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

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Date:	Fri, 22 Jan 2016 16:09:08 -0500 (EST)
From:	David Airlie <airlied@...hat.com>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	Adam Jackson <ajax@...hat.com>,
	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
Subject: Re: clang --target=bpf missing on f23 was:  Re: [PATCH 1/2] perf
 test: Add libbpf relocation checker



----- Original Message -----
> 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>
> Sent: Saturday, 23 January, 2016 3:42:30 AM
> 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.
> 

amdgcn is the other reason we ship llvm, we could probably drop nvptx.

Dave.

>