最初コミット

Makefile

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+all:
+	cc -nostdlib -static -masm=intel -o main main.c

README.md

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+此れはlibcなしの「こんにちは、世界」のデモです。\
+Linux、FreeBSD、OpenBSD、NetBSD、及びmacOSで実行出来ますが、IntelやAMD CPUが必須に成ります。
+
+```sh
+make
+$ cc -nostdlib -static -masm=intel -o main main.c
+$ ls -thal main
+-rwxr-xr-x  1 suwako suwako  1.6K 12月 15 15:57 main
+$ file main
+main: ELF 64-bit LSB executable, x86-64, version 1 (FreeBSD), statically linked, not stripped
+$ objdump -M intel -d main
+
+main:   file format elf64-x86-64
+
+Disassembly of section .text:
+
+00000000002011f0 <_start>:
+  2011f0: 55                            push    rbp
+  2011f1: 48 89 e5                      mov     rbp, rsp
+  2011f4: b8 04 00 00 00                mov     eax, 0x4
+  2011f9: bf 01 00 00 00                mov     edi, 0x1
+  2011fe: 48 c7 c6 20 22 20 00          mov     rsi, 0x202220
+  201205: ba 1c 00 00 00                mov     edx, 0x1c
+  20120a: 0f 05                         syscall
+  20120c: b8 01 00 00 00                mov     eax, 0x1
+  201211: 31 ff                         xor     edi, edi
+  201213: 0f 05                         syscall
+  201215: 5d                            pop     rbp
+  201216: c3                            ret
+```

main.c

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+#if defined(__linux__)
+#define SYS_WRITE 1
+#define SYS_EXIT 60
+#elif defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__)
+#define SYS_WRITE 4
+#define SYS_EXIT 1
+#elif defined(__APPLE__)
+#define SYS_WRITE 0x2000004
+#define SYS_EXIT 0x2000001
+#endif
+
+char msg[] = "こんにちは、世界！\n";
+
+void _start() {
+  asm volatile(
+    ".intel_syntax noprefix\n"
+    "mov eax, %[sys_write]\n"
+    "mov edi, 1\n"
+    "mov rsi, offset msg\n"
+    "mov edx, %[len]\n"
+    "syscall\n"
+
+    "mov eax, %[sys_exit]\n"
+    "xor edi, edi\n"
+    "syscall\n"
+
+    ".att_syntax prefix\n"
+    :: [sys_write] "i" (SYS_WRITE),
+       [sys_exit] "i" (SYS_EXIT),
+       [len] "i" (sizeof(msg) - 1)
+    : "rax", "rdi", "rsi", "rdx", "rcx", "r11"
+  );
+}