netdev - Re: [PATCH v3 binutils] Add BPF support to binutils...

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Message-ID: <76ed19a7-add3-0642-4298-9402c7ff0be8@fb.com>
Date:   Sat, 29 Apr 2017 23:44:59 -0700
From:   Alexei Starovoitov <ast@...com>
To:     David Miller <davem@...emloft.net>
CC:     <daniel@...earbox.net>, <aconole@...heb.org>,
        <netdev@...r.kernel.org>, <xdp-newbies@...r.kernel.org>
Subject: Re: [PATCH v3 binutils] Add BPF support to binutils...

On 4/29/17 7:37 PM, David Miller wrote:
> From: David Miller <davem@...emloft.net>
> Date: Sat, 29 Apr 2017 22:24:50 -0400 (EDT)
>
>> Some of your bugs should be fixed by this patch below, I'll add
>> test cases soon:
>
> Ok, here are all the local changes in my tree.  I made the relocs
> match LLVM and I fixed some dwarf debugging stuff.
>
> With this we are also down to one test case failure under binutils/
> and it's something weird with merging 64-bit notes which I should be
> able to fix soon.
>
> I can fix these bugs fast, keep reporting.
>
> BTW, should I just remove tailcall from the opcode table altogether?

yeah. tailcall is not a special opcode from user space point of view.
Only after normal call with func_id=bpf_tail_call passes verifier
then verifier will change insn->code into CALL|X
It's done only to have two 'case' statement in the interpreter,
so that normal calls and tailcalls don't interfere.
 From user space pov CALL|X opcode is reserved and we can use it
for something in the future. Just need to change interpeter and JITs.

>  	    case 'O':
> -	      (*info->fprintf_func) (stream, "%d", off);
> +	      (*info->fprintf_func) (stream, "%d", (int) off);

tried this diff. It looks better
   10:	7b 1a f8 ff 00 00 00 00 	stdw	[r1+-8], r10
   18:	79 a1 f8 ff 00 00 00 00 	lddw	r10, [r1+-8]
I wonder if '+' can be removed as well.

'-g' still doesn't seem to work:
/w/binutils-gdb/bld/binutils/objdump: invalid relocation type 10
/w/binutils-gdb/bld/binutils/objdump: BFD (GNU Binutils) 
2.28.51.20170429 assertion fail ../../bfd/elf64-bpf.c:139
    0:	18 01 00 00 39 47 98 83 	ldimm64	r0, 590618314553