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: <55C1B717.60501@plumgrid.com>
Date:	Wed, 5 Aug 2015 00:11:19 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	"Wangnan (F)" <wangnan0@...wei.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 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.

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.

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