tashaboot: arm64 bootloader

A small arm64 bootloader. No board code, no device tree porting, the
architecture manual is the whole story: exception vectors in the
fixed 16 slot layout (Table D1-7), ESR_ELx decoded by exception class
(D1-2172), EL entry and eret chains per the programmers model
(D1-2146), cache maintenance by set/way over the CLIDR_EL1 levels,
semihosting for console and file io per DUI 0203, and the A64 boot
protocol from Documentation/arch/arm64/booting.rst.

The loader boots a stock mainline Image end to end on the qemu virt
machine. Boot receipt with 7.3-rc3 (42MB Image):

  tashaboot 0.1
  loaded 43450368 bytes at 40200000, entry 40200000
  jumping
  [    0.000000] Booting Linux on physical CPU 0x0000000000 [0x411fd070]
  [    0.000000] Linux version 7.3.0-rc3
  [    0.000000] Machine model: linux,dummy-virt
  [    0.000000] earlycon: pl11 MMIO32:0x0000000009000000
  ...
  ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs ]---

The panic is the expected end state, no root filesystem is handed
over yet.

The boot chain, state per stage, start to payload:

+-----------+-----+--------------+----------------------------------+
| stage     | EL  | state        | work                             |
+-----------+-----+--------------+----------------------------------+
| firmware  | any | MMU maybe on | x0 = dtb, jump in               |
+-----------+-----+--------------+----------------------------------+
| tashaboot | 3-2 |              | SCR_EL3.NS = 1, eret to EL2     |
+-----------+-----+--------------+----------------------------------+
|           | 2   | virt scrub   | HCR/CNTHCTL/CPTR/HSTR, CNTFRQ,  |
|           |     |              | VBAR_EL2, MMU off, tlbi alle2   |
+-----------+-----+--------------+----------------------------------+
|           | 2   |              | load Image over semihosting,    |
|           |     |              | validate header, place per      |
|           |     |              | booting.rst                     |
+-----------+-----+--------------+----------------------------------+
|           | 2   | caches clean | flush dcache, inval icache,     |
|           |     |              | args ride x20/x21, regs last    |
+-----------+-----+--------------+----------------------------------+
| payload   | 2   | fresh start  | x0 = dtb, x1-x3 = 0, DAIF       |
|           |     |              | masked, br to image entry       |
+-----------+-----+--------------+----------------------------------+

Two handoff bugs the kernel caught, both AAPCS clobbers in the final
jump. Cache maintenance was called after the register setup, x0-x18
are caller saved, so tb_flush_dcache_all() wiped the dtb pointer and
the kernel spun in setup_machine_fdt() with an invalid device tree
blob. The flush helpers also clobbered x1 (u-boot's void call
convention left mov x1, x0 in cache.S) which handed the kernel a wild
x0. The arguments ride in x20/x21 across the cache calls now, callee
saved, and the register setup is the last thing before the branch.

What is missing on purpose: no SMP bringup (secondary cores park),
no PSCI, no initrd or root filesystem handoff, single serial
console. Those come next.

Signed-off-by: Bradley Morgan <brads@mainlining.org>

1 files changed, 93 insertions, 0 deletions

diff --git a/lib/string/memmove.c b/lib/string/memmove.c
new file mode 100644
index 0000000..cb08a6c
--- /dev/null
+++ b/lib/string/memmove.c
@@ -0,0 +1,93 @@
+/*
+** Copyright 2001, Travis Geiselbrecht. All rights reserved.
+** Distributed under the terms of the NewOS License.
+*/
+/*
+ * Copyright (c) 2008 Travis Geiselbrecht
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files
+ * (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge,
+ * publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#include <string.h>
+#include <sys/types.h>
+
+#if !_ASM_MEMMOVE
+
+typedef long word;
+
+#define lsize sizeof(word)
+#define lmask (lsize - 1)
+
+void *
+memmove(void *dest, void const *src, size_t count)
+{
+	char *d = (char *)dest;
+	const char *s = (const char *)src;
+	int len;
+
+	if(count == 0 || dest == src)
+		return dest;
+
+	if((long)d < (long)s) {
+		if(((long)d | (long)s) & lmask) {
+			// src and/or dest do not align on word boundary
+			if((((long)d ^ (long)s) & lmask) || (count < lsize))
+				len = count; // copy the rest of the buffer with the byte mover
+			else
+				len = lsize - ((long)d & lmask); // move the ptrs up to a word boundary
+
+			count -= len;
+			for(; len > 0; len--)
+				*d++ = *s++;
+		}
+		for(len = count / lsize; len > 0; len--) {
+			*(word *)d = *(word *)s;
+			d += lsize;
+			s += lsize;
+		}
+		for(len = count & lmask; len > 0; len--)
+			*d++ = *s++;
+	} else {
+		d += count;
+		s += count;
+		if(((long)d | (long)s) & lmask) {
+			// src and/or dest do not align on word boundary
+			if((((long)d ^ (long)s) & lmask) || (count <= lsize))
+				len = count;
+			else
+				len = ((long)d & lmask);
+
+			count -= len;
+			for(; len > 0; len--)
+				*--d = *--s;
+		}
+		for(len = count / lsize; len > 0; len--) {
+			d -= lsize;
+			s -= lsize;
+			*(word *)d = *(word *)s;
+		}
+		for(len = count & lmask; len > 0; len--)
+			*--d = *--s;
+	}
+
+	return dest;
+}
+
+#endif
+