linux-kernel - [PATCH] ARM: module: fix unwind section relocation out of range error

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Message-ID: <20250920021024.847323-1-william.zhang@broadcom.com>
Date: Fri, 19 Sep 2025 19:09:57 -0700
From: William Zhang <william.zhang@...adcom.com>
To: linux-arm-kernel@...ts.infradead.org
Cc: song@...nel.org,
	linus.walleij@...aro.org,
	florian.fainelli@...adcom.com,
	ardb@...nel.org,
	anand.gore@...adcom.com,
	Broadcom Kernel List <bcm-kernel-feedback-list@...adcom.com>,
	kursad.oney@...adcom.com,
	William Zhang <william.zhang@...adcom.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Petr Pavlu <petr.pavlu@...e.com>,
	Russell King <linux@...linux.org.uk>
Subject: [PATCH] ARM: module: fix unwind section relocation out of range error

In an armv7 system that uses non-3G/1G split and with more than 512MB
physical memory, driver load may fail with following error:
   section 29 reloc 0 sym '': relocation 42 out of range (0xc2ab9be8 ->
0x7fad5998)

This happens when relocation R_ARM_PREL31 from the unwind section
.ARM.extab and .ARM.exidx are allocated from the VMALLOC space while
.text section is from MODULES_VADDR space. It exceeds the +/-1GB
relocation requirement of R_ARM_PREL31 hence triggers the error.

The fix is to mark .ARM.extab and .ARM.exidx sections as executable so
they can be allocated within .text section and always meet range
requirement.

Co-developed-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: William Zhang <william.zhang@...adcom.com>

---

 arch/arm/kernel/module-plts.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
index 354ce16d83cb..5f5bf5e63bd6 100644
--- a/arch/arm/kernel/module-plts.c
+++ b/arch/arm/kernel/module-plts.c
@@ -225,6 +225,18 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
 			mod->arch.init.plt = s;
 		else if (s->sh_type == SHT_SYMTAB)
 			syms = (Elf32_Sym *)s->sh_addr;
+#if defined(CONFIG_ARM_UNWIND) && !defined(CONFIG_VMSPLIT_3G)
+		else if (s->sh_type == ELF_SECTION_UNWIND ||
+			 (strncmp(".ARM.extab", secstrings + s->sh_name, 10) == 0)) {
+			/*
+			 * To avoid the possible relocation out of range issue for
+			 * R_ARM_PREL31, mark unwind section .ARM.extab and .ARM.exidx as
+			 * executable so they will be allocated within .text section to meet
+			 * +/-1GB range requirement of the R_ARM_PREL31 relocation
+			 */
+			s->sh_flags |= SHF_EXECINSTR;
+		}
+#endif
 	}
 
 	if (!mod->arch.core.plt || !mod->arch.init.plt) {
-- 
2.43.7