Commit 2ad45b41 authored by Alexei Starovoitov's avatar Alexei Starovoitov
Browse files

bpf: Add spis_*() helpers for 4-byte stack slot bitmasks 



Add helper functions for manipulating u64[2] bitmasks that represent
4-byte stack slot liveness. The 512-byte BPF stack is divided into
128 4-byte slots, requiring 128 bits (two u64s) to track.

These will be used by the static stack liveness analysis in the
next commit.

Signed-off-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260410-patch-set-v4-3-5d4eecb343db@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent cf3ee1ec

include/linux/bpf_verifier.h

+67 −0
Original line number Diff line number Diff line
@@ -224,6 +224,73 @@ enum bpf_stack_slot_type { 


#define BPF_REG_SIZE 8	/* size of eBPF register in bytes */



/* 4-byte stack slot granularity for liveness analysis */

#define BPF_HALF_REG_SIZE	4

#define STACK_SLOTS		(MAX_BPF_STACK / BPF_HALF_REG_SIZE)	/* 128 */



typedef struct {

	u64 v[2];

} spis_t;



#define SPIS_ZERO	((spis_t){})

#define SPIS_ALL	((spis_t){{ U64_MAX, U64_MAX }})



static inline bool spis_is_zero(spis_t s)

{

	return s.v[0] == 0 && s.v[1] == 0;

}



static inline bool spis_equal(spis_t a, spis_t b)

{

	return a.v[0] == b.v[0] && a.v[1] == b.v[1];

}



static inline spis_t spis_or(spis_t a, spis_t b)

{

	return (spis_t){{ a.v[0] | b.v[0], a.v[1] | b.v[1] }};

}



static inline spis_t spis_and(spis_t a, spis_t b)

{

	return (spis_t){{ a.v[0] & b.v[0], a.v[1] & b.v[1] }};

}



static inline spis_t spis_xor(spis_t a, spis_t b)

{

	return (spis_t){{ a.v[0] ^ b.v[0], a.v[1] ^ b.v[1] }};

}



static inline spis_t spis_not(spis_t s)

{

	return (spis_t){{ ~s.v[0], ~s.v[1] }};

}



static inline bool spis_test_bit(spis_t s, u32 slot)

{

	return s.v[slot / 64] & BIT_ULL(slot % 64);

}



static inline void spis_or_range(spis_t *mask, u32 lo, u32 hi)

{

	u32 w;



	for (w = lo; w <= hi && w < STACK_SLOTS; w++)

		mask->v[w / 64] |= BIT_ULL(w % 64);

}



static inline spis_t spis_one_bit(u32 slot)

{

	if (slot < 64)

		return (spis_t){{ BIT_ULL(slot), 0 }};

	else

		return (spis_t){{ 0, BIT_ULL(slot - 64) }};

}



static inline spis_t spis_single_slot(u32 spi)

{

	return spis_or(spis_one_bit(spi * 2), spis_one_bit(spi * 2 + 1));

}



#define BPF_REGMASK_ARGS ((1 << BPF_REG_1) | (1 << BPF_REG_2) | \

			  (1 << BPF_REG_3) | (1 << BPF_REG_4) | \

			  (1 << BPF_REG_5))