arm64/kernel/entry-ftrace.S

1 /* SPDX-License-Identifier: GPL-2.0-only */
3  * arch/arm64/kernel/entry-ftrace.S
11 #include <asm/asm-offsets.h>
18  * Due to -fpatchable-function-entry=2, the compiler has placed two NOPs before
25  * Each instrumented function follows the AAPCS, so here x0-x8 and x18-x30 are
26  * live (x18 holds the Shadow Call Stack pointer), and x9-x17 are safe to
30  * ftrace callbacks. So that we can get a sensible backtrace, we create frame
33  * record, its caller is missing from the LR and existing chain of frame
41 	 * The literal pointer to the ops is at an 8-byte aligned boundary
47 	 * aligning to an 8-byte boundary and subtracting 16. We do the
52 	ldr	x11, [x11, #-(4 * AARCH64_INSN_SIZE)]		// op
59 	ldr	x17, [x11, #FTRACE_OPS_DIRECT_CALL]		// op->direct_call
67 	/* Make room for ftrace regs, plus two frame records */
68 	sub	sp, sp, #(FREGS_SIZE + 32)
89 	/* Create a frame record for the callsite above the ftrace regs */
93 	/* Create our frame record above the ftrace regs */
98 	sub	x0, x30, #AARCH64_INSN_SIZE		// ip (callsite's BL insn)
104 	ldr	x4, [x2, #FTRACE_OPS_FUNC]		// op->func
105 	blr	x4					// op->func(ip, parent_ip, op, regs)
115  * At the callsite x0-x8 and x19-x30 were live. Any C code will have preserved
116  * x19-x29 per the AAPCS, and we created frame records upon entry, so we need
117  * to restore x0-x8, x29, and x30.
147 	 * The ftrace_regs are live, and x0-x8 and FP have been restored. The
184  * Gcc with -pg will put the following code in the beginning of each function:
193  * as long as the kernel is compiled without -fomit-frame-pointer.
198  * current sp/fp =>  0:+-----+
199  * in _mcount()        | x29 | -> instrumented function's fp
200  *                     +-----+
201  *                     | x30 | -> _mcount()'s lr (= instrumented function's pc)
202  * old sp       => +16:+-----+
207  * instrumented => +xx:+-----+
208  * function's fp       | x29 | -> parent's fp
209  *                     +-----+
210  *                     | x30 | -> instrumented function's lr (= parent's pc)
211  *                     +-----+
216 	stp	x29, x30, [sp, #-16]!
226 	sub	\rd, \rn, #AARCH64_INSN_SIZE
256  * _mcount() is used to build the kernel with -pg option, but all the branch
259  * NOP when disabled per-function base.
273  *     - tracer function to probe instrumented function's entry,
274  *     - ftrace_graph_caller to set up an exit hook
333 	sub sp, sp, #FGRET_REGS_SIZE