Re: [PATCH bpf-next] tools/resolve_btfids: fix setting HOSTCFLAGS

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, May 30, 2023 at 02:33:52PM +0200, Viktor Malik wrote:
> Building BPF selftests with custom HOSTCFLAGS yields an error:
> 
>     # make HOSTCFLAGS="-O2"
>     [...]
>       HOSTCC  ./tools/testing/selftests/bpf/tools/build/resolve_btfids/main.o
>     main.c:73:10: fatal error: linux/rbtree.h: No such file or directory
>        73 | #include <linux/rbtree.h>
>           |          ^~~~~~~~~~~~~~~~
> 
> The reason is that tools/bpf/resolve_btfids/Makefile passes header
> include paths by extending HOSTCFLAGS which is overridden by setting
> HOSTCFLAGS in the make command (because of Makefile rules [1]).
> 
> This patch fixes the above problem by passing the include paths via
> `HOSTCFLAGS_resolve_btfids` which is used by tools/build/Build.include
> and can be combined with overridding HOSTCFLAGS.
> 
> [1] https://www.gnu.org/software/make/manual/html_node/Overriding.html
> 
> Fixes: 56a2df7615fa ("tools/resolve_btfids: Compile resolve_btfids as host program")
> Signed-off-by: Viktor Malik <vmalik@redhat.com>
> ---
>  tools/bpf/resolve_btfids/Makefile | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> index ac548a7baa73..4b8079f294f6 100644
> --- a/tools/bpf/resolve_btfids/Makefile
> +++ b/tools/bpf/resolve_btfids/Makefile
> @@ -67,7 +67,7 @@ $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
>  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
>  LIBELF_LIBS  := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
>  
> -HOSTCFLAGS += -g \
> +HOSTCFLAGS_resolve_btfids += -g \
>            -I$(srctree)/tools/include \
>            -I$(srctree)/tools/include/uapi \
>            -I$(LIBBPF_INCLUDE) \
> @@ -76,7 +76,7 @@ HOSTCFLAGS += -g \
>  
>  LIBS = $(LIBELF_LIBS) -lz
>  
> -export srctree OUTPUT HOSTCFLAGS Q HOSTCC HOSTLD HOSTAR
> +export srctree OUTPUT HOSTCFLAGS_resolve_btfids Q HOSTCC HOSTLD HOSTAR

hum, AFAICS this way the spacified HOSTCFLAGS="-O2" won't be pushed
to the libbpf and libsubcmd dependencies, right?

how about we add the EXTRA_CFLAGS variable like we do in libbpf,
libsubcmd or perf

with the change below you'd need to run:

  $ make EXTRA_CFLAGS="-O2"

I'll dig up the cross build scenarious we broke last time we
touched this stuff, perhaps Ian might remember as well ;-)

jirka


---
diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
index ac548a7baa73..58cfedc9c2db 100644
--- a/tools/bpf/resolve_btfids/Makefile
+++ b/tools/bpf/resolve_btfids/Makefile
@@ -18,8 +18,8 @@ else
 endif
 
 # Overrides for the prepare step libraries.
-HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
-		  CROSS_COMPILE="" EXTRA_CFLAGS="$(HOSTCFLAGS)"
+HOST_OVERRIDES = AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
+		  CROSS_COMPILE=""
 
 RM      ?= rm
 HOSTCC  ?= gcc
@@ -67,7 +67,7 @@ $(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)
 
-HOSTCFLAGS += -g \
+HOSTCFLAGS += $(EXTRA_CFLAGS) -g \
           -I$(srctree)/tools/include \
           -I$(srctree)/tools/include/uapi \
           -I$(LIBBPF_INCLUDE) \
@@ -76,7 +76,7 @@ HOSTCFLAGS += -g \
 
 LIBS = $(LIBELF_LIBS) -lz
 
-export srctree OUTPUT HOSTCFLAGS Q HOSTCC HOSTLD HOSTAR
+export srctree OUTPUT HOSTCFLAGS Q HOSTCC HOSTLD HOSTAR EXTRA_CFLAGS
 include $(srctree)/tools/build/Makefile.include
 
 $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)