linux-kernel - Re: [LLVMdev] Cc llvmdev: Re: llvm bpf debug info. Re: [RFC PATCH v4 3/3] bpf: Introduce function for outputing data to perf event

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Message-ID: <55C1C91D.5080007@huawei.com>
Date:	Wed, 5 Aug 2015 16:28:13 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Alexei Starovoitov <ast@...mgrid.com>,
	He Kuang <hekuang@...wei.com>, pi3orama <pi3orama@....com>
CC:	<llvm-dev@...ts.llvm.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [LLVMdev] Cc llvmdev: Re: llvm bpf debug info. Re: [RFC PATCH
 v4 3/3] bpf: Introduce function for outputing data to perf event



On 2015/8/5 15:11, Alexei Starovoitov wrote:
> On 8/4/15 11:51 PM, Wangnan (F) wrote:
>> void bpf_store_half(void *skb, int off, int val)
>> asm("llvm.bpf.store.half");
>> int func()
>> {
>>          bpf_store_half(0, 0, 0);
>>          return 0;
>> }
>>
>> Compiled with:
>>
>> $ clang -g -target bpf -O2 -S -c test.c
>>
>> And get this:
>>
>>          .text
>>          .globl  func
>>          .align  8
>> func:                                   # @func
>> # BB#0:                                 # %entry
>>          mov     r1, 0
>>          mov     r2, 0
>>          mov     r3, 0
>>          call    llvm.bpf.store.half
>
> it didn't work because number and types of args were incompatible.
> Every samples/bpf/sockex[0-9]_kern.c is using llvm.bpf.load.* intrinsics.
>

Make it work. Thank you.

It doesn't work for me at first since in my llvm there's only 
llvm.bpf.load.*.

I think llvm.bpf.store.* belone to some patches you haven't posted yet?

> the typeid changing ids with order is surprising.
> I think the assertion in ExtractTypeInfo() is not hard.
> Just there were no such use cases. May be we can do something
> similar to what LowerIntrinsicCall() does and lower it differently
> in the backend.
>
But in backend can we still get type information? I thought type is
meaningful in frontend only, and backend behaviors is unable to affect
DWARF generation, right?

Thank you.

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