linux-kernel - Re: Question about "asm/rwonce.h: No such file or directory"

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Date:   Tue, 12 Nov 2019 12:31:26 +0000
From:   Will Deacon <will@...nel.org>
To:     Xiao Yang <ice_yangxiao@....com>
Cc:     linux-arch@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        yamada.masahiro@...ionext.com, ast@...nel.org, daniel@...earbox.net
Subject: Re: Question about "asm/rwonce.h: No such file or directory"

[+lkml, Masahiro, Alexei and Daniel]

On Tue, Nov 12, 2019 at 04:56:39PM +0800, Xiao Yang wrote:
> With your patch[1], I alway get the following error when building
> tools/bpf:

In case people want to reproduce this, my branch is here:

https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/log/?h=lto

> ----------------------------------------------------------------------------------
> 
> make -C tools/bpf/
> make: Entering directory
> '/usr/src/perf_selftests-x86_64-rhel-7.6-642a312d47ceb54603630d9d04f5052f3b46d9a3/tools/bpf'
> 
> Auto-detecting system features:
> ... libbfd: [ on ]
> ... disassembler-four-args: [ OFF ]
> 
> CC bpf_jit_disasm.o
> CC bpf_dbg.o
> In file included from
> /usr/src/perf_selftests-x86_64-rhel-7.6-642a312d47ceb54603630d9d04f5052f3b46d9a3/include/uapi/linux/filter.h:9:0,
> from
> /usr/src/perf_selftests-x86_64-rhel-7.6-642a312d47ceb54603630d9d04f5052f3b46d9a3/tools/bpf/bpf_dbg.c:41:
> /usr/src/perf_selftests-x86_64-rhel-7.6-642a312d47ceb54603630d9d04f5052f3b46d9a3/include/linux/compiler.h:247:24:
> fatal error: asm/rwonce.h: No such file or directory
> #include <asm/rwonce.h>
> ^
> compilation terminated.
> Makefile:61: recipe for target 'bpf_dbg.o' failed
> make: *** [bpf_dbg.o] Error 1
> make: *** Waiting for unfinished jobs....
> make: Leaving directory
> 
> ----------------------------------------------------------------------------------
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/commit/?h=lto&id=642a312d47ceb54603630d9d04f5052f3b46d9a3
> 
> It seems that include/linux/compiler.h cannot find the asm/rwonce.h because
> tools/bpf/Makefile doesn't include arch/*/include/generated/asm/rwonce.h.

The problem with referring to the generated files is that they don't exist
unless you've configured the main source directory. The real problem here
seems to be that tools/bpf/ refers directly to header files in the kernel
sources without any understanding of kbuild, and therefore mandatory-y
headers simply don't exist when it goes looking for them.

Perhaps it's possible to introduce a dependency on a top-level "make
asm-generic" so that we can reference the generated headers from the arch
directly. Thoughts?

Will