From 9dbdb15abf8ffb9dbdd972d6bbbcea9a3591e2a3 Mon Sep 17 00:00:00 2001 From: Bradley Morgan Date: Sat, 3 Oct 2026 20:02:29 +0000 Subject: 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 --- include/limits.h | 121 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 121 insertions(+) create mode 100644 include/limits.h (limited to 'include/limits.h') 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 /* recurse down to the real one */ +#endif + +#endif /* not _GCC_LIMITS_H_ */ -- cgit v1.2.3