Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
On Fri, Aug 30, 2019 at 2:13 PM Nick Desaulniers wrote: > > On Fri, Aug 30, 2019 at 10:28 AM Nathan Chancellor > wrote: > > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > > index a43fc753aa53..23c2bf0fbd30 100644 > > --- a/arch/arm/Makefile > > +++ b/arch/arm/Makefile > > @@ -115,6 +115,10 @@ ifeq ($(CONFIG_ARM_UNWIND),y) > > CFLAGS_ABI +=-funwind-tables > > endif > > > > +ifeq ($(CONFIG_CC_IS_CLANG),y) > > +CFLAGS_ABI +=-meabi gnu Needs a space. `+=-`. -- Thanks, ~Nick Desaulniers
Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
On Fri, Aug 30, 2019 at 10:28 AM Nathan Chancellor wrote: > > On Thu, Aug 29, 2019 at 01:57:35PM -0700, Nick Desaulniers wrote: > > On Thu, Aug 29, 2019 at 1:21 PM Stefan Agner wrote: > > > > > > On 2019-08-29 21:34, Nathan Chancellor wrote: > > > > On Thu, Aug 29, 2019 at 10:55:28AM -0700, Nick Desaulniers wrote: > > > >> On Wed, Aug 28, 2019 at 11:27 PM Nathan Chancellor > > > > I will test with or without CONFIG_AEABI like Matthias asked and I will > > > > implement your Kconfig suggestion if it passes all of my tests. The > > > > reason that I did it this way is because I didn't want a user to end up > > > > with a non-booting kernel since -meabi gnu works with older versions of > > > > clang at build time, the issue happens at boot time but the Kconfig > > > > suggestion + cc-option should fix that. > Disabling CONFIG_AEABI does not work with clang, I get a ton of failures > around undefined references to __aeabi_idivmod and __aeabi_uidivmod. I > don't think this is worth looking into given that CONFIG_AEABI is not > selectable when CONFIG_CPU_V6 or CONFIG_CPU_V7 is selected, which is > what we primarily care about.. We currently build and boot > multi_v5_defconfig but it has CONFIG_AEABI set in it. As a result, I > don't think we need to care about it with this patch. The plan of record is to never support !CONFIG_AEBI (ie OABI) w/ Clang. See also my commit currently in linux-next: ARM: 8875/1: Kconfig: default to AEABI w/ Clang https://github.com/ClangBuiltLinux/linux/issues/482 so !AEABI is a moot point. If we ever changed our minds, then yes we should additionally guard on !CONFIG_AEABI, but I feel like that's a highly unlikely scenario at this point. > > This diff would also solve the issue without the need for the version > check in the Makefile, as it is the combination of -meabi gnu and -pg > that causes the boot issue and -pg gets added when > CONFIG_FUNCTION_TRACER is enabled. Would that be preferred? I do not > think adding cc-option is necessary given that we know GCC universally > does not support this flag; there is no point in adding a small penalty > with cc-option to either compiler. > > Cheers, > Nathan > > > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index a98c7af50bf0..440ad41e77e4 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -83,7 +83,7 @@ config ARM > select HAVE_FAST_GUP if ARM_LPAE > select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL > select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG > - select HAVE_FUNCTION_TRACER if !XIP_KERNEL > + select HAVE_FUNCTION_TRACER if !XIP_KERNEL && (CC_IS_GCC || > CLANG_VERSION >= 10) > select HAVE_GCC_PLUGINS > select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || > CPU_V7) > select HAVE_IDE if PCI || ISA || PCMCIA > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > index a43fc753aa53..23c2bf0fbd30 100644 > --- a/arch/arm/Makefile > +++ b/arch/arm/Makefile > @@ -115,6 +115,10 @@ ifeq ($(CONFIG_ARM_UNWIND),y) > CFLAGS_ABI +=-funwind-tables > endif > > +ifeq ($(CONFIG_CC_IS_CLANG),y) > +CFLAGS_ABI +=-meabi gnu > +endif Reviewed-by: Nick Desaulniers > + > # Accept old syntax despite ".syntax unified" > AFLAGS_NOWARN :=$(call > as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W) > -- Thanks, ~Nick Desaulniers
Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
On Thu, Aug 29, 2019 at 01:57:35PM -0700, Nick Desaulniers wrote: > On Thu, Aug 29, 2019 at 1:21 PM Stefan Agner wrote: > > > > On 2019-08-29 21:34, Nathan Chancellor wrote: > > > On Thu, Aug 29, 2019 at 10:55:28AM -0700, Nick Desaulniers wrote: > > >> On Wed, Aug 28, 2019 at 11:27 PM Nathan Chancellor > > >> wrote: > > >> > > > >> > Currently, multi_v7_defconfig + CONFIG_FUNCTION_TRACER fails to build > > >> > with clang: > > >> > > > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `_local_bh_enable': > > >> > softirq.c:(.text+0x504): undefined reference to `mcount' > > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function > > >> > `__local_bh_enable_ip': > > >> > softirq.c:(.text+0x58c): undefined reference to `mcount' > > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `do_softirq': > > >> > softirq.c:(.text+0x6c8): undefined reference to `mcount' > > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_enter': > > >> > softirq.c:(.text+0x75c): undefined reference to `mcount' > > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_exit': > > >> > softirq.c:(.text+0x840): undefined reference to `mcount' > > >> > arm-linux-gnueabi-ld: kernel/softirq.o:softirq.c:(.text+0xa50): more > > >> > undefined references to `mcount' follow > > >> > > > >> > clang can emit a working mcount symbol, __gnu_mcount_nc, when > > >> > '-meabi gnu' is passed to it. Until r369147 in LLVM, this was > > >> > broken and caused the kernel not to boot because the calling > > >> > convention was not correct. Now that it is fixed, add this to > > >> > the command line when clang is 10.0.0 or newer so everything > > >> > works properly. > > >> > > > >> > Link: https://github.com/ClangBuiltLinux/linux/issues/35 > > >> > Link: https://bugs.llvm.org/show_bug.cgi?id=33845 > > >> > Link: > > >> > https://github.com/llvm/llvm-project/commit/16fa8b09702378bacfa3d07081afe6b353b99e60 > > >> > Signed-off-by: Nathan Chancellor > > >> > --- > > >> > arch/arm/Makefile | 6 ++ > > >> > 1 file changed, 6 insertions(+) > > >> > > > >> > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > > >> > index c3624ca6c0bc..7b5a26a866fc 100644 > > >> > --- a/arch/arm/Makefile > > >> > +++ b/arch/arm/Makefile > > >> > @@ -112,6 +112,12 @@ ifeq ($(CONFIG_ARM_UNWIND),y) > > >> > CFLAGS_ABI +=-funwind-tables > > >> > endif > > >> > > > >> > +ifeq ($(CONFIG_CC_IS_CLANG),y) > > >> > +ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 10; echo $$?),0) > > >> > +CFLAGS_ABI +=-meabi gnu > > >> > +endif > > >> > +endif > > >> > + > > >> > > >> Thanks for the patch! I think this is one of the final issues w/ 32b > > >> ARM configs when building w/ Clang. > > >> > > >> I'm not super enthused about the version check. The flag is indeed > > >> not recognized by GCC, but I think it would actually be more concise > > >> with $(cc-option) and no compiler or version check. > > >> > > >> Further, I think that the working __gnu_mcount_nc in Clang would > > >> better be represented as marking the arch/arm/KConfig option for > > >> CONFIG_FUNCTION_TRACER for dependent on a version of Clang greater > > >> than or equal to Clang 10, not conditionally adding this flag. (We > > >> should always add the flag when supported, IMO. __gnu_mcount_nc's > > >> calling convention being broken is orthogonal to the choice of > > >> __gnu_mcount_nc vs mcount, and it's the former's that should be > > >> checked, not the latter as in this patch. > > > > > > I will test with or without CONFIG_AEABI like Matthias asked and I will > > > implement your Kconfig suggestion if it passes all of my tests. The > > > reason that I did it this way is because I didn't want a user to end up > > > with a non-booting kernel since -meabi gnu works with older versions of > > > clang at build time, the issue happens at boot time but the Kconfig > > > suggestion + cc-option should fix that. > > > > I agree with Nathan here, I'd rather prefer the build system to fail > > building rather than runtime error. > > > > If we decide we want to have it building despite it not building a > > functional kernel, we should at least add a #warning... > > Just to be clear...I was suggesting a build failure, but for > __gnu_mcount_nc not having the correct calling convention in older > clang releases, which is orthogonal to passing `-meabi gnu`. This > patch uses the __gnu_mcount_nc calling convention problem to justify a > version check for a flag that while closely related, is not actually > the problem, IMO. I am not entirely sure what you mean. -meabi gnu has always produced a buildable kernel (see Stefan's original report [1]), it just doesn't boot and that all happens silently. [1]: https://lore.kernel.org/linux-arm-kernel/35ae3d464c7b77a5fe86a732079e3...@agner.ch/ Okay, after doing some further testing... Disabling CONFIG_AEABI does not work with clang, I get a ton of failures around undefined references to __aeabi_idivmod and __aeabi_uidivmod. I don't
Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
On Thu, Aug 29, 2019 at 1:21 PM Stefan Agner wrote: > > On 2019-08-29 21:34, Nathan Chancellor wrote: > > On Thu, Aug 29, 2019 at 10:55:28AM -0700, Nick Desaulniers wrote: > >> On Wed, Aug 28, 2019 at 11:27 PM Nathan Chancellor > >> wrote: > >> > > >> > Currently, multi_v7_defconfig + CONFIG_FUNCTION_TRACER fails to build > >> > with clang: > >> > > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `_local_bh_enable': > >> > softirq.c:(.text+0x504): undefined reference to `mcount' > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function > >> > `__local_bh_enable_ip': > >> > softirq.c:(.text+0x58c): undefined reference to `mcount' > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `do_softirq': > >> > softirq.c:(.text+0x6c8): undefined reference to `mcount' > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_enter': > >> > softirq.c:(.text+0x75c): undefined reference to `mcount' > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_exit': > >> > softirq.c:(.text+0x840): undefined reference to `mcount' > >> > arm-linux-gnueabi-ld: kernel/softirq.o:softirq.c:(.text+0xa50): more > >> > undefined references to `mcount' follow > >> > > >> > clang can emit a working mcount symbol, __gnu_mcount_nc, when > >> > '-meabi gnu' is passed to it. Until r369147 in LLVM, this was > >> > broken and caused the kernel not to boot because the calling > >> > convention was not correct. Now that it is fixed, add this to > >> > the command line when clang is 10.0.0 or newer so everything > >> > works properly. > >> > > >> > Link: https://github.com/ClangBuiltLinux/linux/issues/35 > >> > Link: https://bugs.llvm.org/show_bug.cgi?id=33845 > >> > Link: > >> > https://github.com/llvm/llvm-project/commit/16fa8b09702378bacfa3d07081afe6b353b99e60 > >> > Signed-off-by: Nathan Chancellor > >> > --- > >> > arch/arm/Makefile | 6 ++ > >> > 1 file changed, 6 insertions(+) > >> > > >> > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > >> > index c3624ca6c0bc..7b5a26a866fc 100644 > >> > --- a/arch/arm/Makefile > >> > +++ b/arch/arm/Makefile > >> > @@ -112,6 +112,12 @@ ifeq ($(CONFIG_ARM_UNWIND),y) > >> > CFLAGS_ABI +=-funwind-tables > >> > endif > >> > > >> > +ifeq ($(CONFIG_CC_IS_CLANG),y) > >> > +ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 10; echo $$?),0) > >> > +CFLAGS_ABI +=-meabi gnu > >> > +endif > >> > +endif > >> > + > >> > >> Thanks for the patch! I think this is one of the final issues w/ 32b > >> ARM configs when building w/ Clang. > >> > >> I'm not super enthused about the version check. The flag is indeed > >> not recognized by GCC, but I think it would actually be more concise > >> with $(cc-option) and no compiler or version check. > >> > >> Further, I think that the working __gnu_mcount_nc in Clang would > >> better be represented as marking the arch/arm/KConfig option for > >> CONFIG_FUNCTION_TRACER for dependent on a version of Clang greater > >> than or equal to Clang 10, not conditionally adding this flag. (We > >> should always add the flag when supported, IMO. __gnu_mcount_nc's > >> calling convention being broken is orthogonal to the choice of > >> __gnu_mcount_nc vs mcount, and it's the former's that should be > >> checked, not the latter as in this patch. > > > > I will test with or without CONFIG_AEABI like Matthias asked and I will > > implement your Kconfig suggestion if it passes all of my tests. The > > reason that I did it this way is because I didn't want a user to end up > > with a non-booting kernel since -meabi gnu works with older versions of > > clang at build time, the issue happens at boot time but the Kconfig > > suggestion + cc-option should fix that. > > I agree with Nathan here, I'd rather prefer the build system to fail > building rather than runtime error. > > If we decide we want to have it building despite it not building a > functional kernel, we should at least add a #warning... Just to be clear...I was suggesting a build failure, but for __gnu_mcount_nc not having the correct calling convention in older clang releases, which is orthogonal to passing `-meabi gnu`. This patch uses the __gnu_mcount_nc calling convention problem to justify a version check for a flag that while closely related, is not actually the problem, IMO. -- Thanks, ~Nick Desaulniers
Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
On 2019-08-29 21:34, Nathan Chancellor wrote: > On Thu, Aug 29, 2019 at 10:55:28AM -0700, Nick Desaulniers wrote: >> On Wed, Aug 28, 2019 at 11:27 PM Nathan Chancellor >> wrote: >> > >> > Currently, multi_v7_defconfig + CONFIG_FUNCTION_TRACER fails to build >> > with clang: >> > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `_local_bh_enable': >> > softirq.c:(.text+0x504): undefined reference to `mcount' >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `__local_bh_enable_ip': >> > softirq.c:(.text+0x58c): undefined reference to `mcount' >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `do_softirq': >> > softirq.c:(.text+0x6c8): undefined reference to `mcount' >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_enter': >> > softirq.c:(.text+0x75c): undefined reference to `mcount' >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_exit': >> > softirq.c:(.text+0x840): undefined reference to `mcount' >> > arm-linux-gnueabi-ld: kernel/softirq.o:softirq.c:(.text+0xa50): more >> > undefined references to `mcount' follow >> > >> > clang can emit a working mcount symbol, __gnu_mcount_nc, when >> > '-meabi gnu' is passed to it. Until r369147 in LLVM, this was >> > broken and caused the kernel not to boot because the calling >> > convention was not correct. Now that it is fixed, add this to >> > the command line when clang is 10.0.0 or newer so everything >> > works properly. >> > >> > Link: https://github.com/ClangBuiltLinux/linux/issues/35 >> > Link: https://bugs.llvm.org/show_bug.cgi?id=33845 >> > Link: >> > https://github.com/llvm/llvm-project/commit/16fa8b09702378bacfa3d07081afe6b353b99e60 >> > Signed-off-by: Nathan Chancellor >> > --- >> > arch/arm/Makefile | 6 ++ >> > 1 file changed, 6 insertions(+) >> > >> > diff --git a/arch/arm/Makefile b/arch/arm/Makefile >> > index c3624ca6c0bc..7b5a26a866fc 100644 >> > --- a/arch/arm/Makefile >> > +++ b/arch/arm/Makefile >> > @@ -112,6 +112,12 @@ ifeq ($(CONFIG_ARM_UNWIND),y) >> > CFLAGS_ABI +=-funwind-tables >> > endif >> > >> > +ifeq ($(CONFIG_CC_IS_CLANG),y) >> > +ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 10; echo $$?),0) >> > +CFLAGS_ABI +=-meabi gnu >> > +endif >> > +endif >> > + >> >> Thanks for the patch! I think this is one of the final issues w/ 32b >> ARM configs when building w/ Clang. >> >> I'm not super enthused about the version check. The flag is indeed >> not recognized by GCC, but I think it would actually be more concise >> with $(cc-option) and no compiler or version check. >> >> Further, I think that the working __gnu_mcount_nc in Clang would >> better be represented as marking the arch/arm/KConfig option for >> CONFIG_FUNCTION_TRACER for dependent on a version of Clang greater >> than or equal to Clang 10, not conditionally adding this flag. (We >> should always add the flag when supported, IMO. __gnu_mcount_nc's >> calling convention being broken is orthogonal to the choice of >> __gnu_mcount_nc vs mcount, and it's the former's that should be >> checked, not the latter as in this patch. > > I will test with or without CONFIG_AEABI like Matthias asked and I will > implement your Kconfig suggestion if it passes all of my tests. The > reason that I did it this way is because I didn't want a user to end up > with a non-booting kernel since -meabi gnu works with older versions of > clang at build time, the issue happens at boot time but the Kconfig > suggestion + cc-option should fix that. I agree with Nathan here, I'd rather prefer the build system to fail building rather than runtime error. If we decide we want to have it building despite it not building a functional kernel, we should at least add a #warning... -- Stefan > > I should have a v2 out this evening. > > Cheers, > Nathan
Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
On Thu, Aug 29, 2019 at 10:55:28AM -0700, Nick Desaulniers wrote: > On Wed, Aug 28, 2019 at 11:27 PM Nathan Chancellor > wrote: > > > > Currently, multi_v7_defconfig + CONFIG_FUNCTION_TRACER fails to build > > with clang: > > > > arm-linux-gnueabi-ld: kernel/softirq.o: in function `_local_bh_enable': > > softirq.c:(.text+0x504): undefined reference to `mcount' > > arm-linux-gnueabi-ld: kernel/softirq.o: in function `__local_bh_enable_ip': > > softirq.c:(.text+0x58c): undefined reference to `mcount' > > arm-linux-gnueabi-ld: kernel/softirq.o: in function `do_softirq': > > softirq.c:(.text+0x6c8): undefined reference to `mcount' > > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_enter': > > softirq.c:(.text+0x75c): undefined reference to `mcount' > > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_exit': > > softirq.c:(.text+0x840): undefined reference to `mcount' > > arm-linux-gnueabi-ld: kernel/softirq.o:softirq.c:(.text+0xa50): more > > undefined references to `mcount' follow > > > > clang can emit a working mcount symbol, __gnu_mcount_nc, when > > '-meabi gnu' is passed to it. Until r369147 in LLVM, this was > > broken and caused the kernel not to boot because the calling > > convention was not correct. Now that it is fixed, add this to > > the command line when clang is 10.0.0 or newer so everything > > works properly. > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/35 > > Link: https://bugs.llvm.org/show_bug.cgi?id=33845 > > Link: > > https://github.com/llvm/llvm-project/commit/16fa8b09702378bacfa3d07081afe6b353b99e60 > > Signed-off-by: Nathan Chancellor > > --- > > arch/arm/Makefile | 6 ++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > > index c3624ca6c0bc..7b5a26a866fc 100644 > > --- a/arch/arm/Makefile > > +++ b/arch/arm/Makefile > > @@ -112,6 +112,12 @@ ifeq ($(CONFIG_ARM_UNWIND),y) > > CFLAGS_ABI +=-funwind-tables > > endif > > > > +ifeq ($(CONFIG_CC_IS_CLANG),y) > > +ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 10; echo $$?),0) > > +CFLAGS_ABI +=-meabi gnu > > +endif > > +endif > > + > > Thanks for the patch! I think this is one of the final issues w/ 32b > ARM configs when building w/ Clang. > > I'm not super enthused about the version check. The flag is indeed > not recognized by GCC, but I think it would actually be more concise > with $(cc-option) and no compiler or version check. > > Further, I think that the working __gnu_mcount_nc in Clang would > better be represented as marking the arch/arm/KConfig option for > CONFIG_FUNCTION_TRACER for dependent on a version of Clang greater > than or equal to Clang 10, not conditionally adding this flag. (We > should always add the flag when supported, IMO. __gnu_mcount_nc's > calling convention being broken is orthogonal to the choice of > __gnu_mcount_nc vs mcount, and it's the former's that should be > checked, not the latter as in this patch. I will test with or without CONFIG_AEABI like Matthias asked and I will implement your Kconfig suggestion if it passes all of my tests. The reason that I did it this way is because I didn't want a user to end up with a non-booting kernel since -meabi gnu works with older versions of clang at build time, the issue happens at boot time but the Kconfig suggestion + cc-option should fix that. I should have a v2 out this evening. Cheers, Nathan
Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
On Wed, Aug 28, 2019 at 11:27 PM Nathan Chancellor wrote: > > Currently, multi_v7_defconfig + CONFIG_FUNCTION_TRACER fails to build > with clang: > > arm-linux-gnueabi-ld: kernel/softirq.o: in function `_local_bh_enable': > softirq.c:(.text+0x504): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `__local_bh_enable_ip': > softirq.c:(.text+0x58c): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `do_softirq': > softirq.c:(.text+0x6c8): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_enter': > softirq.c:(.text+0x75c): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_exit': > softirq.c:(.text+0x840): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o:softirq.c:(.text+0xa50): more > undefined references to `mcount' follow > > clang can emit a working mcount symbol, __gnu_mcount_nc, when > '-meabi gnu' is passed to it. Until r369147 in LLVM, this was > broken and caused the kernel not to boot because the calling > convention was not correct. Now that it is fixed, add this to > the command line when clang is 10.0.0 or newer so everything > works properly. > > Link: https://github.com/ClangBuiltLinux/linux/issues/35 > Link: https://bugs.llvm.org/show_bug.cgi?id=33845 > Link: > https://github.com/llvm/llvm-project/commit/16fa8b09702378bacfa3d07081afe6b353b99e60 > Signed-off-by: Nathan Chancellor > --- > arch/arm/Makefile | 6 ++ > 1 file changed, 6 insertions(+) > > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > index c3624ca6c0bc..7b5a26a866fc 100644 > --- a/arch/arm/Makefile > +++ b/arch/arm/Makefile > @@ -112,6 +112,12 @@ ifeq ($(CONFIG_ARM_UNWIND),y) > CFLAGS_ABI +=-funwind-tables > endif > > +ifeq ($(CONFIG_CC_IS_CLANG),y) > +ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 10; echo $$?),0) > +CFLAGS_ABI +=-meabi gnu > +endif > +endif > + Thanks for the patch! I think this is one of the final issues w/ 32b ARM configs when building w/ Clang. I'm not super enthused about the version check. The flag is indeed not recognized by GCC, but I think it would actually be more concise with $(cc-option) and no compiler or version check. Further, I think that the working __gnu_mcount_nc in Clang would better be represented as marking the arch/arm/KConfig option for CONFIG_FUNCTION_TRACER for dependent on a version of Clang greater than or equal to Clang 10, not conditionally adding this flag. (We should always add the flag when supported, IMO. __gnu_mcount_nc's calling convention being broken is orthogonal to the choice of __gnu_mcount_nc vs mcount, and it's the former's that should be checked, not the latter as in this patch. > # Accept old syntax despite ".syntax unified" > AFLAGS_NOWARN :=$(call > as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W) > > -- > 2.23.0 > -- Thanks, ~Nick Desaulniers
Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
On Wed, Aug 28, 2019 at 11:26:35PM -0700, Nathan Chancellor wrote: > Currently, multi_v7_defconfig + CONFIG_FUNCTION_TRACER fails to build > with clang: > > arm-linux-gnueabi-ld: kernel/softirq.o: in function `_local_bh_enable': > softirq.c:(.text+0x504): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `__local_bh_enable_ip': > softirq.c:(.text+0x58c): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `do_softirq': > softirq.c:(.text+0x6c8): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_enter': > softirq.c:(.text+0x75c): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_exit': > softirq.c:(.text+0x840): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o:softirq.c:(.text+0xa50): more > undefined references to `mcount' follow > > clang can emit a working mcount symbol, __gnu_mcount_nc, when > '-meabi gnu' is passed to it. Until r369147 in LLVM, this was > broken and caused the kernel not to boot because the calling > convention was not correct. Now that it is fixed, add this to > the command line when clang is 10.0.0 or newer so everything > works properly. > > Link: https://github.com/ClangBuiltLinux/linux/issues/35 > Link: https://bugs.llvm.org/show_bug.cgi?id=33845 > Link: > https://github.com/llvm/llvm-project/commit/16fa8b09702378bacfa3d07081afe6b353b99e60 > Signed-off-by: Nathan Chancellor > --- > arch/arm/Makefile | 6 ++ > 1 file changed, 6 insertions(+) > > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > index c3624ca6c0bc..7b5a26a866fc 100644 > --- a/arch/arm/Makefile > +++ b/arch/arm/Makefile > @@ -112,6 +112,12 @@ ifeq ($(CONFIG_ARM_UNWIND),y) > CFLAGS_ABI +=-funwind-tables > endif > > +ifeq ($(CONFIG_CC_IS_CLANG),y) > +ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 10; echo $$?),0) > +CFLAGS_ABI +=-meabi gnu > +endif > +endif Is this also correct/needed when CONFIG_AEABI is not set?
Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
On 2019-08-29 08:26, Nathan Chancellor wrote: > Currently, multi_v7_defconfig + CONFIG_FUNCTION_TRACER fails to build > with clang: > > arm-linux-gnueabi-ld: kernel/softirq.o: in function `_local_bh_enable': > softirq.c:(.text+0x504): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `__local_bh_enable_ip': > softirq.c:(.text+0x58c): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `do_softirq': > softirq.c:(.text+0x6c8): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_enter': > softirq.c:(.text+0x75c): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_exit': > softirq.c:(.text+0x840): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o:softirq.c:(.text+0xa50): more > undefined references to `mcount' follow > > clang can emit a working mcount symbol, __gnu_mcount_nc, when > '-meabi gnu' is passed to it. Until r369147 in LLVM, this was > broken and caused the kernel not to boot because the calling > convention was not correct. Now that it is fixed, add this to > the command line when clang is 10.0.0 or newer so everything > works properly. Cool, finally function tracing with Clang :-) > > Link: https://github.com/ClangBuiltLinux/linux/issues/35 > Link: https://bugs.llvm.org/show_bug.cgi?id=33845 > Link: > https://github.com/llvm/llvm-project/commit/16fa8b09702378bacfa3d07081afe6b353b99e60 > Signed-off-by: Nathan Chancellor Reviewed-by: Stefan Agner -- Stefan > --- > arch/arm/Makefile | 6 ++ > 1 file changed, 6 insertions(+) > > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > index c3624ca6c0bc..7b5a26a866fc 100644 > --- a/arch/arm/Makefile > +++ b/arch/arm/Makefile > @@ -112,6 +112,12 @@ ifeq ($(CONFIG_ARM_UNWIND),y) > CFLAGS_ABI +=-funwind-tables > endif > > +ifeq ($(CONFIG_CC_IS_CLANG),y) > +ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 10; echo $$?),0) > +CFLAGS_ABI +=-meabi gnu > +endif > +endif > + > # Accept old syntax despite ".syntax unified" > AFLAGS_NOWARN:=$(call > as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)
