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samples/bpf: remove unnecessary -I flags from libbpf EXTRA_CFLAGS #8156

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samples/bpf: remove unnecessary -I flags from libbpf EXTRA_CFLAGS #8156

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Commits on Dec 3, 2024

  1. adding ci files

    Kernel Patches Daemon committed Dec 3, 2024
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    ea05926 View commit details
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  2. samples/bpf: remove unnecessary -I flags from libbpf EXTRA_CFLAGS 

    Commit [0] breaks samples/bpf build:

    $ make M=samples/bpf
    ...
    make -C /path/to/kernel/samples/bpf/../../tools/lib/bpf \
     ...
     EXTRA_CFLAGS=" \
     ...
     -fsanitize=bounds \
     -I/path/to/kernel/usr/include \
     ...
    	/path/to/kernel/samples/bpf/libbpf/libbpf.a install_headers
      CC      /path/to/kernel/samples/bpf/libbpf/staticobjs/libbpf.o
    In file included from libbpf.c:29:
    /path/to/kernel/tools/include/linux/err.h:35:8: error: 'inline' can only appear on functions
       35 | static inline void * __must_check ERR_PTR(long error_)
          |        ^

The error is caused by `objtree` variable changing definition from `.`
(dot) to an absolute path:
- The variable TPROGS_CFLAGS is constructed as follows:
  ...
  TPROGS_CFLAGS += -I$(objtree)/usr/include
- It is passed as EXTRA_CFLAGS for libbpf compilation:
  $(LIBBPF): ...
    ...
	$(MAKE) -C $(LIBBPF_SRC) RM='rm -rf' EXTRA_CFLAGS="$(TPROGS_CFLAGS)"
- Before commit [0], the line passed to libbpf makefile was
  '-I./usr/include', where '.' referred to LIBBPF_SRC due to -C flag.
  The directory $(LIBBPF_SRC)/usr/include does not exist and thus
  was never resolved by C compiler.
- After commit [0], the line passed to libbpf makefile became:
  '<output-dir>/usr/include', this directory exists and is resolved by
  C compiler.
- Both 'tools/include' and 'usr/include' define files err.h and types.h.
- libbpf expects headers like 'linux/err.h' and 'linux/types.h'
  defined in 'tools/include', not 'usr/include', hence the compilation
  error.

This commit removes unnecessary -I flags from libbpf compilation.
(libbpf sets up the necessary includes at lib/bpf/Makefile:63).

Changes v1 [1] -> v2:
- dropped unnecessary replacement of KBUILD_OUTPUT with $(objtree)
  (Andrii)
Changes v2 [2] -> v3:
- make sure --sysroot option is set for libbpf's EXTRA_CFLAGS,
  if $(SYSROOT) is set (Stanislav)

[0] commit 13b2548 ("kbuild: change working directory to external module directory with M=")
[1] https://lore.kernel.org/bpf/[email protected]/
[2] https://lore.kernel.org/bpf/[email protected]/

Fixes: 13b2548 ("kbuild: change working directory to external module directory with M=")
Acked-by: Stanislav Fomichev <[email protected]>
Signed-off-by: Eduard Zingerman <[email protected]>
    @eddyz87
    eddyz87 authored and Kernel Patches Daemon committed Dec 3, 2024
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    18b0624 View commit details
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