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firmware: Improve low-level trap handler for M-mode to M-mode traps

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This patch extends our low-level trap handler in fw_base.S for
handling M-mode to M-mode traps without overwritting stack.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
This commit is contained in:
Anup Patel
2019-02-19 18:11:22 +05:30
committed by Anup Patel
parent ce6189f7a5
commit 122d00ba67
2 changed files with 58 additions and 40 deletions
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94
firmware/fw_base.S
View File

@@ -181,6 +181,7 @@ _start_warm:
la a4, _hartid_to_scratch
REG_S a4, SBI_SCRATCH_HARTID_TO_SCRATCH_OFFSET(tp)
REG_S zero, SBI_SCRATCH_IPI_TYPE_OFFSET(tp)
REG_S zero, SBI_SCRATCH_TMP0_OFFSET(tp)
/* Setup stack */
add sp, tp, zero
@@ -242,42 +243,64 @@ _start_hang:
.section .entry, "ax", %progbits
.globl _trap_handler
_trap_handler:
/* Swap SP and MSCRATCH */
csrrw sp, CSR_MSCRATCH, sp
/* Swap TP and MSCRATCH */
csrrw tp, CSR_MSCRATCH, tp
/* Save T0 in scratch space */
REG_S t0, SBI_SCRATCH_TMP0_OFFSET(tp)
/* Check which mode we came from */
csrr t0, CSR_MSTATUS
srl t0, t0, MSTATUS_MPP_SHIFT
and t0, t0, PRV_M
xori t0, t0, PRV_M
beq t0, zero, _trap_handler_m_mode
/* We came from S-mode or U-mode */
_trap_handler_s_mode:
/* Set T0 to original SP */
add t0, sp, zero
/* Setup exception stack */
add sp, tp, -(SBI_TRAP_REGS_SIZE)
/* Jump to code common for all modes */
j _trap_handler_all_mode
/* We came from M-mode */
_trap_handler_m_mode:
/* Set T0 to original SP */
add t0, sp, zero
/* Re-use current SP as exception stack */
add sp, sp, -(SBI_TRAP_REGS_SIZE)
/* Save RA, T0, T1, and T2 */
REG_S ra, SBI_TRAP_REGS_OFFSET(ra)(sp)
REG_S t0, SBI_TRAP_REGS_OFFSET(t0)(sp)
REG_S t1, SBI_TRAP_REGS_OFFSET(t1)(sp)
REG_S t2, SBI_TRAP_REGS_OFFSET(t2)(sp)
/* Save original SP and restore MSCRATCH */
add t0, sp, SBI_TRAP_REGS_SIZE
csrrw t0, CSR_MSCRATCH, t0
_trap_handler_all_mode:
/* Save original SP (from T0) on stack */
REG_S t0, SBI_TRAP_REGS_OFFSET(sp)(sp)
/* Restore T0 from scratch space */
REG_L t0, SBI_SCRATCH_TMP0_OFFSET(tp)
/* Save T0 on stack */
REG_S t0, SBI_TRAP_REGS_OFFSET(t0)(sp)
/* Swap TP and MSCRATCH */
csrrw tp, CSR_MSCRATCH, tp
/* Save MEPC and MSTATUS CSRs */
csrr t0, CSR_MEPC
csrr t1, CSR_MSTATUS
/*
* Note: Fast path trap handling can be done here
* using SP, RA, T0, T1, and T2 registers where
* T0 <- MEPC
* T1 <- MSTATUS
*/
/* Save MEPC and MSTATUS CSRs */
REG_S t0, SBI_TRAP_REGS_OFFSET(mepc)(sp)
REG_S t1, SBI_TRAP_REGS_OFFSET(mstatus)(sp)
csrr t0, CSR_MSTATUS
REG_S t0, SBI_TRAP_REGS_OFFSET(mstatus)(sp)
/* Save all general regisers except SP, RA, T0, T1, and T2 */
/* Save all general regisers except SP and T0 */
REG_S zero, SBI_TRAP_REGS_OFFSET(zero)(sp)
REG_S ra, SBI_TRAP_REGS_OFFSET(ra)(sp)
REG_S gp, SBI_TRAP_REGS_OFFSET(gp)(sp)
REG_S tp, SBI_TRAP_REGS_OFFSET(tp)(sp)
REG_S t1, SBI_TRAP_REGS_OFFSET(t1)(sp)
REG_S t2, SBI_TRAP_REGS_OFFSET(t2)(sp)
REG_S s0, SBI_TRAP_REGS_OFFSET(s0)(sp)
REG_S s1, SBI_TRAP_REGS_OFFSET(s1)(sp)
REG_S a0, SBI_TRAP_REGS_OFFSET(a0)(sp)
@@ -308,9 +331,12 @@ _trap_handler:
csrr a1, CSR_MSCRATCH
call sbi_trap_handler
/* Restore all general regisers except SP, RA, T0, T1, T2, and T3 */
/* Restore all general regisers except SP and T0 */
REG_L ra, SBI_TRAP_REGS_OFFSET(ra)(sp)
REG_L gp, SBI_TRAP_REGS_OFFSET(gp)(sp)
REG_L tp, SBI_TRAP_REGS_OFFSET(tp)(sp)
REG_L t1, SBI_TRAP_REGS_OFFSET(t1)(sp)
REG_L t2, SBI_TRAP_REGS_OFFSET(t2)(sp)
REG_L s0, SBI_TRAP_REGS_OFFSET(s0)(sp)
REG_L s1, SBI_TRAP_REGS_OFFSET(s1)(sp)
REG_L a0, SBI_TRAP_REGS_OFFSET(a0)(sp)
@@ -336,26 +362,14 @@ _trap_handler:
REG_L t5, SBI_TRAP_REGS_OFFSET(t5)(sp)
REG_L t6, SBI_TRAP_REGS_OFFSET(t6)(sp)
/* Load T0 and T1 with MEPC and MSTATUS */
REG_L t0, SBI_TRAP_REGS_OFFSET(mepc)(sp)
REG_L t1, SBI_TRAP_REGS_OFFSET(mstatus)(sp)
/*
* Note: Jump here after fast trap handling
* using SP, RA, T0, T1, and T2
* T0 <- MEPC
* T1 <- MSTATUS
*/
/* Restore MEPC and MSTATUS CSRs */
REG_L t0, SBI_TRAP_REGS_OFFSET(mepc)(sp)
csrw CSR_MEPC, t0
csrw CSR_MSTATUS, t1
REG_L t0, SBI_TRAP_REGS_OFFSET(mstatus)(sp)
csrw CSR_MSTATUS, t0
/* Restore RA, T0, T1, and T2 */
REG_L ra, SBI_TRAP_REGS_OFFSET(ra)(sp)
/* Restore T0 */
REG_L t0, SBI_TRAP_REGS_OFFSET(t0)(sp)
REG_L t1, SBI_TRAP_REGS_OFFSET(t1)(sp)
REG_L t2, SBI_TRAP_REGS_OFFSET(t2)(sp)
/* Restore SP */
REG_L sp, SBI_TRAP_REGS_OFFSET(sp)(sp)

4
include/sbi/sbi_scratch.h
View File

@@ -30,6 +30,8 @@
#define SBI_SCRATCH_HARTID_TO_SCRATCH_OFFSET (7 * __SIZEOF_POINTER__)
/** Offset of ipi_type member in sbi_scratch */
#define SBI_SCRATCH_IPI_TYPE_OFFSET (8 * __SIZEOF_POINTER__)
/** Offset of tmp0 member in sbi_scratch */
#define SBI_SCRATCH_TMP0_OFFSET (9 * __SIZEOF_POINTER__)
/** Maximum size of sbi_scratch */
#define SBI_SCRATCH_SIZE 256
@@ -57,6 +59,8 @@ struct sbi_scratch {
unsigned long hartid_to_scratch;
/** IPI type (or flags) */
unsigned long ipi_type;
/** Temporary storage */
unsigned long tmp0;
} __packed;
/** Get pointer to sbi_scratch for current HART */