linux-kernel - Re: clang --target=bpf missing on f23 was: Re: [PATCH 1/2] perf test: Add libbpf relocation checker

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Message-ID: <20160122174230.GB10247@ast-mbp.thefacebook.com>
Date:	Fri, 22 Jan 2016 09:42:30 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Adam Jackson <ajax@...hat.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Wang Nan <wangnan0@...wei.com>, ast@...nel.org,
	linux-kernel@...r.kernel.org,
	Daniel Borkmann <daniel@...earbox.net>,
	Li Zefan <lizefan@...wei.com>, pi3orama@....com,
	Dave Airlie <airlied@...hat.com>
Subject: Re: clang --target=bpf missing on f23 was:  Re: [PATCH 1/2] perf
 test: Add libbpf relocation checker

On Fri, Jan 22, 2016 at 12:35:42PM -0500, Adam Jackson wrote:
> On Fri, 2016-01-22 at 14:22 -0300, Arnaldo Carvalho de Melo wrote:
> 
> > 	the 'bpf' target for clang is being used together with perf to
> > build scriptlets into object code that then gets uploaded to the kernel
> > via sys_bpf(), was the decision not to include 'bpf' just an accident?
> 
> I wouldn't call it a "decision", that would imply intent. The main
> reason I explicitly list targets for llvm is to limit the CPU backends
> to arches Fedora actually runs on (which itself is because I really
> only care about llvmpipe, and am only touching llvm because it's in my
> way). Had no idea there was a bpf backend, so never thought to enable
> it.
> 
> llvm-3.7.0-4.fc2{3,4} are building now with the bpf backend enabled,
> I'll create an update for F23 when it's built.

thanks.
if you want to reduce the size of binaries, you can probably disable
nvptx/amdgcn/r600, since I doubt fedora ships with appropriate sdks
that can take advantage of that.