2600 - teach 'print' about addresses - mu - Soul of a tiny new machine. More thorough tests → More comprehensible and rewrite-friendly software → More resilient society.

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author	Kartik K. Agaram <vc@akkartik.com>	2016-01-23 19:52:11 -0800
committer	Kartik K. Agaram <vc@akkartik.com>	2016-01-23 19:52:11 -0800
commit	9923285547c1cd4e1fdb56262ec85284b39b8779 (patch)
tree	d721842482913b85d62fba3437846328171946de /055parse_tree.cc
parent	f76f402dd8c3b1aaeaca83a0cc43e90437deb293 (diff)
download	mu-9923285547c1cd4e1fdb56262ec85284b39b8779.tar.gz

2600 - teach 'print' about addresses

Unfortunate that our type system requires this to be explicit..

Diffstat (limited to '055parse_tree.cc')

0 files changed, 0 insertions, 0 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 - subx/057stop.subx</title> <meta name="Generator" content="Vim/8.0"> <meta name="plugin-version" content="vim7.4_v2"> <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"> <style type="text/css">  </style> <script type='text/javascript'>  </script> </head> <body onload='JumpToLine();'> <a href='https://github.com/akkartik/mu/blob/master/subx/057stop.subx'>https://github.com/akkartik/mu/blob/master/subx/057stop.subx</a> <pre id='vimCodeElement'> 1 # stop: dependency-injected wrapper around the exit() syscall 2 # 3 # We'd like to be able to write tests for functions that call exit(), and to 4 # make assertions about whether they exit() or not in a given situation. To 5 # achieve this we'll call exit() via a smarter wrapper called 'stop'. 6 # 7 # In the context of a test, calling a function X that calls 'stop' (directly 8 # or through further intervening calls) will unwind the stack until X returns, 9 # so that we can say check any further assertions after the execution of X. To 10 # achieve this end, we'll pass the return address of X as a 'target' argument 11 # into X, plumbing it through to 'stop'. When 'stop' gets a non-null target it 12 # unwinds the stack until the target. If it gets a null target it calls 13 # exit(). 14 # 15 # We'd also like to get the exit status out of 'stop', so we'll combine the 16 # input target with an output status parameter into a type called 'exit-descriptor'. 17 # 18 # So the exit-descriptor looks like this: 19 # target : address # return address for 'stop' to unwind to 20 # value : int # exit status stop was called with 21 # 22 # 'stop' thus takes two parameters: an exit-descriptor and the exit status. 23 # 24 # 'stop' won't bother cleaning up any other processor state besides the stack, 25 # such as registers. Only ESP will have a well-defined value after 'stop' 26 # returns. (This is a poor man's setjmp/longjmp, if you know what that is.) 27 # 28 # Before you can call any function that may call 'stop', you need to pass in an 29 # exit-descriptor to it. To create an exit-descriptor use 'tailor-exit-descriptor' 30 # below. It's not the most pleasant abstraction in the world. 31 # 32 # An exit-descriptor's target is its input, computed during 'tailor-exit-descriptor'. 33 # Its value is its output, computed during stop and available to the test. 34 35 == code 36 # instruction effective address register displacement immediate 37 # . op subop mod rm32 base index scale r32 38 # . 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 39 40 # main: 41 e8/call run-tests/disp32 # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'. 42 #? e8/call test-stop-skips-returns-on-exit/disp32 43 # syscall(exit, Num-test-failures) 44 8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/EBX Num-test-failures/disp32 # copy *Num-test-failures to EBX 45 b8/copy-to-EAX 1/imm32 46 cd/syscall 0x80/imm8 47 48 # Configure an exit-descriptor for a call pushing 'nbytes' bytes of args to 49 # the stack. 50 # Ugly that we need to know the size of args, but so it goes. 51 tailor-exit-descriptor: # ed : (address exit-descriptor), nbytes : int -> <void> 52 # . prolog 53 55/push-EBP 54 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP 55 # . save registers 56 50/push-EAX 57 51/push-ECX 58 # EAX = nbytes 59 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 0/r32/EAX 0xc/disp8 . # copy *(EBP+12) to EAX 60 # Let X be the value of ESP in the caller, before the call to tailor-exit-descriptor. 61 # The return address for a call in the caller's body will be at: 62 # X-8 if the caller takes 4 bytes of args for the exit-descriptor (add 4 bytes for the return address) 63 # X-12 if the caller takes 8 bytes of args 64 # ..and so on 65 # That's the value we need to return: X-nbytes-4 66 # 67 # However, we also need to account for the perturbance to ESP caused by the 68 # call to tailor-exit-descriptor. It pushes 8 bytes of args followed by 4 69 # bytes for the return address and 4 bytes to push EBP above. 70 # So EBP at this point is X-16. 71 # 72 # So the return address for the next call in the caller is: 73 # EBP+8 if the caller takes 4 bytes of args 74 # EBP+4 if the caller takes 8 bytes of args 75 # EBP if the caller takes 12 bytes of args 76 # EBP-4 if the caller takes 16 bytes of args 77 # ..and so on 78 # That's EBP+12-nbytes. 79 # option 1: 6 + 3 bytes 80 #? 2d/subtract 3/mod/direct 0/rm32/EAX . . . . . 8/imm32 # subtract from EAX 81 #? 8d/copy-address 0/mod/indirect 4/rm32/sib 5/base/EBP 0/index/EAX . 0/r32/EAX . . # copy EBP+EAX to EAX 82 # option 2: 2 + 4 bytes 83 f7 3/subop/negate 3/mod/direct 0/rm32/EAX . . . . . . # negate EAX 84 8d/copy-address 1/mod/*+disp8 4/rm32/sib 5/base/EBP 0/index/EAX . 0/r32/EAX 0xc/disp8 . # copy EBP+EAX+12 to EAX 85 # copy EAX to ed->target 86 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 1/r32/ECX 8/disp8 . # copy *(EBP+8) to ECX 87 89/copy 0/mod/indirect 1/rm32/ECX . . . 0/r32/EAX . . # copy EAX to *ECX 88 # initialize ed->value 89 c7/copy 1/mod/*+disp8 1/rm32/ECX . . . . 4/disp8 0/imm32 # copy to *(ECX+4) 90 # . restore registers 91 59/pop-to-ECX 92 58/pop-to-EAX 93 # . epilog 94 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP 95 5d/pop-to-EBP 96 c3/return 97 98 stop: # ed : (address exit-descriptor), value : int 99 # no prolog; one way or another, we're going to clobber registers 100 # EAX = ed 101 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 0/r32/EAX 4/disp8 . # copy *(ESP+4) to EAX 102 # exit(value) if ed->target == 0 103 81 7/subop/compare 0/mod/indirect 0/rm32/EAX . . . . . 0/imm32 # compare *EAX 104 75/jump-if-not-equal $stop:fake/disp8 105 # syscall(exit, value) 106 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 3/r32/EBX 8/disp8 . # copy *(ESP+8) to EBX 107 b8/copy-to-EAX 1/imm32 108 cd/syscall 0x80/imm8 109 $stop:fake: 110 # ed->value = value+1 111 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 1/r32/ECX 8/disp8 . # copy *(ESP+8) to ECX 112 41/inc-ECX 113 89/copy 1/mod/*+disp8 0/rm32/EAX . . . 1/r32/ECX 4/disp8 . # copy ECX to *(EAX+4) 114 # non-local jump to ed->target 115 8b/copy 0/mod/indirect 0/rm32/EAX . . . 4/r32/ESP . . # copy *EAX to ESP 116 c3/return # doesn't return to caller 117 118 test-stop-skips-returns-on-exit: 119 # This looks like the standard prolog, but is here for different reasons. 120 # A function calling 'stop' can't rely on EBP persisting past the call. 121 # 122 # Use EBP here as a stable base to refer to locals and arguments from in the 123 # presence of push/pop/call instructions. 124 # *Don't* use EBP as a way to restore ESP. 125 55/push-EBP 126 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP 127 # Make room for an exit descriptor on the stack. That's almost always the 128 # right place for it, available only as long as it's legal to use. Once this 129 # containing function returns we'll need a new exit descriptor. 130 # var ed/EAX : (address exit-descriptor) 131 81 5/subop/subtract 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # subtract from ESP 132 8d/copy-address 0/mod/indirect 4/rm32/sib 4/base/ESP 4/index/none . 0/r32/EAX . . # copy ESP to EAX 133 # Size the exit-descriptor precisely for the next call below, to _test-stop-1. 134 # tailor-exit-descriptor(ed, 4) 135 # . . push args 136 68/push 4/imm32/nbytes-of-args-for-_test-stop-1 137 50/push-EAX 138 # . . call 139 e8/call tailor-exit-descriptor/disp32 140 # . . discard args 141 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP 142 # . _test-stop-1(ed) 143 # . . push args 144 50/push-EAX 145 # . . call 146 e8/call _test-stop-1/disp32 147 # registers except ESP may be clobbered at this point 148 # restore args 149 58/pop-to-EAX 150 # check that _test-stop-1 tried to call exit(1) 151 # check-ints-equal(ed->value, 2, msg) # i.e. stop was called with value 1 152 # . . push args 153 68/push "F - test-stop-skips-returns-on-exit"/imm32 154 68/push 2/imm32 155 # . . push ed->value 156 ff 6/subop/push 1/mod/*+disp8 0/rm32/EAX . . . . 4/disp8 . # push *(EAX+4) 157 # . . call 158 e8/call check-ints-equal/disp32 159 # . . discard args 160 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP 161 # . epilog 162 5d/pop-to-EBP 163 # don't restore ESP from EBP; manually reclaim locals 164 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP 165 c3/return 166 167 _test-stop-1: # ed : (address exit-descriptor) 168 # . prolog 169 55/push-EBP 170 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP 171 # _test-stop-2(ed) 172 # . . push args 173 ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . . 8/disp8 . # push *(EBP+8) 174 # . . call 175 e8/call _test-stop-2/disp32 176 # should never get past this point 177 # . . discard args 178 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP 179 # signal test failed: check-ints-equal(1, 0, msg) 180 # . . push args 181 68/push "F - test-stop-skips-returns-on-exit"/imm32 182 68/push 0/imm32 183 68/push 1/imm32 184 # . . call 185 e8/call check-ints-equal/disp32 186 # . . discard args 187 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP 188 # . epilog 189 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP 190 5d/pop-to-EBP 191 c3/return 192 193 _test-stop-2: # ed : (address exit-descriptor) 194 # . prolog 195 55/push-EBP 196 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP 197 # . stop(ed, 1) 198 # . . push args 199 68/push 1/imm32 200 ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . . 8/disp8 . # push *(EBP+8) 201 # . . call 202 e8/call stop/disp32 203 # should never get past this point 204 # . epilog 205 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP 206 5d/pop-to-EBP 207 c3/return 208 209 # . . vim:nowrap:textwidth=0 </pre> </body> </html>


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