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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: Song Shuai <songshuaishuai@tinylab.org>
Link: https://lore.kernel.org/r/20230907103304.590739-2-songshuaishuai@tinylab.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Song Shuai 2023-09-07 18:33:02 +08:00 committed by Palmer Dabbelt
parent 06c2afb862
commit 04a6a8eb13
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GPG Key ID: 2E1319F35FBB1889
1 changed files with 23 additions and 29 deletions
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52
arch/riscv/kernel/kexec_relocate.S
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@ -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: