* [PATCH v4 1/3] powerpc: Don't add -mabi= flags when building with Clang
2019-10-14 2:50 ` [PATCH v4 0/3] LLVM/Clang fixes for pseries_defconfig Nathan Chancellor
@ 2019-10-14 2:50 ` Nathan Chancellor
2019-10-14 2:51 ` [PATCH v4 2/3] powerpc: Avoid clang warnings around setjmp and longjmp Nathan Chancellor
` (3 subsequent siblings)
4 siblings, 0 replies; 29+ messages in thread
From: Nathan Chancellor @ 2019-10-14 2:50 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: Nick Desaulniers, linux-kernel, clang-built-linux,
Nathan Chancellor, linuxppc-dev, Daniel Axtens
When building pseries_defconfig, building vdso32 errors out:
error: unknown target ABI 'elfv1'
This happens because -m32 in clang changes the target to 32-bit,
which does not allow the ABI to be changed, as the setABI virtual
function is not overridden:
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/include/clang/Basic/TargetInfo.h#L1073-L1078
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/lib/Basic/Targets/PPC.h#L327-L365
Commit 4dc831aa8813 ("powerpc: Fix compiling a BE kernel with a
powerpc64le toolchain") added these flags to fix building big endian
kernels with a little endian GCC.
Clang doesn't need -mabi because the target triple controls the default
value. -mlittle-endian and -mbig-endian manipulate the triple into
either powerpc64-* or powerpc64le-*, which properly sets the default
ABI:
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/lib/Driver/Driver.cpp#L450-L463
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/llvm/lib/Support/Triple.cpp#L1432-L1516
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/lib/Basic/Targets/PPC.h#L377-L383
Adding a debug print out in the PPC64TargetInfo constructor after line
383 above shows this:
$ echo | ./clang -E --target=powerpc64-linux -mbig-endian -o /dev/null -
Default ABI: elfv1
$ echo | ./clang -E --target=powerpc64-linux -mlittle-endian -o /dev/null -
Default ABI: elfv2
$ echo | ./clang -E --target=powerpc64le-linux -mbig-endian -o /dev/null -
Default ABI: elfv1
$ echo | ./clang -E --target=powerpc64le-linux -mlittle-endian -o /dev/null -
Default ABI: elfv2
Don't specify -mabi when building with clang to avoid the build error
with -m32 and not change any code generation.
-mcall-aixdesc is not an implemented flag in clang so it can be
safely excluded as well, see commit 238abecde8ad ("powerpc: Don't
use gcc specific options on clang").
pseries_defconfig successfully builds after this patch and
powernv_defconfig and ppc44x_defconfig don't regress.
Link: https://github.com/ClangBuiltLinux/linux/issues/240
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
v1 -> v2:
* Improve commit message
v2 -> v3:
* Rebase and merge into a single series.
v3 -> v4:
* Rebase on v5.4-rc3.
* Update links to point to llvmorg-9.0.0 instead of llvmorg-9.0.0-rc2.
arch/powerpc/Makefile | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 83522c9fc7b6..37ac731a556b 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -91,11 +91,13 @@ MULTIPLEWORD := -mmultiple
endif
ifdef CONFIG_PPC64
+ifndef CONFIG_CC_IS_CLANG
cflags-$(CONFIG_CPU_BIG_ENDIAN) += $(call cc-option,-mabi=elfv1)
cflags-$(CONFIG_CPU_BIG_ENDIAN) += $(call cc-option,-mcall-aixdesc)
aflags-$(CONFIG_CPU_BIG_ENDIAN) += $(call cc-option,-mabi=elfv1)
aflags-$(CONFIG_CPU_LITTLE_ENDIAN) += -mabi=elfv2
endif
+endif
ifndef CONFIG_CC_IS_CLANG
cflags-$(CONFIG_CPU_LITTLE_ENDIAN) += -mno-strict-align
@@ -141,6 +143,7 @@ endif
endif
CFLAGS-$(CONFIG_PPC64) := $(call cc-option,-mtraceback=no)
+ifndef CONFIG_CC_IS_CLANG
ifdef CONFIG_CPU_LITTLE_ENDIAN
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv2,$(call cc-option,-mcall-aixdesc))
AFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv2)
@@ -149,6 +152,7 @@ CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv1)
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mcall-aixdesc)
AFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv1)
endif
+endif
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mcmodel=medium,$(call cc-option,-mminimal-toc))
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mno-pointers-to-nested-functions)
--
2.23.0
^ permalink raw reply related [flat|nested] 29+ messages in thread* [PATCH v4 2/3] powerpc: Avoid clang warnings around setjmp and longjmp
2019-10-14 2:50 ` [PATCH v4 0/3] LLVM/Clang fixes for pseries_defconfig Nathan Chancellor
2019-10-14 2:50 ` [PATCH v4 1/3] powerpc: Don't add -mabi= flags when building with Clang Nathan Chancellor
@ 2019-10-14 2:51 ` Nathan Chancellor
2019-10-14 2:51 ` [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp Nathan Chancellor
` (2 subsequent siblings)
4 siblings, 0 replies; 29+ messages in thread
From: Nathan Chancellor @ 2019-10-14 2:51 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: Nick Desaulniers, linux-kernel, stable, clang-built-linux,
Nathan Chancellor, linuxppc-dev
Commit aea447141c7e ("powerpc: Disable -Wbuiltin-requires-header when
setjmp is used") disabled -Wbuiltin-requires-header because of a warning
about the setjmp and longjmp declarations.
r367387 in clang added another diagnostic around this, complaining that
there is no jmp_buf declaration.
In file included from ../arch/powerpc/xmon/xmon.c:47:
../arch/powerpc/include/asm/setjmp.h:10:13: error: declaration of
built-in function 'setjmp' requires the declaration of the 'jmp_buf'
type, commonly provided in the header <setjmp.h>.
[-Werror,-Wincomplete-setjmp-declaration]
extern long setjmp(long *);
^
../arch/powerpc/include/asm/setjmp.h:11:13: error: declaration of
built-in function 'longjmp' requires the declaration of the 'jmp_buf'
type, commonly provided in the header <setjmp.h>.
[-Werror,-Wincomplete-setjmp-declaration]
extern void longjmp(long *, long);
^
2 errors generated.
We are not using the standard library's longjmp/setjmp implementations
for obvious reasons; make this clear to clang by using -ffreestanding
on these files.
Cc: stable@vger.kernel.org # 4.14+
Link: https://github.com/ClangBuiltLinux/linux/issues/625
Link: https://github.com/llvm/llvm-project/commit/3be25e79477db2d31ac46493d97eca8c20592b07
Link: https://godbolt.org/z/B2oQnl
Suggested-by: Segher Boessenkool <segher@kernel.crashing.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
v1 -> v3 (I skipped v2 because the first patch in the series already
had a v2):
* Use -ffreestanding instead of outright disabling the warning because
it is legitimate.
v3 -> v4:
* Rebase on v5.4-rc3
* Add Nick's reviewed-by and Compiler Explorer link.
arch/powerpc/kernel/Makefile | 4 ++--
arch/powerpc/xmon/Makefile | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index a7ca8fe62368..f1f362146135 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -5,8 +5,8 @@
CFLAGS_ptrace.o += -DUTS_MACHINE='"$(UTS_MACHINE)"'
-# Disable clang warning for using setjmp without setjmp.h header
-CFLAGS_crash.o += $(call cc-disable-warning, builtin-requires-header)
+# Avoid clang warnings around longjmp/setjmp declarations
+CFLAGS_crash.o += -ffreestanding
ifdef CONFIG_PPC64
CFLAGS_prom_init.o += $(NO_MINIMAL_TOC)
diff --git a/arch/powerpc/xmon/Makefile b/arch/powerpc/xmon/Makefile
index f142570ad860..c3842dbeb1b7 100644
--- a/arch/powerpc/xmon/Makefile
+++ b/arch/powerpc/xmon/Makefile
@@ -1,8 +1,8 @@
# SPDX-License-Identifier: GPL-2.0
# Makefile for xmon
-# Disable clang warning for using setjmp without setjmp.h header
-subdir-ccflags-y := $(call cc-disable-warning, builtin-requires-header)
+# Avoid clang warnings around longjmp/setjmp declarations
+subdir-ccflags-y := -ffreestanding
GCOV_PROFILE := n
KCOV_INSTRUMENT := n
--
2.23.0
^ permalink raw reply related [flat|nested] 29+ messages in thread* [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
2019-10-14 2:50 ` [PATCH v4 0/3] LLVM/Clang fixes for pseries_defconfig Nathan Chancellor
2019-10-14 2:50 ` [PATCH v4 1/3] powerpc: Don't add -mabi= flags when building with Clang Nathan Chancellor
2019-10-14 2:51 ` [PATCH v4 2/3] powerpc: Avoid clang warnings around setjmp and longjmp Nathan Chancellor
@ 2019-10-14 2:51 ` Nathan Chancellor
2019-10-14 9:35 ` Segher Boessenkool
2019-10-14 16:03 ` [PATCH v4 0/3] LLVM/Clang fixes for pseries_defconfig Nick Desaulniers
2019-11-19 4:57 ` [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs Nathan Chancellor
4 siblings, 1 reply; 29+ messages in thread
From: Nathan Chancellor @ 2019-10-14 2:51 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: clang-built-linux, Nathan Chancellor, Nick Desaulniers,
linuxppc-dev, linux-kernel
r374662 gives LLVM the ability to convert certain loops into a reference
to bcmp as an optimization; this breaks prom_init_check.sh:
CALL arch/powerpc/kernel/prom_init_check.sh
Error: External symbol 'bcmp' referenced from prom_init.c
make[2]: *** [arch/powerpc/kernel/Makefile:196: prom_init_check] Error 1
bcmp is defined in lib/string.c as a wrapper for memcmp so this could be
added to the whitelist. However, commit 450e7dd4001f ("powerpc/prom_init:
don't use string functions from lib/") copied memcmp as prom_memcmp to
avoid KASAN instrumentation so having bcmp be resolved to regular memcmp
would break that assumption. Furthermore, because the compiler is the
one that inserted bcmp, we cannot provide something like prom_bcmp.
To prevent LLVM from being clever with optimizations like this, use
-ffreestanding to tell LLVM we are not hosted so it is not free to make
transformations like this.
Link: https://github.com/ClangBuiltLinux/linux/issues/647
Link: https://github.com/llvm/llvm-project/commit/76cdcf25b883751d83402baea6316772aa73865c
Reviewed-by: Nick Desaulneris <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
v1 -> v3:
* New patch in the series
v3 -> v4:
* Rebase on v5.4-rc3.
* Add Nick's reviewed-by tag.
* Update the LLVM commit reference to the latest applied version (r374662)
as it was originally committed as r370454, reverted in r370788, and
reapplied as r374662.
arch/powerpc/kernel/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index f1f362146135..7f0ee465dfb6 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -21,7 +21,7 @@ CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
-CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
+CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector) -ffreestanding
ifdef CONFIG_FUNCTION_TRACER
# Do not trace early boot code
--
2.23.0
^ permalink raw reply related [flat|nested] 29+ messages in thread* Re: [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
2019-10-14 2:51 ` [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp Nathan Chancellor
@ 2019-10-14 9:35 ` Segher Boessenkool
2019-10-14 15:56 ` Nick Desaulniers
0 siblings, 1 reply; 29+ messages in thread
From: Segher Boessenkool @ 2019-10-14 9:35 UTC (permalink / raw)
To: Nathan Chancellor
Cc: Nick Desaulniers, linux-kernel, clang-built-linux,
Paul Mackerras, linuxppc-dev
On Sun, Oct 13, 2019 at 07:51:01PM -0700, Nathan Chancellor wrote:
> r374662 gives LLVM the ability to convert certain loops into a reference
> to bcmp as an optimization; this breaks prom_init_check.sh:
When/why does LLVM think this is okay? This function has been removed
from POSIX over a decade ago (and before that it always was marked as
legacy).
Segher
^ permalink raw reply [flat|nested] 29+ messages in thread
* Re: [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
2019-10-14 9:35 ` Segher Boessenkool
@ 2019-10-14 15:56 ` Nick Desaulniers
2019-10-14 19:11 ` Segher Boessenkool
0 siblings, 1 reply; 29+ messages in thread
From: Nick Desaulniers @ 2019-10-14 15:56 UTC (permalink / raw)
To: Segher Boessenkool
Cc: LKML, clang-built-linux, Paul Mackerras, Nathan Chancellor, linuxppc-dev
On Mon, Oct 14, 2019 at 2:35 AM Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> On Sun, Oct 13, 2019 at 07:51:01PM -0700, Nathan Chancellor wrote:
> > r374662 gives LLVM the ability to convert certain loops into a reference
> > to bcmp as an optimization; this breaks prom_init_check.sh:
>
> When/why does LLVM think this is okay? This function has been removed
> from POSIX over a decade ago (and before that it always was marked as
> legacy).
Segher, do you have links for any of the above? If so, that would be
helpful to me. I'm arguing against certain transforms that assume that
one library function is faster than another, when such claims are
based on measurements from one stdlib implementation. (There's others
in the pipeline I'm not too thrilled about, too).
The rationale for why it was added was that memcmp takes a measurable
amount of time in Google's fleet, and most calls to memcmp don't care
about the position of the mismatch; bcmp is lower overhead (or at
least for our libc implementation, not sure about others).
--
Thanks,
~Nick Desaulniers
^ permalink raw reply [flat|nested] 29+ messages in thread
* Re: [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
2019-10-14 15:56 ` Nick Desaulniers
@ 2019-10-14 19:11 ` Segher Boessenkool
2019-10-18 19:00 ` Nathan Chancellor
0 siblings, 1 reply; 29+ messages in thread
From: Segher Boessenkool @ 2019-10-14 19:11 UTC (permalink / raw)
To: Nick Desaulniers
Cc: LKML, clang-built-linux, Paul Mackerras, Nathan Chancellor, linuxppc-dev
On Mon, Oct 14, 2019 at 08:56:12AM -0700, Nick Desaulniers wrote:
> On Mon, Oct 14, 2019 at 2:35 AM Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
> >
> > On Sun, Oct 13, 2019 at 07:51:01PM -0700, Nathan Chancellor wrote:
> > > r374662 gives LLVM the ability to convert certain loops into a reference
> > > to bcmp as an optimization; this breaks prom_init_check.sh:
> >
> > When/why does LLVM think this is okay? This function has been removed
> > from POSIX over a decade ago (and before that it always was marked as
> > legacy).
>
> Segher, do you have links for any of the above? If so, that would be
> helpful to me.
Sure!
https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap03.html
Older versions are harder to find online, unfortunately. But there is
https://kernel.org/pub/linux/docs/man-pages/man-pages-posix/
in which man3p/bcmp.3p says:
FUTURE DIRECTIONS
This function may be withdrawn in a future version.
Finally, the Linux man pages say (man bcmp):
CONFORMING TO
4.3BSD. This function is deprecated (marked as LEGACY in
POSIX.1-2001): use memcmp(3) in new programs. POSIX.1-2008 removes the
specification of bcmp().
> I'm arguing against certain transforms that assume that
> one library function is faster than another, when such claims are
> based on measurements from one stdlib implementation.
Wow. The difference between memcmp and bcmp is trivial (just the return
value is different, and that costs hardly anything to add). And memcmp
is guaranteed to exist since C89/C90 at least.
> The rationale for why it was added was that memcmp takes a measurable
> amount of time in Google's fleet, and most calls to memcmp don't care
> about the position of the mismatch; bcmp is lower overhead (or at
> least for our libc implementation, not sure about others).
You just have to do the read of the last words you compare as big-endian,
and then you can just subtract the two words, convert that to "int" (which
is very inconvenient to do, but hardly expensive), and there you go.
Or on x86 use the bswap insn, or something like it.
Or, if you use GCC, it has __builtin_memcmp but also __builtin_memcmp_eq,
and those are automatically used, too.
Segher
^ permalink raw reply [flat|nested] 29+ messages in thread* Re: [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
2019-10-14 19:11 ` Segher Boessenkool
@ 2019-10-18 19:00 ` Nathan Chancellor
2019-10-18 20:02 ` Segher Boessenkool
0 siblings, 1 reply; 29+ messages in thread
From: Nathan Chancellor @ 2019-10-18 19:00 UTC (permalink / raw)
To: Segher Boessenkool
Cc: Nick Desaulniers, LKML, clang-built-linux, Paul Mackerras, linuxppc-dev
On Mon, Oct 14, 2019 at 02:11:41PM -0500, Segher Boessenkool wrote:
> On Mon, Oct 14, 2019 at 08:56:12AM -0700, Nick Desaulniers wrote:
> > On Mon, Oct 14, 2019 at 2:35 AM Segher Boessenkool
> > <segher@kernel.crashing.org> wrote:
> > >
> > > On Sun, Oct 13, 2019 at 07:51:01PM -0700, Nathan Chancellor wrote:
> > > > r374662 gives LLVM the ability to convert certain loops into a reference
> > > > to bcmp as an optimization; this breaks prom_init_check.sh:
> > >
> > > When/why does LLVM think this is okay? This function has been removed
> > > from POSIX over a decade ago (and before that it always was marked as
> > > legacy).
> >
> > Segher, do you have links for any of the above? If so, that would be
> > helpful to me.
>
> Sure!
>
> https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap03.html
>
> Older versions are harder to find online, unfortunately. But there is
>
> https://kernel.org/pub/linux/docs/man-pages/man-pages-posix/
>
> in which man3p/bcmp.3p says:
>
> FUTURE DIRECTIONS
> This function may be withdrawn in a future version.
>
> Finally, the Linux man pages say (man bcmp):
>
> CONFORMING TO
> 4.3BSD. This function is deprecated (marked as LEGACY in
> POSIX.1-2001): use memcmp(3) in new programs. POSIX.1-2008 removes the
> specification of bcmp().
>
>
> > I'm arguing against certain transforms that assume that
> > one library function is faster than another, when such claims are
> > based on measurements from one stdlib implementation.
>
> Wow. The difference between memcmp and bcmp is trivial (just the return
> value is different, and that costs hardly anything to add). And memcmp
> is guaranteed to exist since C89/C90 at least.
>
> > The rationale for why it was added was that memcmp takes a measurable
> > amount of time in Google's fleet, and most calls to memcmp don't care
> > about the position of the mismatch; bcmp is lower overhead (or at
> > least for our libc implementation, not sure about others).
>
> You just have to do the read of the last words you compare as big-endian,
> and then you can just subtract the two words, convert that to "int" (which
> is very inconvenient to do, but hardly expensive), and there you go.
>
> Or on x86 use the bswap insn, or something like it.
>
> Or, if you use GCC, it has __builtin_memcmp but also __builtin_memcmp_eq,
> and those are automatically used, too.
>
>
> Segher
Just as an FYI, there was some more discussion around the availablity
and use of bcmp in this LLVM bug which spawned
commit 5f074f3e192f ("lib/string.c: implement a basic bcmp").
https://bugs.llvm.org/show_bug.cgi?id=41035#c13
I believe this is the proper solution but I am fine with whatever works,
I just want our CI to be green without any out of tree patches again...
Cheers,
Nathan
^ permalink raw reply [flat|nested] 29+ messages in thread* Re: [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
2019-10-18 19:00 ` Nathan Chancellor
@ 2019-10-18 20:02 ` Segher Boessenkool
2019-10-22 5:15 ` Nathan Chancellor
0 siblings, 1 reply; 29+ messages in thread
From: Segher Boessenkool @ 2019-10-18 20:02 UTC (permalink / raw)
To: Nathan Chancellor
Cc: Nick Desaulniers, LKML, clang-built-linux, Paul Mackerras, linuxppc-dev
On Fri, Oct 18, 2019 at 12:00:22PM -0700, Nathan Chancellor wrote:
> Just as an FYI, there was some more discussion around the availablity
> and use of bcmp in this LLVM bug which spawned
> commit 5f074f3e192f ("lib/string.c: implement a basic bcmp").
>
> https://bugs.llvm.org/show_bug.cgi?id=41035#c13
>
> I believe this is the proper solution but I am fine with whatever works,
> I just want our CI to be green without any out of tree patches again...
I think the proper solution is for the kernel to *do* use -ffreestanding,
and then somehow tell the kernel that memcpy etc. are the standard
functions. A freestanding GCC already requires memcpy, memmove, memset,
memcmp, and sometimes abort to exist and do the standard thing; why cannot
programs then also rely on it to be the standard functions.
What exact functions are the reason the kernel does not use -ffreestanding?
Is it just memcpy? Is more wanted?
Segher
^ permalink raw reply [flat|nested] 29+ messages in thread* Re: [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
2019-10-18 20:02 ` Segher Boessenkool
@ 2019-10-22 5:15 ` Nathan Chancellor
2019-10-22 8:57 ` Segher Boessenkool
0 siblings, 1 reply; 29+ messages in thread
From: Nathan Chancellor @ 2019-10-22 5:15 UTC (permalink / raw)
To: Segher Boessenkool
Cc: Nick Desaulniers, LKML, clang-built-linux, Paul Mackerras, linuxppc-dev
On Fri, Oct 18, 2019 at 03:02:10PM -0500, Segher Boessenkool wrote:
> On Fri, Oct 18, 2019 at 12:00:22PM -0700, Nathan Chancellor wrote:
> > Just as an FYI, there was some more discussion around the availablity
> > and use of bcmp in this LLVM bug which spawned
> > commit 5f074f3e192f ("lib/string.c: implement a basic bcmp").
> >
> > https://bugs.llvm.org/show_bug.cgi?id=41035#c13
> >
> > I believe this is the proper solution but I am fine with whatever works,
> > I just want our CI to be green without any out of tree patches again...
>
> I think the proper solution is for the kernel to *do* use -ffreestanding,
> and then somehow tell the kernel that memcpy etc. are the standard
> functions. A freestanding GCC already requires memcpy, memmove, memset,
> memcmp, and sometimes abort to exist and do the standard thing; why cannot
> programs then also rely on it to be the standard functions.
>
> What exact functions are the reason the kernel does not use -ffreestanding?
> Is it just memcpy? Is more wanted?
>
>
> Segher
I think Linus summarized it pretty well here:
https://lore.kernel.org/lkml/CAHk-=wi-epJZfBHDbKKDZ64us7WkF=LpUfhvYBmZSteO8Q0RAg@mail.gmail.com/
Cheers,
Nathan
^ permalink raw reply [flat|nested] 29+ messages in thread* Re: [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
2019-10-22 5:15 ` Nathan Chancellor
@ 2019-10-22 8:57 ` Segher Boessenkool
2019-10-30 4:12 ` Nathan Chancellor
0 siblings, 1 reply; 29+ messages in thread
From: Segher Boessenkool @ 2019-10-22 8:57 UTC (permalink / raw)
To: Nathan Chancellor
Cc: Nick Desaulniers, LKML, clang-built-linux, Paul Mackerras, linuxppc-dev
On Mon, Oct 21, 2019 at 10:15:29PM -0700, Nathan Chancellor wrote:
> On Fri, Oct 18, 2019 at 03:02:10PM -0500, Segher Boessenkool wrote:
> > I think the proper solution is for the kernel to *do* use -ffreestanding,
> > and then somehow tell the kernel that memcpy etc. are the standard
> > functions. A freestanding GCC already requires memcpy, memmove, memset,
> > memcmp, and sometimes abort to exist and do the standard thing; why cannot
> > programs then also rely on it to be the standard functions.
> >
> > What exact functions are the reason the kernel does not use -ffreestanding?
> > Is it just memcpy? Is more wanted?
>
> I think Linus summarized it pretty well here:
>
> https://lore.kernel.org/lkml/CAHk-=wi-epJZfBHDbKKDZ64us7WkF=LpUfhvYBmZSteO8Q0RAg@mail.gmail.com/
GCC recognises __builtin_memcpy (or any other __builtin) just fine even
with -ffreestanding.
So the kernel wants a warning (or error) whenever a call to one of these
library functions is generated by the compiler without the user asking
for it directly (via a __builtin)? And that is all that is needed for
the kernel to use -ffreestanding?
That shouldn't be hard. Anything missing here?
Segher
^ permalink raw reply [flat|nested] 29+ messages in thread
* Re: [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
2019-10-22 8:57 ` Segher Boessenkool
@ 2019-10-30 4:12 ` Nathan Chancellor
0 siblings, 0 replies; 29+ messages in thread
From: Nathan Chancellor @ 2019-10-30 4:12 UTC (permalink / raw)
To: Segher Boessenkool
Cc: Nick Desaulniers, LKML, clang-built-linux, Paul Mackerras, linuxppc-dev
On Tue, Oct 22, 2019 at 03:57:09AM -0500, Segher Boessenkool wrote:
> On Mon, Oct 21, 2019 at 10:15:29PM -0700, Nathan Chancellor wrote:
> > On Fri, Oct 18, 2019 at 03:02:10PM -0500, Segher Boessenkool wrote:
> > > I think the proper solution is for the kernel to *do* use -ffreestanding,
> > > and then somehow tell the kernel that memcpy etc. are the standard
> > > functions. A freestanding GCC already requires memcpy, memmove, memset,
> > > memcmp, and sometimes abort to exist and do the standard thing; why cannot
> > > programs then also rely on it to be the standard functions.
> > >
> > > What exact functions are the reason the kernel does not use -ffreestanding?
> > > Is it just memcpy? Is more wanted?
> >
> > I think Linus summarized it pretty well here:
> >
> > https://lore.kernel.org/lkml/CAHk-=wi-epJZfBHDbKKDZ64us7WkF=LpUfhvYBmZSteO8Q0RAg@mail.gmail.com/
>
> GCC recognises __builtin_memcpy (or any other __builtin) just fine even
> with -ffreestanding.
>
> So the kernel wants a warning (or error) whenever a call to one of these
> library functions is generated by the compiler without the user asking
> for it directly (via a __builtin)? And that is all that is needed for
> the kernel to use -ffreestanding?
>
> That shouldn't be hard. Anything missing here?
>
>
> Segher
Yes, I suppose that would be good enough.
I don't know if there are any other optimizations that are missed out on
by using -ffreestanding. It would probably be worth asking other kernel
developers on a separate thread (or the one I linked above).
Would be nice to get this shored up soon since our PowerPC builds have
been broken since the beginning of August :/
Cheers,
Nathan
^ permalink raw reply [flat|nested] 29+ messages in thread
* Re: [PATCH v4 0/3] LLVM/Clang fixes for pseries_defconfig
2019-10-14 2:50 ` [PATCH v4 0/3] LLVM/Clang fixes for pseries_defconfig Nathan Chancellor
` (2 preceding siblings ...)
2019-10-14 2:51 ` [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp Nathan Chancellor
@ 2019-10-14 16:03 ` Nick Desaulniers
2019-11-19 4:57 ` [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs Nathan Chancellor
4 siblings, 0 replies; 29+ messages in thread
From: Nick Desaulniers @ 2019-10-14 16:03 UTC (permalink / raw)
To: Michael Ellerman
Cc: LKML, clang-built-linux, Paul Mackerras, Nathan Chancellor, linuxppc-dev
On Sun, Oct 13, 2019 at 7:51 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> Hi all,
>
> This series includes a set of fixes for LLVM/Clang when building
> pseries_defconfig. These have been floating around as standalone
> patches so I decided to gather them up as a series so it was easier
> to review/apply them.
>
> This has been broken for a bit now, it would be nice to get these
> reviewed and applied. Please let me know if I need to do anything
> to move these along.
+1, we've been carrying these out of tree for some time now, with this
series merged, we can get back to 0 out of tree patches.
>
> Previous versions:
>
> https://lore.kernel.org/lkml/20190911182049.77853-1-natechancellor@gmail.com/
>
> Cheers,
> Nathan
>
>
--
Thanks,
~Nick Desaulniers
^ permalink raw reply [flat|nested] 29+ messages in thread* [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs
2019-10-14 2:50 ` [PATCH v4 0/3] LLVM/Clang fixes for pseries_defconfig Nathan Chancellor
` (3 preceding siblings ...)
2019-10-14 16:03 ` [PATCH v4 0/3] LLVM/Clang fixes for pseries_defconfig Nick Desaulniers
@ 2019-11-19 4:57 ` Nathan Chancellor
2019-11-19 4:57 ` [PATCH v5 1/3] powerpc: Don't add -mabi= flags when building with Clang Nathan Chancellor
` (3 more replies)
4 siblings, 4 replies; 29+ messages in thread
From: Nathan Chancellor @ 2019-11-19 4:57 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: clang-built-linux, Nick Desaulniers, linuxppc-dev, linux-kernel
Hi all,
This series includes a set of fixes for LLVM/Clang when building
a few defconfigs (powernv, ppc44x, and pseries are the ones that our
CI configuration tests [1]). The first patch fixes pseries_defconfig,
which has never worked in mainline. The second and third patches fixes
issues with all of these configs due to internal changes to LLVM, which
point out issues with the kernel.
These have been broken since July/August, it would be nice to get these
reviewed and applied. Please let me know what I can do to get these
applied soon so we can stop applying them out of tree.
[1]: https://github.com/ClangBuiltLinux/continuous-integration
Previous versions:
v3: https://lore.kernel.org/lkml/20190911182049.77853-1-natechancellor@gmail.com/
v4: https://lore.kernel.org/lkml/20191014025101.18567-1-natechancellor@gmail.com/
Cheers,
Nathan
^ permalink raw reply [flat|nested] 29+ messages in thread* [PATCH v5 1/3] powerpc: Don't add -mabi= flags when building with Clang
2019-11-19 4:57 ` [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs Nathan Chancellor
@ 2019-11-19 4:57 ` Nathan Chancellor
2019-11-26 1:13 ` Michael Ellerman
2019-11-19 4:57 ` [PATCH v5 2/3] powerpc: Avoid clang warnings around setjmp and longjmp Nathan Chancellor
` (2 subsequent siblings)
3 siblings, 1 reply; 29+ messages in thread
From: Nathan Chancellor @ 2019-11-19 4:57 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: Nick Desaulniers, linux-kernel, clang-built-linux,
Nathan Chancellor, linuxppc-dev, Daniel Axtens
When building pseries_defconfig, building vdso32 errors out:
error: unknown target ABI 'elfv1'
This happens because -m32 in clang changes the target to 32-bit,
which does not allow the ABI to be changed, as the setABI virtual
function is not overridden:
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/include/clang/Basic/TargetInfo.h#L1073-L1078
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/lib/Basic/Targets/PPC.h#L327-L365
Commit 4dc831aa8813 ("powerpc: Fix compiling a BE kernel with a
powerpc64le toolchain") added these flags to fix building big endian
kernels with a little endian GCC.
Clang doesn't need -mabi because the target triple controls the default
value. -mlittle-endian and -mbig-endian manipulate the triple into
either powerpc64-* or powerpc64le-*, which properly sets the default
ABI:
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/lib/Driver/Driver.cpp#L450-L463
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/llvm/lib/Support/Triple.cpp#L1432-L1516
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/lib/Basic/Targets/PPC.h#L377-L383
Adding a debug print out in the PPC64TargetInfo constructor after line
383 above shows this:
$ echo | ./clang -E --target=powerpc64-linux -mbig-endian -o /dev/null -
Default ABI: elfv1
$ echo | ./clang -E --target=powerpc64-linux -mlittle-endian -o /dev/null -
Default ABI: elfv2
$ echo | ./clang -E --target=powerpc64le-linux -mbig-endian -o /dev/null -
Default ABI: elfv1
$ echo | ./clang -E --target=powerpc64le-linux -mlittle-endian -o /dev/null -
Default ABI: elfv2
Don't specify -mabi when building with clang to avoid the build error
with -m32 and not change any code generation.
-mcall-aixdesc is not an implemented flag in clang so it can be
safely excluded as well, see commit 238abecde8ad ("powerpc: Don't
use gcc specific options on clang").
pseries_defconfig successfully builds after this patch and
powernv_defconfig and ppc44x_defconfig don't regress.
Link: https://github.com/ClangBuiltLinux/linux/issues/240
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
v1 -> v2:
* Improve commit message
v2 -> v3:
* Rebase and merge into a single series.
v3 -> v4:
* Rebase on v5.4-rc3.
* Update links to point to llvmorg-9.0.0 instead of llvmorg-9.0.0-rc2.
v4 -> v5:
* Rebase on next-20191118
arch/powerpc/Makefile | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index a3ed4f168607..f35730548e42 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -91,11 +91,13 @@ MULTIPLEWORD := -mmultiple
endif
ifdef CONFIG_PPC64
+ifndef CONFIG_CC_IS_CLANG
cflags-$(CONFIG_CPU_BIG_ENDIAN) += $(call cc-option,-mabi=elfv1)
cflags-$(CONFIG_CPU_BIG_ENDIAN) += $(call cc-option,-mcall-aixdesc)
aflags-$(CONFIG_CPU_BIG_ENDIAN) += $(call cc-option,-mabi=elfv1)
aflags-$(CONFIG_CPU_LITTLE_ENDIAN) += -mabi=elfv2
endif
+endif
ifndef CONFIG_CC_IS_CLANG
cflags-$(CONFIG_CPU_LITTLE_ENDIAN) += -mno-strict-align
@@ -141,6 +143,7 @@ endif
endif
CFLAGS-$(CONFIG_PPC64) := $(call cc-option,-mtraceback=no)
+ifndef CONFIG_CC_IS_CLANG
ifdef CONFIG_CPU_LITTLE_ENDIAN
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv2,$(call cc-option,-mcall-aixdesc))
AFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv2)
@@ -149,6 +152,7 @@ CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv1)
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mcall-aixdesc)
AFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv1)
endif
+endif
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mcmodel=medium,$(call cc-option,-mminimal-toc))
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mno-pointers-to-nested-functions)
--
2.24.0
^ permalink raw reply related [flat|nested] 29+ messages in thread* Re: [PATCH v5 1/3] powerpc: Don't add -mabi= flags when building with Clang
2019-11-19 4:57 ` [PATCH v5 1/3] powerpc: Don't add -mabi= flags when building with Clang Nathan Chancellor
@ 2019-11-26 1:13 ` Michael Ellerman
0 siblings, 0 replies; 29+ messages in thread
From: Michael Ellerman @ 2019-11-26 1:13 UTC (permalink / raw)
To: Nathan Chancellor, Benjamin Herrenschmidt, Paul Mackerras
Cc: Nick Desaulniers, linux-kernel, clang-built-linux,
Nathan Chancellor, linuxppc-dev, Daniel Axtens
On Tue, 2019-11-19 at 04:57:10 UTC, Nathan Chancellor wrote:
> When building pseries_defconfig, building vdso32 errors out:
>
> error: unknown target ABI 'elfv1'
>
> This happens because -m32 in clang changes the target to 32-bit,
> which does not allow the ABI to be changed, as the setABI virtual
> function is not overridden:
>
> https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/include/clang/Basic/TargetInfo.h#L1073-L1078
>
> https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/lib/Basic/Targets/PPC.h#L327-L365
>
> Commit 4dc831aa8813 ("powerpc: Fix compiling a BE kernel with a
> powerpc64le toolchain") added these flags to fix building big endian
> kernels with a little endian GCC.
>
> Clang doesn't need -mabi because the target triple controls the default
> value. -mlittle-endian and -mbig-endian manipulate the triple into
> either powerpc64-* or powerpc64le-*, which properly sets the default
> ABI:
>
> https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/lib/Driver/Driver.cpp#L450-L463
>
> https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/llvm/lib/Support/Triple.cpp#L1432-L1516
>
> https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/clang/lib/Basic/Targets/PPC.h#L377-L383
>
> Adding a debug print out in the PPC64TargetInfo constructor after line
> 383 above shows this:
>
> $ echo | ./clang -E --target=powerpc64-linux -mbig-endian -o /dev/null -
> Default ABI: elfv1
>
> $ echo | ./clang -E --target=powerpc64-linux -mlittle-endian -o /dev/null -
> Default ABI: elfv2
>
> $ echo | ./clang -E --target=powerpc64le-linux -mbig-endian -o /dev/null -
> Default ABI: elfv1
>
> $ echo | ./clang -E --target=powerpc64le-linux -mlittle-endian -o /dev/null -
> Default ABI: elfv2
>
> Don't specify -mabi when building with clang to avoid the build error
> with -m32 and not change any code generation.
>
> -mcall-aixdesc is not an implemented flag in clang so it can be
> safely excluded as well, see commit 238abecde8ad ("powerpc: Don't
> use gcc specific options on clang").
>
> pseries_defconfig successfully builds after this patch and
> powernv_defconfig and ppc44x_defconfig don't regress.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/240
> Reviewed-by: Daniel Axtens <dja@axtens.net>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Series applied to powerpc next, thanks.
https://git.kernel.org/powerpc/c/465bfd9c44dea6b55962b5788a23ac87a467c923
cheers
^ permalink raw reply [flat|nested] 29+ messages in thread
* [PATCH v5 2/3] powerpc: Avoid clang warnings around setjmp and longjmp
2019-11-19 4:57 ` [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs Nathan Chancellor
2019-11-19 4:57 ` [PATCH v5 1/3] powerpc: Don't add -mabi= flags when building with Clang Nathan Chancellor
@ 2019-11-19 4:57 ` Nathan Chancellor
2019-11-19 4:57 ` [PATCH v5 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp Nathan Chancellor
2019-11-25 20:15 ` [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs Nick Desaulniers
3 siblings, 0 replies; 29+ messages in thread
From: Nathan Chancellor @ 2019-11-19 4:57 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: Nick Desaulniers, linux-kernel, stable, clang-built-linux,
Nathan Chancellor, linuxppc-dev
Commit aea447141c7e ("powerpc: Disable -Wbuiltin-requires-header when
setjmp is used") disabled -Wbuiltin-requires-header because of a warning
about the setjmp and longjmp declarations.
r367387 in clang added another diagnostic around this, complaining that
there is no jmp_buf declaration.
In file included from ../arch/powerpc/xmon/xmon.c:47:
../arch/powerpc/include/asm/setjmp.h:10:13: error: declaration of
built-in function 'setjmp' requires the declaration of the 'jmp_buf'
type, commonly provided in the header <setjmp.h>.
[-Werror,-Wincomplete-setjmp-declaration]
extern long setjmp(long *);
^
../arch/powerpc/include/asm/setjmp.h:11:13: error: declaration of
built-in function 'longjmp' requires the declaration of the 'jmp_buf'
type, commonly provided in the header <setjmp.h>.
[-Werror,-Wincomplete-setjmp-declaration]
extern void longjmp(long *, long);
^
2 errors generated.
We are not using the standard library's longjmp/setjmp implementations
for obvious reasons; make this clear to clang by using -ffreestanding
on these files.
Cc: stable@vger.kernel.org # 4.14+
Link: https://github.com/ClangBuiltLinux/linux/issues/625
Link: https://github.com/llvm/llvm-project/commit/3be25e79477db2d31ac46493d97eca8c20592b07
Link: https://godbolt.org/z/B2oQnl
Suggested-by: Segher Boessenkool <segher@kernel.crashing.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
v1 -> v3 (I skipped v2 because the first patch in the series already
had a v2):
* Use -ffreestanding instead of outright disabling the warning because
it is legitimate.
v3 -> v4:
* Rebase on v5.4-rc3
* Add Nick's reviewed-by and Compiler Explorer link.
v4 -> v5:
* Rebase on next-20191118
arch/powerpc/kernel/Makefile | 4 ++--
arch/powerpc/xmon/Makefile | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index bb57d168d6f4..3c113ae0de2b 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -5,8 +5,8 @@
CFLAGS_ptrace.o += -DUTS_MACHINE='"$(UTS_MACHINE)"'
-# Disable clang warning for using setjmp without setjmp.h header
-CFLAGS_crash.o += $(call cc-disable-warning, builtin-requires-header)
+# Avoid clang warnings around longjmp/setjmp declarations
+CFLAGS_crash.o += -ffreestanding
ifdef CONFIG_PPC64
CFLAGS_prom_init.o += $(NO_MINIMAL_TOC)
diff --git a/arch/powerpc/xmon/Makefile b/arch/powerpc/xmon/Makefile
index f142570ad860..c3842dbeb1b7 100644
--- a/arch/powerpc/xmon/Makefile
+++ b/arch/powerpc/xmon/Makefile
@@ -1,8 +1,8 @@
# SPDX-License-Identifier: GPL-2.0
# Makefile for xmon
-# Disable clang warning for using setjmp without setjmp.h header
-subdir-ccflags-y := $(call cc-disable-warning, builtin-requires-header)
+# Avoid clang warnings around longjmp/setjmp declarations
+subdir-ccflags-y := -ffreestanding
GCOV_PROFILE := n
KCOV_INSTRUMENT := n
--
2.24.0
^ permalink raw reply related [flat|nested] 29+ messages in thread* [PATCH v5 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
2019-11-19 4:57 ` [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs Nathan Chancellor
2019-11-19 4:57 ` [PATCH v5 1/3] powerpc: Don't add -mabi= flags when building with Clang Nathan Chancellor
2019-11-19 4:57 ` [PATCH v5 2/3] powerpc: Avoid clang warnings around setjmp and longjmp Nathan Chancellor
@ 2019-11-19 4:57 ` Nathan Chancellor
2019-11-25 20:15 ` [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs Nick Desaulniers
3 siblings, 0 replies; 29+ messages in thread
From: Nathan Chancellor @ 2019-11-19 4:57 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: clang-built-linux, Nathan Chancellor, Nick Desaulniers,
linuxppc-dev, linux-kernel
r374662 gives LLVM the ability to convert certain loops into a reference
to bcmp as an optimization; this breaks prom_init_check.sh:
CALL arch/powerpc/kernel/prom_init_check.sh
Error: External symbol 'bcmp' referenced from prom_init.c
make[2]: *** [arch/powerpc/kernel/Makefile:196: prom_init_check] Error 1
bcmp is defined in lib/string.c as a wrapper for memcmp so this could be
added to the whitelist. However, commit 450e7dd4001f ("powerpc/prom_init:
don't use string functions from lib/") copied memcmp as prom_memcmp to
avoid KASAN instrumentation so having bcmp be resolved to regular memcmp
would break that assumption. Furthermore, because the compiler is the
one that inserted bcmp, we cannot provide something like prom_bcmp.
To prevent LLVM from being clever with optimizations like this, use
-ffreestanding to tell LLVM we are not hosted so it is not free to make
transformations like this.
Link: https://github.com/ClangBuiltLinux/linux/issues/647
Link: https://github.com/llvm/llvm-project/commit/76cdcf25b883751d83402baea6316772aa73865c
Reviewed-by: Nick Desaulneris <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
v1 -> v3:
* New patch in the series
v3 -> v4:
* Rebase on v5.4-rc3.
* Add Nick's reviewed-by tag.
* Update the LLVM commit reference to the latest applied version (r374662)
as it was originally committed as r370454, reverted in r370788, and
reapplied as r374662.
v4 -> v5:
* Rebase on next-20191118 to avoid a conflict with commit
6266a4dadb1d ("powerpc/64s: Always disable branch profiling for prom_init.o")
arch/powerpc/kernel/Makefile | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 3c113ae0de2b..82170c155cb6 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -23,6 +23,7 @@ CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
CFLAGS_prom_init.o += -DDISABLE_BRANCH_PROFILING
+CFLAGS_prom_init.o += -ffreestanding
ifdef CONFIG_FUNCTION_TRACER
# Do not trace early boot code
--
2.24.0
^ permalink raw reply related [flat|nested] 29+ messages in thread* Re: [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs
2019-11-19 4:57 ` [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs Nathan Chancellor
` (2 preceding siblings ...)
2019-11-19 4:57 ` [PATCH v5 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp Nathan Chancellor
@ 2019-11-25 20:15 ` Nick Desaulniers
2019-11-28 4:59 ` Michael Ellerman
3 siblings, 1 reply; 29+ messages in thread
From: Nick Desaulniers @ 2019-11-25 20:15 UTC (permalink / raw)
To: Michael Ellerman
Cc: LKML, clang-built-linux, Paul Mackerras, Nathan Chancellor, linuxppc-dev
Hi Michael,
Do you have feedback for Nathan? Rebasing these patches is becoming a
nuisance for our CI, and we would like to keep building PPC w/ Clang.
On Mon, Nov 18, 2019 at 8:57 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> Hi all,
>
> This series includes a set of fixes for LLVM/Clang when building
> a few defconfigs (powernv, ppc44x, and pseries are the ones that our
> CI configuration tests [1]). The first patch fixes pseries_defconfig,
> which has never worked in mainline. The second and third patches fixes
> issues with all of these configs due to internal changes to LLVM, which
> point out issues with the kernel.
>
> These have been broken since July/August, it would be nice to get these
> reviewed and applied. Please let me know what I can do to get these
> applied soon so we can stop applying them out of tree.
>
> [1]: https://github.com/ClangBuiltLinux/continuous-integration
>
> Previous versions:
>
> v3: https://lore.kernel.org/lkml/20190911182049.77853-1-natechancellor@gmail.com/
>
> v4: https://lore.kernel.org/lkml/20191014025101.18567-1-natechancellor@gmail.com/
>
> Cheers,
> Nathan
>
>
--
Thanks,
~Nick Desaulniers
^ permalink raw reply [flat|nested] 29+ messages in thread* Re: [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs
2019-11-25 20:15 ` [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs Nick Desaulniers
@ 2019-11-28 4:59 ` Michael Ellerman
2019-11-28 7:45 ` Nathan Chancellor
0 siblings, 1 reply; 29+ messages in thread
From: Michael Ellerman @ 2019-11-28 4:59 UTC (permalink / raw)
To: Nick Desaulniers
Cc: LKML, clang-built-linux, Paul Mackerras, Nathan Chancellor, linuxppc-dev
Nick Desaulniers <ndesaulniers@google.com> writes:
> Hi Michael,
> Do you have feedback for Nathan? Rebasing these patches is becoming a
> nuisance for our CI, and we would like to keep building PPC w/ Clang.
Sorry just lost in the flood of patches.
Merged now.
cheers
> On Mon, Nov 18, 2019 at 8:57 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
>>
>> Hi all,
>>
>> This series includes a set of fixes for LLVM/Clang when building
>> a few defconfigs (powernv, ppc44x, and pseries are the ones that our
>> CI configuration tests [1]). The first patch fixes pseries_defconfig,
>> which has never worked in mainline. The second and third patches fixes
>> issues with all of these configs due to internal changes to LLVM, which
>> point out issues with the kernel.
>>
>> These have been broken since July/August, it would be nice to get these
>> reviewed and applied. Please let me know what I can do to get these
>> applied soon so we can stop applying them out of tree.
>>
>> [1]: https://github.com/ClangBuiltLinux/continuous-integration
>>
>> Previous versions:
>>
>> v3: https://lore.kernel.org/lkml/20190911182049.77853-1-natechancellor@gmail.com/
>>
>> v4: https://lore.kernel.org/lkml/20191014025101.18567-1-natechancellor@gmail.com/
>>
>> Cheers,
>> Nathan
>>
>>
>
>
> --
> Thanks,
> ~Nick Desaulniers
^ permalink raw reply [flat|nested] 29+ messages in thread
* Re: [PATCH v5 0/3] LLVM/Clang fixes for a few defconfigs
2019-11-28 4:59 ` Michael Ellerman
@ 2019-11-28 7:45 ` Nathan Chancellor
0 siblings, 0 replies; 29+ messages in thread
From: Nathan Chancellor @ 2019-11-28 7:45 UTC (permalink / raw)
To: Michael Ellerman
Cc: Nick Desaulniers, LKML, clang-built-linux, Paul Mackerras, linuxppc-dev
On Thu, Nov 28, 2019 at 03:59:07PM +1100, Michael Ellerman wrote:
> Nick Desaulniers <ndesaulniers@google.com> writes:
> > Hi Michael,
> > Do you have feedback for Nathan? Rebasing these patches is becoming a
> > nuisance for our CI, and we would like to keep building PPC w/ Clang.
>
> Sorry just lost in the flood of patches.
>
> Merged now.
>
> cheers
Thank you very much for picking them up :)
Cheers,
Nathan
^ permalink raw reply [flat|nested] 29+ messages in thread