| Message ID | 20220831184408.2778264-3-ndesaulniers@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fix debug info for asm and DEBUG_INFO_SPLIT | expand |
On Wed, Aug 31, 2022 at 11:44:05AM -0700, Nick Desaulniers wrote: > as-instr uses KBUILD_AFLAGS, but as-option uses KBUILD_CFLAGS. This can > cause as-option to fail unexpectedly because clang will emit > -Werror,-Wunused-command-line-argument for various -m and -f flags for > assembler sources. Now that I am looking closer at it, where does that '-Werror' come from? For cc-option, we add it to elevate clang's warnings about unused '-f', '-m', and '-W' flags to errors so that we do not add those flags. However, I do not see '-Werror' in as-option. I am going to assume it came from CONFIG_WERROR, as I believe Android has that turned on by default. I think that is the real problem: without '-Werror', the only error that should come from as-option is when an option isn't supported by the assembler, as clang will still warn but those will not be fatal but with '-Werror', those warnings turn fatal, causing all subsequent as-option calls to fail. Do not get me wrong, I still believe this is the correct fix but I think it would be good to describe exactly under which conditions this is a real issue in case we ever have to revisit this. > Callers of as-option (and as-instr) likely want to be adding flags to > KBUILD_AFLAGS/aflags-y, not KBUILD_CFLAGS/cflags-y. > > Link: https://github.com/ClangBuiltLinux/linux/issues/1699 > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Regardless of changes to the commit message: Reviewed-by: Nathan Chancellor <nathan@kernel.org> > --- > Changes v1 -> v2: > * Split off changes to arch/x86/boot/compressed/Makefile into parent > patch, as per Masahiro. > > scripts/Makefile.compiler | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler > index 94d0d40cddb3..d1739f0d3ce3 100644 > --- a/scripts/Makefile.compiler > +++ b/scripts/Makefile.compiler > @@ -29,13 +29,13 @@ try-run = $(shell set -e; \ > fi) > > # as-option > -# Usage: cflags-y += $(call as-option,-Wa$(comma)-isa=foo,) > +# Usage: aflags-y += $(call as-option,-Wa$(comma)-isa=foo,) > > as-option = $(call try-run,\ > - $(CC) $(KBUILD_CFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2)) > + $(CC) $(KBUILD_AFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2)) > > # as-instr > -# Usage: cflags-y += $(call as-instr,instr,option1,option2) > +# Usage: aflags-y += $(call as-instr,instr,option1,option2) > > as-instr = $(call try-run,\ > printf "%b\n" "$(1)" | $(CC) $(KBUILD_AFLAGS) -c -x assembler -o "$$TMP" -,$(2),$(3)) > -- > 2.37.2.672.g94769d06f0-goog >
On Thu, Sep 1, 2022 at 4:53 AM Nathan Chancellor <nathan@kernel.org> wrote: > > On Wed, Aug 31, 2022 at 11:44:05AM -0700, Nick Desaulniers wrote: > > as-instr uses KBUILD_AFLAGS, but as-option uses KBUILD_CFLAGS. This can > > cause as-option to fail unexpectedly because clang will emit > > -Werror,-Wunused-command-line-argument for various -m and -f flags for > > assembler sources. > > Now that I am looking closer at it, where does that '-Werror' come from? The related commit is c3f0d0bc5b01ad90c45276952802455750444b4f The previous discussion with Arnd is https://lore.kernel.org/linux-kbuild/20170314213724.3836900-1-arnd@arndb.de/ > For cc-option, we add it to elevate clang's warnings about unused '-f', > '-m', and '-W' flags to errors so that we do not add those flags. > However, I do not see '-Werror' in as-option. I am going to assume it > came from CONFIG_WERROR, as I believe Android has that turned on by > default. CONFIG_WERROR is added to CFLAGS. But, I guess it is more correct to do likewise for others. (https://patchwork.kernel.org/project/linux-kbuild/patch/20220905083619.672091-1-masahiroy@kernel.org/) > I think that is the real problem: without '-Werror', the only > error that should come from as-option is when an option isn't supported > by the assembler, as clang will still warn but those will not be fatal > but with '-Werror', those warnings turn fatal, causing all subsequent > as-option calls to fail. Presumably, it is correct to add -Werror to as-option as well. We have no reason to add it to cc-option, but not to as-option. I also believe '-x assembler' should be changed to '-x assembler-with-cpp'. As I mentioned somewhere before, our assembly code (*.S) is always preprocessed. There is no *.s file in the kernel source tree. So, '-x assembler-with-cpp' matches the real situation. One interesting thing is, clang does not warn [-Wunused-command-line-argument] for *.S files. $ clang -fomit-frame-pointer -c -x assembler /dev/null -o /dev/null clang: warning: argument unused during compilation: '-fomit-frame-pointer' [-Wunused-command-line-argument] $ clang -fomit-frame-pointer -c -x assembler-with-cpp /dev/null -o /dev/null The root cause is we are using '-x assembler', which never happens in the kernel tree. To sum up, the code I think correct is: as-option = $(call try-run,\ $(CC) -Werror $(KBUILD_AFLAGS) $(1) -c -x assembler-with-cpp /dev/null -o "$$TMP",$(1),$(2)) > Do not get me wrong, I still believe this is the correct fix but I think > it would be good to describe exactly under which conditions this is a > real issue in case we ever have to revisit this. > > > Callers of as-option (and as-instr) likely want to be adding flags to > > KBUILD_AFLAGS/aflags-y, not KBUILD_CFLAGS/cflags-y. > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/1699 > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > Regardless of changes to the commit message: > > Reviewed-by: Nathan Chancellor <nathan@kernel.org> > > > --- > > Changes v1 -> v2: > > * Split off changes to arch/x86/boot/compressed/Makefile into parent > > patch, as per Masahiro. > > > > scripts/Makefile.compiler | 6 +++--- > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler > > index 94d0d40cddb3..d1739f0d3ce3 100644 > > --- a/scripts/Makefile.compiler > > +++ b/scripts/Makefile.compiler > > @@ -29,13 +29,13 @@ try-run = $(shell set -e; \ > > fi) > > > > # as-option > > -# Usage: cflags-y += $(call as-option,-Wa$(comma)-isa=foo,) > > +# Usage: aflags-y += $(call as-option,-Wa$(comma)-isa=foo,) > > > > as-option = $(call try-run,\ > > - $(CC) $(KBUILD_CFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2)) > > + $(CC) $(KBUILD_AFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2)) > > > > # as-instr > > -# Usage: cflags-y += $(call as-instr,instr,option1,option2) > > +# Usage: aflags-y += $(call as-instr,instr,option1,option2) > > > > as-instr = $(call try-run,\ > > printf "%b\n" "$(1)" | $(CC) $(KBUILD_AFLAGS) -c -x assembler -o "$$TMP" -,$(2),$(3)) > > -- > > 2.37.2.672.g94769d06f0-goog > > -- Best Regards Masahiro Yamada
On Mon, Sep 05, 2022 at 06:09:28PM +0900, Masahiro Yamada wrote: > On Thu, Sep 1, 2022 at 4:53 AM Nathan Chancellor <nathan@kernel.org> wrote: > > > > On Wed, Aug 31, 2022 at 11:44:05AM -0700, Nick Desaulniers wrote: > > > as-instr uses KBUILD_AFLAGS, but as-option uses KBUILD_CFLAGS. This can > > > cause as-option to fail unexpectedly because clang will emit > > > -Werror,-Wunused-command-line-argument for various -m and -f flags for > > > assembler sources. > > > > Now that I am looking closer at it, where does that '-Werror' come from? > > The related commit is > c3f0d0bc5b01ad90c45276952802455750444b4f > > The previous discussion with Arnd is > https://lore.kernel.org/linux-kbuild/20170314213724.3836900-1-arnd@arndb.de/ Right, although this is for cc-option, not as-option, no? > > For cc-option, we add it to elevate clang's warnings about unused '-f', > > '-m', and '-W' flags to errors so that we do not add those flags. > > However, I do not see '-Werror' in as-option. I am going to assume it > > came from CONFIG_WERROR, as I believe Android has that turned on by > > default. > > CONFIG_WERROR is added to CFLAGS. > But, I guess it is more correct to do likewise for others. > (https://patchwork.kernel.org/project/linux-kbuild/patch/20220905083619.672091-1-masahiroy@kernel.org/) Ack. > > I think that is the real problem: without '-Werror', the only > > error that should come from as-option is when an option isn't supported > > by the assembler, as clang will still warn but those will not be fatal > > but with '-Werror', those warnings turn fatal, causing all subsequent > > as-option calls to fail. > > Presumably, it is correct to add -Werror to as-option as well. > We have no reason to add it to cc-option, but not to as-option. > > I also believe '-x assembler' should be changed to > '-x assembler-with-cpp'. > > As I mentioned somewhere before, our assembly code (*.S) is always > preprocessed. There is no *.s file in the kernel source tree. > > So, '-x assembler-with-cpp' matches the real situation. All good points, I think that is a good fix as well. > One interesting thing is, clang does not warn > [-Wunused-command-line-argument] for *.S files. > > $ clang -fomit-frame-pointer -c -x assembler /dev/null -o /dev/null > clang: warning: argument unused during compilation: > '-fomit-frame-pointer' [-Wunused-command-line-argument] > > $ clang -fomit-frame-pointer -c -x assembler-with-cpp /dev/null -o /dev/null Interesting... I suspect that is likely intentional, as some compiler flags could be used during preprocessing (it's come up before: https://github.com/llvm/llvm-project/issues/55656) but I was not able to figure out exactly where in clang the flags were consumed but Driver.cpp is quite large and I didn't look too hard :) More importantly, it still allows us to catch invalid assembler arguments: $ clang -c -x assembler-with-cpp /dev/null -o /dev/null -Wa,-foo clang-16: error: unsupported argument '-foo' to option '-Wa,' $ clang -c -x assembler-with-cpp /dev/null -o /dev/null -Wa,--noexecstack > The root cause is we are using '-x assembler', which > never happens in the kernel tree. > > To sum up, the code I think correct is: > > as-option = $(call try-run,\ > $(CC) -Werror $(KBUILD_AFLAGS) $(1) -c -x assembler-with-cpp > /dev/null -o "$$TMP",$(1),$(2)) > Agreed. Thank you as always for your feedback! Cheers, Nathan
On Mon, Sep 5, 2022 at 2:11 AM Masahiro Yamada <masahiroy@kernel.org> wrote: > > On Thu, Sep 1, 2022 at 4:53 AM Nathan Chancellor <nathan@kernel.org> wrote: > > > > On Wed, Aug 31, 2022 at 11:44:05AM -0700, Nick Desaulniers wrote: > > > as-instr uses KBUILD_AFLAGS, but as-option uses KBUILD_CFLAGS. This can > > > cause as-option to fail unexpectedly because clang will emit > > > -Werror,-Wunused-command-line-argument for various -m and -f flags for > > > assembler sources. > > > > Now that I am looking closer at it, where does that '-Werror' come from? > > > > > The related commit is > c3f0d0bc5b01ad90c45276952802455750444b4f > > The previous discussion with Arnd is > https://lore.kernel.org/linux-kbuild/20170314213724.3836900-1-arnd@arndb.de/ > > > > > > > For cc-option, we add it to elevate clang's warnings about unused '-f', > > '-m', and '-W' flags to errors so that we do not add those flags. > > However, I do not see '-Werror' in as-option. I am going to assume it > > came from CONFIG_WERROR, as I believe Android has that turned on by > > default. > > > CONFIG_WERROR is added to CFLAGS. > But, I guess it is more correct to do likewise for others. > (https://patchwork.kernel.org/project/linux-kbuild/patch/20220905083619.672091-1-masahiroy@kernel.org/) > > > > > I think that is the real problem: without '-Werror', the only > > error that should come from as-option is when an option isn't supported > > by the assembler, as clang will still warn but those will not be fatal > > but with '-Werror', those warnings turn fatal, causing all subsequent > > as-option calls to fail. > > > > Presumably, it is correct to add -Werror to as-option as well. > We have no reason to add it to cc-option, but not to as-option. > > > > > I also believe '-x assembler' should be changed to > '-x assembler-with-cpp'. > > > As I mentioned somewhere before, our assembly code (*.S) is always > preprocessed. There is no *.s file in the kernel source tree. > > > So, '-x assembler-with-cpp' matches the real situation. Should I do this for as-instr then as well? In the same patch? > > > One interesting thing is, clang does not warn > [-Wunused-command-line-argument] for *.S files. > > > > > $ clang -fomit-frame-pointer -c -x assembler /dev/null -o /dev/null > clang: warning: argument unused during compilation: > '-fomit-frame-pointer' [-Wunused-command-line-argument] > > $ clang -fomit-frame-pointer -c -x assembler-with-cpp /dev/null -o /dev/null > > > > The root cause is we are using '-x assembler', which > never happens in the kernel tree. > > > > > To sum up, the code I think correct is: > > > as-option = $(call try-run,\ > $(CC) -Werror $(KBUILD_AFLAGS) $(1) -c -x assembler-with-cpp > /dev/null -o "$$TMP",$(1),$(2)) Does your recent patch affect this? https://lore.kernel.org/linux-kbuild/20220905083619.672091-1-masahiroy@kernel.org/ If so, then I should not add -Werror as you suggest above?
On Wed, Sep 7, 2022 at 1:08 AM Nathan Chancellor <nathan@kernel.org> wrote: > > On Mon, Sep 05, 2022 at 06:09:28PM +0900, Masahiro Yamada wrote: > > On Thu, Sep 1, 2022 at 4:53 AM Nathan Chancellor <nathan@kernel.org> wrote: > > > > > > On Wed, Aug 31, 2022 at 11:44:05AM -0700, Nick Desaulniers wrote: > > > > as-instr uses KBUILD_AFLAGS, but as-option uses KBUILD_CFLAGS. This can > > > > cause as-option to fail unexpectedly because clang will emit > > > > -Werror,-Wunused-command-line-argument for various -m and -f flags for > > > > assembler sources. > > > > > > Now that I am looking closer at it, where does that '-Werror' come from? > > > > The related commit is > > c3f0d0bc5b01ad90c45276952802455750444b4f > > > > The previous discussion with Arnd is > > https://lore.kernel.org/linux-kbuild/20170314213724.3836900-1-arnd@arndb.de/ > > Right, although this is for cc-option, not as-option, no? Sorry, I misunderstood your comments. My reference is about -Werror in cc-option. It is unrelated to as-option. You are right. Currently, as-option takes KBUILD_CFLAGS instead of KBUILD_AFLAGS. The '-Werror,' of -Werror,-Wunused-command-line-argument presumably came from CONFIG_WERROR.
On Wed, Sep 7, 2022 at 12:12 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > > > > > > > > > I also believe '-x assembler' should be changed to > > '-x assembler-with-cpp'. > > > > > > As I mentioned somewhere before, our assembly code (*.S) is always > > preprocessed. There is no *.s file in the kernel source tree. > > > > > > So, '-x assembler-with-cpp' matches the real situation. > > Should I do this for as-instr then as well? In the same patch? Probably we should fix as-instr in the same way. You can do it in the same patch, or in a separate one. It is up to you. > > > > > > One interesting thing is, clang does not warn > > [-Wunused-command-line-argument] for *.S files. > > > > > > > > > > $ clang -fomit-frame-pointer -c -x assembler /dev/null -o /dev/null > > clang: warning: argument unused during compilation: > > '-fomit-frame-pointer' [-Wunused-command-line-argument] > > > > $ clang -fomit-frame-pointer -c -x assembler-with-cpp /dev/null -o /dev/null > > > > > > > > The root cause is we are using '-x assembler', which > > never happens in the kernel tree. > > > > > > > > > > To sum up, the code I think correct is: > > > > > > as-option = $(call try-run,\ > > $(CC) -Werror $(KBUILD_AFLAGS) $(1) -c -x assembler-with-cpp > > /dev/null -o "$$TMP",$(1),$(2)) > > Does your recent patch affect this? > https://lore.kernel.org/linux-kbuild/20220905083619.672091-1-masahiroy@kernel.org/ No, I do not think so. > If so, then I should not add -Werror as you suggest above? I think we should always add -Werror to as-option. as-option checks the command line options with /dev/null as the source input (that is, source input is always valid). If as-option results in a warning, that option will sprinkle the same warning for all *.S files in the source tree. So, any warning in as-option should be considered as an error.
diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler index 94d0d40cddb3..d1739f0d3ce3 100644 --- a/scripts/Makefile.compiler +++ b/scripts/Makefile.compiler @@ -29,13 +29,13 @@ try-run = $(shell set -e; \ fi) # as-option -# Usage: cflags-y += $(call as-option,-Wa$(comma)-isa=foo,) +# Usage: aflags-y += $(call as-option,-Wa$(comma)-isa=foo,) as-option = $(call try-run,\ - $(CC) $(KBUILD_CFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2)) + $(CC) $(KBUILD_AFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2)) # as-instr -# Usage: cflags-y += $(call as-instr,instr,option1,option2) +# Usage: aflags-y += $(call as-instr,instr,option1,option2) as-instr = $(call try-run,\ printf "%b\n" "$(1)" | $(CC) $(KBUILD_AFLAGS) -c -x assembler -o "$$TMP" -,$(2),$(3))
as-instr uses KBUILD_AFLAGS, but as-option uses KBUILD_CFLAGS. This can cause as-option to fail unexpectedly because clang will emit -Werror,-Wunused-command-line-argument for various -m and -f flags for assembler sources. Callers of as-option (and as-instr) likely want to be adding flags to KBUILD_AFLAGS/aflags-y, not KBUILD_CFLAGS/cflags-y. Link: https://github.com/ClangBuiltLinux/linux/issues/1699 Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> --- Changes v1 -> v2: * Split off changes to arch/x86/boot/compressed/Makefile into parent patch, as per Masahiro. scripts/Makefile.compiler | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)