| Message ID | 20171106184756.24404-1-ndesaulniers@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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.
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 -- 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
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?
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)