binutils - question on decoding decision tree for aarch64

[Virendra Kumar Pathak]

Hi Linaro Toolchain Group,

I am trying to learn the 'decoding decision tree' for aarch64 in binutils
by trying to add a new assembly instruction 'addvp'.
For example: addvp x0, x0, 9

For this, I added a entry in struct aarch64_opcode aarch64_opcode_table[]
(file opcodes/aarch64-tbl.h) as below:
{"addvp", 0x01000000, 0x7f000000, addsub_imm, 0, CORE, OP3 (Rd_SP, Rn_SP,
AIMM), QL_R2NIL, F_SF},

ARM manual say, bit 27 & bit 28 are unallocated. Thus for addvp, I am
giving opcode 01000000 (with bit 27 & 28 as 0).
With this, generating object file from assembly file is successful (test.s
--> test.o); but while disassembling using objdump, it say undefined
instruction.
From objdump log:
81002400 .inst 0x81002400 ; undefined
(but instruction was generated correct i.e. 81002400 !!!).
I know since addvp is a hack instruction, it won't execute on cpu. But
still disassembly should succeed.

1. Please help me in knowing what I am doing wrong here ? What else I
should do to add a new instruction in binutils ?
2. I also saw some printf in opcodes/aarch64-gen.c which I guess create
decoding tree (initialize_decoder_tree()). How to print them ? I made debug
=1 but still print is not coming.
3. There are some auto-generated files
like aarch64-asm-2.c, aarch64-dis-2.c. How to re-generate them ?

Thanks.

[Jim Wilson]

On Sat, Jul 25, 2015 at 6:19 AM, Virendra Kumar Pathak

1. Please help me in knowing what I am doing wrong here ? What else I should
do to add a new instruction in binutils ?

I don't know offhand, but see below.

2. I also saw some printf in opcodes/aarch64-gen.c which I guess create
decoding tree (initialize_decoder_tree()). How to print them ? I made debug
=1 but still print is not coming.

It looks like it prints debug info to stdout, so the debugging info is
in the output files like aarch64-asm-2.c.

3. There are some auto-generated files like aarch64-asm-2.c,
aarch64-dis-2.c. How to re-generate them ?

Use --enable-maintainer-mode when running configure. This enables
makefiles rules for the auto-generated sources. These are normally
disabled by default to make it easier to build the source tree. With
this enabled, you may need extra utilities installed for a build to
work, especially if you haven't been careful about preserving file
timestamps. This enables rules to generate flex/bison output files,
and autoconf/automake output files, and files like aarch64-asm-2.c.

If you didn't do this before modifying aarch64-tbl.h, then this may be
why your changes aren't working. With --enable-maintainer-mode,
changing aarcht64-tbl.h will automatically rebuild aarch64-gen on the
next make, and that will then automatically be rerun to regenerate
files like aarch64-asm-2.c.

Jim