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.

1 files changed, 125 insertions, 0 deletions

diff --git a/include/fmt.h b/include/fmt.h
new file mode 100644
index 0000000..c74ac4c
--- /dev/null
+++ b/include/fmt.h
@@ -0,0 +1,125 @@
+// Copyright (c) 2020 Johannes Stoelp
+
+#pragma once
+
+#include <stdarg.h>
+
+#define ALLOW_UNUSED __attribute__((unused))
+
+ALLOW_UNUSED
+static const char* num2dec(char* buf, unsigned long len, unsigned long long num) {
+    char* pbuf = buf + len - 1;
+    *pbuf = '\0';
+
+    if (num == 0) {
+        *(--pbuf) = '0';
+    }
+
+    while (num > 0 && pbuf != buf) {
+        char d = (num % 10) + '0';
+        *(--pbuf) = d;
+        num /= 10;
+    }
+    return pbuf;
+}
+
+ALLOW_UNUSED
+static const char* num2hex(char* buf, unsigned long len, unsigned long long num) {
+    char* pbuf = buf + len - 1;
+    *pbuf = '\0';
+
+    if (num == 0) {
+        *(--pbuf) = '0';
+    }
+
+    while (num > 0 && pbuf != buf) {
+        char d = (num & 0xf);
+        *(--pbuf) = d + (d > 9 ? 'a' - 10 : '0');
+        num >>= 4;
+    }
+    return pbuf;
+}
+
+ALLOW_UNUSED
+static int dynld_vsnprintf(char* buf, unsigned long len, const char* fmt, va_list ap) {
+    unsigned i = 0;
+
+#define put(c)           \
+    {                    \
+        char _c = (c);   \
+        if (i < len) {   \
+            buf[i] = _c; \
+        }                \
+        ++i;             \
+    }
+
+#define puts(s)    \
+    while (*s) {   \
+        put(*s++); \
+    }
+
+    char scratch[16];
+    int l_cnt = 0;
+
+    while (*fmt) {
+        if (*fmt != '%') {
+            put(*fmt++);
+            continue;
+        }
+
+        l_cnt = 0;
+
+    continue_fmt:
+        switch (*(++fmt /* constume '%' */)) {
+            case 'l':
+                ++l_cnt;
+                goto continue_fmt;
+            case 'd': {
+                long val = l_cnt > 0 ? va_arg(ap, long) : va_arg(ap, int);
+                if (val < 0) {
+                    val *= -1;
+                    put('-');
+                }
+                const char* ptr = num2dec(scratch, sizeof(scratch), val);
+                puts(ptr);
+            } break;
+            case 'x': {
+                unsigned long val = l_cnt > 0 ? va_arg(ap, unsigned long) : va_arg(ap, unsigned);
+                const char* ptr = num2hex(scratch, sizeof(scratch), val);
+                puts(ptr);
+            } break;
+            case 's': {
+                const char* ptr = va_arg(ap, const char*);
+                puts(ptr);
+            } break;
+            case 'p': {
+                const void* val = va_arg(ap, const void*);
+                const char* ptr = num2hex(scratch, sizeof(scratch), (unsigned long long)val);
+                put('0');
+                put('x');
+                puts(ptr);
+            } break;
+            default:
+                put(*fmt);
+                break;
+        }
+        ++fmt;
+    }
+
+#undef puts
+#undef put
+
+    if (buf) {
+        i < len ? (buf[i] = '\0') : (buf[len - 1] = '\0');
+    }
+    return i;
+}
+
+ALLOW_UNUSED
+static int dynld_snprintf(char* buf, unsigned long len, const char* fmt, ...) {
+    va_list ap;
+    va_start(ap, fmt);
+    int ret = dynld_vsnprintf(buf, len, fmt, ap);
+    va_end(ap);
+    return ret;
+}