netdev - Re: tools/bpf: Compilation issue on powerpc: unknown type name '_

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Date:   Mon, 26 Oct 2020 15:45:55 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Vitaly Chikunov <vt@...linux.org>, bpf@...r.kernel.org,
        Will Deacon <will@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Sandipan Das <sandipan@...ux.ibm.com>
Cc:     "Dmitry V. Levin" <ldv@...linux.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: tools/bpf: Compilation issue on powerpc: unknown type name '__vector128'

Vitaly Chikunov <vt@...linux.org> writes:
> Adding netdev and PowerPC maintainers JFYI.

Thanks.

> On Sat, Oct 24, 2020 at 11:23:19AM +0300, Dmitry V. Levin wrote:
>> Hi,
>> 
>> On Sat, Oct 24, 2020 at 02:06:41AM +0300, Vitaly Chikunov wrote:
>> > Hi,
>> > 
>> > Commit f143c11bb7b9 ("tools: bpf: Use local copy of headers including
>> > uapi/linux/filter.h") introduces compilation issue on powerpc:
>> >  
>> >   builder@...erpc64le:~/linux$ make -C tools/bpf V=1
>> >   make: Entering directory '/usr/src/linux/tools/bpf'
>> >   gcc -Wall -O2 -D__EXPORTED_HEADERS__ -I/usr/src/linux/tools/include/uapi -I/usr/src/linux/tools/include -DDISASM_FOUR_ARGS_SIGNATURE -c -o bpf_dbg.o /usr/src/linux/tools/bpf/bpf_dbg.c

Defining __EXPORTED_HEADERS__ is a hack to circumvent the checks in the
uapi headers.

So first comment is to stop doing that, although it doesn't actually fix
this issue.

>> >   In file included from /usr/include/asm/sigcontext.h:14,
>> > 		   from /usr/include/bits/sigcontext.h:30,
>> > 		   from /usr/include/signal.h:291,
>> > 		   from /usr/src/linux/tools/bpf/bpf_dbg.c:51:
>> >   /usr/include/asm/elf.h:160:9: error: unknown type name '__vector128'
>> >     160 | typedef __vector128 elf_vrreg_t;
>> > 	|         ^~~~~~~~~~~
>> >   make: *** [Makefile:67: bpf_dbg.o] Error 1
>> >   make: Leaving directory '/usr/src/linux/tools/bpf'
>> 
>> __vector128 is defined in arch/powerpc/include/uapi/asm/types.h;
>> while include/uapi/linux/types.h does #include <asm/types.h>,
>> tools/include/uapi/linux/types.h doesn't, resulting to this
>> compilation error.
>
> This is too puzzling to fix portably.

I don't really understand how this is expected to work.

We have tools/include/uapi/linux/types.h which is some sort of hand
hacked types.h, but doesn't match the real types.h from
include/uapi/linux.

In particular the tools/include types.h doesn't include asm/types.h,
which is why this breaks.

I can build bpf_dbg if I copy the properly exported header in:

  $ make INSTALL_HDR_PATH=$PWD/headers headers_install
  $ cp headers/include/linux/types.h tools/include/uapi/linux/
  $ make -C tools/bpf bpf_dbg
  make: Entering directory '/home/michael/linux/tools/bpf'
  
  Auto-detecting system features:
  ...                        libbfd: [ on  ]
  ...        disassembler-four-args: [ on  ]
  
    CC       bpf_dbg.o
    LINK     bpf_dbg
  make: Leaving directory '/home/michael/linux/tools/bpf


I'm not sure what the proper fix is.

Maybe sync the tools/include types.h with the real one?

Or TBH I would have thought the best option is to not have
tools/include/uapi at all, but instead just run headers_install before
building and use the properly exported headers.

cheers