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

From: Alexei Starovoitov
Date: Wed Aug 05 2015 - 03:11:29 EST


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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