# Checking null-terminated strings. # # By default we create strings as arrays of bytes, and all arrays have a 4-byte # size prefix. # # However, we sometimes need to deal with null-terminated strings when # interacting with the Linux kernel. This layer implements a function for # comparing a null-terminated 'kernel string' with a size-prefixed 'SubX # string'. # # To run (from the subx directory): # $ ./bootstrap translate 05[0-2]*.subx -o /tmp/tmp52 # $ ./bootstrap run /tmp/tmp52 # runs a series of tests # ...... # all tests pass # # (We can't yet run the tests when given a "test" commandline argument, # because checking for it would require the function being tested! Breakage # would cause tests to not run, rather than to fail as we'd like.) == 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 Entry: # run all tests e8/call run-tests/disp32 # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'. # syscall(exit, Num-test-failures) 8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/ebx Num-test-failures/disp32 # copy *Num-test-failures to ebx e8/call syscall_exit/disp32 kernel-string-equal?: # s: (addr kernel-string), benchmark: (addr array byte) -> result/eax: boolean # pseudocode: # n = benchmark->size # s1 = s # s2 = benchmark->data # i = 0 # while (i < n) # c1 = *s1 # c2 = *s2 # if (c1 == 0) return false # if (c1 != c2) return false # ++s1, ++s2, ++i # return *s1 == 0 # # registers: # i: ecx # n: edx # s1: edi # s2: esi # c1: eax # c2: ebx # # . prologue 55/push-ebp 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp # . save registers 51/push-ecx 52/push-edx 53/push-ebx 56/push-esi 57/push-edi # var s1/edi: (addr byte) = s 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 7/r32/edi 8/disp8 . # copy *(ebp+8) to edi # var n/edx: int = benchmark->size 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 2/r32/edx 0xc/disp8 . # copy *(ebp+12) to edx 8b/copy 0/mod/indirect 2/rm32/edx . . . 2/r32/edx . . # copy *edx to edx # var s2/esi: (addr byte) = benchmark->data 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 6/r32/esi 0xc/disp8 . # copy *(ebp+12) to esi 81 0/subop/add 3/mod/direct 6/rm32/esi . . . . . 4/imm32 # add to esi # var i/ecx: int = 0 b9/copy-to-ecx 0/imm32/exit # var c1/eax: byte = 0

proc foo[T](thing: T) =
    discard thing

var a: proc (thing: int) {.nimcall.} = foo[int]

op/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp # check-ints-equal(eax, 0, msg) # . . push args 68/push "F - test-compare-kernel-string-with-shorter-array"/imm32 68/push 0/imm32/false 50/push-eax # . . call e8/call check-ints-equal/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp c3/return test-compare-kernel-string-with-longer-array: # eax = kernel-string-equal?(_test-Abc-kernel-string, "Abcd") # . . push args 68/push "Abcd"/imm32 68/push _test-Abc-kernel-string/imm32 # . . call e8/call kernel-string-equal?/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp # check-ints-equal(eax, 0, msg) # . . push args 68/push "F - test-compare-kernel-string-with-longer-array"/imm32 68/push 0/imm32/false 50/push-eax # . . call e8/call check-ints-equal/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp c3/return == data Null-kernel-string: # (addr kernel-string) 00/null _test-Abc-kernel-string: # (addr kernel-string) 41/A 62/b 63/c 00/null # . . vim:nowrap:textwidth=0