linux-kernel - Re: [RFC PATCH v7 23/37] perf tools: Introduce llvm config options

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Message-Id: <C2FBB0D8-51CC-4CDC-9E8F-88137EFBEE19@163.com>
Date:	Sat, 13 Jun 2015 11:31:31 +0800
From:	pi3orama <pi3orama@....com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Wang Nan <wangnan0@...wei.com>,
	"acme@...nel.org" <acme@...nel.org>,
	"brendan.d.gregg@...il.com" <brendan.d.gregg@...il.com>,
	"daniel@...earbox.net" <daniel@...earbox.net>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"masami.hiramatsu.pt@...achi.com" <masami.hiramatsu.pt@...achi.com>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"jolsa@...nel.org" <jolsa@...nel.org>,
	"dsahern@...il.com" <dsahern@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lizefan@...wei.com" <lizefan@...wei.com>,
	"hekuang@...wei.com" <hekuang@...wei.com>,
	"xiakaixu@...wei.com" <xiakaixu@...wei.com>
Subject: Re: [RFC PATCH v7 23/37] perf tools: Introduce llvm config options



发自我的 iPhone

> 在 2015年6月13日，上午11:03，Alexei Starovoitov <ast@...mgrid.com> 写道：
> 
>> On 6/12/15 7:52 PM, pi3orama wrote:
>> 
>> 
>> 发自我的 iPhone
>> 
>>>> 在 2015年6月13日，上午10:31，Alexei Starovoitov <ast@...mgrid.com> 写道：
>>>> 
>>>> On 6/11/15 10:35 PM, Wang Nan wrote:
>>>>         # Path to clang. If omit, search it from $PATH.
>>>>    clang-path = "/path/to/clang"
>>> 
>>> I think this bit and search_program() from the next patch is
>>> overly flexible. It's always delicate to search file paths.
>>> Unless this is really needed, I would drop this bit.
>> 
>> I think searching clang before execution is still equired. If not, we are unable to know the exact reason why the shell script failed. If there's no clang at all, we can simply return an error instead of trying to detect kbuild and kernel header. Which is slower than clang compiling itself.
>> 
>> What about creating another shell script simply run 'clang --version' to check availability of clang? Then search_program can be dropped.
> 
> Hmm, I'm missing something.
> If clang is not in a path, the string from popen will be something like:
> /bin/sh: clang: command not found
> ?

Yes, user will get this error message from sh, but: 1. After kbuild and kernel include detection (which is expensive, takes even longer time than compiling), 2. Perf can't find the exact reason of the problem (error message is printed to sdterr, popen can only get an empty string and a !0 error code, which is similar to the result of compiling error).

> but if you want to call 'clang --version' as well that's also fine.
> 

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