Make improvements

libc/sysv/macros.internal.h

@@ -0,0 +1,38 @@
+#ifndef COSMOPOLITAN_LIBC_SYSV_MACROS_H_
+#define COSMOPOLITAN_LIBC_SYSV_MACROS_H_
+#ifdef __ASSEMBLER__
+#include "libc/macros.internal.inc"
+/* clang-format off */
+
+/**
+ * @fileoverview System Five jump slot generator.
+ *
+ * We need to pass a magic number to the SYSCALL instruction in %rax.
+ * That's only possible to do in C using asm() macro wrappers, like in
+ * Chromium's "System Call Support" library. This technique is simpler
+ * to implement, gains us object-level ABI compatibility, hookability,
+ * and the ability to support significantly more functions, without the
+ * risk of slowing down builds too much with complicated headers.
+ */
+
+.macro	.scall	name:req num:req kw1 kw2
+  .ifnb	\kw2
+	.align	16
+\name:	movabs	$\num,%rax
+	jmp	*__systemfive(%rip)
+  .else
+\name:	push	%rbp
+	mov	%rsp,%rbp
+	movabs	$\num,%rax
+	.hookable
+	call	*__systemfive(%rip)
+	pop	%rbp
+	ret
+  .endif
+	.endfn	\name,\kw1,\kw2
+	.previous
+.endm
+
+/* clang-format on */
+#endif /* __ASSEMBLER__ */
+#endif /* COSMOPOLITAN_LIBC_SYSV_MACROS_H_ */