diff options
| -rw-r--r-- | subx/010---vm.cc | 3 | ||||
| -rw-r--r-- | subx/020syscalls.cc | 78 | ||||
| -rwxr-xr-x | subx/ex8 | bin | 0 -> 313 bytes | |||
| -rw-r--r-- | subx/ex8.subx | 99 |
4 files changed, 180 insertions, 0 deletions
diff --git a/subx/010---vm.cc b/subx/010---vm.cc index 5bdd1dd1..33ebe51a 100644 --- a/subx/010---vm.cc +++ b/subx/010---vm.cc @@ -120,6 +120,9 @@ inline uint8_t* mem_addr_u8(uint32_t addr) { inline int8_t* mem_addr_i8(uint32_t addr) { return reinterpret_cast<int8_t*>(&Mem.at(addr-Mem_offset)); } +inline char* mem_addr_string(uint32_t addr) { + return reinterpret_cast<char*>(&Mem.at(addr-Mem_offset)); +} inline uint32_t* mem_addr_u32(uint32_t addr) { return reinterpret_cast<uint32_t*>(&Mem.at(addr-Mem_offset)); } diff --git a/subx/020syscalls.cc b/subx/020syscalls.cc index 177ba6f1..2f6ca994 100644 --- a/subx/020syscalls.cc +++ b/subx/020syscalls.cc @@ -21,12 +21,90 @@ void process_int80() { exit(/*exit code*/Reg[EBX].u); break; case 3: + trace(91, "run") << "read: " << Reg[EBX].u << ' ' << Reg[ECX].u << '/' << mem_addr_string(Reg[ECX].u) << ' ' << Reg[EDX].u << end(); Reg[EAX].i = read(/*file descriptor*/Reg[EBX].u, /*memory buffer*/mem_addr_u8(Reg[ECX].u), /*size*/Reg[EDX].u); + trace(91, "run") << "result: " << Reg[EAX].i << end(); + if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end(); break; case 4: + trace(91, "run") << "write: " << Reg[EBX].u << ' ' << Reg[ECX].u << '/' << mem_addr_string(Reg[ECX].u) << ' ' << Reg[EDX].u << end(); Reg[EAX].i = write(/*file descriptor*/Reg[EBX].u, /*memory buffer*/mem_addr_u8(Reg[ECX].u), /*size*/Reg[EDX].u); + trace(91, "run") << "result: " << Reg[EAX].i << end(); + if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end(); + break; + case 5: { + check_flags(ECX); + check_mode(EDX); + trace(91, "run") << "open: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << ' ' << Reg[ECX].u << end(); + Reg[EAX].i = open(/*filename*/mem_addr_string(Reg[EBX].u), /*flags*/Reg[ECX].u, /*mode*/0640); + trace(91, "run") << "result: " << Reg[EAX].i << end(); + if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end(); + break; + } + case 6: + trace(91, "run") << "close: " << Reg[EBX].u << end(); + Reg[EAX].i = close(/*file descriptor*/Reg[EBX].u); + trace(91, "run") << "result: " << Reg[EAX].i << end(); + if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end(); + break; + case 8: + check_mode(ECX); + trace(91, "run") << "creat: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << end(); + Reg[EAX].i = creat(/*filename*/mem_addr_string(Reg[EBX].u), /*mode*/0640); + trace(91, "run") << "result: " << Reg[EAX].i << end(); + if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end(); + break; + case 10: + trace(91, "run") << "unlink: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << end(); + Reg[EAX].i = unlink(/*filename*/mem_addr_string(Reg[EBX].u)); + trace(91, "run") << "result: " << Reg[EAX].i << end(); + if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end(); + break; + case 38: + trace(91, "run") << "rename: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << " -> " << Reg[ECX].u << '/' << mem_addr_string(Reg[ECX].u) << end(); + Reg[EAX].i = rename(/*old filename*/mem_addr_string(Reg[EBX].u), /*new filename*/mem_addr_string(Reg[ECX].u)); + trace(91, "run") << "result: " << Reg[EAX].i << end(); + if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end(); + break; + case 45: // brk: modify size of data segment + trace(91, "run") << "grow data segment to " << Reg[EBX].u << end(); + resize_mem(/*new end address*/Reg[EBX].u); break; default: raise << HEXWORD << EIP << ": unimplemented syscall " << Reg[EAX].u << '\n' << end(); } } + +// SubX is oblivious to file permissions, directories, symbolic links, terminals, and much else besides. +// Also ignoring any concurrency considerations for now. +void check_flags(int reg) { + uint32_t flags = Reg[reg].u; + if (flags != ((flags & O_RDONLY) | (flags & O_WRONLY))) { + raise << HEXWORD << EIP << ": most POSIX flags to the open() syscall are not supported. Just O_RDONLY and O_WRONLY for now. Zero concurrent access support.\n" << end(); + exit(1); + } + if ((flags & O_RDONLY) && (flags & O_WRONLY)) { + raise << HEXWORD << EIP << ": can't open a file for both reading and writing at once. See http://man7.org/linux/man-pages/man2/open.2.html.\n" << end(); + exit(1); + } +} + +void check_mode(int reg) { + if (Reg[reg].u != 0600) { + raise << HEXWORD << EIP << ": SubX is oblivious to file permissions; register " << reg << " must be 0.\n" << end(); + exit(1); + } +} + +void resize_mem(uint32_t new_end_address) { + if (new_end_address < Mem_offset) { + raise << HEXWORD << EIP << ": can't shrink data segment to before code segment\n"; + return; + } + int32_t new_size = new_end_address - Mem_offset; + if (new_size < SIZE(Mem)) { + raise << HEXWORD << EIP << ": shrinking data segment is not supported.\n" << end(); + return; + } + Mem.resize(new_size); // will throw exception on failure +} diff --git a/subx/ex8 b/subx/ex8 new file mode 100755 index 00000000..d756271e --- /dev/null +++ b/subx/ex8 Binary files differdiff --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& |