| ahi p set base to htons(port) (3)
| ahi S set base to syscall (80)
| ahi s set base to string (1)
[0x00003d54]> pd 2
0x00003d54 0583000000 add eax, 0x83
0x00003d59 3d13010000 cmp eax, 0x113
[0x00003d54]> ahi d
[0x00003d54]> pd 2
0x00003d54 0583000000 add eax, 131
0x00003d59 3d13010000 cmp eax, 0x113
[0x00003d54]> ahi b
[0x00003d54]> pd 2
0x00003d54 0583000000 add eax, 10000011b
0x00003d59 3d13010000 cmp eax, 0x113
It is notable that some analysis stages or commands add the internal analysis hints, which can be checked with ah command:
[0x00003d54]> ah
0x00003d54 - 0x00003d54 => immbase=2
[0x00003d54]> ah*
ahi 2 @ 0x3d54
Sometimes we need to override jump or call address, for example in case of tricky relocation, which is unknown for radare2, thus we can change the value manually. The current analysis information about a particular opcode can be checked with ao command. We can use ahc command for performing such a change:
[0x00003cee]> pd 2
0x00003cee e83d080100 call sub.__errno_location_530
0x00003cf3 85c0 test eax, eax
[0x00003cee]> ao
address: 0x3cee
opcode: call 0x14530
mnemonic: call
prefix: 0
id: 56
bytes: e83d080100
refptr: 0
size: 5
sign: false
type: call
cycles: 3
esiclass="underline" 83248,rip,8,rsp,-=,rsp,=[],rip,=
jump: 0x00014530
direction: exec
faiclass="underline" 0x00003cf3
stack: null
family: cpu
stackop: null
[0x00003cee]> ahc 0x5382
[0x00003cee]> pd 2
0x00003cee e83d080100 call sub.__errno_location_530
0x00003cf3 85c0 test eax, eax
[0x00003cee]> ao
address: 0x3cee
opcode: call 0x14530
mnemonic: call
prefix: 0
id: 56
bytes: e83d080100
refptr: 0
size: 5
sign: false
type: call
cycles: 3
esiclass="underline" 83248,rip,8,rsp,-=,rsp,=[],rip,=
jump: 0x00005382
direction: exec
faiclass="underline" 0x00003cf3
stack: null
family: cpu
stackop: null
[0x00003cee]> ah
0x00003cee - 0x00003cee => jump: 0x5382
As you can see, despite the unchanged disassembly view the jump address in opcode was changed (jump option).
If anything of the previously described didn't help, you can simply override shown disassembly with anything you like:
[0x00003d54]> pd 2
0x00003d54 0583000000 add eax, 10000011b
0x00003d59 3d13010000 cmp eax, 0x113
[0x00003d54]> "ahd myopcode bla, foo"
[0x00003d54]> pd 2
0x00003d54 myopcode bla, foo
0x00003d55 830000 add dword [rax], 0
Radare2 allows managing local variables, no matter their location, stack or registers. The variables' auto analysis is enabled by default but can be disabled with anal.vars configuration option.
The main variables commands are located in afv namespace:
Usage: afv [rbs]
| afv* output r2 command to add args/locals to flagspace
| afv-([name]) remove all or given var
| afv= list function variables and arguments with disasm refs
| afva analyze function arguments/locals
| afvb[?] manipulate bp based arguments/locals
| afvd name output r2 command for displaying the value of args/locals in the debugger
| afvf show BP relative stackframe variables
| afvn [new_name] ([old_name]) rename argument/local
| afvr[?] manipulate register based arguments
| afvR [varname] list addresses where vars are accessed (READ)
| afvs[?] manipulate sp based arguments/locals
| afvt [name] [new_type] change type for given argument/local
| afvW [varname] list addresses where vars are accessed (WRITE)
| afvx show function variable xrefs (same as afvR+afvW)
afvr, afvb and afvs commands are uniform but allow manipulation of register-based arguments and variables, BP/FP-based arguments and variables, and SP-based arguments and variables respectively. If we check the help for afvr we will get the way two others commands works too:
|Usage: afvr [reg] [type] [name]
| afvr list register based arguments
| afvr* same as afvr but in r2 commands
| afvr [reg] [name] ([type]) define register arguments
| afvrj return list of register arguments in JSON format
| afvr- [name] delete register arguments at the given index
| afvrg [reg] [addr] define argument get reference
| afvrs [reg] [addr] define argument set reference
Like many other things variables detection is performed by radare2 automatically, but results can be changed with those arguments/variables control commands. This kind of analysis relies heavily on preloaded function prototypes and the calling-convention, thus loading symbols can improve it. Moreover, after changing something we can rerun variables analysis with afva command. Quite often variables analysis is accompanied with types analysis, see afta command.
The most important aspect of reverse engineering - naming things. Of course, you can rename variable too, affecting all places it was referenced. This can be achieved with afvn for any type of argument or variable. Or you can simply remove the variable or argument with afv- command.
As mentioned before the analysis loop relies heavily on types information while performing variables analysis stages. Thus comes next very important command - afvt, which allows you to change the type of variable:
[0x00003b92]> afvs
var int local_8h @ rsp+0x8
var int local_10h @ rsp+0x10
var int local_28h @ rsp+0x28
var int local_30h @ rsp+0x30
var int local_32h @ rsp+0x32
var int local_38h @ rsp+0x38
var int local_45h @ rsp+0x45
var int local_46h @ rsp+0x46
var int local_47h @ rsp+0x47
var int local_48h @ rsp+0x48
[0x00003b92]> afvt local_10h char*
[0x00003b92]> afvs
var int local_8h @ rsp+0x8
var char* local_10h @ rsp+0x10
var int local_28h @ rsp+0x28
var int local_30h @ rsp+0x30
var int local_32h @ rsp+0x32
var int local_38h @ rsp+0x38
var int local_45h @ rsp+0x45
var int local_46h @ rsp+0x46
var int local_47h @ rsp+0x47
var int local_48h @ rsp+0x48
Less commonly used feature, which is still under heavy development - distinction between variables being read and written. You can list those being read with afvR command and those being written with afvW command. Both commands provide a list of the places those operations are performed:
[0x00003b92]> afvR
local_48h 0x48ee
local_30h 0x3c93,0x520b,0x52ea,0x532c,0x5400,0x3cfb
local_10h 0x4b53,0x5225,0x53bd,0x50cc
local_8h 0x4d40,0x4d99,0x5221,0x53b9,0x50c8,0x4620
local_28h 0x503a,0x51d8,0x51fa,0x52d3,0x531b
local_38h
local_45h 0x50a1
local_47h
local_46h
local_32h 0x3cb1
[0x00003b92]> afvW
local_48h 0x3adf
local_30h 0x3d3e,0x4868,0x5030
local_10h 0x3d0e,0x5035
local_8h 0x3d13,0x4d39,0x5025
local_28h 0x4d00,0x52dc,0x53af,0x5060,0x507a,0x508b
local_38h 0x486d
local_45h 0x5014,0x5068
local_47h 0x501b
local_46h 0x5083
local_32h
[0x00003b92]>