Re: [PATCH v3 20/30] perf clang jit: add PerfModule::doJIT to JIT perfhook functions

[Wangnan (F)]

On 2016/11/27 1:29, Alexei Starovoitov wrote:
> On Sat, Nov 26, 2016 at 07:03:44AM +0000, Wang Nan wrote:
> > PerfModule::doJIT JIT compile perfhook functions and saves result into
> > a map. Add a test case for it.
> >
> > At this stage perfhook functions can do no useful things because they
> > can't invoke external functions and can't return value. Following
> > commits are going to make improvment.
> >
> > Don't hook functions right after jitted because bpf_object is unavailable
> > during jitting but it should be the context of jitted functions.
> >
> > Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> ...
> > +	for (Function *F : JITFunctions) {
> > +		JITSymbol sym = CompileLayer.findSymbol(F->getName().str(), true);
> > +
> > +		/*
> > +		 * Type of F->getSection() is moving from
> > +		 * const char * to StringRef.
> > +		 * Convert it to std::string so we don't need
> > +		 * consider this API change.
> > +		 */
> > +		std::string sec(F->getSection());
> > +		std::string hook(&sec.c_str()[sizeof("perfhook:") - 1]);
> > +		perf_hook_func_t func = (perf_hook_func_t)(intptr_t)sym.getAddress();
> > +
> > +		if (JITResult[hook])
> > +			llvm::errs() << "Warning: multiple functions on hook "
> > +				     << hook << ", only one is used\n";
> > +		JITResult[hook] = func;
> > +	}
> > +	return 0;
> > +}
> > +
> >   class ClangOptions {
> >   	llvm::SmallString<PATH_MAX> FileName;
> >   	llvm::SmallString<64> KVerDef;
> > @@ -292,6 +359,10 @@ void perf_clang__init(void)
> >   	LLVMInitializeBPFTarget();
> >   	LLVMInitializeBPFTargetMC();
> >   	LLVMInitializeBPFAsmPrinter();
> > +
> > +	llvm::InitializeNativeTarget();
> > +	llvm::InitializeNativeTargetAsmPrinter();
> > +	llvm::InitializeNativeTargetAsmParser();
> Looks great. I bet a lot of people reading perf code
> won't be able to understand what you're doing here.
> Could you please add a design doc on how perf<->clang/llvm interaction
> is done.

I'll put a perf-clang.txt in tools/perf/Documentation.

Thank you.

> Acked-by: Alexei Starovoitov <ast@xxxxxxxxxx>