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, 121 insertions, 0 deletions

diff --git a/include/limits.h b/include/limits.h
new file mode 100644
index 0000000..ec83068
--- /dev/null
+++ b/include/limits.h
@@ -0,0 +1,121 @@
+/* This administrivia gets added to the beginning of limits.h
+   if the system has its own version of limits.h.  */
+
+/* We use _GCC_LIMITS_H_ because we want this not to match
+   any macros that the system's limits.h uses for its own purposes.  */
+#ifndef _GCC_LIMITS_H_  /* Terminated in limity.h.  */
+#define _GCC_LIMITS_H_
+
+#ifndef _LIMITS_H___
+#define _LIMITS_H___
+
+/* Number of bits in a `char'.  */
+#undef CHAR_BIT
+#define CHAR_BIT __CHAR_BIT__
+
+/* Maximum length of a multibyte character.  */
+#ifndef MB_LEN_MAX
+#define MB_LEN_MAX 1
+#endif
+
+/* Minimum and maximum values a `signed char' can hold.  */
+#undef SCHAR_MIN
+#define SCHAR_MIN (-SCHAR_MAX - 1)
+#undef SCHAR_MAX
+#define SCHAR_MAX __SCHAR_MAX__
+
+/* Maximum value an `unsigned char' can hold.  (Minimum is 0).  */
+#undef UCHAR_MAX
+#if __SCHAR_MAX__ == __INT_MAX__
+# define UCHAR_MAX (SCHAR_MAX * 2U + 1U)
+#else
+# define UCHAR_MAX (SCHAR_MAX * 2 + 1)
+#endif
+
+/* Minimum and maximum values a `char' can hold.  */
+#ifdef __CHAR_UNSIGNED__
+# undef CHAR_MIN
+# if __SCHAR_MAX__ == __INT_MAX__
+#  define CHAR_MIN 0U
+# else
+#  define CHAR_MIN 0
+# endif
+# undef CHAR_MAX
+# define CHAR_MAX UCHAR_MAX
+#else
+# undef CHAR_MIN
+# define CHAR_MIN SCHAR_MIN
+# undef CHAR_MAX
+# define CHAR_MAX SCHAR_MAX
+#endif
+
+/* Minimum and maximum values a `signed short int' can hold.  */
+#undef SHRT_MIN
+#define SHRT_MIN (-SHRT_MAX - 1)
+#undef SHRT_MAX
+#define SHRT_MAX __SHRT_MAX__
+
+/* Maximum value an `unsigned short int' can hold.  (Minimum is 0).  */
+#undef USHRT_MAX
+#if __SHRT_MAX__ == __INT_MAX__
+# define USHRT_MAX (SHRT_MAX * 2U + 1U)
+#else
+# define USHRT_MAX (SHRT_MAX * 2 + 1)
+#endif
+
+/* Minimum and maximum values a `signed int' can hold.  */
+#undef INT_MIN
+#define INT_MIN (-INT_MAX - 1)
+#undef INT_MAX
+#define INT_MAX __INT_MAX__
+
+/* Maximum value an `unsigned int' can hold.  (Minimum is 0).  */
+#undef UINT_MAX
+#define UINT_MAX (INT_MAX * 2U + 1U)
+
+/* Minimum and maximum values a `signed long int' can hold.
+   (Same as `int').  */
+#undef LONG_MIN
+#define LONG_MIN (-LONG_MAX - 1L)
+#undef LONG_MAX
+#define LONG_MAX __LONG_MAX__
+
+/* Maximum value an `unsigned long int' can hold.  (Minimum is 0).  */
+#undef ULONG_MAX
+#define ULONG_MAX (LONG_MAX * 2UL + 1UL)
+
+#if defined (__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
+/* Minimum and maximum values a `signed long long int' can hold.  */
+# undef LLONG_MIN
+# define LLONG_MIN (-LLONG_MAX - 1LL)
+# undef LLONG_MAX
+# define LLONG_MAX __LONG_LONG_MAX__
+
+/* Maximum value an `unsigned long long int' can hold.  (Minimum is 0).  */
+# undef ULLONG_MAX
+# define ULLONG_MAX (LLONG_MAX * 2ULL + 1ULL)
+#endif
+
+#if defined (__GNU_LIBRARY__) ? defined (__USE_GNU) : !defined (__STRICT_ANSI__)
+/* Minimum and maximum values a `signed long long int' can hold.  */
+# undef LONG_LONG_MIN
+# define LONG_LONG_MIN (-LONG_LONG_MAX - 1LL)
+# undef LONG_LONG_MAX
+# define LONG_LONG_MAX __LONG_LONG_MAX__
+
+/* Maximum value an `unsigned long long int' can hold.  (Minimum is 0).  */
+# undef ULONG_LONG_MAX
+# define ULONG_LONG_MAX (LONG_LONG_MAX * 2ULL + 1ULL)
+#endif
+
+#endif /* _LIMITS_H___ */
+/* This administrivia gets added to the end of limits.h
+   if the system has its own version of limits.h.  */
+
+#else /* not _GCC_LIMITS_H_ */
+
+#ifdef _GCC_NEXT_LIMITS_H
+#include_next <limits.h>		/* recurse down to the real one */
+#endif
+
+#endif /* not _GCC_LIMITS_H_ */