1 files changed, 193 insertions, 0 deletions
diff --git a/linux/bootstrap/012elf.cc b/linux/bootstrap/012elf.cc
new file mode 100644
index 00000000..c852e372
--- /dev/null
+++ b/linux/bootstrap/012elf.cc
@@ -0,0 +1,193 @@
+//: Loading SubX programs from ELF binaries.
+//: This will allow us to run them natively on a Linux kernel.
+//: Based on https://github.com/kragen/stoneknifeforth/blob/702d2ebe1b/386.c
+
+:(before "End Main")
+assert(argc > 1);
+if (is_equal(argv[1], "run")) {
+  // Outside of tests, traces must be explicitly requested.
+  if (Trace_file.is_open()) Trace_stream = new trace_stream;
+  trace(2, "run") << "=== Starting to run" << end();
+  if (argc <= 2) {
+    raise << "Not enough arguments provided.\n" << die();
+  }
+  reset();
+  cerr << std::hex;
+  load_elf(argv[2], argc, argv);
+  while (EIP < End_of_program)  // weak final-gasp termination check
+    run_one_instruction();
+  raise << "executed past end of the world: " << EIP << " vs " << End_of_program << '\n' << end();
+  return 1;
+}
+
+:(code)
+void load_elf(const string& filename, int argc, char* argv[]) {
+  int fd = open(filename.c_str(), O_RDONLY);
+  if (fd < 0) raise << filename.c_str() << ": open" << perr() << '\n' << die();
+  off_t size = lseek(fd, 0, SEEK_END);
+  lseek(fd, 0, SEEK_SET);
+  uint8_t* elf_contents = static_cast<uint8_t*>(malloc(size));
+  if (elf_contents == NULL) raise << "malloc(" << size << ')' << perr() << '\n' << die();
+  ssize_t read_size = read(fd, elf_contents, size);
+  if (size != read_size) raise << "read → " << size << " (!= " << read_size << ')' << perr() << '\n' << die();
+  load_elf_contents(elf_contents, size, argc, argv);
+  free(elf_contents);
+}
+
+void load_elf_contents(uint8_t* elf_contents, size_t size, int argc, char* argv[]) {
+  uint8_t magic[5] = {0};
+  memcpy(magic, elf_contents, 4);
+  if (memcmp(magic, "\177ELF", 4) != 0)
+    raise << "Invalid ELF file; starts with \"" << magic << '"' << die();
+  if (elf_contents[4] != 1)
+    raise << "Only 32-bit ELF files (4-byte words; virtual addresses up to 4GB) supported.\n" << die();
+  if (elf_contents[5] != 1)
+    raise << "Only little-endian ELF files supported.\n" << die();
+  // unused: remaining 10 bytes of e_ident
+  uint32_t e_machine_type = u32_in(&elf_contents[16]);
+  if (e_machine_type != 0x00030002)
+    raise << "ELF type/machine 0x" << HEXWORD << e_machine_type << " isn't i386 executable\n" << die();
+  // unused: e_version. We only support version 1, and later versions will be backwards compatible.
+  uint32_t e_entry = u32_in(&elf_contents[24]);
+  uint32_t e_phoff = u32_in(&elf_contents[28]);
+  // unused: e_shoff
+  // unused: e_flags
+  uint32_t e_ehsize = u16_in(&elf_contents[40]);
+  if (e_ehsize < 52) raise << "Invalid binary; ELF header too small\n" << die();
+  uint32_t e_phentsize = u16_in(&elf_contents[42]);
+  uint32_t e_phnum = u16_in(&elf_contents[44]);
+  trace(90, "load") << e_phnum << " entries in the program header, each " << e_phentsize << " bytes long" << end();
+  // unused: e_shentsize
+  // unused: e_shnum
+  // unused: e_shstrndx
+
+  set<uint32_t> overlap;  // to detect overlapping segments
+  for (size_t i = 0;  i < e_phnum;  ++i)
+    load_segment_from_program_header(elf_contents, i, size, e_phoff + i*e_phentsize, e_ehsize, overlap);
+
+  // initialize code and stack
+  assert(overlap.find(STACK_SEGMENT) == overlap.end());
+  Mem.push_back(vma(STACK_SEGMENT));
+  assert(overlap.find(AFTER_STACK) == overlap.end());
+  // The stack grows downward.
+  Reg[ESP].u = AFTER_STACK;
+  Reg[EBP].u = 0;
+  EIP = e_entry;
+
+  // initialize args on stack
+  // no envp for now
+  // we wastefully use a separate page of memory for argv
+  Mem.push_back(vma(ARGV_DATA_SEGMENT));
+  uint32_t argv_data = ARGV_DATA_SEGMENT;
+  for (int i = argc-1;  i >= /*skip 'subx_bin' and 'run'*/2;  --i) {
+    push(argv_data);
+    for (size_t j = 0;  j <= strlen(argv[i]);  ++j) {
+      assert(overlap.find(argv_data) == overlap.end());  // don't bother comparing ARGV and STACK
+      write_mem_u8(argv_data, argv[i][j]);
+      argv_data += sizeof(char);
+      assert(argv_data < ARGV_DATA_SEGMENT + SEGMENT_ALIGNMENT);
+    }
+  }
+  push(argc-/*skip 'subx_bin' and 'run'*/2);
+}
+
+void push(uint32_t val) {
+  Reg[ESP].u -= 4;
+  if (Reg[ESP].u < STACK_SEGMENT) {
+    raise << "The stack overflowed its segment. "
+          << "Maybe SPACE_FOR_SEGMENT should be larger? "
+          << "Or you need to carve out an exception for the stack segment "
+          << "to be larger.\n" << die();
+  }
+  trace(Callstack_depth+1, "run") << "decrementing ESP to 0x" << HEXWORD << Reg[ESP].u << end();
+  trace(Callstack_depth+1, "run") << "pushing value 0x" << HEXWORD << val << end();
+  write_mem_u32(Reg[ESP].u, val);
+}
+
+void load_segment_from_program_header(uint8_t* elf_contents, int segment_index, size_t size, uint32_t offset, uint32_t e_ehsize, set<uint32_t>& overlap) {
+  uint32_t p_type = u32_in(&elf_contents[offset]);
+  trace(90, "load") << "program header at offset " << offset << ": type " << p_type << end();
+  if (p_type != 1) {
+    trace(90, "load") << "ignoring segment at offset " << offset << " of non PT_LOAD type " << p_type << " (see http://refspecs.linuxbase.org/elf/elf.pdf)" << end();
+    return;
+  }
+  uint32_t p_offset = u32_in(&elf_contents[offset + 4]);
+  uint32_t p_vaddr = u32_in(&elf_contents[offset + 8]);
+  if (e_ehsize > p_vaddr) raise << "Invalid binary; program header overlaps ELF header\n" << die();
+  // unused: p_paddr
+  uint32_t p_filesz = u32_in(&elf_contents[offset + 16]);
+  uint32_t p_memsz = u32_in(&elf_contents[offset + 20]);
+  if (p_filesz != p_memsz)
+    raise << "Can't yet handle segments where p_filesz != p_memsz (see http://refspecs.linuxbase.org/elf/elf.pdf)\n" << die();
+
+  if (p_offset + p_filesz > size)
+    raise << "Invalid binary; segment at offset " << offset << " is too large: wants to end at " << p_offset+p_filesz << " but the file ends at " << size << '\n' << die();
+  if (p_memsz >= SEGMENT_ALIGNMENT) {
+    raise << "Code segment too small for SubX; for now please manually increase SEGMENT_ALIGNMENT.\n" << end();
+    return;
+  }
+  trace(90, "load") << "blitting file offsets (" << p_offset << ", " << (p_offset+p_filesz) << ") to addresses (" << p_vaddr << ", " << (p_vaddr+p_memsz) << ')' << end();
+  if (size > p_memsz) size = p_memsz;
+  Mem.push_back(vma(p_vaddr));
+  for (size_t i = 0;  i < p_filesz;  ++i) {
+    assert(overlap.find(p_vaddr+i) == overlap.end());
+    write_mem_u8(p_vaddr+i, elf_contents[p_offset+i]);
+    overlap.insert(p_vaddr+i);
+  }
+  if (segment_index == 0 && End_of_program < p_vaddr+p_memsz)
+    End_of_program = p_vaddr+p_memsz;
+}
+
+:(before "End Includes")
+// Very primitive/fixed/insecure ELF segments for now.
+//   --- inaccessible:        0x00000000 -> 0x08047fff
+//   code:                    0x09000000 -> 0x09ffffff (specified in ELF binary)
+//   data:                    0x0a000000 -> 0x0affffff (specified in ELF binary)
+//                      --- heap gets mmap'd somewhere here ---
+//   stack:                   0xbdffffff -> 0xbd000000 (downward; not in ELF binary)
+//   argv hack:               0xbf000000 -> 0xbfffffff (not in ELF binary)
+//   --- reserved for kernel: 0xc0000000 -> ...
+const uint32_t START_HEAP        = 0x0b000000;
+const uint32_t END_HEAP          = 0xbd000000;
+const uint32_t STACK_SEGMENT     = 0xbd000000;
+const uint32_t AFTER_STACK       = 0xbe000000;
+const uint32_t ARGV_DATA_SEGMENT = 0xbf000000;
+// When updating the above memory map, don't forget to update `mmap`'s
+// implementation in the 'syscalls' layer.
+:(before "End Dump Info for Instruction")
+//? dump_stack();  // slow
+:(code)
+void dump_stack() {
+  ostringstream out;
+  trace(Callstack_depth+1, "run") << "stack:" << end();
+  for (uint32_t a = AFTER_STACK-4;  a > Reg[ESP].u;  a -= 4)
+    trace(Callstack_depth+2, "run") << "  0x" << HEXWORD << a << " => 0x" << HEXWORD << read_mem_u32(a) << end();
+  trace(Callstack_depth+2, "run") << "  0x" << HEXWORD << Reg[ESP].u << " => 0x" << HEXWORD << read_mem_u32(Reg[ESP].u) << "  <=== ESP" << end();
+  for (uint32_t a = Reg[ESP].u-4;  a > Reg[ESP].u-40;  a -= 4)
+    trace(Callstack_depth+2, "run") << "  0x" << HEXWORD << a << " => 0x" << HEXWORD << read_mem_u32(a) << end();
+}
+
+inline uint32_t u32_in(uint8_t* p) {
+  return p[0] | p[1] << 8 | p[2] << 16 | p[3] << 24;
+}
+
+inline uint16_t u16_in(uint8_t* p) {
+  return p[0] | p[1] << 8;
+}
+
+:(before "End Types")
+struct perr {};
+:(code)
+ostream& operator<<(ostream& os, perr /*unused*/) {
+  if (errno)
+    os << ": " << strerror(errno);
+  return os;
+}
+
+:(before "End Includes")
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdarg.h>
+#include <errno.h>
+#include <unistd.h>