[PATCH v2 13/21] ARM: use relative jumps in exception table

[Sascha Hauer]

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>
---
 arch/arm/cpu/exceptions_32.S    | 20 ++++++++++++++++++++
 arch/arm/cpu/interrupts_32.c    |  7 ++-----
 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 ++++
 6 files changed, 31 insertions(+), 18 deletions(-)

diff --git a/arch/arm/cpu/exceptions_32.S b/arch/arm/cpu/exceptions_32.S
index dc3d42663cbedd37947e27d449eb4ac8c3d8c3f1..85ee4ca3fd4e5aff8e1e02aa3d7375173a923072 100644
--- a/arch/arm/cpu/exceptions_32.S
+++ b/arch/arm/cpu/exceptions_32.S
@@ -155,6 +155,26 @@ 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 0b88db10fe487378fe08018701bc672f63139fc1..5dc4802fafbfdbcd54707b84835f40177e10742b 100644
--- a/arch/arm/cpu/interrupts_32.c
+++ b/arch/arm/cpu/interrupts_32.c
@@ -231,10 +231,8 @@ static __maybe_unused int arm_init_vectors(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))
 		return 0;
-	}
 
 	/*
 	 * Next try high vectors at 0xffff0000.
@@ -264,7 +262,6 @@ 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/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 c704dd6d70f3ab157ceb67dfb14760e03f2a5d62..17e0970ba4989e5213ed38ea5ff87bdf5bfa2740 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

-- 
2.47.3