xv6-riscv-kernel/kernel/riscv.h

#pragma once

#ifndef __ASSEMBLER__

#include "types.h"

// which hart (core) is this?
static inline u64
r_mhartid()
{
  u64 x;
  asm volatile("csrr %0, mhartid" : "=r"(x));
  return x;
}

// Machine Status Register, mstatus

#define MSTATUS_MPP_MASK (3L << 11) // previous mode.
#define MSTATUS_MPP_M    (3L << 11)
#define MSTATUS_MPP_S    (1L << 11)
#define MSTATUS_MPP_U    (0L << 11)
#define MSTATUS_MIE      (1L << 3) // machine-mode interrupt enable.

static inline u64
r_mstatus()
{
  u64 x;
  asm volatile("csrr %0, mstatus" : "=r"(x));
  return x;
}

static inline void
w_mstatus(u64 x)
{
  asm volatile("csrw mstatus, %0" : : "r"(x));
}

// machine exception program counter, holds the
// instruction address to which a return from
// exception will go.
static inline void
w_mepc(u64 x)
{
  asm volatile("csrw mepc, %0" : : "r"(x));
}

// Supervisor Status Register, sstatus

/** Supervisor Previous Privilege */
#define SSTATUS_SPP (1L << 8) // Previous mode, 1=Supervisor, 0=User

/** Supervisor Previous Interrupt Enable */
#define SSTATUS_SPIE (1L << 5)

/** User Previous Interrupt Enable */
#define SSTATUS_UPIE (1L << 4)

/** Supervisor Interrupt Enable */
#define SSTATUS_SIE (1L << 1)

/** User Interrupt Enable */
#define SSTATUS_UIE (1L << 0)

/**
 * Read the value of the sstatus register.
 * (Supervisor Status Register)
 */
static inline u64
r_sstatus()
{
  u64 x;
  asm volatile("csrr %0, sstatus" : "=r"(x));
  return x;
}

/**
 * Write a value to the sstatus register.
 * (Supervisor Status Register)
 */
static inline void
w_sstatus(u64 x)
{
  asm volatile("csrw sstatus, %0" : : "r"(x));
}

/** Read Suporvisor Interrupt Pending */
static inline u64
r_sip()
{
  u64 x;
  asm volatile("csrr %0, sip" : "=r"(x));
  return x;
}

/** Write Suporvisor Interrupt Pending */
static inline void
w_sip(u64 x)
{
  asm volatile("csrw sip, %0" : : "r"(x));
}

/** Supervisor External Interrup Enable */
#define SIE_SEIE (1L << 9)

/** Supervisor Timer Interrupt Enable */
#define SIE_STIE (1L << 5)

/** Supervisor Software Interrupt Enable */
#define SIE_SSIE (1L << 1)

/**
 * Read the value of the sie register.
 * (Supervisor Interrupt Enable)
 */
static inline u64
r_sie()
{
  u64 x;
  asm volatile("csrr %0, sie" : "=r"(x));
  return x;
}

/**
 * Write the valie to the sie rgister
 * (Supervisor Interrupt Enable)
 */
static inline void
w_sie(u64 x)
{
  asm volatile("csrw sie, %0" : : "r"(x));
}

/** Machine External Interrupt Enable */
#define MIE_MEIE (1L << 11)

/** Machine Timer Interrupt Enable */
#define MIE_MTIE (1L << 7)

/** Machine Software Interrupt Enable */
#define MIE_MSIE (1L << 3)

/**
 * Read the value of the mie register.
 * (Machine Interrupt Enable)
 */
static inline u64
r_mie()
{
  u64 x;
  asm volatile("csrr %0, mie" : "=r"(x));
  return x;
}

/**
 * Write the value to the mie register.
 * (Machine Interrupt Enable)
 */
static inline void
w_mie(u64 x)
{
  asm volatile("csrw mie, %0" : : "r"(x));
}

// The supervisor exception program counter holds the
// instruction address to which a return from
// exception will go.
//
// It is automatically set when an exception occurs.
// It can also be set with the w_sepc() function.
// (A wrapper for csrw sepc, x)
//
// Information related to the cause of the exception
// will be in the scause register. Readable with the
// r_scause() defined below.

/** Write Supervisor Exception Program Counter */
static inline void
w_sepc(u64 x)
{
  asm volatile("csrw sepc, %0" : : "r"(x));
}

/** Read Supervisor Exception Program Counter */
static inline u64
r_sepc()
{
  u64 x;
  asm volatile("csrr %0, sepc" : "=r"(x));
  return x;
}

/** Read Machine Exception Delegation */
static inline u64
r_medeleg()
{
  u64 x;
  asm volatile("csrr %0, medeleg" : "=r"(x));
  return x;
}

/** Write Machine Exception Delegation */
static inline void
w_medeleg(u64 x)
{
  asm volatile("csrw medeleg, %0" : : "r"(x));
}

/** Read Machine Interrupt Delegation */
static inline u64
r_mideleg()
{
  u64 x;
  asm volatile("csrr %0, mideleg" : "=r"(x));
  return x;
}

/** Write Machine Interrupt Delegation */
static inline void
w_mideleg(u64 x)
{
  asm volatile("csrw mideleg, %0" : : "r"(x));
}

/** Write Supervisor Trap-Vector Base Address */
static inline void
w_stvec(u64 x)
{
  asm volatile("csrw stvec, %0" : : "r"(x));
}

/** Read Supervisor Trap-Vector Base Address */
static inline u64
r_stvec()
{
  u64 x;
  asm volatile("csrr %0, stvec" : "=r"(x));
  return x;
}

/** Write Machine Trap-Vector Base Address */
static inline void
w_mtvec(u64 x)
{
  asm volatile("csrw mtvec, %0" : : "r"(x));
}

/** Read Physical Memory Protection Configuration */
static inline void
w_pmpcfg0(u64 x)
{
  asm volatile("csrw pmpcfg0, %0" : : "r"(x));
}

/** Write Physical Memory Protection Configuration */
static inline void
w_pmpaddr0(u64 x)
{
  asm volatile("csrw pmpaddr0, %0" : : "r"(x));
}

/** Risc-v's sv39 page table scheme. */
#define SATP_SV39 (8L << 60)

/** Make Supervisor Address Translation and Protection */
#define MAKE_SATP(pagetable) (SATP_SV39 | (((u64)pagetable) >> 12))

/**
 * Write the value to the satp register.
 * (Supervisor Address Translation and Protection)
 *
 * This register holds the address of the page table.
 */
static inline void
w_satp(u64 x)
{
  asm volatile("csrw satp, %0" : : "r"(x));
}

/**
 * Read the value of the satp register.
 * (Supervisor Address Translation and Protection)
 * Returns the address of the page table.
 */
static inline u64
r_satp()
{
  u64 x;
  asm volatile("csrr %0, satp" : "=r"(x));
  return x;
}

/** Read Supervisor Scratch Register */
static inline void
w_mscratch(u64 x)
{
  asm volatile("csrw mscratch, %0" : : "r"(x));
}

/** Supervisor Trap Cause */
static inline u64
r_scause()
{
  u64 x;
  asm volatile("csrr %0, scause" : "=r"(x));
  return x;
}

/** Supervisor Trap Value */
static inline u64
r_stval()
{
  u64 x;
  asm volatile("csrr %0, stval" : "=r"(x));
  return x;
}

/** Write Machine-mode Counter-Enable Register */
static inline void
w_mcounteren(u64 x)
{
  asm volatile("csrw mcounteren, %0" : : "r"(x));
}

/** Read Machine-mode Counter-Enable Register */
static inline u64
r_mcounteren()
{
  u64 x;
  asm volatile("csrr %0, mcounteren" : "=r"(x));
  return x;
}

/**
 * Machine-mode cycle counter
 * Reports the current wall-clock time from the timer device.
 */
static inline u64
r_time()
{
  u64 x;
  asm volatile("csrr %0, time" : "=r"(x));
  return x;
}

/** Enable device interrupts */
static inline void
intr_on()
{
  w_sstatus(r_sstatus() | SSTATUS_SIE);
}

/** Disable device interrupts */
static inline void
intr_off()
{
  w_sstatus(r_sstatus() & ~SSTATUS_SIE);
}

/** Are device interrupts enabled? */
static inline int
intr_get()
{
  u64 x = r_sstatus();
  return (x & SSTATUS_SIE) != 0;
}

/** Read stack pointer */
static inline u64
r_sp()
{
  u64 x;
  asm volatile("mv %0, sp" : "=r"(x));
  return x;
}

// read and write tp, the thread pointer, which xv6 uses to hold
// this core's hartid (core number), the index into cpus[].

/** Read thread pointer */
static inline u64
r_tp()
{
  u64 x;
  asm volatile("mv %0, tp" : "=r"(x));
  return x;
}

/** Write thread pointer */
static inline void
w_tp(u64 x)
{
  asm volatile("mv tp, %0" : : "r"(x));
}

/** Read the return address */
static inline u64
r_ra()
{
  u64 x;
  asm volatile("mv %0, ra" : "=r"(x));
  return x;
}

/** Flush the TLB (Translation Lookaside Buffer) */
static inline void
sfence_vma()
{
  // the zero, zero means flush all TLB entries.
  asm volatile("sfence.vma zero, zero");
}

/** Page Table Entry Type */
typedef u64 pte_t;

/** Page Table Type */
typedef u64 *pagetable_t; // 512 PTEs

#endif // __ASSEMBLER__

/** Page Size */
#define PGSIZE 4096 // bytes per page

/** Page Shift, bits of offset within a page */
#define PGSHIFT 12

#define PGROUNDUP(sz)  (((sz) + PGSIZE - 1) & ~(PGSIZE - 1))
#define PGROUNDDOWN(a) (((a)) & ~(PGSIZE - 1))

/**
 * Page Table Entry Flags
 */

#define PTE_V (1L << 0) /** PTE Valid */
#define PTE_R (1L << 1) /** PTE Readable */
#define PTE_W (1L << 2) /** PTE Writeable */
#define PTE_X (1L << 3) /** PTE Executable */
#define PTE_U (1L << 4) /** PTE User Accessible */

/**
 * Helper macros to shift a physical address
 * to the right place for a PTE.
 */

/** Physical Address to Page Table Entry */
#define PA2PTE(pa) ((((u64)pa) >> 12) << 10)

/** Page Table Entry to Physical Address */
#define PTE2PA(pte) (((pte) >> 10) << 12)

/** Page Table Entry Flags */
#define PTE_FLAGS(pte) ((pte) & 0x3FF)

/**
 * Helper macros to extract the three 9-bit
 * page table indices from a virtual address.
 */

/** Page Extract Mask */
#define PXMASK 0x1FF // 9 bits, 0b111111111

/** Page Extract Shift */
#define PXSHIFT(level) (PGSHIFT + (9 * (level)))

/** Page Extract */
#define PX(level, va) ((((u64)(va)) >> PXSHIFT(level)) & PXMASK)

/**
 * One beyond the highest possible virtual address.
 * MAXVA is actually one bit less than the max allowed by
 * Sv39, to avoid having to sign-extend virtual addresses
 * that have the high bit set.
 */
#define MAXVA (1L << (9 + 9 + 9 + 12 - 1))