gem5: update to 7bfb7f3a43f382eb49853f47b140bfd6caad0fb8

The update is required to include 3c3ca64b5f0dd9eef7b1ce1c65cc6e8e9147dd38
otherwise baremetal does not on VExpress.

baremetal: create a baremetal setup with crosstool-ng

buildroot: improve directory location: move out/dl inside
out/buildroot/download, and add a new out/buildroot/build level

tagline: generalize, deliver more value than howto, since now howtos
are starting to multiply

rename all top scripts to separate words with hyphen more consistently,
e.g. run-gdb instead of rungdb

getvar: list all variables

gem5: make m5out section to focus all releated information at

Prevent m5term Text file busy when rebuilding gem5 while it is running.

baremetal/lib/aarch64.S

@@ -0,0 +1,11 @@
+.global mystart
+mystart:
+    /* = NEON setup */
+    mov x1, #(0x3 << 20)
+    msr cpacr_el1, x1
+    isb
+
+    ldr x0, =stack_top
+    mov sp, x0
+    bl main
+    b .

baremetal/lib/arm.S

@@ -0,0 +1,5 @@
+.global mystart
+mystart:
+    ldr sp, =stack_top
+    bl main
+    b .

baremetal/lib/common.c

@@ -0,0 +1,65 @@
+#include <sys/stat.h>
+
+enum {
+    UART_FR_RXFE = 0x10,
+};
+
+#define UART_DR(baseaddr) (*(unsigned int *)(baseaddr))
+#define UART_FR(baseaddr) (*(((unsigned int *)(baseaddr))+6))
+
+int _close(int file) { return -1; }
+
+int _fstat(int file, struct stat *st) {
+    st->st_mode = S_IFCHR;
+    return 0;
+}
+
+int _isatty(int file) { return 1; }
+int _lseek(int file, int ptr, int dir) { return 0; }
+int _open(const char *name, int flags, int mode) { return -1; }
+
+int _read(int file, char *ptr, int len) {
+    int todo;
+    if (len == 0)
+        return 0;
+    while (UART_FR(UART0_ADDR) & UART_FR_RXFE);
+    *ptr++ = UART_DR(UART0_ADDR);
+    for (todo = 1; todo < len; todo++) {
+        if (UART_FR(UART0_ADDR) & UART_FR_RXFE) {
+            break;
+        }
+        *ptr++ = UART_DR(UART0_ADDR);
+    }
+    return todo;
+}
+
+char *heap_end = 0;
+caddr_t _sbrk(int incr) {
+    extern char heap_low;
+    extern char heap_top;
+    char *prev_heap_end;
+    if (heap_end == 0) {
+        heap_end = &heap_low;
+    }
+    prev_heap_end = heap_end;
+    if (heap_end + incr > &heap_top) {
+        /* Heap and stack collision */
+        return (caddr_t)0;
+    }
+    heap_end += incr;
+    return (caddr_t)prev_heap_end;
+}
+
+int _write(int file, char *ptr, int len) {
+    int todo;
+    for (todo = 0; todo < len; todo++) {
+        UART_DR(UART0_ADDR) = *ptr++;
+    }
+    return len;
+}
+
+void _exit(int status) {
+#if defined(__arm__)
+    __asm__ __volatile__ ("mov r0, #0x18; ldr r1, =#0x20026; svc 0x00123456");
+#endif
+}