Re: [PATCH v4 2/2] tools/resolve_btfids: Alter how HOSTCC is forced

Ian Rogers
2023-01-31T22:50:47Z

On Tue, Jan 31, 2023 at 2:40 PM Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Tue, Jan 31, 2023 at 02:17:08PM -0700, Nathan Chancellor wrote:
> > On Tue, Jan 31, 2023 at 12:59:04PM -0800, Ian Rogers wrote:
> > > On Tue, Jan 31, 2023 at 11:33 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > > >
> > > > On Tue, Jan 31, 2023 at 11:25:38AM -0800, Ian Rogers wrote:
> > > > > On Tue, Jan 31, 2023 at 10:08 AM Ian Rogers <irogers@google.com> wrote:
> > > > > >
> > > > > > On Tue, Jan 31, 2023 at 9:21 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > > > > > >
> > > > > > > Hi Ian,
> > > > > > >
> > > > > > > On Mon, Jan 23, 2023 at 10:43:24PM -0800, Ian Rogers wrote:
> > > > > > > > HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> > > > > > > > after tools/scripts/Makefile.include is included, meaning flags are
> > > > > > > > set assuming say CC is gcc, but then it can be later set to HOSTCC
> > > > > > > > which may be clang. tools/scripts/Makefile.include is needed for host
> > > > > > > > set up and common macros in objtool's Makefile. Rather than override
> > > > > > > > CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> > > > > > > > builds and the linkage step. This means the Makefiles don't see things
> > > > > > > > like CC changing and tool flag determination, and similar, work
> > > > > > > > properly.
> > > > > > > >
> > > > > > > > Also, clear the passed subdir as otherwise an outer build may break by
> > > > > > > > inadvertently passing an inappropriate value.
> > > > > > > >
> > > > > > > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > > > > > > ---
> > > > > > > > tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
> > > > > > > > 1 file changed, 7 insertions(+), 10 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > > > > > > > index 1fe0082b2ecc..daed388aa5d7 100644
> > > > > > > > --- a/tools/bpf/resolve_btfids/Makefile
> > > > > > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > > > > > @@ -18,14 +18,11 @@ else
> > > > > > > > endif
> > > > > > > >
> > > > > > > > # always use the host compiler
> > > > > > > > -AR = $(HOSTAR)
> > > > > > > > -CC = $(HOSTCC)
> > > > > > > > -LD = $(HOSTLD)
> > > > > > > > -ARCH = $(HOSTARCH)
> > > > > > > > +HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> > > > > > > > + EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > > > > +
> > > > > > > > RM ?= rm
> > > > > > > > CROSS_COMPILE =
> > > > > > > > -CFLAGS := $(KBUILD_HOSTCFLAGS)
> > > > > > > > -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
> > > > > > > >
> > > > > > > > OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > > > > > >
> > > > > > > > @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
> > > > > > > >
> > > > > > > > $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
> > > > > > > > $(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> > > > > > > > - DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> > > > > > > > + DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > > > > > $(abspath $@) install_headers
> > > > > > > >
> > > > > > > > $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
> > > > > > > > $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT) \
> > > > > > > > - DESTDIR=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> > > > > > > > + DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > > > > > $(abspath $@) install_headers
> > > > > > > >
> > > > > > > > LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> > > > > > > > @@ -80,11 +77,11 @@ export srctree OUTPUT CFLAGS Q
> > > > > > > > include $(srctree)/tools/build/Makefile.include
> > > > > > > >
> > > > > > > > $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> > > > > > > > - $(Q)$(MAKE) $(build)=resolve_btfids
> > > > > > > > + $(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
> > > > > > > >
> > > > > > > > $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
> > > > > > > > $(call msg,LINK,$@)
> > > > > > > > - $(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > > > > > + $(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > > > > >
> > > > > > > > clean_objects := $(wildcard $(OUTPUT)/*.o \
> > > > > > > > $(OUTPUT)/.*.o.cmd \
> > > > > > > > --
> > > > > > > > 2.39.0.246.g2a6d74b583-goog
> > > > > > > >
> > > > > > >
> > > > > > > I just bisected a linking failure when building resolve_btfids with
> > > > > > > clang to this change as commit 13e07691a16f ("tools/resolve_btfids:
> > > > > > > Alter how HOSTCC is forced") in the bpf-next tree.
> > > > > > >
> > > > > > > It appears to be related to whether or not CROSS_COMPILE is specified,
> > > > > > > which we have to do for certain architectures and configurations still.
> > > > > > > arm64 is not one of those but it helps demonstrate the issue.
> > > > > > >
> > > > > > > # Turn off CONFIG_DEBUG_INFO_REDUCED and turn on CONFIG_DEBUG_INFO_BTF
> > > > > > > $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 defconfig menuconfig
> > > > > > >
> > > > > > > $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 prepare
> > > > > > > ld.lld: error: $LINUX_SRC/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> > > > > > > clang-17: error: linker command failed with exit code 1 (use -v to see invocation)
> > > > > > > ...
> > > > > > >
> > > > > > > Before your change, with V=1, I see:
> > > > > > >
> > > > > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -Wdeclaration-after-statement -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > > > > >
> > > > > > > After, I see:
> > > > > > >
> > > > > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o --target=aarch64-linux-gnu -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > > > > >
> > > > > > > We seem to have taken on a '--target=aarch64-linux-gnu' (changing the
> > > > > > > target of resolve_btfids-in.o) and we dropped the warning flags.
> > > > > > >
> > > > > > > I think this comes from the clang block in
> > > > > > > tools/scripts/Makefile.include, which is included into the
> > > > > > > resolve_btfids Makefile via tools/lib/bpf/Makefile.
> > > > > > >
> > > > > > > I am not super familiar with the tools build system, otherwise I would
> > > > > > > try to provide a patch. I tried moving CROSS_COMPILE from a recursive to
> > > > > > > simple variable ('=' -> ':=') and moving it to HOST_OVERRIDES but those
> > > > > > > did not appear to resolve it for me.
> > > > > > >
> > > > > > > If there is any other information I can provide or patches I can test,
> > > > > > > please let me know.
> > > > > > >
> > > > > > > Cheers,
> > > > > > > Nathan
> > > > > >
> > > > > > Thanks Nathan, and thanks for all the details in the bug report. I'm
> > > > > > looking into this.
> > > > > >
> > > > > > Ian
> > > > >
> > > > > Given the somewhat complicated cross compile I wasn't able to get a
> > > > > reproduction. Could you see if the following addresses the problem:
> > > >
> > > > As long as you have an LLVM toolchain that targets AArch64 and your
> > > > host, you should be able to reproduce this issue with those commands
> > > > verbatim, as that command should not use any GNU binutils. I am pretty
> > > > sure I tried it in a fresh container before reporting it but it is
> > > > possible that I did not.
> > >
> > > Thanks, do you have instructions on setting up the container?
> >
> > Sure thing, this worked for me in the Linux source you would like to
> > build (I marked it readonly to make sure any modifications were done in
> > my host environment, remove the ':ro' if you would like to make edits to
> > the source within the container). Docker should work as well but I did
> > not test it.
> >
> > $ podman run --rm -ti -v $PWD:/linux:ro docker.io/archlinux:base-devel
> > # pacman -Syyu --noconfirm bc clang lib32-glibc lld llvm python
> > ...
> >
> > # To turn on CONFIG_DEBUG_INFO_BTF
> > # make -C /linux -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 O=/build defconfig menuconfig
> >
> > # make -C /linux -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 O=/build prepare
> > ld.lld: error: /build/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> > clang-15: error: linker command failed with exit code 1 (use -v to see invocation)
> >
> > > > > ```
> > > > > diff --git a/tools/bpf/resolve_btfids/Makefile
> > > > > b/tools/bpf/resolve_btfids/Makefile
> > > > > index daed388aa5d7..a06966841df4 100644
> > > > > --- a/tools/bpf/resolv
> > >
> > > Ian
> > > e_btfids/Makefile
> > > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > > @@ -19,10 +19,9 @@ endif
> > > > >
> > > > > # always use the host compiler
> > > > > HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
> > > > > ARCH="$(HOSTARCH)" \
> > > > > - EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > + EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > CROSS_COMPILE=""
> > > > >
> > > > > RM ?= rm
> > > > > -CROSS_COMPILE =
> > > > >
> > > > > OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > > > ```
> > > > >
> > > >
> > > > Unfortunately, it does not. I still see '--target=' end up in the
> > > > CFLAGS of those files.
>
> hi,
> I can reproduce that and I think the reason is that the patch removes
> CFLAGS setup
>
> CFLAGS := $(KBUILD_HOSTCFLAGS)
>
> so now the 'include ../../scripts/Makefile.include' will set CFLAGS
> with the --target=... and we fail
>
> I can compile with the change below.. we could also set CROSS_COMPILE
> before including tools/scripts/Makefile.include ... not sure which
> on is better
>
> also I need to check if we should keep LDFLAGS setup as well
>
> jirka

Right, but the code shouldn't be doing that - it was the purpose of
the patch to remove it. If you include tools/scripts/Makefile.include,
which is done on line 2, then a bunch of warnings, cflags, etc. are
set based on CC. To then overwrite those values with various HOST
values is at best confusing - CC no longer being CC but HOSTCC, but
other values may or may not have changed. As we build using submakes,
the goal here was to push the problem into the submake which will only
ever see CC and other values being passed in.

So perhaps:
HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
ARCH="$(HOSTARCH)" \
EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)" CROSS_COMPILE=""

should be:
HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
ARCH="$(HOSTARCH)" \
CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)" CROSS_COMPILE=""

I'm still trying to get a reproduction.

Thanks,
Ian

>
> ---
> diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> index daed388aa5d7..875e3fcce7cd 100644
> --- a/tools/bpf/resolve_btfids/Makefile
> +++ b/tools/bpf/resolve_btfids/Makefile
> @@ -64,6 +64,7 @@ $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
> LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> LIBELF_LIBS := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
>
> +CFLAGS := $(KBUILD_HOSTCFLAGS)
> CFLAGS += -g \
> -I$(srctree)/tools/include \
> -I$(srctree)/tools/include/uapi \
>