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

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Submitter Nick Desaulniers
Date Oct. 27, 2017, 8:13 p.m.
Message ID <20171027201345.87383-1-ndesaulniers@google.com>
Download mbox | patch
Permalink /patch/10030583/
State New
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Comments

Nick Desaulniers - Oct. 27, 2017, 8:13 p.m.
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(-)
Masahiro Yamada - Oct. 28, 2017, 3 p.m.
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!
Masahiro Yamada - Oct. 30, 2017, 6:50 a.m.
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))
Masahiro Yamada - Oct. 30, 2017, 3:46 p.m.
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.
Nick Desaulniers - Oct. 30, 2017, 4:13 p.m.
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

Patch

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)