The Official Radare2 Book

Syscalls

Radare2 allows manual search for assembly code looking like a syscall operation. For example on ARM platform usually they are represented by the svc instruction, on the others can be a different instructions, e.g. syscall on x86 PC.

[0x0001ece0]> /ad/ svc

...

0x000187c2 # 2: svc 0x76

0x000189ea # 2: svc 0xa9

0x00018a0e # 2: svc 0x82

...

Syscalls detection is driven by asm.os, asm.bits, and asm.arch. Be sure to setup those configuration options accordingly. You can use asl command to check if syscalls' support is set up properly and as you expect. The command lists syscalls supported for your platform.

[0x0001ece0]> asl

...

sd_softdevice_enable = 0x80.16

sd_softdevice_disable = 0x80.17

sd_softdevice_is_enabled = 0x80.18

...

If you setup ESIL stack with aei or aeim, you can use /as command to search the addresses where particular syscalls were found and list them.

[0x0001ece0]> aei

[0x0001ece0]> /as

0x000187c2 sd_ble_gap_disconnect

0x000189ea sd_ble_gatts_sys_attr_set

0x00018a0e sd_ble_gap_sec_info_reply

...

To reduce searching time it is possible to restrict the searching range for only executable segments or sections with /as @e:search.in=io.maps.x

Using the ESIL emulation radare2 can print syscall arguments in the disassembly output. To enable the linear (but very rough) emulation use asm.emu configuration variable:

[0x0001ece0]> e asm.emu=true

[0x0001ece0]> s 0x000187c2

[0x000187c2]> pdf~svc

0x000187c2 svc 0x76 ; 118 = sd_ble_gap_disconnect

[0x000187c2]>

In case of executing aae (or aaaa which calls aae) command radare2 will push found syscalls to a special syscall. flagspace, which can be useful for automation purpose:

[0x000187c2]> fs

0 0 * imports

1 0 * symbols

2 1523 * functions

3 420 * strings

4 183 * syscalls

[0x000187c2]> f~syscall

...

0x000187c2 1 syscall.sd_ble_gap_disconnect.0

0x000189ea 1 syscall.sd_ble_gatts_sys_attr_set

0x00018a0e 1 syscall.sd_ble_gap_sec_info_reply

...

It also can be interactively navigated through within HUD mode (V_)

0> syscall.sd_ble_gap_disconnect

- 0x000187b2 syscall.sd_ble_gap_disconnect

0x000187c2 syscall.sd_ble_gap_disconnect.0

0x00018a16 syscall.sd_ble_gap_disconnect.1

0x00018b32 syscall.sd_ble_gap_disconnect.2

0x0002ac36 syscall.sd_ble_gap_disconnect.3

When debugging in radare2, you can use dcs to continue execution until the next syscall. You can also run dcs* to trace all syscalls.

[0xf7fb9120]> dcs*

Running child until syscalls:-1

child stopped with signal 133

--> SN 0xf7fd3d5b syscall 45 brk (0xffffffda)

child stopped with signal 133

--> SN 0xf7fd28f3 syscall 384 arch_prctl (0xffffffda 0x3001)

child stopped with signal 133

--> SN 0xf7fc81b2 syscall 33 access (0xffffffda 0xf7fd8bf1)

child stopped with signal 133

radare2 also has a syscall name to syscall number utility. You can return the syscall name of a given syscall number or vice versa, without leaving the shell.

[0x08048436]> asl 1

exit

[0x08048436]> asl write

4

[0x08048436]> ask write

0x80,4,3,iZi

See as? for more information about the utility.