[v2] kbuild: fix linker feature test macros when cross compiling with Clang
diff mbox series

Message ID 20171027201345.87383-1-ndesaulniers@google.com
State New, archived
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Series
  • [v2] kbuild: fix linker feature test macros when cross compiling with Clang
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Commit Message

Nick Desaulniers Oct. 27, 2017, 8:13 p.m. UTC
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(-)

Comments

Masahiro Yamada Oct. 28, 2017, 3 p.m. UTC | #1
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. UTC | #2
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. UTC | #3
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. UTC | #4
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
Nick Desaulniers Nov. 6, 2017, 6:47 p.m. UTC | #5
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
diff mbox series

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)