todo: finished #63: limit filesize in previews - ranger - mirror of ranger

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author	hut <hut@lavabit.com>	2010-02-25 16:41:25 +0100
committer	hut <hut@lavabit.com>	2010-02-25 20:37:11 +0100
commit	7a268c8be8896d3ec71952a6fd261012e39c1c1a (patch)
tree	101d930825a43be2ba53e37ae301d4a38111996e /TODO
parent	0c2c782dd8ff7cfc74fc46dd68eda0b94d540058 (diff)
download	ranger-7a268c8be8896d3ec71952a6fd261012e39c1c1a.tar.gz

todo: finished #63: limit filesize in previews

Diffstat (limited to 'TODO')

-rw-r--r--

TODO

1 files changed, 2 insertions, 1 deletions

<!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 == code 20 # instruction effective address register displacement immediate 21 # . op subop mod rm32 base index scale r32 22 # . 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 23 24 # Claim the next 'n' bytes of memory starting at ad->curr and update ad->curr. 25 # Abort if there isn't enough memory in 'ad'. 26 allocate: # ad : (address allocation-descriptor), n : int -> address-or-null/eax 27 # . prolog 28 55/push-ebp 29 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 30 # . save registers 31 51/push-ecx 32 52/push-edx 33 # ecx = ad 34 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 1/r32/ecx 8/disp8 . # copy *(ebp+8) to ecx 35 # save ad->curr 36 8b/copy 0/mod/indirect 1/rm32/ecx . . . 0/r32/eax . . # copy *ecx to eax 37 # check if there's enough space 38 # . edx = ad->curr + n 39 89/copy 3/mod/direct 2/rm32/edx . . . 0/r32/eax . . # copy eax to edx 40 03/add 1/mod/*+disp8 5/rm32/ebp . . . 2/r32/edx 0xc/disp8 . # add *(ebp+12) to edx 41 3b/compare 1/mod/*+disp8 1/rm32/ecx . . . 2/r32/edx 4/disp8 . # compare edx with *(ecx+4) 42 73/jump-if-greater-or-equal-signed $allocate:abort/disp8 43 $allocate:commit: 44 # update ad->curr 45 89/copy 0/mod/indirect 1/rm32/ecx . . . 2/r32/edx . . # copy edx to *ecx 46 $allocate:end: 47 # . restore registers 48 5a/pop-to-edx 49 59/pop-to-ecx 50 # . epilog 51 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 52 5d/pop-to-ebp 53 c3/return 54 55 $allocate:abort: 56 # . _write(2/stderr, error) 57 # . . push args 58 68/push "allocate: failed to allocate\n"/imm32 59 68/push 2/imm32/stderr 60 # . . call 61 e8/call <a href='050_write.subx.html#L14'>_write</a>/disp32 62 # . . discard args 63 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 64 # . syscall(exit, 1) 65 bb/copy-to-ebx 1/imm32 66 b8/copy-to-eax 1/imm32/exit 67 cd/syscall 0x80/imm8 68 # never gets here 69 70 test-allocate-success: 71 # . prolog 72 55/push-ebp 73 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 74 # var ad/ecx : (address allocation-descriptor) = {11, 15} 75 68/push 0xf/imm32/limit 76 68/push 0xb/imm32/curr 77 89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx 78 # eax = allocate(ad, 3) 79 # . . push args 80 68/push 3/imm32 81 51/push-ecx 82 # . . call 83 e8/call <a href='069allocate.subx.html#L26'>allocate</a>/disp32 84 # . . discard args 85 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 86 # check-ints-equal(eax, 11, msg) 87 # . . push args 88 68/push "F - <a href='069allocate.subx.html#L70'>test-allocate-success</a>: returns current pointer of allocation descriptor"/imm32 89 68/push 0xb/imm32 90 50/push-eax 91 # . . call 92 e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32 93 # . . discard args 94 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 95 # check-ints-equal(ad->curr, 14, msg) 96 # . . push args 97 68/push "F - <a href='069allocate.subx.html#L70'>test-allocate-success</a>: updates allocation descriptor"/imm32 98 68/push 0xe/imm32 99 ff 6/subop/push 0/mod/indirect 1/rm32/ecx . . . . . . # push *ecx 100 # . . call 101 e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32 102 # . . discard args 103 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 104 # . epilog 105 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 106 5d/pop-to-ebp 107 c3/return 108 109 _pending-test-allocate-failure: 110 # . prolog 111 55/push-ebp 112 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 113 # var ad/ecx : (address allocation-descriptor) = {11, 15} 114 68/push 0xf/imm32/limit 115 68/push 0xb/imm32/curr 116 89/copy 3/mod/direct 1/rm32/ecx . . . 4/r32/esp . . # copy esp to ecx 117 # eax = allocate(ad, 6) 118 # . . push args 119 68/push 6/imm32 120 51/push-ecx 121 # . . call 122 e8/call <a href='069allocate.subx.html#L26'>allocate</a>/disp32 123 # . . discard args 124 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 125 # check-ints-equal(eax, 0, msg) 126 # . . push args 127 68/push "F - test-allocate-failure: returns null"/imm32 128 68/push 0/imm32 129 50/push-eax 130 # . . call 131 e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32 132 # . . discard args 133 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 134 # no change to ad->curr 135 # . check-ints-equal(ad->curr, 11) 136 # . . push args 137 68/push "F - test-allocate-failure: updates allocation descriptor"/imm32 138 68/push 0xb/imm32 139 ff 6/subop/push 0/mod/indirect 1/rm32/ecx . . . . . . # push *ecx 140 # . . call 141 e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32 142 # . . discard args 143 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 144 # . epilog 145 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 146 5d/pop-to-ebp 147 c3/return 148 149 # helper: create a nested allocation descriptor (useful for tests) 150 allocate-region: # ad : (address allocation-descriptor), n : int -> new-ad : (address allocation-descriptor) 151 # . prolog 152 55/push-ebp 153 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 154 # . save registers 155 51/push-ecx 156 # eax = allocate(ad, n) 157 # . . push args 158 ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 0xc/disp8 . # push *(ebp+12) 159 ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8) 160 # . . call 161 e8/call <a href='069allocate.subx.html#L26'>allocate</a>/disp32 162 # . . discard args 163 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 164 # if (eax == 0) abort 165 3d/compare-eax-and 0/imm32 166 74/jump-if-equal $allocate-region:abort/disp8 167 # earmark 8 bytes at the start for a new allocation descriptor 168 # . *eax = eax + 8 169 89/copy 3/mod/direct 1/rm32/ecx . . . 0/r32/eax . . # copy eax to ecx 170 81 0/subop/add 3/mod/direct 1/rm32/ecx . . . . . 8/imm32 # add to ecx 171 89/copy 0/mod/indirect 0/rm32/eax . . . 1/r32/ecx . . # copy ecx to *eax 172 # . *(eax+4) = eax + n 173 89/copy 3/mod/direct 1/rm32/ecx . . . 0/r32/eax . . # copy eax to ecx 174 03/add 1/mod/*+disp8 5/rm32/ebp . . . 1/r32/ecx 0xc/disp8 . # add *(ebp+12) to ecx 175 89/copy 1/mod/*+disp8 0/rm32/eax . . . 1/r32/ecx 4/disp8 . # copy ecx to *(eax+4) 176 # . restore registers 177 59/pop-to-ecx 178 # . epilog 179 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 180 5d/pop-to-ebp 181 c3/return 182 183 # We could create a more general '$abort' jump target, but then we'd need to do 184 # a conditional jump followed by loading the error message and an unconditional 185 # jump. Or we'd need to unconditionally load the error message before a 186 # conditional jump, even if it's unused the vast majority of the time. This way 187 # we bloat a potentially cold segment in RAM so we can abort with a single 188 # instruction. 189 $allocate-region:abort: 190 # . _write(2/stderr, error) 191 # . . push args 192 68/push "allocate-region: failed to allocate\n"/imm32 193 68/push 2/imm32/stderr 194 # . . call 195 e8/call <a href='050_write.subx.html#L14'>_write</a>/disp32 196 # . . discard args 197 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 198 # . syscall(exit, 1) 199 bb/copy-to-ebx 1/imm32 200 b8/copy-to-eax 1/imm32/exit 201 cd/syscall 0x80/imm8 202 # never gets here 203 204 # . . vim:nowrap:textwidth=0 </pre> </body> </html>


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