arch/arm64/kernel/ftrace-mod.S

/*
 * Copyright (C) 2017 Linaro Ltd <ard.biesheuvel@linaro.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/linkage.h>
#include <asm/assembler.h>

	.section	".text.ftrace_trampoline", "ax"
	.align		3
0:	.quad		0
__ftrace_trampoline:
	ldr		x16, 0b
	br		x16
ENDPROC(__ftrace_trampoline)
arm64: ftrace: add support for far branches to dynamic ftrace Currently, dynamic ftrace support in the arm64 kernel assumes that all core kernel code is within range of ordinary branch instructions that occur in module code, which is usually the case, but is no longer guaranteed now that we have support for module PLTs and address space randomization. Since on arm64, all patching of branch instructions involves function calls to the same entry point [ftrace_caller()], we can emit the modules with a trampoline that has unlimited range, and patch both the trampoline itself and the branch instruction to redirect the call via the trampoline. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> [will: minor clarification to smp_wmb() comment] Signed-off-by: Will Deacon <will.deacon@arm.com> 2017-06-06 17:00:22 +00:00			`/*`
			`* Copyright (C) 2017 Linaro Ltd <ard.biesheuvel@linaro.org>`
			`*`
			`* This program is free software; you can redistribute it and/or modify`
			`* it under the terms of the GNU General Public License version 2 as`
			`* published by the Free Software Foundation.`
			`*/`

			`#include <linux/linkage.h>`
			`#include <asm/assembler.h>`

			`.section ".text.ftrace_trampoline", "ax"`
			`.align 3`
			`0: .quad 0`
			`__ftrace_trampoline:`
			`ldr x16, 0b`
			`br x16`
			`ENDPROC(__ftrace_trampoline)`