kl-bits

Bit-level view

Canonical: kernlens-bits
Category: bit & integer primitives
Synopsis: kl-bits [-h] value [bit]

Shows a 64-bit value in binary and reports the bit statistics that come up in exploit work: population count, leading and trailing zeros, highest and lowest set bit, and whether the value is a power of two.

Options

Option	Argument	Meaning
	—	value to inspect (0x hex, decimal, bare hex)
	(optional)	bit index 0-63 to test/set/clear/toggle

With a bit to test

Invocation

kl-bits 0xff 3

Output

value: 0xff  0000000000000000000000000000000000000000000000000000000011111111
scan: popcount=8 leading_zeros=56 trailing_zeros=0 first_set=1 last_set=8
power: is_power_of_2=False  log2_floor=7  log2_ceil=8
bit 3: test=True  set=0xff  clear=0xf7  toggle=0xf7

Reading it

The value: row pairs the hex form with a 64-bit binary rendering, so the bit positions can be counted directly. scan: gives popcount, the leading and trailing zero counts (1-based first_set/last_set), and power: reports the floor and ceiling log2 -- equal values mean the number IS a power of two. The final row tests, sets, clears and toggles the given bit, showing each result, so one invocation answers all four questions.

An address

Invocation

kl-bits 0xffffffffae900000

Output

value: 0xffffffffae900000  1111111111111111111111111111111110101110100100000000000000000000
scan: popcount=39 leading_zeros=0 trailing_zeros=20 first_set=21 last_set=64
power: is_power_of_2=False  log2_floor=63  log2_ceil=64

Reading it

trailing_zeros=20 is the page offset of this address (2 MiB aligned), which is the kind of fact that jumps out of the binary rendering and is tedious to compute by hand. log2_ceil=64 on a value with the top bit set is correct, not a bug: the next power of two above it does not fit in 64 bits.

Notes

The value is masked to 64 bits, so a negative input is read as its two's-complement form -- which is what you want when analysing a raw register.

---

Part of the KernLens tutorial. Every output block on this page was captured from the kernel described in the tutorial index.