mu - Soul of a tiny new machine. More thorough tests → More comprehensible and rewrite-friendly software → More resilient society.

	Commit message (Expand)	Author	Age	Files	Lines
*	5485 - promote SubX to top-level	Kartik Agaram	2019-07-27	1	-0/+416

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <title>Mu - 069allocate.subx</title> <meta name="Generator" content="Vim/8.1"> <meta name="plugin-version" content="vim8.1_v1"> <meta name="syntax" content="none"> <meta name="settings" content="number_lines,use_css,no_foldcolumn,expand_tabs,line_ids,prevent_copy="> <meta name="colorscheme" content="minimal-light"> <style type="text/css">  </style> <script type='text/javascript'>  </script> </head> <body onload='JumpToLine();'> <a href='https://github.com/akkartik/mu/blob/master/069allocate.subx'>https://github.com/akkartik/mu/blob/master/069allocate.subx</a> <pre id='vimCodeElement'> 1 # Helper to dynamically allocate memory on the heap. 2 # 3 # We'd like to be able to write tests for functions that allocate memory, 4 # making assertions on the precise addresses used. To achieve this we'll pass 5 # in an *allocation descriptor* to allocate from. 6 # 7 # Allocation descriptors are also useful outside of tests. Assembly and machine 8 # code are of necessity unsafe languages, and one of the most insidious kinds 9 # of bugs unsafe languages expose us to are dangling pointers to memory that 10 # has been freed and potentially even reused for something totally different. 11 # To reduce the odds of such "use after free" errors, SubX programs tend to not 12 # reclaim and reuse dynamically allocated memory. (Running out of memory is far 13 # easier to debug.) Long-running programs that want to reuse memory are mostly 14 # on their own to be careful. However, they do get one bit of help: they can 15 # carve out chunks of memory and then allocate from them manually using this 16 # very same 'allocate' helper. They just need a new allocation descriptor for 17 # their book-keeping. 18 19 == data 20 21 # A default allocation descriptor for programs to use. 22 Heap: # allocation-descriptor 23 # curr 24 0/imm32 25 # limit 26 0/imm32 27 28 # a reasonable default 29 Heap-size: # int 30 0x200000/imm32/2MB 31 32 == code 33 # instruction effective address register displacement immediate 34 # . op subop mod rm32 base index scale r32 35 # . 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 36 37 # Let's start initializing the default allocation descriptor. 38 39 Entry: 40 # initialize heap 41 # . Heap = new-segment(Heap-size) 42 # . . push args 43 68/push <a href='069allocate.subx.html#L22'>Heap</a>/imm32 44 ff 6/subop/push 0/mod/indirect 5/rm32/.disp32 . . . <a href='069allocate.subx.html#L29'>Heap-size</a>/disp32 # push *Heap-size 45 # . . call 46 e8/call <a href='053new-segment.subx.html#L41'>new-segment</a>/disp32 47 # . . discard args 48 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 49 50 e8/call run-tests/disp32 # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'. 51 $array-equal-main:end: 52 # syscall(exit, Num-test-failures) 53 8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/ebx <a href='051test.subx.html#L90'>Num-test-failures</a>/disp32 # copy *Num-test-failures to ebx 54 b8/copy-to-eax 1/imm32/exit 55 cd/syscall 0x80/imm8 56 57 # Claim the next 'n' bytes of memory starting at ad->curr and update ad->curr. 58 # Abort if there isn't enough memory in 'ad'. 59 allocate: # ad: (addr allocation-descriptor), n: int -> address-or-null/eax: (addr _) 60 # . prologue 61 55/push-ebp 62 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 63 # . save registers 64 51/push-ecx 65 52/push-edx 66 # ecx = ad 67 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 1/r32/ecx 8/disp8 . # copy *(ebp+8) to ecx 68 # save ad->curr 69 8b/copy 0/mod/indirect 1/rm32/ecx . . . 0/r32/eax . . # copy *ecx to eax 70 # check if there's enough space 71 # . edx = ad->curr + n 72 89/copy 3/mod/direct 2/rm32/edx . . . 0/r32/eax . . # copy eax to edx 73 03/add 1/mod/*+disp8 5/rm32/ebp . . . 2/r32/edx 0xc/disp8 . # add *(ebp+12) to edx 74 3b/compare 1/mod/*+disp8 1/rm32/ecx . . . 2/r32/edx 4/disp8 . # compare edx with *(ecx+4) 75 73/jump-if->=-signed $allocate:abort/disp8 76 $allocate:commit: 77 # update ad->curr 78 89/copy 0/mod/indirect 1/rm32/ecx . . . 2/r32/edx . . # copy edx to *ecx 79 $allocate:end: 80 # . restore registers 81 5a/pop-to-edx 82 59/pop-to-ecx 83 # . epilogue 84 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 85 5d/pop-to-ebp 86 c3/return 87 88 $allocate:abort: 89 # . _write(2/stderr, error) 90 # . . push args 91 68/push "allocate: failed to allocate\n"/imm32 92 68/push 2/imm32/stderr 93 # . . call 94 e8/call <a href='050_write.subx.html#L14'>_write</a>/disp32 95 # . . discard args 96 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 97 # . syscall(exit, 1) 98 bb/copy-to-ebx 1/imm32 99 b8/copy-to-eax 1/imm32/exit 100 cd/syscall 0x80/imm8 101 # never gets here 102 103 test-allocate-success: 104 # . prologue 105 55/push-ebp 106 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 107 # var ad/ecx: allocation-descriptor = {11, 15} 108 68/push 0xf/imm32/limit 109 68/push 0xb/imm32/curr 110 89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx 111 # var eax: (handle byte) = allocate(ad, 3) 112 # . . push args 113 68/push 3/imm32 114 51/push-ecx 115 # . . call 116 e8/call <a href='069allocate.subx.html#L59'>allocate</a>/disp32 117 # . . discard args 118 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 119 # check-ints-equal(eax, 11, msg) 120 # . . push args 121 68/push "F - <a href='069allocate.subx.html#L103'>test-allocate-success</a>: returns current pointer of allocation descriptor"/imm32 122 68/push 0xb/imm32 123 50/push-eax 124 # . . call 125 e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32 126 # . . discard args 127 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 128 # check-ints-equal(ad->curr, 14, msg) 129 # . . push args 130 68/push "F - <a href='069allocate.subx.html#L103'>test-allocate-success</a>: updates allocation descriptor"/imm32 131 68/push 0xe/imm32 132 ff 6/subop/push 0/mod/indirect 1/rm32/ecx . . . . . . # push *ecx 133 # . . call 134 e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32 135 # . . discard args 136 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 137 # . epilogue 138 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 139 5d/pop-to-ebp 140 c3/return 141 142 _pending-test-allocate-failure: 143 # . prologue 144 55/push-ebp 145 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 146 # var ad/ecx: allocation-descriptor = {11, 15} 147 68/push 0xf/imm32/limit 148 68/push 0xb/imm32/curr 149 89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx 150 # var eax: (handle byte) = allocate(ad, 6) 151 # . . push args 152 68/push 6/imm32 153 51/push-ecx 154 # . . call 155 e8/call <a href='069allocate.subx.html#L59'>allocate</a>/disp32 156 # . . discard args 157 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 158 # check-ints-equal(eax, 0, msg) 159 # . . push args 160 68/push "F - test-allocate-failure: returns null"/imm32 161 68/push 0/imm32 162 50/push-eax 163 # . . call 164 e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32 165 # . . discard args 166 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 167 # no change to ad->curr 168 # . check-ints-equal(ad->curr, 11) 169 # . . push args 170 68/push "F - test-allocate-failure: updates allocation descriptor"/imm32 171 68/push 0xb/imm32 172 ff 6/subop/push 0/mod/indirect 1/rm32/ecx . . . . . . # push *ecx 173 # . . call 174 e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32 175 # . . discard args 176 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 177 # . epilogue 178 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 179 5d/pop-to-ebp 180 c3/return 181 182 # helper: create a nested allocation descriptor (useful for tests) 183 allocate-region: # ad: (addr allocation-descriptor), n: int -> new-ad: (handle allocation-descriptor) 184 # . prologue 185 55/push-ebp 186 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 187 # . save registers 188 51/push-ecx 189 # eax = allocate(ad, n) 190 # . . push args 191 ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 0xc/disp8 . # push *(ebp+12) 192 ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8) 193 # . . call 194 e8/call <a href='069allocate.subx.html#L59'>allocate</a>/disp32 195 # . . discard args 196 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 197 # if (eax == 0) abort 198 3d/compare-eax-and 0/imm32 199 74/jump-if-= $allocate-region:abort/disp8 200 # earmark 8 bytes at the start for a new allocation descriptor 201 # . *eax = eax + 8 202 89/copy 3/mod/direct 1/rm32/ecx . . . 0/r32/eax . . # copy eax to ecx 203 81 0/subop/add 3/mod/direct 1/rm32/ecx . . . . . 8/imm32 # add to ecx 204 89/copy 0/mod/indirect 0/rm32/eax . . . 1/r32/ecx . . # copy ecx to *eax 205 # . *(eax+4) = eax + n 206 89/copy 3/mod/direct 1/rm32/ecx . . . 0/r32/eax . . # copy eax to ecx 207 03/add 1/mod/*+disp8 5/rm32/ebp . . . 1/r32/ecx 0xc/disp8 . # add *(ebp+12) to ecx 208 89/copy 1/mod/*+disp8 0/rm32/eax . . . 1/r32/ecx 4/disp8 . # copy ecx to *(eax+4) 209 # . restore registers 210 59/pop-to-ecx 211 # . epilogue 212 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 213 5d/pop-to-ebp 214 c3/return 215 216 # We could create a more general '$abort' jump target, but then we'd need to do 217 # a conditional jump followed by loading the error message and an unconditional 218 # jump. Or we'd need to unconditionally load the error message before a 219 # conditional jump, even if it's unused the vast majority of the time. This way 220 # we bloat a potentially cold segment in RAM so we can abort with a single 221 # instruction. 222 $allocate-region:abort: 223 # . _write(2/stderr, error) 224 # . . push args 225 68/push "allocate-region: failed to allocate\n"/imm32 226 68/push 2/imm32/stderr 227 # . . call 228 e8/call <a href='050_write.subx.html#L14'>_write</a>/disp32 229 # . . discard args 230 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 231 # . syscall(exit, 1) 232 bb/copy-to-ebx 1/imm32 233 b8/copy-to-eax 1/imm32/exit 234 cd/syscall 0x80/imm8 235 # never gets here 236 237 # . . vim:nowrap:textwidth=0 </pre> </body> </html>