lib/crypto/arm/chacha-scalar-core.S

Source file repositories/reference/linux-study-clean/lib/crypto/arm/chacha-scalar-core.S

File Facts

System
Linux kernel
Corpus path
lib/crypto/arm/chacha-scalar-core.S
Extension
.S
Size
10524 bytes
Lines
445
Domain
Kernel Services
Bucket
lib
Inferred role
Kernel Services: lib
Status
atlas-only

Why This File Exists

Shared kernel service surface used by multiple subsystems, including helpers, cryptography, virtualization support, and async I/O infrastructure.

Dependency Surface

Detected Declarations

Annotated Snippet

#include <linux/linkage.h>
#include <asm/assembler.h>

/*
 * Design notes:
 *
 * 16 registers would be needed to hold the state matrix, but only 14 are
 * available because 'sp' and 'pc' cannot be used.  So we spill the elements
 * (x8, x9) to the stack and swap them out with (x10, x11).  This adds one
 * 'ldrd' and one 'strd' instruction per round.
 *
 * All rotates are performed using the implicit rotate operand accepted by the
 * 'add' and 'eor' instructions.  This is faster than using explicit rotate
 * instructions.  To make this work, we allow the values in the second and last
 * rows of the ChaCha state matrix (rows 'b' and 'd') to temporarily have the
 * wrong rotation amount.  The rotation amount is then fixed up just in time
 * when the values are used.  'brot' is the number of bits the values in row 'b'
 * need to be rotated right to arrive at the correct values, and 'drot'
 * similarly for row 'd'.  (brot, drot) start out as (0, 0) but we make it such
 * that they end up as (25, 24) after every round.
 */

	// ChaCha state registers
	X0	.req	r0
	X1	.req	r1
	X2	.req	r2
	X3	.req	r3
	X4	.req	r4
	X5	.req	r5
	X6	.req	r6
	X7	.req	r7
	X8_X10	.req	r8	// shared by x8 and x10
	X9_X11	.req	r9	// shared by x9 and x11
	X12	.req	r10
	X13	.req	r11
	X14	.req	r12
	X15	.req	r14

.macro _le32_bswap_4x	a, b, c, d,  tmp
#ifdef __ARMEB__
	rev_l		\a,  \tmp
	rev_l		\b,  \tmp
	rev_l		\c,  \tmp
	rev_l		\d,  \tmp
#endif
.endm

.macro __ldrd		a, b, src, offset
#if __LINUX_ARM_ARCH__ >= 6
	ldrd		\a, \b, [\src, #\offset]
#else
	ldr		\a, [\src, #\offset]
	ldr		\b, [\src, #\offset + 4]
#endif
.endm

.macro __strd		a, b, dst, offset
#if __LINUX_ARM_ARCH__ >= 6
	strd		\a, \b, [\dst, #\offset]
#else
	str		\a, [\dst, #\offset]
	str		\b, [\dst, #\offset + 4]
#endif
.endm

.macro _halfround	a1, b1, c1, d1,  a2, b2, c2, d2

	// a += b; d ^= a; d = rol(d, 16);
	add		\a1, \a1, \b1, ror #brot
	add		\a2, \a2, \b2, ror #brot

Annotation

Implementation Notes