commit 63904ea09f75249760b45fea6bdd349feb2fb2d3
Author: Bryan McShea <cat71602@gmail.com>
Date:   Tue Oct 11 17:54:20 2022 -0400

    initial commit

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..1180811
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,9 @@
+CC = riscv64-linux-gnu-gcc
+GCC_ARGS = -static -g -nostdlib
+SOURCES = $(wildcard src/*.s src/**/*.s)
+
+build/main: $(SOURCES)
+	$(CC) $(GCC_ARGS) -o build/main $(SOURCES)
+
+clean:
+	rm -r build/*
diff --git a/build/main b/build/main
new file mode 100755
index 0000000..82aaee1
Binary files /dev/null and b/build/main differ
diff --git a/build/test.txt b/build/test.txt
new file mode 100644
index 0000000..4c5e6c4
Binary files /dev/null and b/build/test.txt differ
diff --git a/run b/run
new file mode 100755
index 0000000..8231ec4
--- /dev/null
+++ b/run
@@ -0,0 +1,13 @@
+#!/bin/sh
+make -s || exit
+cd build
+
+if [ "$1" = "d" ]; then
+    qemu-riscv64 -g 1234 main &
+    riscv64-linux-gnu-gdb -q \
+        -ex "target remote :1234" \
+        main
+else
+    qemu-riscv64 main
+fi
+
diff --git a/src/lib/format.s b/src/lib/format.s
new file mode 100644
index 0000000..c975b6e
--- /dev/null
+++ b/src/lib/format.s
@@ -0,0 +1,62 @@
+.align 2
+.section .text
+
+
+
+# args:
+# a0 - number
+#
+# returns:
+# a0,a1 - hex string
+.global format_hex
+format_hex:
+    addi    sp, sp, -(3*8)
+    sd      ra, 0(sp)
+    sd      s0, 8(sp)
+    sd      s1, 16(sp)
+
+    move    s0, a0
+    jal     format_hex_lower
+    move    s1, a0
+
+    srli    a0, s0, 32
+    jal     format_hex_lower
+
+    move    a1, s1
+
+    ld      ra, 0(sp)
+    ld      s0, 8(sp)
+    ld      s1, 16(sp)
+    addi    sp, sp, +(3*8)
+    ret
+
+# args:
+# a0 - number
+#
+# returns:
+# a0 - lower hex string
+.global format_hex_lower
+format_hex_lower:
+    move    t0, a0
+    li      t1, 0xffffffff
+    and     t0, t0, t1
+    li      a0, 0
+    li      t1, 8*7
+    li      t4, 16*4
+0:
+    bltz    t1, 0f
+
+    andi    t2, t0, 0xf
+    addi    t2, t2, 0x30
+    li      t3, 0x30+9
+    ble     t2, t3, 1f
+    addi    t2, t2, 0x61-0x30-10
+1:
+    sll     t2, t2, t1
+    addi    t1, t1, -8
+    srli    t0, t0, 4
+    or      a0, a0, t2
+    j       0b
+0:
+    ret
+
diff --git a/src/lib/heap.s b/src/lib/heap.s
new file mode 100644
index 0000000..8ae1e5c
--- /dev/null
+++ b/src/lib/heap.s
@@ -0,0 +1,225 @@
+# This is a heap implemented with brk.
+# It's slow / unoptimized, and only for
+# learning how to set up a basic heap
+
+# mask and imask are used to floor & ceil
+# to get correct bounds
+.equ align_imask,   0b111
+.equ align_mask,    ~align_imask
+
+.equ used_mask,     0b001
+.equ size_mask,     align_mask
+
+# block node
+
+.equ bsize, 0
+.equ fb_next, 8     # free only
+# free also contains its address at the end
+
+# sizes of metadata
+
+.equ sizeof_fb, (8*3 + align_imask) & align_mask
+.equ sizeof_ub, (8*1 + align_imask) & align_mask
+
+.equ PAGE_SIZE, 4096
+
+
+
+.align 2
+.section .rodata
+
+.word 0f - heap_oom
+heap_oom:
+    .string "Heap ran out of memory!\n"
+0:
+
+.section .data
+
+.align 4
+.equ heap_start, 0
+.equ heap_first_free, 8 # matches fb_next
+.equ heap_end, 16
+.global heap_info       # for testing only
+heap_info:
+    .dword __global_pointer$
+    .dword 0
+    .dword 0
+
+
+
+.align 2
+.section .text
+
+.global heap_init
+heap_init:
+    addi    sp, sp, -8
+    sd      ra, 0(sp)
+
+    # get heap info (t0)
+
+    la      t0, heap_info
+
+    # set heap start (t1)
+
+    ld      t1, heap_start(t0)
+    addi    t1, t1, align_imask
+    andi    t1, t1, align_mask
+    sd      t1, heap_start(t0)
+
+    # set heap end (a0)
+    # also calculate heap size (t2)
+
+    li      a0, 0
+    jal     brk
+    andi    a0, a0, align_mask
+    sub     t2, a0, t1      # size = end - start (t2)
+    li      t3, sizeof_fb
+    bgeu    t2, t3, 0f      # check if enough mem to start
+
+    move    a1, a0
+    add     a0, t1, t3
+    jal     brk_or_panic    # if not, get more
+    sub     t2, a0, t1      # recalc size (t2)
+0:
+    sd      a0, heap_end(t0)
+
+    # create initial free block
+
+    ori     t2, t2, 0x1     # add prev used
+    sd      t2, bsize(t1)   # store size
+    sd      t0, fb_next(t1) # store next
+    sd      t1, -8(a0)      # store addr at end
+
+    sd      t1, heap_first_free(t0)
+
+    ld      ra, 0(sp)
+    addi    sp, sp, +8
+    ret
+
+# args:
+# a0 - size
+#
+# returns:
+# a0 - address
+.global heap_alloc
+heap_alloc:
+    addi    sp, sp, -8
+    sd      ra, 0(sp)
+
+    # align size properly (t0)
+
+    move    t0, a0
+    addi    t0, t0, sizeof_ub
+    addi    t0, t0, align_imask
+    andi    t0, t0, align_mask
+
+    # get a free block that will fit (t1)
+    # and its free space
+
+    la      t3, heap_info
+    ld      t4, heap_first_free(t3)
+    ld      a1, heap_end(t3)
+
+    move    t6, t3              # prev block (t6)
+
+    bne     t4, t3, 0f          # if no free blocks
+    move    t4, a1              # pretend end is start
+    j       3f
+0:
+
+    move    t1, t4              # current block (t1)
+
+0:
+    ld      t2, bsize(t1)       # size of current block (t2)
+    andi    t2, t2, size_mask
+    bgeu    t2, t0, 0f          # is it big enough
+    ld      t5, fb_next(t1)     # if not, get the next
+    beq     t5, t3, 1f
+    move    t6, t1
+    move    t1, t5
+    j       0b
+1:  # if no blocks are big enough
+    add     t5, t1, t2          # get end of last free block
+    beq     t5, a1, 2f          # if no free block at end of heap:
+    move    t6, t1
+3:
+    move    t1, a1              # immitate new free block at end
+2:
+    add     a0, t1, t0          # get needed heap end (a0)
+    jal     brk_or_panic        # set heap end (a0)
+    sd      a0, heap_end(t3)    # update end in info
+    sub     t2, a0, t1          # new free space (t2)
+    andi    t5, t2, 1           # prev used bit
+    sd      t5, bsize(t1)       # update size
+    sd      t3, fb_next(t1)     # update next (for case 3)
+
+0:
+
+    # deal with extra free space
+
+    sub     t5, t2, t0          # unneeded free space (t5)
+    li      t4, sizeof_fb
+    bltu    t5, t4, 0f          # check if enough for a free block
+
+    add     t3, t1, t0          # if so, get addr (t3)
+    sd      t3, fb_next(t6)     # set prev block next to new
+    add     t6, t3, t5          # store addr at end
+    sd      t3, -8(t6)
+    ori     t6, t5, 1           # store size with prev in use
+    sd      t6, bsize(t3)
+    ld      t6, fb_next(t1)     # copy next
+    sd      t6, fb_next(t3)
+    j       1f
+0:
+    move    t0, t2              # if no space, fill in with used
+    ld      t4, fb_next(t1)
+    sd      t4, fb_next(t6)     # set prev next to cur next
+    ld      t4, heap_end(t3)
+    add     t3, t1, t0
+    beq     t3, t4, 1f          # if this is not at the end
+    ld      t4, bsize(t3)       # set next's prev used to 1
+    ori     t4, t4, 1
+    sd      t4, bsize(t3)
+1:
+
+    # create used block
+
+    add     t2, t0, t1          # end of block
+    ori     t0, t0, 1           # prev used bit
+    sd      t0, bsize(t1)       # store size
+    sd      zero, fb_next(t1)   # remove free block stuff
+    sd      zero, -8(t2)
+
+    move    a0, t1
+    addi    a0, a0, sizeof_ub
+
+    ld      ra, 0(sp)
+    addi    sp, sp, +8
+    ret
+
+# args:
+# a0 - address
+.global heap_free
+heap_free:
+    ret
+
+# args:
+# a0 - min address needed
+# a1 - old address
+#
+# returns:
+# a0 - new address, aligned
+brk_or_panic:
+    addi    sp, sp, -8
+    sd      ra, 0(sp)
+
+    jal     brk
+    andi    a0, a0, align_mask
+    bgtu    a0, a1, 0f      # make sure brk worked
+    la      a0, heap_oom    # if not, panic
+    lw      a1, -4(a0)
+    j       panic
+0:
+    ld      ra, 0(sp)
+    addi    sp, sp, +8
+    ret
diff --git a/src/lib/print.s b/src/lib/print.s
new file mode 100644
index 0000000..888c158
--- /dev/null
+++ b/src/lib/print.s
@@ -0,0 +1,95 @@
+.section .rodata
+
+newline:
+    .half '\n'
+space:
+    .half ' '
+
+
+
+.align 2
+.section .text
+
+# only uses a regs for convenience
+#
+# args:
+# a0 - string
+# a1 - length
+.global print
+print:
+    addi    sp, sp, -8
+    sd      ra, (sp)
+
+    move    a2, a1
+    move    a1, a0
+    li      a0, 1 # stdout
+    jal write
+
+    ld      ra, (sp)
+    addi    sp, sp, +8
+    ret
+
+# only uses a regs for convenience
+.global printnl
+printnl:
+    addi    sp, sp, -8
+    sd      ra, (sp)
+
+    la      a0, newline
+    li      a1, 1
+    jal     print
+
+    ld      ra, (sp)
+    addi    sp, sp, +8
+    ret
+
+# only uses a regs for convenience
+#
+# args:
+# a0 - string
+# a1 - length
+.global println
+println:
+    addi    sp, sp, -8
+    sd      ra, (sp)
+
+    jal     print
+    jal     printnl
+
+    ld      ra, (sp)
+    addi    sp, sp, +8
+    ret
+
+.global print_space
+print_space:
+    addi    sp, sp, -8
+    sd      ra, (sp)
+
+    la      a0, space
+    li      a1, 1
+    jal     print
+
+    ld      ra, (sp)
+    addi    sp, sp, +8
+    ret
+
+# args:
+# a0 - the hex value to print
+.global print_hex
+print_hex:
+    addi    sp, sp, -(8+16)
+    sd      ra, (sp)
+
+    jal     format_hex
+    addi    t0, sp, 8
+    sd      a0, 0(t0)
+    sd      a1, 8(t0)
+
+    move    a0, t0
+    li      a1, 16
+    jal     print
+
+    ld      ra, (sp)
+    addi    sp, sp, +(8+16)
+    ret
+
diff --git a/src/lib/start.s b/src/lib/start.s
new file mode 100644
index 0000000..11e61b1
--- /dev/null
+++ b/src/lib/start.s
@@ -0,0 +1,9 @@
+.align 2
+.section .text
+
+.global _start
+_start:
+    jal     heap_init
+    jal     main
+    j       exit
+
diff --git a/src/lib/str.s b/src/lib/str.s
new file mode 100644
index 0000000..b412e10
--- /dev/null
+++ b/src/lib/str.s
@@ -0,0 +1,37 @@
+.align 2
+.section .text
+
+# args:
+# a0 - string
+#
+# returns:
+# a0 - length
+.global strlen
+strlen:
+    li      t0, 0
+0:
+    beq     t0, a1, 0f
+    lb      t1, (a0)
+    beqz    t1, 0f
+    addi    a0, a0, 1
+    addi    t0, t0, 1
+    j       0b
+0:
+    move    a0, t0
+    ret
+
+# args:
+# a0 - dest
+# a1 - src
+.global strcpy
+strcpy:
+0:
+    lb      t0, (a1)
+    beqz    t0, 0f
+    sb      t0, (a0)
+    addi    a0, a0, 1
+    addi    a1, a1, 1
+    j       0b
+0:
+    sb      t0, (a0)
+    ret
diff --git a/src/lib/sys.s b/src/lib/sys.s
new file mode 100644
index 0000000..b8b5bd5
--- /dev/null
+++ b/src/lib/sys.s
@@ -0,0 +1,50 @@
+# This contains all syscalls used,
+# as functions for convenience.
+# These are guaranteed to not modify
+# any registers other than the
+# arguments needed for the syscalls
+
+.align 2
+.section .text
+
+# args:
+# a0 - code
+.global exit
+exit:
+    li      a7, 93
+    ecall
+0: j 0b # loop if failed for safety
+
+# args:
+# a0 - relative dir fd;
+#      0 for none, -100 for cwd
+# a1 - path / name
+# a2 - flags
+# a3 - mode
+#
+# returns:
+# a0 - fd
+.global openat
+openat:
+    li      a7, 56
+    ecall
+    ret
+
+# args:
+# a0 - fd
+# a1 - content buf
+# a2 - size
+.global write
+write:
+    li      a7, 64
+    ecall
+    ret
+
+# args:
+# a0 - address to end at
+#      returns current addr if 0
+.global brk
+brk:
+    li      a7, 214
+    ecall
+    ret
diff --git a/src/lib/util.s b/src/lib/util.s
new file mode 100644
index 0000000..f111e7a
--- /dev/null
+++ b/src/lib/util.s
@@ -0,0 +1,11 @@
+.align 2
+.section .text
+
+# args:
+# a0 - message
+# a1 - length
+.global panic
+panic:
+    jal     print
+    li      a0, 1
+    j       exit
diff --git a/src/main.s b/src/main.s
new file mode 100644
index 0000000..5680c92
--- /dev/null
+++ b/src/main.s
@@ -0,0 +1,20 @@
+.align 2
+.section .text
+
+.global main
+main:
+    addi    sp, sp, -8
+    sd      ra, 0(sp)
+
+    # do stuff
+
+    #jal     write_test
+    jal     heap_test
+
+    # exit with code 0
+
+    ld      ra, 0(sp)
+    addi    sp, sp, +8
+
+    li      a0, 0
+    ret
diff --git a/src/test/heap.s b/src/test/heap.s
new file mode 100644
index 0000000..3b4ccc8
--- /dev/null
+++ b/src/test/heap.s
@@ -0,0 +1,125 @@
+.section .rodata
+
+.word 0f - print_msg
+print_msg:
+    .string "Current heap:"
+0:
+
+.word 0f - dots
+dots:
+    .string "................"
+0:
+
+.word 0f - hexstr
+hexstr:
+    .string "0x"
+0:
+
+
+
+.align 2
+.section .text
+
+.global heap_test
+heap_test:
+    addi    sp, sp, -(3*8)
+    sd      ra, 0(sp)
+    sd      s0, 8(sp)
+    sd      s1, 16(sp)
+
+    # empty heap
+
+    jal     print_heap
+    jal     printnl
+
+    # put stuff on heap
+
+    li      a0, 8*4
+    jal     heap_alloc
+    li      t0, 0x1111111111111111
+    sd      t0, (a0)
+    sd      t0, 8(a0)
+    sd      t0, 24(a0)
+
+    li      s0, 0x0f
+0:
+    bltz    s0, 0f
+
+    li      a0, 8*3
+    jal     heap_alloc
+    sd      s0, (a0)
+    li      t0, 0xf000000000000000
+    add     t0, s0, t0
+    sd      t0, 16(a0)
+
+    addi    s0, s0, -1
+    j       0b
+0:
+
+    li      a0, 8*7
+    jal     heap_alloc
+    li      t0, 0xffff
+    sd      t0, 6*8(a0)
+
+    li      a0, 8*3
+    jal     heap_alloc
+
+    jal     print_heap
+
+    ld      ra, 0(sp)
+    ld      s0, 8(sp)
+    ld      s1, 16(sp)
+    addi    sp, sp, +(3*8)
+    ret
+
+print_heap:
+    addi    sp, sp, -(3*8)
+    sd      ra, 0(sp)
+    sd      s0, 8(sp)
+    sd      s1, 16(sp)
+
+    la      a0, print_msg
+    lw      a1, -4(a0)
+    jal     println
+
+    la      t0, heap_info
+    ld      s0, 0(t0)
+    ld      s1, 16(t0)
+0:
+    la      a0, hexstr
+    lw      a1, -4(a0)
+    jal     print
+    move    a0, s0
+    jal     print_hex
+    jal     print_space
+
+    ld      a0, 0(s0)
+    jal     print_hex
+    jal     print_space
+
+    ld      a0, 8(s0)
+    jal     print_hex
+    jal     print_space
+
+    la      a0, dots
+    lw      a1, -4(a0)
+    jal     print
+    jal     print_space
+
+    ld      t0, 0(s0)
+    andi    t0, t0, ~0b11
+    add     t0, s0, t0
+    ld      a0, -8(t0)
+    move    s0, t0
+    jal     print_hex
+    jal     printnl
+
+    beq     s0, s1, 0f
+    j 0b
+0:
+
+    ld      ra, 0(sp)
+    ld      s0, 8(sp)
+    ld      s1, 16(sp)
+    addi    sp, sp, +(3*8)
+    ret
diff --git a/src/test/write.s b/src/test/write.s
new file mode 100644
index 0000000..5a13b07
--- /dev/null
+++ b/src/test/write.s
@@ -0,0 +1,55 @@
+.equ PATH_MAX,  255
+
+.section .rodata
+
+    .word 0f - start_msg
+start_msg:
+    .string "Writing file..."
+0:
+
+    .word 0f - file_name
+file_name:
+    .string "test.txt"
+0:
+
+    .word 0f - content
+content:
+    .string "Hello world!\n"
+0:
+
+
+
+.align 2
+.section .text
+
+.global write_test
+write_test:
+    addi    sp, sp, -8-PATH_MAX
+    sd      ra, 0(sp)
+
+    # print msg
+
+    la      a0, start_msg
+    lw      a1, -4(a0)
+    jal     println
+
+    # open file
+
+    li      a0, -100
+    la      a1, file_name
+    li      a2, 01102       # TRUNC | CREAT | RDWR
+    li      a3, 0b110100100 # -rw-r--r--
+    jal     openat
+
+    # write to file
+
+    la      a1, content
+    lw      a2, -4(a1)
+    jal     write
+
+    # return
+
+    ld      ra, 0(sp)
+    addi    sp, sp, +8+PATH_MAX
+
+    ret