esp-hal/esp32c3-hal/asm.S

#define STORE    sw
#define LOAD     lw
#define LOG_REGBYTES 2
#define REGBYTES (1 << LOG_REGBYTES)


/*
    Entry point of all programs (_start).
    It initializes DWARF call frame information, the stack pointer, the
    frame pointer (needed for closures to work in start_rust) and the global
    pointer. Then it calls _start_rust.
*/

.section .init, "ax"
.global _start

_start_hal:
    /* Jump to the absolute address defined by the linker script. */
    lui ra, %hi(_abs_start_hal)
    jr %lo(_abs_start_hal)(ra)

_abs_start_hal:
    .cfi_startproc
    .cfi_undefined ra

    // unsupported on ESP32C3
    // csrw mie, 0
    // csrw mip, 0

    li  x1, 0
    li  x2, 0
    li  x3, 0
    li  x4, 0
    li  x5, 0
    li  x6, 0
    li  x7, 0
    li  x8, 0
    li  x9, 0
    li  x10,0
    li  x11,0
    li  x12,0
    li  x13,0
    li  x14,0
    li  x15,0
    li  x16,0
    li  x17,0
    li  x18,0
    li  x19,0
    li  x20,0
    li  x21,0
    li  x22,0
    li  x23,0
    li  x24,0
    li  x25,0
    li  x26,0
    li  x27,0
    li  x28,0
    li  x29,0
    li  x30,0
    li  x31,0

    .option push
    .option norelax
    la gp, __global_pointer$
    .option pop

    // Check hart id
    csrr a2, mhartid
    lui t0, %hi(_max_hart_id)
    add t0, t0, %lo(_max_hart_id)
    bgtu a2, t0, abort

    // Allocate stacks
    la sp, _stack_start
    lui t0, %hi(_hart_stack_size)
    add t0, t0, %lo(_hart_stack_size)
#ifdef __riscv_mul
    mul t0, a2, t0
#else
    beqz a2, 2f  // Jump if single-hart
    mv t1, a2
    mv t2, t0
1:
    add t0, t0, t2
    addi t1, t1, -1
    bnez t1, 1b
2:
#endif
    sub sp, sp, t0

    // Set frame pointer
    add s0, sp, zero

    jal zero, _start_rust

    .cfi_endproc


/*
    Trap entry point (_start_trap)
    Saves registers and calls _start_trap_rust_hal,
    restores registers and then returns.
*/
.section .trap, "ax"
.global _start_trap_hal
.option norelax
.align 6

_start_trap_hal:
    addi sp, sp, -32*REGBYTES

    STORE ra, 0*REGBYTES(sp)
    STORE t0, 1*REGBYTES(sp)
    STORE t1, 2*REGBYTES(sp)
    STORE t2, 3*REGBYTES(sp)
    STORE t3, 4*REGBYTES(sp)
    STORE t4, 5*REGBYTES(sp)
    STORE t5, 6*REGBYTES(sp)
    STORE t6, 7*REGBYTES(sp)
    STORE a0, 8*REGBYTES(sp)
    STORE a1, 9*REGBYTES(sp)
    STORE a2, 10*REGBYTES(sp)
    STORE a3, 11*REGBYTES(sp)
    STORE a4, 12*REGBYTES(sp)
    STORE a5, 13*REGBYTES(sp)
    STORE a6, 14*REGBYTES(sp)
    STORE a7, 15*REGBYTES(sp)
    STORE s0, 16*REGBYTES(sp)
    STORE s1, 17*REGBYTES(sp)
    STORE s2, 18*REGBYTES(sp)
    STORE s3, 19*REGBYTES(sp)
    STORE s4, 20*REGBYTES(sp)
    STORE s5, 21*REGBYTES(sp)
    STORE s6, 22*REGBYTES(sp)
    STORE s7, 23*REGBYTES(sp)
    STORE s8, 24*REGBYTES(sp)
    STORE s9, 25*REGBYTES(sp)
    STORE s10, 26*REGBYTES(sp)
    STORE s11, 27*REGBYTES(sp)
    STORE gp, 28*REGBYTES(sp)
    STORE tp, 29*REGBYTES(sp)

    addi s0, sp, 32*REGBYTES
    STORE s0, 30*REGBYTES(sp)

    add a0, sp, zero
    jal ra, _start_trap_rust_hal

    LOAD ra, 0*REGBYTES(sp)
    LOAD t0, 1*REGBYTES(sp)
    LOAD t1, 2*REGBYTES(sp)
    LOAD t2, 3*REGBYTES(sp)
    LOAD t3, 4*REGBYTES(sp)
    LOAD t4, 5*REGBYTES(sp)
    LOAD t5, 6*REGBYTES(sp)
    LOAD t6, 7*REGBYTES(sp)
    LOAD a0, 8*REGBYTES(sp)
    LOAD a1, 9*REGBYTES(sp)
    LOAD a2, 10*REGBYTES(sp)
    LOAD a3, 11*REGBYTES(sp)
    LOAD a4, 12*REGBYTES(sp)
    LOAD a5, 13*REGBYTES(sp)
    LOAD a6, 14*REGBYTES(sp)
    LOAD a7, 15*REGBYTES(sp)
    LOAD s0, 16*REGBYTES(sp)
    LOAD s1, 17*REGBYTES(sp)
    LOAD s2, 18*REGBYTES(sp)
    LOAD s3, 19*REGBYTES(sp)
    LOAD s4, 20*REGBYTES(sp)
    LOAD s5, 21*REGBYTES(sp)
    LOAD s6, 22*REGBYTES(sp)
    LOAD s7, 23*REGBYTES(sp)
    LOAD s8, 24*REGBYTES(sp)
    LOAD s9, 25*REGBYTES(sp)
    LOAD s10, 26*REGBYTES(sp)
    LOAD s11, 27*REGBYTES(sp)
    LOAD gp, 28*REGBYTES(sp)
    LOAD tp, 29*REGBYTES(sp)
    LOAD sp, 30*REGBYTES(sp)

    # SP was restored from the original SP
    mret

.section .trap, "ax"
.balign 0x100
.global _vector_table
.type _vector_table, @function

_vector_table:
    .option push
    .option norvc
    .rept 31
    j _start_trap_hal
    .endr