diff options
| author | Kartik Agaram <vc@akkartik.com> | 2018-08-13 20:44:28 -0700 |
|---|---|---|
| committer | Kartik Agaram <vc@akkartik.com> | 2018-08-13 21:01:04 -0700 |
| commit | 5cec03b41425940ff5fa73c10ea8fb402a3b5ffa (patch) | |
| tree | d4459386da0712f7b5a8f1ad930bd2feb3c0042f /subx/ex8.subx | |
| parent | fd7198b290e9d8c619a2e69a9bb0404855d1dc13 (diff) | |
| download | mu-5cec03b41425940ff5fa73c10ea8fb402a3b5ffa.tar.gz | |
4520 - several syscalls for files
Diffstat (limited to 'subx/ex8.subx')
| -rw-r--r-- | subx/ex8.subx | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/subx/ex8.subx b/subx/ex8.subx new file mode 100644 index 00000000..0512157f --- /dev/null +++ b/subx/ex8.subx @@ -0,0 +1,99 @@ +## example showing file syscalls +# Create a file, open it for writing, write a character to it, close it, open +# it for reading, read a character from it, close it, delete it, and return +# the character read. +# +# To run: +# $ subx translate ex8.subx ex8 +# $ subx run ex8 +# Expected result: +# $ echo $? +# 97 + +== 0x08048074 # code segment, after leaving room for ELF header and segment headers +# instruction effective address operand 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 + + ## creat(filename) + bb/copy . . . . . . . 0x08049131/imm32/fname # copy to EBX + b9/copy . . . . . . . 0x180/imm32/fixed-perms # copy 0 to ECX + b8/copy . . . . . . . 8/imm32/creat # copy 8 to EAX + cd/syscall . . . . . . . 0x80/imm8 # int 80h + + ## fd = open(filename, O_WRONLY, 0) + bb/copy . . . . . . . 0x08049131/imm32/fname # copy to EBX + b9/copy . . . . . . . 1/imm32/wronly # copy 1 to ECX + ba/copy . . . . . . . 0x180/imm32/fixed-perms # copy 0 to EDX + b8/copy . . . . . . . 5/imm32/open # copy 5 to EAX + cd/syscall . . . . . . . 0x80/imm8 # int 80h + # save fd + bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX + 89/copy 0/mod/indirect 3/rm32/EBX 0/r32/EAX # copy EAX to *EBX + + ## write(fd, "a", 1) + # load fd + bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX + 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX + # + b9/copy . . . . . . . 0x08049129/imm32/a # copy to ECX + ba/copy . . . . . . . 1/imm32/size # copy 1 to EDX + b8/copy . . . . . . . 4/imm32/write # copy 4 to EAX + cd/syscall . . . . . . . 0x80/imm8 # int 80h + + ## close(fd) + # load fd + bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX + 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX + # + b8/copy . . . . . . . 6/imm32/close # copy 6 to EAX + cd/syscall . . . . . . . 0x80/imm8 # int 80h + + ## fd = open(filename, O_RDONLY, 0) + bb/copy . . . . . . . 0x08049131/imm32/fname # copy to EBX + b9/copy . . . . . . . 0/imm32/rdonly # copy 0 to ECX + ba/copy . . . . . . . 0x180/imm32/fixed-perms # copy 0 to EDX + b8/copy . . . . . . . 5/imm32/open # copy 5 to EAX + cd/syscall . . . . . . . 0x80/imm8 # int 80h + # save fd + bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX + 89/copy 0/mod/indirect 3/rm32/EBX 0/r32/EAX # copy EAX to *EBX + + ## read(fd, b, 1) + # load fd + bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX + 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX + # + b9/copy . . . . . . . 0x0804912d/imm32/b # copy to ECX + ba/copy . . . . . . . 1/imm32/size # copy 1 to EDX + b8/copy . . . . . . . 3/imm32/read # copy 3 to EAX + cd/syscall . . . . . . . 0x80/imm8 # int 80h + + ## close(fd) + # load fd + bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX + 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX + # + b8/copy . . . . . . . 6/imm32/close # copy 8 to EAX + cd/syscall . . . . . . . 0x80/imm8 # int 80h + + ## unlink(filename) + bb/copy . . . . . . . 0x08049131/imm32/fname # copy to EBX + b8/copy . . . . . . . 0xa/imm32/unlink # copy 8 to EAX + cd/syscall . . . . . . . 0x80/imm8 # int 80h + + ## exit(b) + # load b + bb . . . . . . . 0x0804912d/imm32/b # copy to EBX + 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX + # + b8/copy . . . . . . . 1/imm32/exit # copy 1 to EAX + cd/syscall . . . . . . . 0x80/imm8 # int 80h + +== 0x08049125 # data segment +00 00 00 00 # fd +61 00 00 00 # a: string to write to file: 'a' +00 00 00 00 # b: space for string read from file +2e 66 6f 6f 00 00 00 00 # filename: '.foo' + +# vim:ft=subx:nowrap:tw& |