Unverified Commit 04a6a8eb authored by Song Shuai's avatar Song Shuai Committed by Palmer Dabbelt
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riscv: kexec: Cleanup riscv_kexec_relocate 



For readability and simplicity, cleanup the riscv_kexec_relocate code:

- Re-sort the first 4 `mv` instructions against `riscv_kexec_method()`
- Eliminate registers for debugging (s9,s10,s11) and storing const-value (s5,s6)
- Replace `jalr` with `jr` for no-link jump

I tested this on Qemu virt machine and works as it was.

Signed-off-by: default avatarSong Shuai <songshuaishuai@tinylab.org>
Link: https://lore.kernel.org/r/20230907103304.590739-2-songshuaishuai@tinylab.org


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent 06c2afb8

arch/riscv/kernel/kexec_relocate.S

+23 −29
Original line number Diff line number Diff line
@@ -17,27 +17,17 @@ SYM_CODE_START(riscv_kexec_relocate) 
	 * s1: (const) Phys address to jump to after relocation

	 * s2: (const) Phys address of the FDT image

	 * s3: (const) The hartid of the current hart

	 * s4: Pointer to the destination address for the relocation

	 * s5: (const) Number of words per page

	 * s6: (const) 1, used for subtraction

	 * s7: (const) kernel_map.va_pa_offset, used when switching MMU off

	 * s8: (const) Physical address of the main loop

	 * s9: (debug) indirection page counter

	 * s10: (debug) entry counter

	 * s11: (debug) copied words counter

	 * s4: (const) kernel_map.va_pa_offset, used when switching MMU off

	 * s5: Pointer to the destination address for the relocation

	 * s6: (const) Physical address of the main loop

	 */

	mv	s0, a0

	mv	s1, a1

	mv	s2, a2

	mv	s3, a3

	mv	s4, zero

	li	s5, (PAGE_SIZE / RISCV_SZPTR)

	li	s6, 1

	mv	s7, a4

	mv	s8, zero

	mv	s9, zero

	mv	s10, zero

	mv	s11, zero

	mv	s4, a4

	mv	s5, zero

	mv	s6, zero



	/* Disable / cleanup interrupts */

	csrw	CSR_SIE, zero
@@ -52,21 +42,27 @@ SYM_CODE_START(riscv_kexec_relocate) 
	 * the start of the loop below so that we jump there in

	 * any case.

	 */

	la	s8, 1f

	sub	s8, s8, s7

	csrw	CSR_STVEC, s8

	la	s6, 1f

	sub	s6, s6, s4

	csrw	CSR_STVEC, s6



	/*

	 * With C-extension, here we get 42 Bytes and the next

	 * .align directive would pad zeros here up to 44 Bytes.

	 * So manually put a nop here to avoid zeros padding.

	*/

	nop



	/* Process entries in a loop */

.align 2

1:

	addi	s10, s10, 1

	REG_L	t0, 0(s0)		/* t0 = *image->entry */

	addi	s0, s0, RISCV_SZPTR	/* image->entry++ */



	/* IND_DESTINATION entry ? -> save destination address */

	andi	t1, t0, 0x1

	beqz	t1, 2f

	andi	s4, t0, ~0x1

	andi	s5, t0, ~0x1

	j	1b



2:
@@ -74,9 +70,8 @@ SYM_CODE_START(riscv_kexec_relocate) 
	andi	t1, t0, 0x2

	beqz	t1, 2f

	andi	s0, t0, ~0x2

	addi	s9, s9, 1

	csrw	CSR_SATP, zero

	jalr	zero, s8, 0

	jr	s6



2:

	/* IND_DONE entry ? -> jump to done label */
@@ -92,14 +87,13 @@ SYM_CODE_START(riscv_kexec_relocate) 
	andi	t1, t0, 0x8

	beqz	t1, 1b		/* Unknown entry type, ignore it */

	andi	t0, t0, ~0x8

	mv	t3, s5		/* i = num words per page */

	li	t3, (PAGE_SIZE / RISCV_SZPTR)	/* i = num words per page */

3:	/* copy loop */

	REG_L	t1, (t0)	/* t1 = *src_ptr */

	REG_S	t1, (s4)	/* *dst_ptr = *src_ptr */

	REG_S	t1, (s5)	/* *dst_ptr = *src_ptr */

	addi	t0, t0, RISCV_SZPTR /* stc_ptr++ */

	addi	s4, s4, RISCV_SZPTR /* dst_ptr++ */

	sub	t3, t3, s6	/* i-- */

	addi	s11, s11, 1	/* c++ */

	addi	s5, s5, RISCV_SZPTR /* dst_ptr++ */

	addi	t3, t3, -0x1	/* i-- */

	beqz	t3, 1b		/* copy done ? */

	j	3b
@@ -146,7 +140,7 @@ SYM_CODE_START(riscv_kexec_relocate) 
	 */

	fence.i



	jalr	zero, a2, 0

	jr	a2



SYM_CODE_END(riscv_kexec_relocate)

riscv_kexec_relocate_end: