Add file descriptors and basic cat

meson.build

@@ -223,3 +223,42 @@ custom_target(
   command: ['objcopy', '-O', 'binary', '@INPUT@', '@OUTPUT@'],
   build_by_default: true,
 )
+
+cat_start = custom_target(
+  'cat_start',
+  input:  'src/user/start.asm',
+  output: 'cat_start.o',
+  command: [nasm, '-f', 'elf64', '-o', '@OUTPUT@', '@INPUT@'],
+)
+
+cat_syscall = custom_target(
+  'cat_syscall',
+  input:  'src/user/syscall.asm',
+  output: 'cat_syscall.o',
+  command: [nasm, '-f', 'elf64', '-o', '@OUTPUT@', '@INPUT@'],
+)
+
+cat_elf = executable(
+  'cat.elf',
+  sources: [cat_start, cat_syscall, lib_sources, 'src/user/app/cat/cat.c'],
+  c_args: [
+    '-ffreestanding',
+    '-nostdlib',
+    '-fno-stack-protector',
+    '-mcmodel=large',
+    '-DVERSION="' + meson.project_version() + '"',
+  ],
+  link_args: [
+    '-T', meson.project_source_root() / 'src/user/linker.ld',
+    '-nostdlib',
+  ],
+  link_depends: 'src/user/linker.ld',
+)
+
+custom_target(
+  'cat',
+  input:  cat_elf,
+  output: 'cat',
+  command: ['objcopy', '-O', 'binary', '@INPUT@', '@OUTPUT@'],
+  build_by_default: true,
+)