[PATCH] kbuild: fix linker feature test macros when cross compiling with Clang

[PATCH] kbuild: fix linker feature test macros when cross compiling with Clang

[Nick Desaulniers]

I was not seeing my linker flags getting added when using ld-option when
cross compiling with Clang. Upon investigation, this seems to be due to
a difference in how GCC vs Clang handle cross compilation.

GCC is configured at build time to support one backend, that is implicit
when compiling.  Clang is explicit via the use of `-target <triple>` and
ships with all supported backends by default.

GNU Make feature test macros that compile then link will always fail
when cross compiling with Clang unless Clang's triple is passed along to
the compiler. For example:

$ clang -x c /dev/null -c -o temp.o
$ aarch64-linux-android/bin/ld -E temp.o
aarch64-linux-android/bin/ld:
unknown architecture of input file `temp.o' is incompatible with
aarch64 output
aarch64-linux-android/bin/ld:
warning: cannot find entry symbol _start; defaulting to
0000000000400078
$ echo $?
1

$ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
$ aarch64-linux-android/bin/ld -E temp.o
aarch64-linux-android/bin/ld:
warning: cannot find entry symbol _start; defaulting to 00000000004002e4
$ echo $?
0

This causes conditional checks that invoke $(CC) without the target
triple, then $(LD) on the result, to always fail.

Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
---
 scripts/Kbuild.include | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 9ffd3dda3889..23c4df90e8ff 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -160,12 +160,12 @@ cc-if-fullversion = $(shell [ $(cc-fullversion) $(1) $(2) ] && echo $(3) || echo
 # cc-ldoption
 # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
 cc-ldoption = $(call try-run,\
-	$(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
+	$(CC) $(CLANG_TARGET) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
 
 # ld-option
 # Usage: LDFLAGS += $(call ld-option, -X)
 ld-option = $(call try-run,\
-	$(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
+	$(CC) $(CLANG_TARGET) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
 
 # ar-option
 # Usage: KBUILD_ARFLAGS := $(call ar-option,D)
-- 
2.15.0.rc2.357.g7e34df9404-goog

Re: [PATCH] kbuild: fix linker feature test macros when cross compiling with Clang

[Masahiro Yamada]

Hi Nick

2017-10-27 5:17 GMT+09:00 Nick Desaulniers <ndesaulniers@google.com>:
> I was not seeing my linker flags getting added when using ld-option when
> cross compiling with Clang. Upon investigation, this seems to be due to
> a difference in how GCC vs Clang handle cross compilation.
>
> GCC is configured at build time to support one backend, that is implicit
> when compiling.  Clang is explicit via the use of `-target <triple>` and
> ships with all supported backends by default.
>
> GNU Make feature test macros that compile then link will always fail
> when cross compiling with Clang unless Clang's triple is passed along to
> the compiler. For example:
>
> $ clang -x c /dev/null -c -o temp.o
> $ aarch64-linux-android/bin/ld -E temp.o
> aarch64-linux-android/bin/ld:
> unknown architecture of input file `temp.o' is incompatible with
> aarch64 output
> aarch64-linux-android/bin/ld:
> warning: cannot find entry symbol _start; defaulting to
> 0000000000400078
> $ echo $?
> 1
>
> $ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
> $ aarch64-linux-android/bin/ld -E temp.o
> aarch64-linux-android/bin/ld:
> warning: cannot find entry symbol _start; defaulting to 00000000004002e4
> $ echo $?
> 0
>
> This causes conditional checks that invoke $(CC) without the target
> triple, then $(LD) on the result, to always fail.
>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
> ---
>  scripts/Kbuild.include | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index 9ffd3dda3889..23c4df90e8ff 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -160,12 +160,12 @@ cc-if-fullversion = $(shell [ $(cc-fullversion) $(1) $(2) ] && echo $(3) || echo
>  # cc-ldoption
>  # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
>  cc-ldoption = $(call try-run,\
> -       $(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
> +       $(CC) $(CLANG_TARGET) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
>
>  # ld-option
>  # Usage: LDFLAGS += $(call ld-option, -X)
>  ld-option = $(call try-run,\
> -       $(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
> +       $(CC) $(CLANG_TARGET) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
>
>  # ar-option
>  # Usage: KBUILD_ARFLAGS := $(call ar-option,D)
> --

I do not like to add $(CLANG_TARGET) to a place for common helpers.


Instead of $(CLANG_TARGET), please add

$(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS)

to cc-ldoption and ld-option.



I have two requests next time:
  - please include  linux-kbuild@vger.kernel.org in your To list
  - please base your patch on linux-kbuild/kbuild branch


The URL of the tree is described in MAINTAINERS.


Thanks.


-- 
Best Regards
Masahiro Yamada

Re: [PATCH] kbuild: fix linker feature test macros when cross compiling with Clang

[Nick Desaulniers]

+ linux-kbuild@vger.kernel.org

On Fri, Oct 27, 2017 at 4:20 AM, Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> I do not like to add $(CLANG_TARGET) to a place for common helpers.
> Instead of $(CLANG_TARGET), please add
> $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS)
> to cc-ldoption and ld-option.

Thanks for the review.  I agree that sounds like a better option.

> I have two requests next time:
>   - please include  linux-kbuild@vger.kernel.org in your To list

Sure thing. scripts/get_maintainer.pl does not recommend that list for
this file; is there a way to explicitly add that list to the
recommendation for that source file?

>   - please base your patch on linux-kbuild/kbuild branch

Will do. Do I need to note it's based off that branch? Otherwise wont
0-day bot complain that my patch doesn't apply/build on torvalds/linux
?

Re: [PATCH] kbuild: fix linker feature test macros when cross compiling with Clang

[Nick Desaulniers]

On Fri, Oct 27, 2017 at 11:28 AM, Nick Desaulniers
<ndesaulniers@google.com> wrote:
> On Fri, Oct 27, 2017 at 4:20 AM, Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
>>   - please base your patch on linux-kbuild/kbuild branch
>
> Will do. Do I need to note it's based off that branch? Otherwise wont
> 0-day bot complain that my patch doesn't apply/build on torvalds/linux
> ?

Talked to some teammates about this, sounds like it's not a problem,
so I'll just send v2 with a note to the reviewer.

[PATCH v2] kbuild: fix linker feature test macros when cross compiling with Clang

[Nick Desaulniers]

I was not seeing my linker flags getting added when using ld-option when
cross compiling with Clang. Upon investigation, this seems to be due to
a difference in how GCC vs Clang handle cross compilation.

GCC is configured at build time to support one backend, that is implicit
when compiling.  Clang is explicit via the use of `-target <triple>` and
ships with all supported backends by default.

GNU Make feature test macros that compile then link will always fail
when cross compiling with Clang unless Clang's triple is passed along to
the compiler. For example:

$ clang -x c /dev/null -c -o temp.o
$ aarch64-linux-android/bin/ld -E temp.o
aarch64-linux-android/bin/ld:
unknown architecture of input file `temp.o' is incompatible with
aarch64 output
aarch64-linux-android/bin/ld:
warning: cannot find entry symbol _start; defaulting to
0000000000400078
$ echo $?
1

$ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
$ aarch64-linux-android/bin/ld -E temp.o
aarch64-linux-android/bin/ld:
warning: cannot find entry symbol _start; defaulting to 00000000004002e4
$ echo $?
0

This causes conditional checks that invoke $(CC) without the target
triple, then $(LD) on the result, to always fail.

Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
---
Changes since v1:
* base patch off of
  git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
  kbuild branch, per Masahiro.
* Use $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) rather than $(CLANG_TRIPLE), per
  Masahiro.

 scripts/Kbuild.include | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 064f477dfdca..0f09e4508554 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -228,12 +228,13 @@ cc-if-fullversion = $(shell [ $(cc-fullversion) $(1) $(2) ] && echo $(3) || echo
 # cc-ldoption
 # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
 cc-ldoption = $(call try-run-cached,\
-	$(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
+	$(CC) $(1) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
 
 # ld-option
 # Usage: LDFLAGS += $(call ld-option, -X)
 ld-option = $(call try-run-cached,\
-	$(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
+	$(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c -o "$$TMPO"; \
+	$(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
 
 # ar-option
 # Usage: KBUILD_ARFLAGS := $(call ar-option,D)
-- 
2.15.0.rc2.357.g7e34df9404-goog

Re: [PATCH] kbuild: fix linker feature test macros when cross compiling with Clang

[Masahiro Yamada]

2017-10-28 3:28 GMT+09:00 Nick Desaulniers <ndesaulniers@google.com>:
> + linux-kbuild@vger.kernel.org
>
> On Fri, Oct 27, 2017 at 4:20 AM, Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
>> I do not like to add $(CLANG_TARGET) to a place for common helpers.
>> Instead of $(CLANG_TARGET), please add
>> $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS)
>> to cc-ldoption and ld-option.
>
> Thanks for the review.  I agree that sounds like a better option.
>
>> I have two requests next time:
>>   - please include  linux-kbuild@vger.kernel.org in your To list
>
> Sure thing. scripts/get_maintainer.pl does not recommend that list for
> this file; is there a way to explicitly add that list to the
> recommendation for that source file?

Ah, I realized MAINTAINERS does not claim the maintainership
of this file.

There are so many misc scripts
in scripts/, so I hesitate to add
scripts/* pattern to MAINTAINERS.




>>   - please base your patch on linux-kbuild/kbuild branch
>
> Will do. Do I need to note it's based off that branch? Otherwise wont
> 0-day bot complain that my patch doesn't apply/build on torvalds/linux
> ?

I am not sure in which case the 0-day bot complain about it.

Now, I applied v2.
If the bot find a problem, it will send us a report.


-- 
Best Regards
Masahiro Yamada

Re: [PATCH v2] kbuild: fix linker feature test macros when cross compiling with Clang

[Masahiro Yamada]

2017-10-28 5:13 GMT+09:00 Nick Desaulniers <ndesaulniers@google.com>:
> I was not seeing my linker flags getting added when using ld-option when
> cross compiling with Clang. Upon investigation, this seems to be due to
> a difference in how GCC vs Clang handle cross compilation.
>
> GCC is configured at build time to support one backend, that is implicit
> when compiling.  Clang is explicit via the use of `-target <triple>` and
> ships with all supported backends by default.
>
> GNU Make feature test macros that compile then link will always fail
> when cross compiling with Clang unless Clang's triple is passed along to
> the compiler. For example:
>
> $ clang -x c /dev/null -c -o temp.o
> $ aarch64-linux-android/bin/ld -E temp.o
> aarch64-linux-android/bin/ld:
> unknown architecture of input file `temp.o' is incompatible with
> aarch64 output
> aarch64-linux-android/bin/ld:
> warning: cannot find entry symbol _start; defaulting to
> 0000000000400078
> $ echo $?
> 1
>
> $ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
> $ aarch64-linux-android/bin/ld -E temp.o
> aarch64-linux-android/bin/ld:
> warning: cannot find entry symbol _start; defaulting to 00000000004002e4
> $ echo $?
> 0
>
> This causes conditional checks that invoke $(CC) without the target
> triple, then $(LD) on the result, to always fail.
>
> Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
> ---
> Changes since v1:
> * base patch off of
>   git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
>   kbuild branch, per Masahiro.
> * Use $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) rather than $(CLANG_TRIPLE), per
>   Masahiro.
>
>  scripts/Kbuild.include | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index 064f477dfdca..0f09e4508554 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -228,12 +228,13 @@ cc-if-fullversion = $(shell [ $(cc-fullversion) $(1) $(2) ] && echo $(3) || echo
>  # cc-ldoption
>  # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
>  cc-ldoption = $(call try-run-cached,\
> -       $(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
> +       $(CC) $(1) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
>
>  # ld-option
>  # Usage: LDFLAGS += $(call ld-option, -X)
>  ld-option = $(call try-run-cached,\
> -       $(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
> +       $(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c -o "$$TMPO"; \
> +       $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
>
>  # ar-option
>  # Usage: KBUILD_ARFLAGS := $(call ar-option,D)
> --
> 2.15.0.rc2.357.g7e34df9404-goog
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


Applied to linux-kbuild/kbuild.  Thanks!


-- 
Best Regards
Masahiro Yamada

Re: [PATCH v2] kbuild: fix linker feature test macros when cross compiling with Clang

[Masahiro Yamada]

2017-10-29 0:00 GMT+09:00 Masahiro Yamada <yamada.masahiro@socionext.com>:
> 2017-10-28 5:13 GMT+09:00 Nick Desaulniers <ndesaulniers@google.com>:
>> I was not seeing my linker flags getting added when using ld-option when
>> cross compiling with Clang. Upon investigation, this seems to be due to
>> a difference in how GCC vs Clang handle cross compilation.
>>
>> GCC is configured at build time to support one backend, that is implicit
>> when compiling.  Clang is explicit via the use of `-target <triple>` and
>> ships with all supported backends by default.
>>
>> GNU Make feature test macros that compile then link will always fail
>> when cross compiling with Clang unless Clang's triple is passed along to
>> the compiler. For example:
>>
>> $ clang -x c /dev/null -c -o temp.o
>> $ aarch64-linux-android/bin/ld -E temp.o
>> aarch64-linux-android/bin/ld:
>> unknown architecture of input file `temp.o' is incompatible with
>> aarch64 output
>> aarch64-linux-android/bin/ld:
>> warning: cannot find entry symbol _start; defaulting to
>> 0000000000400078
>> $ echo $?
>> 1
>>
>> $ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
>> $ aarch64-linux-android/bin/ld -E temp.o
>> aarch64-linux-android/bin/ld:
>> warning: cannot find entry symbol _start; defaulting to 00000000004002e4
>> $ echo $?
>> 0
>>
>> This causes conditional checks that invoke $(CC) without the target
>> triple, then $(LD) on the result, to always fail.
>>
>> Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
>> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
>> ---
>> Changes since v1:
>> * base patch off of
>>   git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
>>   kbuild branch, per Masahiro.
>> * Use $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) rather than $(CLANG_TRIPLE), per
>>   Masahiro.
>>
>>  scripts/Kbuild.include | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
>> index 064f477dfdca..0f09e4508554 100644
>> --- a/scripts/Kbuild.include
>> +++ b/scripts/Kbuild.include
>> @@ -228,12 +228,13 @@ cc-if-fullversion = $(shell [ $(cc-fullversion) $(1) $(2) ] && echo $(3) || echo
>>  # cc-ldoption
>>  # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
>>  cc-ldoption = $(call try-run-cached,\
>> -       $(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
>> +       $(CC) $(1) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
>>
>>  # ld-option
>>  # Usage: LDFLAGS += $(call ld-option, -X)
>>  ld-option = $(call try-run-cached,\
>> -       $(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
>> +       $(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c -o "$$TMPO"; \
>> +       $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
>>
>>  # ar-option
>>  # Usage: KBUILD_ARFLAGS := $(call ar-option,D)
>> --
>> 2.15.0.rc2.357.g7e34df9404-goog
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
> Applied to linux-kbuild/kbuild.  Thanks!



I do not know the cause of the problem reported by the 0-day bot, but
if the problem happens in the following line,

ifeq ($(CONFIG_X86_32),y)
LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
else



Does the following solve the issue?    (adding $(LDFLAGS))

ld-option = $(call try-run,\
        $(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c
-o "$$TMPO"; \
        $(LD) $(LDFLAGS) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))




-- 
Best Regards
Masahiro Yamada

Re: [PATCH v2] kbuild: fix linker feature test macros when cross compiling with Clang

[Masahiro Yamada]

2017-10-30 15:50 GMT+09:00 Masahiro Yamada <yamada.masahiro@socionext.com>:
> 2017-10-29 0:00 GMT+09:00 Masahiro Yamada <yamada.masahiro@socionext.com>:
>> 2017-10-28 5:13 GMT+09:00 Nick Desaulniers <ndesaulniers@google.com>:
>>> I was not seeing my linker flags getting added when using ld-option when
>>> cross compiling with Clang. Upon investigation, this seems to be due to
>>> a difference in how GCC vs Clang handle cross compilation.
>>>
>>> GCC is configured at build time to support one backend, that is implicit
>>> when compiling.  Clang is explicit via the use of `-target <triple>` and
>>> ships with all supported backends by default.
>>>
>>> GNU Make feature test macros that compile then link will always fail
>>> when cross compiling with Clang unless Clang's triple is passed along to
>>> the compiler. For example:
>>>
>>> $ clang -x c /dev/null -c -o temp.o
>>> $ aarch64-linux-android/bin/ld -E temp.o
>>> aarch64-linux-android/bin/ld:
>>> unknown architecture of input file `temp.o' is incompatible with
>>> aarch64 output
>>> aarch64-linux-android/bin/ld:
>>> warning: cannot find entry symbol _start; defaulting to
>>> 0000000000400078
>>> $ echo $?
>>> 1
>>>
>>> $ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
>>> $ aarch64-linux-android/bin/ld -E temp.o
>>> aarch64-linux-android/bin/ld:
>>> warning: cannot find entry symbol _start; defaulting to 00000000004002e4
>>> $ echo $?
>>> 0
>>>
>>> This causes conditional checks that invoke $(CC) without the target
>>> triple, then $(LD) on the result, to always fail.
>>>
>>> Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>>> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
>>> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
>>> ---
>>> Changes since v1:
>>> * base patch off of
>>>   git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
>>>   kbuild branch, per Masahiro.
>>> * Use $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) rather than $(CLANG_TRIPLE), per
>>>   Masahiro.
>>>
>>>  scripts/Kbuild.include | 5 +++--
>>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
>>> index 064f477dfdca..0f09e4508554 100644
>>> --- a/scripts/Kbuild.include
>>> +++ b/scripts/Kbuild.include
>>> @@ -228,12 +228,13 @@ cc-if-fullversion = $(shell [ $(cc-fullversion) $(1) $(2) ] && echo $(3) || echo
>>>  # cc-ldoption
>>>  # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
>>>  cc-ldoption = $(call try-run-cached,\
>>> -       $(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
>>> +       $(CC) $(1) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
>>>
>>>  # ld-option
>>>  # Usage: LDFLAGS += $(call ld-option, -X)
>>>  ld-option = $(call try-run-cached,\
>>> -       $(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
>>> +       $(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c -o "$$TMPO"; \
>>> +       $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
>>>
>>>  # ar-option
>>>  # Usage: KBUILD_ARFLAGS := $(call ar-option,D)
>>> --
>>> 2.15.0.rc2.357.g7e34df9404-goog
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>> Applied to linux-kbuild/kbuild.  Thanks!
>
>
>
> I do not know the cause of the problem reported by the 0-day bot, but
> if the problem happens in the following line,
>
> ifeq ($(CONFIG_X86_32),y)
> LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
> else
>
>
>
> Does the following solve the issue?    (adding $(LDFLAGS))
>
> ld-option = $(call try-run,\
>         $(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c
> -o "$$TMPO"; \
>         $(LD) $(LDFLAGS) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
>
>


I dropped this patch for now.

-- 
Best Regards
Masahiro Yamada

Re: [PATCH v2] kbuild: fix linker feature test macros when cross compiling with Clang

[Nick Desaulniers]

That's safe to do for now.  Here's the 0-day failure thread:
https://lists.01.org/pipermail/lkp/2017-October/007427.html  If I can
sort out the issue, I'll submit a v3.

On Mon, Oct 30, 2017 at 8:46 AM, Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> 2017-10-30 15:50 GMT+09:00 Masahiro Yamada <yamada.masahiro@socionext.com>:
>> 2017-10-29 0:00 GMT+09:00 Masahiro Yamada <yamada.masahiro@socionext.com>:
>>> 2017-10-28 5:13 GMT+09:00 Nick Desaulniers <ndesaulniers@google.com>:
>>>> I was not seeing my linker flags getting added when using ld-option when
>>>> cross compiling with Clang. Upon investigation, this seems to be due to
>>>> a difference in how GCC vs Clang handle cross compilation.
>>>>
>>>> GCC is configured at build time to support one backend, that is implicit
>>>> when compiling.  Clang is explicit via the use of `-target <triple>` and
>>>> ships with all supported backends by default.
>>>>
>>>> GNU Make feature test macros that compile then link will always fail
>>>> when cross compiling with Clang unless Clang's triple is passed along to
>>>> the compiler. For example:
>>>>
>>>> $ clang -x c /dev/null -c -o temp.o
>>>> $ aarch64-linux-android/bin/ld -E temp.o
>>>> aarch64-linux-android/bin/ld:
>>>> unknown architecture of input file `temp.o' is incompatible with
>>>> aarch64 output
>>>> aarch64-linux-android/bin/ld:
>>>> warning: cannot find entry symbol _start; defaulting to
>>>> 0000000000400078
>>>> $ echo $?
>>>> 1
>>>>
>>>> $ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
>>>> $ aarch64-linux-android/bin/ld -E temp.o
>>>> aarch64-linux-android/bin/ld:
>>>> warning: cannot find entry symbol _start; defaulting to 00000000004002e4
>>>> $ echo $?
>>>> 0
>>>>
>>>> This causes conditional checks that invoke $(CC) without the target
>>>> triple, then $(LD) on the result, to always fail.
>>>>
>>>> Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>>>> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
>>>> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
>>>> ---
>>>> Changes since v1:
>>>> * base patch off of
>>>>   git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
>>>>   kbuild branch, per Masahiro.
>>>> * Use $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) rather than $(CLANG_TRIPLE), per
>>>>   Masahiro.
>>>>
>>>>  scripts/Kbuild.include | 5 +++--
>>>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
>>>> index 064f477dfdca..0f09e4508554 100644
>>>> --- a/scripts/Kbuild.include
>>>> +++ b/scripts/Kbuild.include
>>>> @@ -228,12 +228,13 @@ cc-if-fullversion = $(shell [ $(cc-fullversion) $(1) $(2) ] && echo $(3) || echo
>>>>  # cc-ldoption
>>>>  # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
>>>>  cc-ldoption = $(call try-run-cached,\
>>>> -       $(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
>>>> +       $(CC) $(1) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
>>>>
>>>>  # ld-option
>>>>  # Usage: LDFLAGS += $(call ld-option, -X)
>>>>  ld-option = $(call try-run-cached,\
>>>> -       $(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
>>>> +       $(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c -o "$$TMPO"; \
>>>> +       $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
>>>>
>>>>  # ar-option
>>>>  # Usage: KBUILD_ARFLAGS := $(call ar-option,D)
>>>> --
>>>> 2.15.0.rc2.357.g7e34df9404-goog
>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>>
>>> Applied to linux-kbuild/kbuild.  Thanks!
>>
>>
>>
>> I do not know the cause of the problem reported by the 0-day bot, but
>> if the problem happens in the following line,
>>
>> ifeq ($(CONFIG_X86_32),y)
>> LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
>> else
>>
>>
>>
>> Does the following solve the issue?    (adding $(LDFLAGS))
>>
>> ld-option = $(call try-run,\
>>         $(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c
>> -o "$$TMPO"; \
>>         $(LD) $(LDFLAGS) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
>>
>>
>
>
> I dropped this patch for now.
>
> --
> Best Regards
> Masahiro Yamada



-- 
Thanks,
~Nick Desaulniers

Re: [PATCH v2] kbuild: fix linker feature test macros when cross compiling with Clang

[Nick Desaulniers]

Comparing make V=1 with the suggested config before my patch, after my
patch, and after Masahiro's suggestion to add $(LDFLAGS):

before:
...
ld -m elf_i386  -pie    -T arch/x86/boot/compressed/vmlinux.lds ...
...

after my:
...
ld -m elf_i386     -T arch/x86/boot/compressed/vmlinux.lds ...
...

after my+Masahiro:
...
ld -m elf_i386 -pie    -T arch/x86/boot/compressed/vmlinux.lds ...
...

:)

Just to dig into this a little more (though I suspect we've found the issue):

Next is to debug what we're passing to try-run and see what errors
it's masking.  Adding to arch/x86/boot/compressed/Makefile:
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -44,6 +44,10 @@ LDFLAGS := -m elf_$(UTS_MACHINE)
 # Compressed kernel should be built as PIE since it may be loaded at any
 # address by the bootloader.
 ifeq ($(CONFIG_X86_32),y)
+$(info "XXX")
+$(info "KBUILD_CPPFLAGS: ${KBUILD_CPPFLAGS}")
+$(info "CC_OPTION_CFLAGS: ${CC_OPTION_CFLAGS}")
+$(info "LDFLAGS: ${LDFLAGS}")
 LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
 else
 # To build 64-bit compressed kernel as PIE, we disable relocation

then grepping for XXX in a build output:
"XXX"
"KBUILD_CPPFLAGS: -D__KERNEL__  "
"CC_OPTION_CFLAGS: -m32 -D__KERNEL__ -O2 -fno-strict-aliasing -fPIE
-DDISABLE_BRANCH_PROFILING -march=i386 -mno-mmx -mno-sse
-ffreestanding -fno-stack-protector"
"LD_FLAGS: "

then trying this on the command line:
➜  kernel-all git:(kbuild) ✗ cc -pie -D__KERNEL__ -m32 -D__KERNEL__
-O2 -fno-strict-aliasing -fPIE -DDISABLE_BRANCH_PROFILING -march=i386
-mno-mmx -mno-sse -ffreestanding -fno-stack-protector -x c /dev/null
-c -o temp.o
➜  kernel-all git:(kbuild) ✗ ld -pie temp.o -o temp
ld: i386 architecture of input file `temp.o' is incompatible with
i386:x86-64 output
ld: warning: cannot find entry symbol _start; defaulting to 0000000000000078
➜  kernel-all git:(kbuild) ✗ echo $?
1
➜  kernel-all git:(kbuild) ✗ file temp.o
temp.o: ELF 32-bit LSB  relocatable, Intel 80386, version 1 (SYSV), not stripped

So it looks like without LDFLAGS, we don't tell the linker to link as
32b, causing ld-option to fail to add -pie to LDFLAGS.

➜  kernel-all git:(kbuild) ✗ ld -pie -m elf_i386 temp.o -o temp
ld: warning: cannot find entry symbol _start; defaulting to 0000000000000185
➜  kernel-all git:(kbuild) ✗ echo $?
0

sure enough, just before the call to ld-option from
arch/x86/boot/compressed/Makefile:

 43 LDFLAGS := -m elf_$(UTS_MACHINE)

so looks like Masahiro's suggestion is correct.  Will send a v3.

[PATCH v3] kbuild: fix linker feature test macros when cross compiling with Clang

[Nick Desaulniers]

I was not seeing my linker flags getting added when using ld-option when
cross compiling with Clang. Upon investigation, this seems to be due to
a difference in how GCC vs Clang handle cross compilation.

GCC is configured at build time to support one backend, that is implicit
when compiling.  Clang is explicit via the use of `-target <triple>` and
ships with all supported backends by default.

GNU Make feature test macros that compile then link will always fail
when cross compiling with Clang unless Clang's triple is passed along to
the compiler. For example:

$ clang -x c /dev/null -c -o temp.o
$ aarch64-linux-android/bin/ld -E temp.o
aarch64-linux-android/bin/ld:
unknown architecture of input file `temp.o' is incompatible with
aarch64 output
aarch64-linux-android/bin/ld:
warning: cannot find entry symbol _start; defaulting to
0000000000400078
$ echo $?
1

$ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
$ aarch64-linux-android/bin/ld -E temp.o
aarch64-linux-android/bin/ld:
warning: cannot find entry symbol _start; defaulting to 00000000004002e4
$ echo $?
0

This causes conditional checks that invoke $(CC) without the target
triple, then $(LD) on the result, to always fail.

Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
---
Changes since v2:
* Add LDFLAGS to ld-option, as per Masahiro, and spotted by 0-day bot:
  https://lists.01.org/pipermail/lkp/2017-October/007427.html

 scripts/Kbuild.include | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 064f477dfdca..be1c9d65eaf4 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -228,12 +228,13 @@ cc-if-fullversion = $(shell [ $(cc-fullversion) $(1) $(2) ] && echo $(3) || echo
 # cc-ldoption
 # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
 cc-ldoption = $(call try-run-cached,\
-	$(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
+	$(CC) $(1) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
 
 # ld-option
 # Usage: LDFLAGS += $(call ld-option, -X)
 ld-option = $(call try-run-cached,\
-	$(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
+	$(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c -o "$$TMPO"; \
+	$(LD) $(LDFLAGS) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
 
 # ar-option
 # Usage: KBUILD_ARFLAGS := $(call ar-option,D)
-- 
2.15.0.403.gc27cc4dac6-goog

Re: [PATCH v3] kbuild: fix linker feature test macros when cross compiling with Clang

[Masahiro Yamada]

2017-11-07 3:47 GMT+09:00 Nick Desaulniers <ndesaulniers@google.com>:
> I was not seeing my linker flags getting added when using ld-option when
> cross compiling with Clang. Upon investigation, this seems to be due to
> a difference in how GCC vs Clang handle cross compilation.
>
> GCC is configured at build time to support one backend, that is implicit
> when compiling.  Clang is explicit via the use of `-target <triple>` and
> ships with all supported backends by default.
>
> GNU Make feature test macros that compile then link will always fail
> when cross compiling with Clang unless Clang's triple is passed along to
> the compiler. For example:
>
> $ clang -x c /dev/null -c -o temp.o
> $ aarch64-linux-android/bin/ld -E temp.o
> aarch64-linux-android/bin/ld:
> unknown architecture of input file `temp.o' is incompatible with
> aarch64 output
> aarch64-linux-android/bin/ld:
> warning: cannot find entry symbol _start; defaulting to
> 0000000000400078
> $ echo $?
> 1
>
> $ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
> $ aarch64-linux-android/bin/ld -E temp.o
> aarch64-linux-android/bin/ld:
> warning: cannot find entry symbol _start; defaulting to 00000000004002e4
> $ echo $?
> 0
>
> This causes conditional checks that invoke $(CC) without the target
> triple, then $(LD) on the result, to always fail.
>
> Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
> ---
> Changes since v2:
> * Add LDFLAGS to ld-option, as per Masahiro, and spotted by 0-day bot:
>   https://lists.01.org/pipermail/lkp/2017-October/007427.html
>
>  scripts/Kbuild.include | 5 +++--


Applied to linux-kbuild/kbuild.


-- 
Best Regards
Masahiro Yamada

Re: [PATCH v3] kbuild: fix linker feature test macros when cross compiling with Clang

[Arnd Bergmann]

On Mon, Nov 6, 2017 at 7:47 PM, Nick Desaulniers
<ndesaulniers@google.com> wrote:
> I was not seeing my linker flags getting added when using ld-option when
> cross compiling with Clang. Upon investigation, this seems to be due to
> a difference in how GCC vs Clang handle cross compilation.
>
> GCC is configured at build time to support one backend, that is implicit
> when compiling.  Clang is explicit via the use of `-target <triple>` and
> ships with all supported backends by default.
>
> GNU Make feature test macros that compile then link will always fail
> when cross compiling with Clang unless Clang's triple is passed along to
> the compiler. For example:
>
> $ clang -x c /dev/null -c -o temp.o
> $ aarch64-linux-android/bin/ld -E temp.o
> aarch64-linux-android/bin/ld:
> unknown architecture of input file `temp.o' is incompatible with
> aarch64 output
> aarch64-linux-android/bin/ld:
> warning: cannot find entry symbol _start; defaulting to
> 0000000000400078
> $ echo $?
> 1
>
> $ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
> $ aarch64-linux-android/bin/ld -E temp.o
> aarch64-linux-android/bin/ld:
> warning: cannot find entry symbol _start; defaulting to 00000000004002e4
> $ echo $?
> 0
>
> This causes conditional checks that invoke $(CC) without the target
> triple, then $(LD) on the result, to always fail.
>
> Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>

After this patch, I get the following warning in arm64 kernel builds
with CONFIG_ARM64_ERRATUM_843419:

arch/arm64/Makefile:27: ld does not support --fix-cortex-a53-843419;
kernel may be susceptible to erratum

This only happens on the first build though, when the cached variable
is being set. On the second build we get the contents from the cache
and the warning disappears.

I've tried debugging it further but did not get anywhere with that.

        Arnd

Re: [PATCH v3] kbuild: fix linker feature test macros when cross compiling with Clang

[Masahiro Yamada]

2017-12-11 19:17 GMT+09:00 Arnd Bergmann <arnd@arndb.de>:
> On Mon, Nov 6, 2017 at 7:47 PM, Nick Desaulniers
> <ndesaulniers@google.com> wrote:
>> I was not seeing my linker flags getting added when using ld-option when
>> cross compiling with Clang. Upon investigation, this seems to be due to
>> a difference in how GCC vs Clang handle cross compilation.
>>
>> GCC is configured at build time to support one backend, that is implicit
>> when compiling.  Clang is explicit via the use of `-target <triple>` and
>> ships with all supported backends by default.
>>
>> GNU Make feature test macros that compile then link will always fail
>> when cross compiling with Clang unless Clang's triple is passed along to
>> the compiler. For example:
>>
>> $ clang -x c /dev/null -c -o temp.o
>> $ aarch64-linux-android/bin/ld -E temp.o
>> aarch64-linux-android/bin/ld:
>> unknown architecture of input file `temp.o' is incompatible with
>> aarch64 output
>> aarch64-linux-android/bin/ld:
>> warning: cannot find entry symbol _start; defaulting to
>> 0000000000400078
>> $ echo $?
>> 1
>>
>> $ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
>> $ aarch64-linux-android/bin/ld -E temp.o
>> aarch64-linux-android/bin/ld:
>> warning: cannot find entry symbol _start; defaulting to 00000000004002e4
>> $ echo $?
>> 0
>>
>> This causes conditional checks that invoke $(CC) without the target
>> triple, then $(LD) on the result, to always fail.
>>
>> Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
>> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
>
> After this patch, I get the following warning in arm64 kernel builds
> with CONFIG_ARM64_ERRATUM_843419:
>
> arch/arm64/Makefile:27: ld does not support --fix-cortex-a53-843419;
> kernel may be susceptible to erratum
>
> This only happens on the first build though, when the cached variable
> is being set. On the second build we get the contents from the cache
> and the warning disappears.
>
> I've tried debugging it further but did not get anywhere with that.
>
>         Arnd


Hmm.  I cannot reproduce this issue.



With Linaro 4.9 compiler,
I got "Detected assembler with broken .inst",
which is I think expected behavior.


With Linaro 7.2 compiler,
I did not get the warning,
which is also I think expected behavior.



$ make clean
  CLEAN   .
  CLEAN   .tmp_versions
$ make ARCH=arm64
CROSS_COMPILE=~/toolchains/aarch64-linaro-4.9/bin/aarch64-linux-gnu-
arch/arm64/Makefile:48: Detected assembler with broken .inst;
disassembly will be unreliable
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  HOSTCC  scripts/basic/fixdep
  HOSTCC  scripts/basic/bin2c
  CC      kernel/bounds.s
  CHK     include/generated/bounds.h
  CHK     include/generated/timeconst.h
   ...

$ make ARCH=arm64
CROSS_COMPILE=~/toolchains/aarch64-linaro-7.2/bin/aarch64-linux-gnu-
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CHK     include/generated/bounds.h
  CHK     include/generated/timeconst.h
  CHK     include/generated/asm-offsets.h
  CALL    scripts/checksyscalls.sh
  CHK     scripts/mod/devicetable-offsets.h
  CHK     include/generated/compile.h
    ...


Can you provide detailed steps to reproduce the problem?



-- 
Best Regards
Masahiro Yamada