[PATCH 03/14] ARM: add exception handling support for PBL

Ahmad Fatoum a.fatoum at pengutronix.de
Fri Jun 27 08:30:17 PDT 2025 

On 6/27/25 16:07, Sascha Hauer wrote:
> Exception handling in PBL can be very useful for debugging PBL code.
> This patch adds support for it.

\o/

> 
> This is currently only implemented for ARMv7 and ARMv8. Only on these
> architectures we can tell the CPU where the exception table is. On ARMv6
> and older we would have to copy the exception table either to 0x0 or
> 0xffff0000. Not all SoCs have writable memory at these locations, so we
> would have to utilize the MMU to map writable memory there. We are not
> there yet, so for now skip exception handling support on these older
> architectures.
> 
> Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>

Reviewed-by: Ahmad Fatoum <a.fatoum at pengutronix.de>

> ---
>  arch/arm/Kconfig                   | 10 ++++++++++
>  arch/arm/cpu/Makefile              |  1 +
>  arch/arm/cpu/interrupts_32.c       | 14 +++++++++++++-
>  arch/arm/cpu/interrupts_64.c       | 10 +++++++++-
>  arch/arm/cpu/uncompress.c          |  2 ++
>  arch/arm/include/asm/barebox-arm.h |  8 ++++++++
>  arch/arm/lib/pbl.lds.S             |  4 ++++
>  7 files changed, 47 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 0800b15d784ca0ab975cf7ceb2f7b47ed10643b1..eaccee9f2f7a128a820e1c55fba816ec5ac4c02d 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -378,6 +378,16 @@ config ARM_EXCEPTIONS
>  	bool "enable arm exception handling support"
>  	default y
>  
> +config ARM_EXCEPTIONS_PBL
> +	select ARCH_HAS_DATA_ABORT_MASK_PBL
> +	depends on CPU_V7 || CPU_V8
> +	bool "enable arm exception handling support in PBL"
> +	help
> +	  Say yes here to enable exception handling in PBL. Note that the exception
> +	  table has to be initialized by calling arm_pbl_init_exceptions(). This is
> +	  done in barebox_pbl_start(). If you need exception handling earlier then
> +	  you have to call arm_pbl_init_exceptions() earlier from your board code.
> +
>  config ARM_UNWIND
>  	bool "enable stack unwinding support"
>  	depends on AEABI
> diff --git a/arch/arm/cpu/Makefile b/arch/arm/cpu/Makefile
> index 39e59c2a2f733d668d57a2f28bdd99f69a016229..9550592796702759f950a3bc4de385100ef2b2e8 100644
> --- a/arch/arm/cpu/Makefile
> +++ b/arch/arm/cpu/Makefile
> @@ -3,6 +3,7 @@
>  obj-pbl-y += cpu.o
>  
>  obj-$(CONFIG_ARM_EXCEPTIONS) += exceptions_$(S64_32).o interrupts_$(S64_32).o
> +pbl-$(CONFIG_ARM_EXCEPTIONS_PBL) += exceptions_$(S64_32).o interrupts_$(S64_32).o
>  obj-$(CONFIG_MMU) += mmu-common.o
>  obj-pbl-$(CONFIG_MMU) += mmu_$(S64_32).o
>  obj-$(CONFIG_MMU) += dma_$(S64_32).o
> diff --git a/arch/arm/cpu/interrupts_32.c b/arch/arm/cpu/interrupts_32.c
> index 623efb3966f0c34632e678d9e1edf2b6affcb4c5..cd503b38eeea551f27bbab0663bbfabdda7ffeea 100644
> --- a/arch/arm/cpu/interrupts_32.c
> +++ b/arch/arm/cpu/interrupts_32.c
> @@ -12,6 +12,7 @@
>  #include <asm/ptrace.h>
>  #include <asm/barebox-arm.h>
>  #include <asm/unwind.h>
> +#include <asm/system_info.h>
>  #include <init.h>
>  
>  /* Avoid missing prototype warning, called from assembly */
> @@ -61,7 +62,7 @@ void show_regs (struct pt_regs *regs)
>  		fast_interrupts_enabled (regs) ? "on" : "off",
>  		processor_modes[processor_mode (regs)],
>  		thumb_mode (regs) ? " (T)" : "");
> -#ifdef CONFIG_ARM_UNWIND
> +#if defined CONFIG_ARM_UNWIND && IN_PROPER
>  	unwind_backtrace(regs);
>  #endif
>  }
> @@ -181,3 +182,14 @@ int data_abort_unmask(void)
>  
>  	return arm_data_abort_occurred != 0;
>  }
> +
> +#if IS_ENABLED(CONFIG_ARM_EXCEPTIONS_PBL)
> +void arm_pbl_init_exceptions(void)
> +{
> +	if (cpu_architecture() < CPU_ARCH_ARMv7)
> +		return;
> +
> +	set_vbar((unsigned long)__exceptions_start);
> +	arm_fixup_vectors();
> +}
> +#endif
> diff --git a/arch/arm/cpu/interrupts_64.c b/arch/arm/cpu/interrupts_64.c
> index 4d4ef2bab88ef46a7be1cd4add8f3e51423a283b..574ab6a7ec220d2239b6e27c05426e2d4c67d426 100644
> --- a/arch/arm/cpu/interrupts_64.c
> +++ b/arch/arm/cpu/interrupts_64.c
> @@ -88,7 +88,8 @@ static void __noreturn do_exception(struct pt_regs *pt_regs)
>  {
>  	show_regs(pt_regs);
>  
> -	unwind_backtrace(pt_regs);
> +	if (IN_PROPER)
> +		unwind_backtrace(pt_regs);
>  
>  	panic_no_stacktrace("panic: unhandled exception");
>  }
> @@ -226,3 +227,10 @@ static int aarch64_init_vectors(void)
>  	return 0;
>  }
>  core_initcall(aarch64_init_vectors);
> +
> +#if IS_ENABLED(CONFIG_ARM_EXCEPTIONS_PBL)
> +void arm_pbl_init_exceptions(void)
> +{
> +	aarch64_init_vectors();
> +}
> +#endif
> diff --git a/arch/arm/cpu/uncompress.c b/arch/arm/cpu/uncompress.c
> index 4657a4828e67e1b0acfa9dec3aef33bc4c525468..4529ef5e3821e5b31a3673de6285d2f37e0ecba2 100644
> --- a/arch/arm/cpu/uncompress.c
> +++ b/arch/arm/cpu/uncompress.c
> @@ -63,6 +63,8 @@ void __noreturn barebox_pbl_start(unsigned long membase, unsigned long memsize,
>  
>  	pr_debug("memory at 0x%08lx, size 0x%08lx\n", membase, memsize);
>  
> +	arm_pbl_init_exceptions();
> +
>  	if (IS_ENABLED(CONFIG_MMU))
>  		mmu_early_enable(membase, memsize);
>  	else if (IS_ENABLED(CONFIG_ARMV7R_MPU))
> diff --git a/arch/arm/include/asm/barebox-arm.h b/arch/arm/include/asm/barebox-arm.h
> index 7d35e88c812393d45e331f238baecfa91cbbe299..3ab442bd373e50a84b26145395e42879fc96757f 100644
> --- a/arch/arm/include/asm/barebox-arm.h
> +++ b/arch/arm/include/asm/barebox-arm.h
> @@ -52,6 +52,14 @@ static inline void arm_fixup_vectors(void)
>  }
>  #endif
>  
> +#if IS_ENABLED(CONFIG_ARM_EXCEPTIONS_PBL)
> +void arm_pbl_init_exceptions(void);
> +#else
> +static inline void arm_pbl_init_exceptions(void)
> +{
> +}
> +#endif
> +
>  void *barebox_arm_boot_dtb(void);
>  
>  /*
> diff --git a/arch/arm/lib/pbl.lds.S b/arch/arm/lib/pbl.lds.S
> index dad37c9e9bca98beb4f34360fa53a0421662f03c..9c51f5eb3a3d8256752a78e03fed851c84d92edb 100644
> --- a/arch/arm/lib/pbl.lds.S
> +++ b/arch/arm/lib/pbl.lds.S
> @@ -52,6 +52,10 @@ SECTIONS
>  		__bare_init_start = .;
>  		*(.text_bare_init*)
>  		__bare_init_end = .;
> +		. = ALIGN(0x20);
> +		__exceptions_start = .;
> +		KEEP(*(.text_exceptions*))
> +		__exceptions_stop = .;
>  		*(.text*)
>  	}
>  
> 

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