Date: Sat, 26 Nov 2016 09:32:29 -0800
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Wang Nan <wangnan0@huawei.com>
Cc: acme@redhat.com, ast@fb.com, lizefan@huawei.com, hekuang@huawei.com,
        linux-kernel@vger.kernel.org, pi3orama@163.com, joe@ovn.org,
        Jiri Olsa <jolsa@kernel.org>
Subject: Re: [PATCH v3 19/30] perf clang jit: Insignt BPF and JIT functions
 in a Module
Message-ID: <20161126173228.GH83987@ast-mbp.thefacebook.com>
References: <20161126070354.141764-1-wangnan0@huawei.com>
 <20161126070354.141764-20-wangnan0@huawei.com>
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On Sat, Nov 26, 2016 at 07:03:43AM +0000, Wang Nan wrote:
> Identify BPF functions, JIT functions and maps during init. Functions in
> section starting with "perfhook:" are JIT functions. They will be JIT
> compiled and hooked at perfhooks.
> 
> During init of PerfModule, mark JIT functions as AvailableExternallyLinkage.
> LLVM skips functions with linkage like this so they won't be compiled
> into BPF objects.
> 
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
...
> +void PerfModule::prepareBPF(void)
> +{
> +	for (llvm::Function *F : JITFunctions)
> +		F->setLinkage(llvm::GlobalValue::AvailableExternallyLinkage);
> +	for (llvm::Function *F : BPFFunctions)
> +		F->setLinkage(llvm::GlobalValue::ExternalLinkage);
> +
> +}
> +
> +void PerfModule::prepareJIT(void)
> +{
> +	for (llvm::Function *F : BPFFunctions)
> +		F->setLinkage(llvm::GlobalValue::AvailableExternallyLinkage);
> +	for (llvm::Function *F : JITFunctions)
> +		F->setLinkage(llvm::GlobalValue::ExternalLinkage);
> +
> +}

Nice trick.
Please document it in the perf+llvm design doc.

Acked-by: Alexei Starovoitov <ast@kernel.org>