netdev - Re: [PATCH bpf-next v5 00/10] BTF: BPF Type Format

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Date:   Thu, 14 Jun 2018 15:00:17 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Alexei Starovoitov <ast@...com>
Cc:     Martin KaFai Lau <kafai@...com>, netdev@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>, kernel-team@...com,
        Wang Nan <wangnan0@...wei.com>, Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH bpf-next v5 00/10] BTF: BPF Type Format

Em Thu, Jun 14, 2018 at 02:47:59PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Thu, Jun 14, 2018 at 10:21:30AM -0700, Alexei Starovoitov escreveu:
> > On 6/14/18 10:18 AM, Arnaldo Carvalho de Melo wrote:
> > > Just out of curiosity, is there any plan to have this as a clang option?
  
> > I think
> > clang ... -mllvm -mattr=dwarfris
> > should work.
 
> The message "(LLVM option parsing)" implies what you suggest, but didn't
> worked :-\
 
>   -mllvm <value>          Additional arguments to forward to LLVM's option processing
 
> Almost there tho :-\

So I thought that this -mattr=dwarfris would be available only after I
set the target, because I tried 'llc -mattr=help' and dwarfris wasn't
there:

[acme@...et perf]$ llc -mattr=help |& grep dwarf
[acme@...et perf]$

Only after I set the arch it appears:

[acme@...et perf]$ llc -march=bpf -mattr=help |& grep dwarf
  dwarfris - Disable MCAsmInfo DwarfUsesRelocationsAcrossSections.
  dwarfris - Disable MCAsmInfo DwarfUsesRelocationsAcrossSections.
  dwarfris - Disable MCAsmInfo DwarfUsesRelocationsAcrossSections.
[acme@...et perf]$ 

But even after moving the '-mllvm -mattr=dwarfris' to after '-target
bpf' it still can't grok it :-\

/usr/local/bin/clang -D__KERNEL__ -D__NR_CPUS__=4 -DLINUX_VERSION_CODE=0x41100 -g -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include -I/home/acme/git/linux/arch/x86/include -I./arch/x86/include/generated  -I/home/acme/git/linux/include -I./include -I/home/acme/git/linux/arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I/home/acme/git/linux/include/uapi -I./include/generated/uapi -include /home/acme/git/linux/include/linux/kconfig.h  -I/home/acme/lib/include/perf/bpf -Wno-unused-value -Wno-pointer-sign -working-directory /lib/modules/4.17.0-rc5/build -c /home/acme/bpf/hello.c -target bpf -mllvm -mattr=dwarfris -O2 -o hello.o

So onlye with 'clang ... -target bpf -emit-llvm -O2 -o - | llc -march=bpf -mattr=dwarfris ...'
things work as we expect.

- Arnaldo