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Message-Id: <20240502-mips_debug_ll-v3-4-3b61f30e484c@flygoat.com> Date: Thu, 02 May 2024 10:59:31 +0100 From: Jiaxun Yang <jiaxun.yang@...goat.com> To: Thomas Bogendoerfer <tsbogend@...ha.franken.de> Cc: linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org, Jiaxun Yang <jiaxun.yang@...goat.com> Subject: [PATCH v3 4/9] MIPS: debug: Provide an early exception vector for low-level debugging This is helpful for debugging of early boot crash when exceptions happens before trap_init(), or for debugging SMP bringup code. It will install exception handler very early on kernel_entry by setting ebase or copy itself to start of CKSEG0, and print off exception vectors and other status registers like: Low level exception: ffffffff8011e180 GlobalNumber: 0x00000000 EBase: 0xffffffff8011e000 Xcontext: 0x0000000000000000 Cause: 0x0000000c Status: 0x14000082 EPC: 0xffffffff80d324e0 BadVAddr: 0x0000000000000000 BadInstr: 0xac000000 Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com> --- arch/mips/Kconfig.debug | 9 ++ arch/mips/kernel/Makefile | 1 + arch/mips/kernel/debug-vec.S | 194 +++++++++++++++++++++++++++++++++++++++++++ arch/mips/kernel/head.S | 4 + 4 files changed, 208 insertions(+) diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug index 6ef42edc7d67..323ad3ec643b 100644 --- a/arch/mips/Kconfig.debug +++ b/arch/mips/Kconfig.debug @@ -180,6 +180,15 @@ config DEBUG_LL this option should not be enabled for kernels that are intended to be portable. +config DEBUG_LL_EXCEPT + bool "Kernel low-level debugging of exceptions" + depends on DEBUG_LL + help + Say Y here to enable debugging prints for low-level exceptions. + This is helpful if you are debugging a early boot crash when + exceptions happens before trap_init(), or if you are debugging + SMP bringup code. + choice prompt "Kernel low-level debugging port" depends on DEBUG_LL diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile index bfac35a64ae5..6641c3370e68 100644 --- a/arch/mips/kernel/Makefile +++ b/arch/mips/kernel/Makefile @@ -79,6 +79,7 @@ obj-$(CONFIG_MIPS32_N32) += scall64-n32.o signal_n32.o obj-$(CONFIG_MIPS32_O32) += scall64-o32.o signal_o32.o obj-$(CONFIG_DEBUG_LL) += debug.o +obj-$(CONFIG_DEBUG_LL_EXCEPT) += debug-vec.o obj-$(CONFIG_KGDB) += kgdb.o obj-$(CONFIG_PROC_FS) += proc.o diff --git a/arch/mips/kernel/debug-vec.S b/arch/mips/kernel/debug-vec.S new file mode 100644 index 000000000000..4530bf3d5b75 --- /dev/null +++ b/arch/mips/kernel/debug-vec.S @@ -0,0 +1,194 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2023, Jiaxun Yang <jiaxun.yang@...goat.com> + * MIPS Low level exception vectors and handler + */ + +#include <asm/addrspace.h> +#include <asm/asm.h> +#include <asm/asm-offsets.h> +#include <asm/asmmacro.h> + + +.balign 0x1000 +LEAF(debug_ll_vecs) + .set push + .set noreorder + move a0, zero + PTR_LA t9, debug_ll_exception + jalr t9 + nop + b . + nop + +.org 0x80 + move a0, zero + PTR_LA t9, debug_ll_exception + jalr t9 + nop + b . + nop + +.org 0x100 + move a0, zero + PTR_LA t9, debug_ll_exception + jalr t9 + nop + b . + nop + +.org 0x180 + move a0, zero + PTR_LA t9, debug_ll_exception + jalr t9 + nop + b . + nop + +.org 0x200 + move a0, zero + PTR_LA t9, debug_ll_exception + jalr t9 + nop + b . + nop + +.org 0x280 + move a0, zero + PTR_LA t9, debug_ll_exception + jalr t9 + nop + b . + nop + +.org 0x300 + move a0, zero + PTR_LA t9, debug_ll_exception + jalr t9 + nop + b . + nop + +.org 0x380 + move a0, zero + PTR_LA t9, debug_ll_exception + jalr t9 + nop + b . + nop + +.org 0x400 + move a0, zero + PTR_LA t9, debug_ll_exception + jalr t9 + nop + b . + nop + +.org 0x480 + move a0, zero + PTR_LA t9, debug_ll_exception + jalr t9 + nop + b . + nop + + .set pop +END(debug_ll_vecs) + + +/** + * debug_ll_exception() - dump relevant exception state to LL outputs + * @a0: pointer to NULL-terminated ASCII string naming the exception + * + * If a0 is NULL, it will print out exception vector number calculated + * from the ra insted. This is useful for debugging exceptions that + * happen before the exception handler is set up, or routed from BEV. + */ +LEAF(debug_ll_exception) + move k0, ra + move k1, a0 + PTR_LA t3, printascii + + PTR_LA a0, str_newline + jalr t3 /* Call printascii */ + PTR_LA a0, str_exp + jalr t3 /* Call printascii */ + beqz k1, 1f + move a0, k1 + jalr t3 /* Call printascii */ + b 2f +1: + PTR_SRL a0, k0, 7 + PTR_SLL a0, a0, 7 + PTR_LA t2, printhexl + jalr t2 +2: + PTR_LA a0, str_newline + jalr t3 /* Call printascii */ + PTR_LA a0, str_newline + jalr t3 /* Call printascii */ + +#define DUMP_COP0_REG(reg, name, sz, _mfc0) \ + PTR_LA a0, 8f; \ + jalr t3; \ + _mfc0 a0, reg; \ + PTR_LA t2, printhex##sz; \ + jalr t2; \ + PTR_LA a0, str_newline; \ + jalr t3; \ + TEXT(name) + +#if defined(CONFIG_SMP) && defined(CONFIG_CPU_MIPSR6) + DUMP_COP0_REG(CP0_GLOBALNUMBER, "GlobalNumber: 0x", 4, mfc0) +#endif +#if MIPS_ISA_REV >= 2 + DUMP_COP0_REG(CP0_EBASE, "EBase: 0x", l, MFC0) +#endif +#ifdef CONFIG_64BIT + DUMP_COP0_REG(CP0_XCONTEXT, "Xcontext: 0x", 8, dmfc0) +#else + DUMP_COP0_REG(CP0_CONTEXT, "Context: 0x", 4, mfc0) +#endif + DUMP_COP0_REG(CP0_CAUSE, "Cause: 0x", 4, mfc0) + DUMP_COP0_REG(CP0_STATUS, "Status: 0x", 4, mfc0) + DUMP_COP0_REG(CP0_EPC, "EPC: 0x", l, MFC0) + DUMP_COP0_REG(CP0_BADVADDR, "BadVAddr: 0x", l, MFC0) +#if MIPS_ISA_REV >= 6 + DUMP_COP0_REG(CP0_BADINSTR, "BadInstr: 0x", 4, mfc0) +#endif + PTR_LA a0, str_newline + jalr t3 /* Call printascii */ + jr k0 + END(debug_ll_exception) + +.pushsection .rodata.str +str_exp: .asciiz "Low level exception: " +str_newline: .asciiz "\r\n" +.popsection + +NESTED(setup_debug_ll_exception, 0, ra) + PTR_LA t0, debug_ll_vecs +#if MIPS_ISA_REV >= 2 + /* Set ebase to debug_ll_vecs */ +#if defined (CONFIG_64BIT) && !defined(KBUILD_64BIT_SYM32) + ori t0, MIPS_EBASE_WG +#endif + MTC0 t0, CP0_EBASE +#else + /* Copy debug_ll_vecs to start of KSEG0 */ + PTR_LI t1, CKSEG0 + PTR_ADDIU t2, t0, 0x400 /* Only copy 0x400 as that is what reserved on old systems */ +copy_word: + PTR_LW t3, 0(t0) + PTR_SW t3, 0(t1) + PTR_ADDIU t0, t0, PTRSIZE + PTR_ADDIU t1, t1, PTRSIZE + PTR_BNE t0, t2, copy_word +#endif + /* Clear BEV bit in status register */ + mfc0 t0, CP0_STATUS + and t0, t0, ~ST0_BEV + mtc0 t0, CP0_STATUS + jr ra + END(setup_debug_ll_exception) diff --git a/arch/mips/kernel/head.S b/arch/mips/kernel/head.S index b825ed4476c7..9be1c4ce6324 100644 --- a/arch/mips/kernel/head.S +++ b/arch/mips/kernel/head.S @@ -106,6 +106,10 @@ NESTED(kernel_entry, 16, sp) # kernel entry point LONG_S a2, fw_arg2 LONG_S a3, fw_arg3 +#ifdef CONFIG_DEBUG_LL_EXCEPT + jal setup_debug_ll_exception +#endif + MTC0 zero, CP0_CONTEXT # clear context register #ifdef CONFIG_64BIT MTC0 zero, CP0_XCONTEXT -- 2.34.1
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