Add v8-dereference command

[lordidiot]

v8-dereference command

A new command meant to aid with debugging the v8 javascript engine that now uses pointer compression

Usage

Use just as you would with dereference (https://gef.readthedocs.io/en/master/commands/dereference/)
but s/deref/veref/g

d8> let a = {};                                                                                                                                                                                                                        
undefined                                                                                                                                                                                                                              
d8> %DebugPrint(a);                                                                                                                                                                                                                    
DebugPrint: 0x2ce608084a1d: [JS_OBJECT_TYPE]                                                                                                                                                                                           
...

gef➤  veref 0x2ce608084a1d
0x00002ce608084a1c│+0x0000: 0x00002ce6082422cd
                  │+0x0004: 0x00002ce6080426dd
0x00002ce608084a24│+0x0008: 0x00002ce6080426dd
                  │+0x000c: 0x00002ce608042301
0x00002ce608084a2c│+0x0010: 0x00002ce608042301
                  │+0x0014: 0x00002ce608042301
0x00002ce608084a34│+0x0018: 0x00002ce608042301
                  │+0x001c: 0x00002ce608042545
0x00002ce608084a3c│+0x0020: 0x00000adc9a4f2b76
0x00002ce608084a44│+0x0028: "(function() {\n"use strict";\n\n// A more universa[...]"
0x00002ce608084a4c│+0x0030: "on() {\n"use strict";\n\n// A more universal strin[...]"
0x00002ce608084a54│+0x0038: "use strict";\n\n// A more universal stringify that[...]"
0x00002ce608084a5c│+0x0040: "ct";\n\n// A more universal stringify that support[...]"
0x00002ce608084a64│+0x0048: "A more universal stringify that supports more type"
gef➤  veref 0x00002ce608042301
0x00002ce608042300│+0x0000: 0x00002ce60804231d
                  │+0x0004:         0x00000000 (SMI: 0x0)
0x00002ce608042308│+0x0008:         0x7ff80000 (SMI: 0x3ffc0000)
                  │+0x000c: 0x00002ce6080422e9
0x00002ce608042310│+0x0010: 0x00002ce608042345
                  │+0x0014: 0x00002ce6080422e9
0x00002ce608042318│+0x0018:         0x0000000a (SMI: 0x5)
                  │+0x001c: 0x00002ce60804213d
0x00002ce608042320│+0x0020: 0x181000431f000007
0x00002ce608042328│+0x0028:         0x004003ff
                  │+0x002c: 0x00002ce608042165
0x00002ce608042330│+0x0030: 0x00002ce608042165
                  │+0x0034: 0x00002ce6080421a9
0x00002ce608042338│+0x0038: 0x00002ce6080421e1
                  │+0x003c:         0x00000000 (SMI: 0x0)
0x00002ce608042340│+0x0040:         0x00000000 (SMI: 0x0)
                  │+0x0044: 0x00002ce608042351
0x00002ce608042348│+0x0048: 0x7ff8000000000000

Issues

1. Doesn't check for v8 version (Older versions don't use compressed pointers)
   • There may be some flags / easy indications in memory that we can parse and detect
2. Currently uses a primitive check to differentiate between compressed pointers and
   random values in memory that happen to hit the compressed pointer range
3. Doesn't even check if v8/d8 is running
4. Doesn't dereference tagged ptrs more than 1 level, although I don't see a purpose for this

Sorry to make a PR with quite incomplete code, but I thought maybe the general idea would be useful

[hugsy]

Sorry to make a PR with quite incomplete code, but I thought maybe the general idea would be useful

It's already a great start! Thanks for the PR!