.globl _start
.option rvc # enable compressed instructions
#.option norelax

.data
sigaction:
    .dword segv # sa_handler
    .dword 0  # sa_flags
    .dword 0  # sa_mask

.data
buf: .zero 8

.text
_start:
    # set up the gp register so that relaxed loads work
    .option norelax
    la gp, __global_pointer$
    .option relax
    # the following is what the la instruction above gets expanded to,
    # but writing it out explicitly like this causes ld to segfault
    #auipc gp, %pcrel_hi(__global_pointer$)
    #addi gp, gp, %pcrel_lo(__global_pointer$)

    # set up a signal handler for SIGSEGV
    # XXX we don't actually need this because write will
    # return EFAULT if the address isn't mapped
    li a7, 134  # sys_rt_sigaction
    li a0, 11   # SIGSEGv
    la a1, sigaction # action
    li a2, 0    # oldact = NULL
    li a3, 8    # signal set size (bytes)
    ecall

    # save sp
    la s7, buf
    sd sp, 0(s7)

    # print sp
    li a7, 64      # sys_write
    li a0, 1       # fd = stdout
    mv a1, s7     # pointer to string
    li a2, 8      # size of data
    ecall
    bltz a0, write_error

    # round sp down to multiple of 512
    # and move to s0
    andi s0, sp, -512

loop:
    # print sp
    sd s0, 0(s7)
    li a7, 64      # sys_write
    li a0, 1       # fd = stdout
    mv a1, s7     # pointer to string
    li a2, 8      # size of data
    ecall
    bltz a0, write_error

    # print 512 bytes of stack
    li a7, 64 # sys_write
    li a0, 1
    mv a1, s0
    li a2, 512
    ecall
    bltz a0, write_error

    # increment sp by 512
    addi s0, s0, 512

    beqz s0, segv
    j loop

write_error:
    li a7, 93 # exit
    li a0, 1
    ecall


segv:
    li a7, 93 # exit
    li a0, 0
    ecall