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/arch/arm/gem5_assert.S

@@ -0,0 +1,19 @@
+/* assert 0x12345678 + 1 == 0x12345679 */
+.global main
+main:
+    movw r0, #:lower16:myvar
+    movt r0, #:upper16:myvar
+    ldr r1, [r0]
+    add r1, r1, #1
+    str r1, [r0]
+    movw r2, #0x5679
+    movt r2, #0x1234
+    cmp r1, r2
+    beq ok
+    # m5 fail 1
+    mov r0, #0; mov r1, #0; mov r2, #1; mov r3, #0; .inst 0xEE000110 | (0x22 << 16);
+ok:
+    # m5 exit
+    mov r0, #0; mov r1, #0; .inst 0xEE000110 | (0x21 << 16);
+myvar:
+    .word 0x12345678

baremetal/arch/arm/no_bootloader/semihost_exit.S

@@ -0,0 +1,5 @@
+.global mystart
+mystart:
+    mov r0, #0x18
+    ldr r1, =#0x20026
+    svc 0x00123456

baremetal/arch/arm/semihost_exit.S

@@ -0,0 +1,5 @@
+.global main
+main:
+    mov r0, #0x18
+    ldr r1, =#0x20026
+    svc 0x00123456

baremetal/exit.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+void main(void) {
+	exit(0);
+}
+

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
+}

baremetal/link.ld

@@ -0,0 +1,19 @@
+ENTRY(mystart)
+SECTIONS
+{
+  .text : {
+    */bootloader.o(.text)
+    *(.text)
+    *(.rodata)
+    *(.data)
+    *(COMMON)
+  }
+  /* gem5 uses the bss as a measure of the kernel size. */
+  .bss : { *(.bss) }
+  heap_low = .;
+  . = . + 0x1000000;
+  heap_top = .;
+  . = . + 0x1000000;
+  stack_top = .;
+}
+

baremetal/prompt.c

@@ -0,0 +1,22 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+void main(void) {
+    char c;
+    char *ptr = NULL;
+    size_t alloc_size = 1;
+    while (1) {
+        printf("enter a character\n");
+        c = getchar();
+        printf("got: %c\n", c);
+        ptr = realloc(ptr, alloc_size);
+        if (ptr == NULL) {
+            puts("out of memory");
+            break;
+        } else {
+            printf("new alloc of %d bytes at address 0x%p\n", alloc_size, ptr);
+            alloc_size <<= 1;
+        }
+    }
+}
+