From f9f2b6bb2d685556bc3346ca3f7e55f4c865fc16 Mon Sep 17 00:00:00 2001
From: johannst <johannes.stoelp@gmail.com>
Date: Tue, 24 Nov 2020 21:23:08 +0100
Subject: add process init chapter

Add chapter on process initialization.
Add program to visualize data provided by the Linux Kernel as
specified in the SysV ABI.
Add utils for syscalls and printing + tests.
---
 include/syscall.h | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 include/syscall.h

(limited to 'include/syscall.h')

diff --git a/include/syscall.h b/include/syscall.h
new file mode 100644
index 0000000..0460ede
--- /dev/null
+++ b/include/syscall.h
@@ -0,0 +1,56 @@
+// Copyright (c) 2020 Johannes Stoelp
+
+#pragma once
+
+#if !defined(__linux__) || !defined(__x86_64__)
+# error "Only supported on linux(x86_64)!"
+#endif
+
+// Inline ASM
+//   Syntax:
+//     asm asm-qualifiers (AssemblerTemplate : OutputOperands : InputOperands : Clobbers)
+//
+//   Output operand constraints:
+//     = | operand (variable) is written to by this instruction
+//     + | operand (variable) is written to / read from by this instruction
+//
+//   Input/Output operand constraints:
+//     r | allocate general purpose register
+//
+//   Machine specific constraints (x86_64):
+//     a  | a register (eg rax)
+//     d  | d register (eg rdx)
+//     D  | di register (eg rdi)
+//     S  | si register (eg rsi)
+//
+//  Local register variables:
+//    In case a specific register is required which can not be specified via a
+//    machine specific constraint.
+//    ```c
+//    register long r12 asm ("r12") = 42;
+//    asm("nop" : : "r"(r10));
+//    ```
+//
+// Reference:
+//   https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
+//   https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html#Machine-Constraints
+//   https://gcc.gnu.org/onlinedocs/gcc/Local-Register-Variables.html
+
+// Linux syscall ABI
+//  x86-64
+//    #syscall: rax
+//    ret     : rax
+//    instr   : syscall
+//    args    : rdi   rsi   rdx   r10   r8    r9
+//
+// Reference:
+//   syscall(2)
+
+#define argcast(A) ((long)(A))
+#define syscall3(n,a1,a2,a3) _syscall3(n, argcast(a1), argcast(a2), argcast(a3))
+
+static inline long _syscall3(long n, long a1, long a2, long a3) {
+    long ret;
+    asm volatile("syscall" : "=a"(ret) : "a"(n), "D"(a1), "S"(a2), "d"(a3) : "memory");
+    return ret;
+}
-- 
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