[PATCH 12/19] ARM: use relative jumps in exception table
Ahmad Fatoum
a.fatoum at pengutronix.de
Mon Jan 5 03:44:13 PST 2026
Hello Sascha,
On 1/5/26 12:26 PM, Sascha Hauer wrote:
> Create position-independent exception vectors using relative branches
> instead of absolute addresses. This works on ARMv7 onwards which
> supports setting the address of the exception vectors.
>
> New .text_inplace_exceptions section contains PC-relative branches,
> enabling barebox proper to start with MMU already configured using
> ELF segment addresses.
>
> Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
Why do we even need arm_fixup_vectors? There should already be
relocation entries emitted for .word symbol lines, so given that we only
install the vector table after relocation, it should be possible to
simply drop arm_fixup_vectors?
Cheers,
Ahmad
> ---
> arch/arm/cpu/exceptions_32.S | 20 ++++++++++++++++++++
> arch/arm/cpu/interrupts_32.c | 3 +--
> arch/arm/cpu/mmu_32.c | 5 +++--
> arch/arm/cpu/no-mmu.c | 11 +----------
> arch/arm/include/asm/sections.h | 1 +
> arch/arm/lib/pbl.lds.S | 6 +++---
> arch/arm/lib32/barebox.lds.S | 4 ++++
> 7 files changed, 33 insertions(+), 17 deletions(-)
>
> diff --git a/arch/arm/cpu/exceptions_32.S b/arch/arm/cpu/exceptions_32.S
> index 235996f7ec296b44261637bc98c1c5ee30a3cbe1..302e4d030d6347e8fdb488db73a0a3a4bb1c0ec7 100644
> --- a/arch/arm/cpu/exceptions_32.S
> +++ b/arch/arm/cpu/exceptions_32.S
> @@ -156,6 +156,26 @@ ENTRY(arm_fixup_vectors)
> ENDPROC(arm_fixup_vectors)
> #endif
>
> +.section .text_inplace_exceptions
> +1: b 1b /* barebox_arm_reset_vector */
> +#ifdef CONFIG_ARM_EXCEPTIONS
> + b undefined_instruction /* undefined instruction */
> + b software_interrupt /* software interrupt (SWI) */
> + b prefetch_abort /* prefetch abort */
> + b data_abort /* data abort */
> +1: b 1b /* (reserved) */
> + b irq /* irq (interrupt) */
> + b fiq /* fiq (fast interrupt) */
> +#else
> +1: b 1b /* undefined instruction */
> +1: b 1b /* software interrupt (SWI) */
> +1: b 1b /* prefetch abort */
> +1: b 1b /* data abort */
> +1: b 1b /* (reserved) */
> +1: b 1b /* irq (interrupt) */
> +1: b 1b /* fiq (fast interrupt) */
> +#endif
> +
> .section .text_exceptions
> .globl extable
> extable:
> diff --git a/arch/arm/cpu/interrupts_32.c b/arch/arm/cpu/interrupts_32.c
> index 185646e38195b2bdc9f0d7e30d53a0506932fa13..6ebcbcd8dc1299c0333da87e496bc57172691fa8 100644
> --- a/arch/arm/cpu/interrupts_32.c
> +++ b/arch/arm/cpu/interrupts_32.c
> @@ -181,7 +181,6 @@ void arm_pbl_init_exceptions(void)
> if (cpu_architecture() < CPU_ARCH_ARMv7)
> return;
>
> - set_vbar((unsigned long)__exceptions_start);
> - arm_fixup_vectors();
> + set_vbar((unsigned long)__inplace_exceptions_start);
> }
> #endif
> diff --git a/arch/arm/cpu/mmu_32.c b/arch/arm/cpu/mmu_32.c
> index 86a55d165ba3cec5154c345a1a3a9cb959f0996f..9ce77078d5e35810f2239d82f29f67e2aa2e4d8e 100644
> --- a/arch/arm/cpu/mmu_32.c
> +++ b/arch/arm/cpu/mmu_32.c
> @@ -629,8 +629,9 @@ void setup_trap_pages(void)
> * First try to use the vectors where they actually are, works
> * on ARMv7 and later.
> */
> - if (!set_vector_table((unsigned long)__exceptions_start)) {
> - arm_fixup_vectors();
> + if (!set_vector_table((unsigned long)__inplace_exceptions_start)) {
> + pr_debug("Using inplace exception vectors at 0x%08lx\n",
> + (unsigned long)__inplace_exceptions_start);
> create_zero_page();
> return;
> }
> diff --git a/arch/arm/cpu/no-mmu.c b/arch/arm/cpu/no-mmu.c
> index c4ef5d1f9d55136d606c244309dbeeb8fd988784..68246d71156c7c84b9faff452cebb37132b83573 100644
> --- a/arch/arm/cpu/no-mmu.c
> +++ b/arch/arm/cpu/no-mmu.c
> @@ -21,8 +21,6 @@
> #include <asm/sections.h>
> #include <asm/cputype.h>
>
> -#define __exceptions_size (__exceptions_stop - __exceptions_start)
> -
> static bool has_vbar(void)
> {
> u32 mainid;
> @@ -41,7 +39,6 @@ static bool has_vbar(void)
>
> static int nommu_v7_vectors_init(void)
> {
> - void *vectors;
> u32 cr;
>
> if (cpu_architecture() < CPU_ARCH_ARMv7)
> @@ -58,13 +55,7 @@ static int nommu_v7_vectors_init(void)
> cr &= ~CR_V;
> set_cr(cr);
>
> - arm_fixup_vectors();
> -
> - vectors = xmemalign(PAGE_SIZE, PAGE_SIZE);
> - memset(vectors, 0, PAGE_SIZE);
> - memcpy(vectors, __exceptions_start, __exceptions_size);
> -
> - set_vbar((unsigned int)vectors);
> + set_vbar((unsigned int)__inplace_exceptions_start);
>
> return 0;
> }
> diff --git a/arch/arm/include/asm/sections.h b/arch/arm/include/asm/sections.h
> index 15b1a6482a5b148284ab47de2db1c2653909da09..bf4fb7b109a7a22d9a298257af23a11b9efe6861 100644
> --- a/arch/arm/include/asm/sections.h
> +++ b/arch/arm/include/asm/sections.h
> @@ -13,6 +13,7 @@ extern char __dynsym_start[];
> extern char __dynsym_end[];
> extern char __exceptions_start[];
> extern char __exceptions_stop[];
> +extern char __inplace_exceptions_start[];
>
> #endif
>
> diff --git a/arch/arm/lib/pbl.lds.S b/arch/arm/lib/pbl.lds.S
> index 9c51f5eb3a3d8256752a78e03fed851c84d92edb..53b21084cff2e3d916cd37485281f2f78166c37d 100644
> --- a/arch/arm/lib/pbl.lds.S
> +++ b/arch/arm/lib/pbl.lds.S
> @@ -53,9 +53,9 @@ SECTIONS
> *(.text_bare_init*)
> __bare_init_end = .;
> . = ALIGN(0x20);
> - __exceptions_start = .;
> - KEEP(*(.text_exceptions*))
> - __exceptions_stop = .;
> + __inplace_exceptions_start = .;
> + KEEP(*(.text_inplace_exceptions*))
> + __inplace_exceptions_stop = .;
> *(.text*)
> }
>
> diff --git a/arch/arm/lib32/barebox.lds.S b/arch/arm/lib32/barebox.lds.S
> index ede6889991f16d00f2bad79dd777ae9b5e639ff4..9b2b65e2f17d62d5134fc367621cce733dcea06a 100644
> --- a/arch/arm/lib32/barebox.lds.S
> +++ b/arch/arm/lib32/barebox.lds.S
> @@ -26,6 +26,10 @@ SECTIONS
> __exceptions_start = .;
> KEEP(*(.text_exceptions*))
> __exceptions_stop = .;
> + . = ALIGN(0x20);
> + __inplace_exceptions_start = .;
> + KEEP(*(.text_inplace_exceptions*))
> + __inplace_exceptions_stop = .;
> *(.text*)
> }
> BAREBOX_BARE_INIT_SIZE
>
--
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