Re: [PATCH v2 4/4] perf build: Filter out BTF sources without a .BTF section

[Namhyung Kim]

Hi Ian,

On Mon, Jun 5, 2023 at 1:28 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> If generating vmlinux.h, make the code to generate it more tolerant by
> filtering out paths to kernels that lack a .BTF section.
>
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
>  tools/perf/Makefile.perf | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index f1840af195c0..c3bb27a912b0 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -193,6 +193,7 @@ FLEX    ?= flex
>  BISON   ?= bison
>  STRIP   = strip
>  AWK     = awk
> +READELF ?= readelf
>
>  # include Makefile.config by default and rule out
>  # non-config cases
> @@ -1080,12 +1081,28 @@ $(BPFTOOL): | $(SKEL_TMP_OUT)
>         $(Q)CFLAGS= $(MAKE) -C ../bpf/bpftool \
>                 OUTPUT=$(SKEL_TMP_OUT)/ bootstrap
>
> -VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux)                           \
> +# Paths to search for a kernel to generate vmlinux.h from.
> +VMLINUX_BTF_ELF_PATHS ?= $(if $(O),$(O)/vmlinux)                       \
>                      $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)    \
>                      ../../vmlinux                                      \
> -                    /sys/kernel/btf/vmlinux                            \
>                      /boot/vmlinux-$(shell uname -r)
> -VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
> +
> +# Paths to BTF information.
> +VMLINUX_BTF_BTF_PATHS ?= /sys/kernel/btf/vmlinux
> +
> +# Filter out kernels that don't exist or without a BTF section.
> +VMLINUX_BTF_ELF_ABSPATHS ?= $(abspath $(wildcard $(VMLINUX_BTF_ELF_PATHS)))
> +VMLINUX_BTF_PATHS ?= $(shell for file in $(VMLINUX_BTF_ELF_ABSPATHS); \
> +                       do \
> +                               if [ -f $$file ] && ($(READELF) -t "$$file" | grep .BTF); \

Wouldn't it be `readelf -S` instead?  Also I think grep needs -q to
suppress output.


> +                               then \
> +                                       echo "$$file"; \
> +                               fi; \
> +                       done) \
> +                       $(wildcard $(VMLINUX_BTF_BTF_PATHS))

This changes the order of processing the sysfs file.
But I'm not sure it matters much as both /boot/vmlinux and sysfs
should refer to the running kernel.

Thanks,
Namhyung


> +
> +# Select the first as the source of vmlinux.h.
> +VMLINUX_BTF ?= $(firstword $(VMLINUX_BTF_PATHS))
>
>  $(SKEL_OUT)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL)
>  ifeq ($(VMLINUX_H),)
> --
> 2.41.0.rc0.172.g3f132b7071-goog
>