f6ba59f 100644 > --- a/arch/mips/Kconfig > +++ b/arch/mips/Kconfig > @@ -3318,6 +3318,8 @@ config SYSVIPC_COMPAT > config MIPS32_O32 > bool "Kernel support for o32 binaries" > depends on 64BIT > + # https://bugs.llvm.org/show_bug.cgi?id=38063 > + depends on !CC_IS_CLANG > select ARCH_WANT_OLD_COMPAT_IPC > select COMPAT > select MIPS32_COMPAT > > Thanks, > Tiezhu >
On Thu, 4 Mar 2021, Tiezhu Yang wrote: > This is a known bug [2] with Clang, as Simon Atanasyan said, > "There is no plan on support O32 for MIPS64 due to lack of > resources". Huh? Is that a joke? From the o32 psABI's point of view a MIPS64 CPU is exactly the same as a MIPS32 one (for whatever ISA revision), so there's nothing to support there really other than the CPU/ISA name. As much as I dislike all the hacks the Clang community seems to come up with for the shortcomings of their tool there has to be a saner workaround available rather than forcibly disabling support for the o32 ABI with CONFIG_64BIT kernels, but the report is missing the compiler invocation line triggering the issue (V=1 perhaps?), which should be included with any commit description anyway, so I can't suggest anything based on the limited information provided. Maciej
在 2021/3/5 上午7:08, Maciej W. Rozycki 写道: > On Thu, 4 Mar 2021, Tiezhu Yang wrote: > >> This is a known bug [2] with Clang, as Simon Atanasyan said, >> "There is no plan on support O32 for MIPS64 due to lack of >> resources". > > Huh? Is that a joke? From the o32 psABI's point of view a MIPS64 CPU is > exactly the same as a MIPS32 one (for whatever ISA revision), so there's > nothing to support there really other than the CPU/ISA name. Clang treat MIPS32 as a different backend so we may need some extra effort.... TBH it is a toolchain issue and kernel workaround seems bogus. From my point view we can "s/mips64r2/mips32r2" when doing syscall checks to workaround clang issue instead of disable it for kernel. Thanks. - Jiaxun > > As much as I dislike all the hacks the Clang community seems to come up > with for the shortcomings of their tool there has to be a saner workaround > available rather than forcibly disabling support for the o32 ABI with > CONFIG_64BIT kernels, but the report is missing the compiler invocation > line triggering the issue (V=1 perhaps?), which should be included with > any commit description anyway, so I can't suggest anything based on the > limited information provided. > > Maciej >
On Fri, 5 Mar 2021, Jiaxun Yang wrote: > > Huh? Is that a joke? From the o32 psABI's point of view a MIPS64 CPU is > > exactly the same as a MIPS32 one (for whatever ISA revision), so there's > > nothing to support there really other than the CPU/ISA name. > > Clang treat MIPS32 as a different backend so we may need some extra effort.... > > TBH it is a toolchain issue and kernel workaround seems bogus. > > From my point view we can "s/mips64r2/mips32r2" when doing syscall checks > to workaround clang issue instead of disable it for kernel. I had something like this in mind, but obviously that has to be done in a consistent manner across all the possible 64-bit `-march=...' selections, as I suppose that is where the problem comes from. So we'd have to handle things like say `octeon'. But I'd like to see the invocation line to be sure (I could try and check that myself, but I don't have Clang and it's the patch submitter's job anyway to explain things and not the reviewer's to chase them). Maybe we could cheat and wire everything to a single setting so as to keep the hack to the minimum, but we need to know what the right setting is from the Clang people. NB only MIPS IV is special in that it has 32-bit extensions beyond MIPS III but not a corresponding 32-bit ISA. The corresponding 32-bit ISA for MIPS III is MIPS II, and obviously all the modern MIPS ISAs come in pairs. So it's only MIPS IV where o32 may want special support (at the hardware level the ISA had the CP0.Status.XX bit to control the ISA extensions), and I guess only a few people care at this point, though some are present on this mailing list. Maciej
diff --git a/arch/mips/configs/loongson3_defconfig b/arch/mips/configs/loongson3_defconfig index 0e79f81..cacf9dd 100644 --- a/arch/mips/configs/loongson3_defconfig +++ b/arch/mips/configs/loongson3_defconfig @@ -35,6 +35,9 @@ CONFIG_NUMA=y CONFIG_SMP=y CONFIG_HZ_256=y CONFIG_KEXEC=y +# Please remove CONFIG_MIPS32_O32=y when build with Clang +# due to "ABI 'o32' is not supported on CPU 'mips64r2'", +# https://bugs.llvm.org/show_bug.cgi?id=38063 CONFIG_MIPS32_O32=y CONFIG_MIPS32_N32=y CONFIG_VIRTUALIZATION=y
When build kernel with Clang [1]: $ make CC=clang loongson3_defconfig $ make CC=clang there exists the following error: Checking missing-syscalls for O32 CALL scripts/checksyscalls.sh error: ABI 'o32' is not supported on CPU 'mips64r2' make[1]: *** [Kbuild:48: missing-syscalls] Error 1 make: *** [arch/mips/Makefile:419: archprepare] Error 2 This is a known bug [2] with Clang, as Simon Atanasyan said, "There is no plan on support O32 for MIPS64 due to lack of resources". It is not a good idea to remove this config due to GCC works well, so add comment to point out this bug and suggest the users to remove CONFIG_MIPS32_O32=y in defconfig when build kernel with Clang. [1] https://www.kernel.org/doc/html/latest/kbuild/llvm.html [2] https://bugs.llvm.org/show_bug.cgi?id=38063 Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn> --- arch/mips/configs/loongson3_defconfig | 3 +++ 1 file changed, 3 insertions(+)