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lib: Redirect illegal instruction trap to S-mode when not handled

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Currently, we fail with error SBI_ENOTSUPP when we are not able
to handle illegal instruction trap. Instead, we should just
redirect illegal instruction trap to S-mode when not handled.

This redirection of illegal instruction trap will help lazy
save/restore of floating point registers to work correctly in
Linux kernel.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
This commit is contained in:
Anup Patel 2018-12-27 21:39:13 +05:30 • committed by Anup Patel
parent 56e41f7a8d
commit 5959312a5c
4 changed files with 56 additions and 6 deletions
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9
include/sbi/riscv_encoding.h
View file

@ -19,12 +19,15 @@
#define MSTATUS_HIE 0x00000004
#define MSTATUS_MIE 0x00000008
#define MSTATUS_UPIE 0x00000010
#define MSTATUS_SPIE 0x00000020
#define MSTATUS_SPIE_SHIFT 5
#define MSTATUS_SPIE (1UL << MSTATUS_SPIE_SHIFT)
#define MSTATUS_HPIE 0x00000040
#define MSTATUS_MPIE 0x00000080
#define MSTATUS_SPP 0x00000100
#define MSTATUS_SPP_SHIFT 8
#define MSTATUS_SPP (1UL << MSTATUS_SPP_SHIFT)
#define MSTATUS_HPP 0x00000600
#define MSTATUS_MPP 0x00001800
#define MSTATUS_MPP_SHIFT 11
#define MSTATUS_MPP (3UL << MSTATUS_MPP_SHIFT)
#define MSTATUS_FS 0x00006000
#define MSTATUS_XS 0x00018000
#define MSTATUS_MPRV 0x00020000

4
include/sbi/sbi_trap.h
View file

@ -51,6 +51,10 @@ struct sbi_trap_regs {
struct sbi_scratch;
int sbi_trap_redirect(struct sbi_trap_regs *regs,
struct sbi_scratch *scratch,
ulong epc, ulong cause, ulong tval);
void sbi_trap_handler(struct sbi_trap_regs *regs,
struct sbi_scratch *scratch);

6
lib/sbi_illegal_insn.c
View file

@ -26,8 +26,7 @@ static int truly_illegal_insn(ulong insn,
struct sbi_trap_regs *regs,
struct sbi_scratch *scratch)
{
/* For now, always fails */
return SBI_ENOTSUPP;
return sbi_trap_redirect(regs, scratch, regs->mepc, mcause, insn);
}
static int system_opcode_insn(ulong insn,
@ -132,7 +131,8 @@ int sbi_illegal_insn_handler(u32 hartid, ulong mcause,
insn = get_insn(regs->mepc, &mstatus);
}
if ((insn & 3) != 3)
return SBI_ENOTSUPP;
return truly_illegal_insn(insn, hartid, mcause,
regs, scratch);
}
return illegal_insn_table[(insn & 0x7c) >> 2](insn, hartid, mcause,

43
lib/sbi_trap.c
View file

@ -66,6 +66,49 @@ static void __attribute__((noreturn)) sbi_trap_error(const char *msg,
sbi_hart_hang();
}
int sbi_trap_redirect(struct sbi_trap_regs *regs,
struct sbi_scratch *scratch,
ulong epc, ulong cause, ulong tval)
{
ulong new_mstatus, prev_mode;
/* Sanity check on previous mode */
prev_mode = (regs->mstatus & MSTATUS_MPP) >> MSTATUS_MPP_SHIFT;
if (prev_mode != PRV_S && prev_mode != PRV_U)
return SBI_ENOTSUPP;
/* Update S-mode exception info */
csr_write(stval, tval);
csr_write(sepc, epc);
csr_write(scause, cause);
/* Set MEPC to S-mode exception vector base */
regs->mepc = csr_read(stvec);
/* Initial value of new MSTATUS */
new_mstatus = regs->mstatus;
/* Clear MPP, SPP, SPIE, and SIE */
new_mstatus &= ~(MSTATUS_MPP |
MSTATUS_SPP | MSTATUS_SPIE | MSTATUS_SIE);
/* Set SPP */
if (prev_mode == PRV_S)
new_mstatus |= (1UL << MSTATUS_SPP_SHIFT);
/* Set SPIE */
if (regs->mstatus & MSTATUS_SIE)
new_mstatus |= (1UL << MSTATUS_SPIE_SHIFT);
/* Set MPP */
new_mstatus |= (PRV_S << MSTATUS_MPP_SHIFT);
/* Set new value in MSTATUS */
regs->mstatus = new_mstatus;
return 0;
}
void sbi_trap_handler(struct sbi_trap_regs *regs,
struct sbi_scratch *scratch)
{