https://github.com/akkartik/mu/blob/main/linux/111read.subx
  1 # read: analogously to write, support reading from in-memory streams in
  2 # addition to file descriptors.
  3 #
  4 # We can pass it either a file descriptor or an address to a stream. If a
  5 # file descriptor is passed in, we _read from it using the right syscall. If a
  6 # stream is passed in (a fake file descriptor), we read from it instead. This
  7 # lets us initialize input for tests.
  8 #
  9 # A little counter-intuitively, the output of 'read' ends up in.. a stream. So
 10 # tests end up doing a redundant copy. Why? Well, consider the alternatives:
 11 #
 12 #   a) Reading into a string, and returning a pointer to the end of the read
 13 #   region, or a count of bytes written. Now this count or end pointer must be
 14 #   managed separately by the caller, which can be error-prone.
 15 #
 16 #   b) Having 'read' return a buffer that it allocates. But there's no way to
 17 #   know in advance how large to make the buffer. If you read less than the
 18 #   size of the buffer you again end up needing to manage initialized vs
 19 #   uninitialized memory.
 20 #
 21 #   c) Creating more helpful variants like 'read-byte' or 'read-until' which
 22 #   also can take a file descriptor or stream, just like 'write'. But such
 23 #   primitives don't exist in the Linux kernel, so we'd be implementing them
 24 #   somehow, either with more internal buffering or by making multiple
 25 #   syscalls.
 26 #
 27 # Reading into a stream avoids these problems. The buffer is externally
 28 # provided and the caller has control over where it's allocated, its lifetime,
 29 # and so on. The buffer's read and write pointers are internal to it so it's
 30 # easier to keep in a consistent state. And it can now be passed directly to
 31 # helpers like 'read-byte' or 'read-until' that only need to support streams,
 32 # never file descriptors.
 33 #
 34 # Like with 'write', we assume our data segment will never begin at an address
 35 # shorter than 0x08000000, so any smaller arguments are assumed to be real
 36 # file descriptors.
 37 #
 38 # As a reminder, a stream looks like this:
 39 #   write: int  # index at which to write to next
 40 #   read: int  # index at which to read next
 41 #   data: (array byte)  # prefixed by size as usual
 42 
 43 == code
 44 #   instruction                     effective address                                                   register    displacement    immediate
 45 # . op          subop               mod             rm32          base        index         scale       r32
 46 # . 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
 47 
 48 read:  # f: fd or (addr stream byte), s: (addr stream byte) -> num-bytes-read/eax: int
 49     # . prologue
 50     55/push-ebp
 51     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
 52     # if (f < 0x08000000) return _read(f, s)  # f can't be a user-mode address, so treat it as a kernel file descriptor
 53     81          7/subop/compare     1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         0x08000000/imm32  # compare *(ebp+8)
 54     73/jump-if-addr>=  $read:fake/disp8
 55     # . . push args
 56     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
 57     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         .                 # push *(ebp+8)
 58     # . . call
 59     e8/call  _read/disp32
 60     # . . discard args
 61     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
 62     # return
 63     eb/jump  $read:end/disp8
 64 $read:fake:
 65     # otherwise, treat 'f' as a stream to scan from
 66     # . save registers
 67     56/push-esi
 68     57/push-edi
 69     # esi = f
 70     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           6/r32/esi   8/disp8         .                 # copy *(ebp+8) to esi
 71     # edi = s
 72     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           7/r32/edi   0xc/disp8       .                 # copy *(ebp+12) to esi
 73     # eax = _buffer-4(out = &s->data[s->write], outend = &s->data[s->size],
 74     #                 in  = &f->data[f->read],  inend  = &f->data[f->write])
 75     # . . push &f->data[f->write]
 76     8b/copy                         0/mod/indirect  6/rm32/esi    .           .             .           0/r32/eax   .               .                 # copy *esi to eax
 77     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    6/base/esi  0/index/eax   .           0/r32/eax   0xc/disp8       .                 # copy esi+eax+12 to eax
 78     50/push-eax
 79     # . . push &f->data[f->read]
 80     8b/copy                         1/mod/*+disp8   6/rm32/esi    .           .             .           0/r32/eax   4/disp8         .                 # copy *(esi+4) to eax
 81     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    6/base/esi  0/index/eax   .           0/r32/eax   0xc/disp8       .                 # copy esi+eax+12 to eax
 82     50/push-eax
 83     # . . push &s->data[s->size]
 84     8b/copy                         1/mod/*+disp8   7/rm32/edi    .           .             .           0/r32/eax   8/disp8         .                 # copy *(edi+8) to eax
 85     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    7/base/edi  0/index/eax   .           0/r32/eax   0xc/disp8       .                 # copy edi+eax+12 to eax
 86     50/push-eax
 87     # . . push &s->data[s->write]
 88     8b/copy                         0/mod/indirect  7/rm32/edi    .           .             .           0/r32/eax   .               .                 # copy *edi to eax
 89     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    7/base/edi  0/index/eax   .           0/r32/eax   0xc/disp8       .                 # copy edi+eax+12 to eax
 90     50/push-eax
 91     # . . call
 92     e8/call  _buffer-4/disp32
 93     # . . discard args
 94     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0x10/imm32        # add to esp
 95     # s->write += eax
 96     01/add                          0/mod/indirect  7/rm32/edi    .           .             .           0/r32/eax   .               .                 # add eax to *edi
 97     # f->read += eax
 98     01/add                          1/mod/*+disp8   6/rm32/esi    .           .             .           0/r32/eax   4/disp8         .                 # add eax to *(esi+4)
 99     # . restore registers
100     5f/pop-to-edi
101     5e/pop-to-esi
102 $read:end:
103     # . epilogue
104     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 pre { line-height: 125%; }
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Console

   (X) #0   09/12/06  console commands
   (X) #1   09/12/06  quick find
   (X) #2   09/12/06  open with
   (X) #4   09/12/06  history for console
   (X) #13  09/12/27  display docstring of a command


General

   (X) #5   09/12/06  move code from fm into objects
   (X) #6   09/12/06  move main to __init__
   (X) #7   09/12/06  cooler titlebar
   (X) #8   09/12/17  Add operations to modify files/directories
   (X) #9   09/12/24  add a widget for managing running operations
   (X) #10  09/12/24  sorting
   (X) #11  09/12/27  filter
   (X) #12  09/12/27  jump through the list in a specific order
   (X) #14  09/12/29  make filelists inherit from pagers
   (X) #15  09/12/29  better way of running processes!!~
   (X) #16  10/01/01  list of bookmarks
   (X) #21  10/01/01  write help!
   ( ) #22  10/01/03  add getopt options to change flags/mode


Bugs

   (X) #17  10/01/01  why do bookmarks disappear sometimes?
   (X) #18  10/01/01  fix notify widget (by adding a LogView?)
   (X) #19  10/01/01  resizing after pressing g
   ( ) #23  10/01/04  stop dir loading with ^C -> wont load anymore


Ideas

   ( ) #20  10/01/01  use inotify to monitor filesystem changes
   ( ) #24  10/01/06  progress bar
class="Normal"> . . 4/r32/esp . . # copy esp to ebp 149 # . save registers 150 51/push-ecx 151 52/push-edx 152 53/push-ebx 153 56/push-esi 154 57/push-edi 155 # eax/num_bytes_buffered = 0 156 b8/copy-to-eax 0/imm32 157 # edi = out 158 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 7/r32/edi 8/disp8 . # copy *(ebp+8) to edi 159 # edx = outend 160 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 2/r32/edx 0xc/disp8 . # copy *(ebp+12) to edx 161 # esi = in 162 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 6/r32/esi 0x10/disp8 . # copy *(ebp+16) to esi 163 # ecx = inend 164 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 1/r32/ecx 0x14/disp8 . # copy *(ebp+20) to ecx 165 $_buffer-4:loop: 166 # if (in >= inend) break 167 39/compare 3/mod/direct 6/rm32/esi . . . 1/r32/ecx . . # compare esi with ecx 168 73/jump-if-addr>= $_buffer-4:end/disp8 169 # if (out >= outend) break # for now silently ignore filled up buffer 170 39/compare 3/mod/direct 7/rm32/edi . . . 2/r32/edx . . # compare edi with edx 171 73/jump-if-addr>= $_buffer-4:end/disp8 172 # *out = *in 173 8a/copy-byte 0/mod/indirect 6/rm32/esi . . . 3/r32/BL . . # copy byte at *esi to BL 174 88/copy-byte 0/mod/indirect 7/rm32/edi . . . 3/r32/BL . . # copy byte at BL to *edi 175 # ++num_bytes_buffered 176 40/increment-eax 177 # ++in 178 46/increment-esi 179 # ++out 180 47/increment-edi 181 eb/jump $_buffer-4:loop/disp8 182 $_buffer-4:end: 183 # . restore registers 184 5f/pop-to-edi 185 5e/pop-to-esi 186 5b/pop-to-ebx 187 5a/pop-to-edx 188 59/pop-to-ecx 189 # . epilogue 190 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 191 5d/pop-to-ebp 192 c3/return 193 194 # idea: a clear-if-empty method on streams that clears only if f->read == f->write 195 # Unclear how I'd use it, though. Callers seem to need the check anyway. 196 # Maybe a better helper would be 'empty-stream?' 197 198 _read: # fd: int, s: (addr stream byte) -> num-bytes-read/eax: int 199 # . prologue 200 55/push-ebp 201 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 202 # . save registers 203 51/push-ecx 204 52/push-edx 205 53/push-ebx 206 56/push-esi 207 # esi = s 208 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 6/r32/esi 0xc/disp8 . # copy *(ebp+12) to esi 209 # eax = s->write 210 8b/copy 0/mod/indirect 6/rm32/esi . . . 0/r32/eax . . # copy *esi to eax 211 # edx = s->size 212 8b/copy 1/mod/*+disp8 6/rm32/esi . . . 2/r32/edx 8/disp8 . # copy *(esi+8) to edx 213 # syscall(read, fd, &s->data[s->write], s->size - s->write) 214 # . . fd: ebx 215 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 3/r32/ebx 8/disp8 . # copy *(ebp+8) to ebx 216 # . . data: ecx = &s->data[s->write] 217 8d/copy-address 1/mod/*+disp8 4/rm32/sib 6/base/esi 0/index/eax . 1/r32/ecx 0xc/disp8 . # copy esi+eax+12 to ecx 218 # . . size: edx = s->size - s->write 219 29/subtract 3/mod/direct 2/rm32/edx . . . 0/r32/eax . . # subtract eax from edx 220 # . . syscall 221 e8/call syscall_read/disp32 222 # add the result eax to s->write 223 01/add 0/mod/indirect 6/rm32/esi . . . 0/r32/eax . . # add eax to *esi 224 $_read:end: 225 # . restore registers 226 5e/pop-to-esi 227 5b/pop-to-ebx 228 5a/pop-to-edx 229 59/pop-to-ecx 230 # . epilogue 231 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp 232 5d/pop-to-ebp 233 c3/return 234 235 # Two options: 236 # 1 (what we have above): 237 # ecx = s 238 # eax = s->write 239 # edx = s->size 240 # # syscall 241 # ecx = lea ecx+eax+12 242 # edx = sub edx eax 243 # 244 # 2: 245 # ecx = s 246 # edx = s->size 247 # ecx = &s->data 248 # # syscall 249 # ecx = add ecx, s->write 250 # edx = sub edx, s->write 251 # 252 # Not much to choose between the two? Option 2 performs a duplicate load to 253 # use one less register, but doesn't increase the amount of spilling (ecx 254 # and edx must be used, and eax must be clobbered anyway). 255 256 # - tests 257 258 test-read-single: 259 # - write a single character into _test-stream, then read from it 260 # clear-stream(_test-stream) 261 # . . push args 262 68/push _test-stream/imm32 263 # . . call 264 e8/call clear-stream/disp32 265 # . . discard args 266 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp 267 # clear-stream(_test-tmp-stream) 268 # . . push args 269 68/push _test-tmp-stream/imm32 270 # . . call 271 e8/call clear-stream/disp32 272 # . . discard args 273 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp 274 # write(_test-stream, "Ab") 275 # . . push args 276 68/push "Ab"/imm32 277 68/push _test-stream/imm32 278 # . . call 279 e8/call write/disp32 280 # . . discard args 281 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 282 # eax = read(_test-stream, _test-tmp-stream) 283 # . . push args 284 68/push _test-tmp-stream/imm32 285 68/push _test-stream/imm32 286 # . . call 287 e8/call read/disp32 288 # . . discard args 289 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 290 # check-ints-equal(eax, 2, msg) 291 # . . push args 292 68/push "F - test-read-single: return value"/imm32 293 68/push 2/imm32 294 50/push-eax 295 # . . call 296 e8/call check-ints-equal/disp32 297 # . . discard args 298 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 299 # check-stream-equal(_test-tmp-stream, "Ab", msg) 300 # . . push args 301 68/push "F - test-read-single"/imm32 302 68/push "Ab"/imm32 303 68/push _test-tmp-stream/imm32 304 # . . call 305 e8/call check-stream-equal/disp32 306 # . . discard args 307 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 308 # end 309 c3/return 310 311 test-read-is-stateful: 312 # - make two consecutive reads, check that their results are appended 313 # clear-stream(_test-stream) 314 # . . push args 315 68/push _test-stream/imm32 316 # . . call 317 e8/call clear-stream/disp32 318 # . . discard args 319 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp 320 # clear-stream(_test-tmp-stream) 321 # . . push args 322 68/push _test-tmp-stream/imm32 323 # . . call 324 e8/call clear-stream/disp32 325 # . . discard args 326 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp 327 # write(_test-stream, "C") 328 # . . push args 329 68/push "C"/imm32 330 68/push _test-stream/imm32 331 # . . call 332 e8/call write/disp32 333 # . . discard args 334 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 335 # read(_test-stream, _test-tmp-stream) 336 # . . push args 337 68/push _test-tmp-stream/imm32 338 68/push _test-stream/imm32 339 # . . call 340 e8/call read/disp32 341 # . . discard args 342 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 343 # write(_test-stream, "D") 344 # . . push args 345 68/push "D"/imm32 346 68/push _test-stream/imm32 347 # . . call 348 e8/call write/disp32 349 # . . discard args 350 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 351 # read(_test-stream, _test-tmp-stream) 352 # . . push args 353 68/push _test-tmp-stream/imm32 354 68/push _test-stream/imm32 355 # . . call 356 e8/call read/disp32 357 # . . discard args 358 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 359 # check-stream-equal(_test-tmp-stream, "CD", msg) 360 # . . push args 361 68/push "F - test-read-is-stateful"/imm32 362 68/push "CD"/imm32 363 68/push _test-tmp-stream/imm32 364 # . . call 365 e8/call check-stream-equal/disp32 366 # . . discard args 367 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 368 # end 369 c3/return 370 371 test-read-returns-0-on-end-of-file: 372 # - read after hitting end-of-file, check that result is 0 373 # setup 374 # . clear-stream(_test-stream) 375 # . . push args 376 68/push _test-stream/imm32 377 # . . call 378 e8/call clear-stream/disp32 379 # . . discard args 380 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp 381 # . clear-stream(_test-tmp-stream) 382 # . . push args 383 68/push _test-tmp-stream/imm32 384 # . . call 385 e8/call clear-stream/disp32 386 # . . discard args 387 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp 388 # . write(_test-stream, "Ab") 389 # . . push args 390 68/push "Ab"/imm32 391 68/push _test-stream/imm32 392 # . . call 393 e8/call write/disp32 394 # . . discard args 395 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 396 # first read gets to end-of-file 397 # . read(_test-stream, _test-tmp-stream) 398 # . . push args 399 68/push _test-tmp-stream/imm32 400 68/push _test-stream/imm32 401 # . . call 402 e8/call read/disp32 403 # . . discard args 404 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 405 # second read 406 # . read(_test-stream, _test-tmp-stream) 407 # . . push args 408 68/push _test-tmp-stream/imm32 409 68/push _test-stream/imm32 410 # . . call 411 e8/call read/disp32 412 # . . discard args 413 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp 414 # check-ints-equal(eax, 0, msg) 415 # . . push args 416 68/push "F - test-read-returns-0-on-end-of-file"/imm32 417 68/push 0/imm32 418 50/push-eax 419 # . . call 420 e8/call check-ints-equal/disp32 421 # . . discard args 422 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp 423 # end 424 c3/return 425 426 == data 427 428 _test-tmp-stream: # (stream byte) 429 # current write index 430 0/imm32 431 # current read index 432 0/imm32 433 # size 434 8/imm32 435 # data 436 00 00 00 00 00 00 00 00 # 8 bytes 437 438 # . . vim:nowrap:textwidth=0