akkartik
/
mu
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

7500 - baremetal: bounds-check screen space before drawing

This commit is contained in:
Kartik Agaram 2021-01-11 23:59:17 -08:00
parent ebf912eb7a
commit 589eba07e2
4 changed files with 106 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

74
baremetal/106stream.subx Normal file
View File

@ -0,0 +1,74 @@
# streams: data structure for operating on arrays in a stateful manner
#
# A stream looks like this:
# write: int # index at which writes go
# read: int # index that we've read until
# data: (array byte) # prefixed by size as usual
#
# some primitives for operating on streams:
# - clear-stream (clears everything but the data size)
# - rewind-stream (resets read pointer)
== code
# instruction effective address register displacement immediate
# . op subop mod rm32 base index scale r32
# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes
clear-stream: # f: (addr stream byte)
# . prologue
55/push-ebp
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
# . save registers
50/push-eax
51/push-ecx
# eax = f
8b/copy 1/mod/*+disp8 5/rm32/ebp . . 0/r32/eax 8/disp8 . # copy *(ebp+8) to eax
# var count/ecx: int = f->size
8b/copy 1/mod/*+disp8 0/rm32/eax . . . 1/r32/ecx 8/disp8 . # copy *(eax+8) to ecx
# var max/ecx: (addr byte) = &f->data[f->size]
8d/copy-address 1/mod/*+disp8 4/rm32/sib 0/base/eax 1/index/ecx . 1/r32/ecx 0xc/disp8 . # copy eax+ecx+12 to ecx
# f->write = 0
c7 0/subop/copy 0/mod/direct 0/rm32/eax . . . . . 0/imm32 # copy to *eax
# f->read = 0
c7 0/subop/copy 1/mod/*+disp8 0/rm32/eax . . . . 4/disp8 0/imm32 # copy to *(eax+4)
# - clear all stream data
# - this isn't strictly necessary, and it can slow things down *a lot*, but better safe than sorry.
# var curr/eax: (addr byte) = f->data
81 0/subop/add 3/mod/direct 0/rm32/eax . . . . . 0xc/imm32 # add to eax
$clear-stream:loop:
# if (curr >= max) break
39/compare 3/mod/direct 0/rm32/eax . . . 1/r32/ecx . . # compare eax with ecx
73/jump-if-addr>= $clear-stream:end/disp8
# *curr = 0
c6 0/subop/copy-byte 0/mod/direct 0/rm32/eax . . . . . 0/imm8 # copy byte to *eax
# ++curr
40/increment-eax
eb/jump $clear-stream:loop/disp8
$clear-stream:end:
# . restore registers
59/pop-to-ecx
58/pop-to-eax
# . epilogue
89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
5d/pop-to-ebp
c3/return
rewind-stream: # f: (addr stream byte)
# . prologue
55/push-ebp
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
# . save registers
50/push-eax
# eax = f
8b/copy 1/mod/*+disp8 5/rm32/ebp . . 0/r32/eax 8/disp8 . # copy *(ebp+8) to eax
# f->read = 0
c7 0/subop/copy 1/mod/*+disp8 0/rm32/eax . . . . 4/disp8 0/imm32 # copy to *(eax+4)
$rewind-stream:end:
# . restore registers
58/pop-to-eax
# . epilogue
89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
5d/pop-to-ebp
c3/return
# . . vim:nowrap:textwidth=0

3
baremetal/400.mu
View File

@ -1,7 +1,8 @@
sig pixel screen: (addr screen), x: int, y: int, color: int
sig read-key kbd: (addr keyboard) -> _/eax: byte
sig draw-grapheme screen: (addr screen), g: grapheme, x: int, y: int, color: int
sig clear-stream f: (addr stream _)
sig rewind-stream f: (addr stream _)
sig write f: (addr stream byte), s: (addr array byte)
sig append-byte f: (addr stream byte), n: int
sig read-byte s: (addr stream byte) -> _/eax: byte

29
baremetal/501draw-text.mu
View File

@ -1,13 +1,36 @@
fn draw-text-rightward screen: (addr screen), text: (addr array byte), x: int, y: int, color: int {
# draw a single line of text from x, y to xmax
# return the next 'x' coordinate
# if there isn't enough space, return 0 without modifying the screen
fn draw-text-rightward screen: (addr screen), text: (addr array byte), x: int, xmax: int, y: int, color: int -> _/eax: int {
var stream-storage: (stream byte 0x100)
var stream/esi: (addr stream byte) <- address stream-storage
write stream, text
# check if we have enough space
var xcurr/ecx: int <- copy x
{
compare xcurr, xmax
break-if->
var g/eax: grapheme <- read-grapheme stream
compare g, 0xffffffff # end-of-file
break-if-=
xcurr <- add 8 # font-width
loop
}
compare xcurr, xmax
{
break-if-<=
return 0
}
# we do; actually draw
rewind-stream stream
xcurr <- copy x
{
var g/eax: grapheme <- read-grapheme stream
compare g, 0xffffffff # end-of-file
break-if-=
draw-grapheme screen, g, x, y, color
add-to x, 8 # font-width
draw-grapheme screen, g, xcurr, y, color
xcurr <- add 8 # font-width
loop
}
return xcurr
}

6
baremetal/ex5.mu
View File

@ -1,4 +1,5 @@
# Draw an ASCII string using the built-in font (GNU unifont)
# Draw a single line of ASCII text using the built-in font (GNU unifont)
# Also demonstrates bounds-checking _before_ drawing.
#
# To build a disk image:
# ./translate_mu_baremetal baremetal/ex5.mu # emits disk.img
@ -10,5 +11,6 @@
# Expected output: text in green near the top-left corner of screen
fn main {
draw-text-rightward 0, "hello from baremetal Mu!", 0x10, 0x10, 0xa
var dummy/eax: int <- draw-text-rightward 0, "hello from baremetal Mu!", 0x10, 0x400, 0x10, 0xa # xmax = end of screen, plenty of space
dummy <- draw-text-rightward 0, "you shouldn't see this", 0x10, 0xa0, 0x30, 0x3 # xmax = 0xa0, which is too narrow
}