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+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * arch/arm64/kernel/entry-ftrace.S
+ *
+ * Copyright (C) 2013 Linaro Limited
+ * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
+ */
+
+#include <linux/linkage.h>
+#include <linux/cfi_types.h>
+#include <asm/asm-offsets.h>
+#include <asm/assembler.h>
+#include <asm/ftrace.h>
+#include <asm/insn.h>
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+/*
+ * Due to -fpatchable-function-entry=2, the compiler has placed two NOPs before
+ * the regular function prologue. For an enabled callsite, ftrace_init_nop() and
+ * ftrace_make_call() have patched those NOPs to:
+ *
+ * MOV X9, LR
+ * BL <entry>
+ *
+ * ... where <entry> is either ftrace_caller or ftrace_regs_caller.
+ *
+ * Each instrumented function follows the AAPCS, so here x0-x8 and x18-x30 are
+ * live (x18 holds the Shadow Call Stack pointer), and x9-x17 are safe to
+ * clobber.
+ *
+ * We save the callsite's context into a pt_regs before invoking any ftrace
+ * callbacks. So that we can get a sensible backtrace, we create a stack record
+ * for the callsite and the ftrace entry assembly. This is not sufficient for
+ * reliable stacktrace: until we create the callsite stack record, its caller
+ * is missing from the LR and existing chain of frame records.
+ */
+ .macro ftrace_regs_entry, allregs=0
+ /* Make room for pt_regs, plus a callee frame */
+ sub sp, sp, #(PT_REGS_SIZE + 16)
+
+ /* Save function arguments (and x9 for simplicity) */
+ stp x0, x1, [sp, #S_X0]
+ stp x2, x3, [sp, #S_X2]
+ stp x4, x5, [sp, #S_X4]
+ stp x6, x7, [sp, #S_X6]
+ stp x8, x9, [sp, #S_X8]
+
+ /* Optionally save the callee-saved registers, always save the FP */
+ .if \allregs == 1
+ stp x10, x11, [sp, #S_X10]
+ stp x12, x13, [sp, #S_X12]
+ stp x14, x15, [sp, #S_X14]
+ stp x16, x17, [sp, #S_X16]
+ stp x18, x19, [sp, #S_X18]
+ stp x20, x21, [sp, #S_X20]
+ stp x22, x23, [sp, #S_X22]
+ stp x24, x25, [sp, #S_X24]
+ stp x26, x27, [sp, #S_X26]
+ stp x28, x29, [sp, #S_X28]
+ .else
+ str x29, [sp, #S_FP]
+ .endif
+
+ /* Save the callsite's SP and LR */
+ add x10, sp, #(PT_REGS_SIZE + 16)
+ stp x9, x10, [sp, #S_LR]
+
+ /* Save the PC after the ftrace callsite */
+ str x30, [sp, #S_PC]
+
+ /* Create a frame record for the callsite above pt_regs */
+ stp x29, x9, [sp, #PT_REGS_SIZE]
+ add x29, sp, #PT_REGS_SIZE
+
+ /* Create our frame record within pt_regs. */
+ stp x29, x30, [sp, #S_STACKFRAME]
+ add x29, sp, #S_STACKFRAME
+ .endm
+
+SYM_CODE_START(ftrace_regs_caller)
+ bti c
+ ftrace_regs_entry 1
+ b ftrace_common
+SYM_CODE_END(ftrace_regs_caller)
+
+SYM_CODE_START(ftrace_caller)
+ bti c
+ ftrace_regs_entry 0
+ b ftrace_common
+SYM_CODE_END(ftrace_caller)
+
+SYM_CODE_START(ftrace_common)
+ sub x0, x30, #AARCH64_INSN_SIZE // ip (callsite's BL insn)
+ mov x1, x9 // parent_ip (callsite's LR)
+ ldr_l x2, function_trace_op // op
+ mov x3, sp // regs
+
+SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
+ bl ftrace_stub
+
+/*
+ * At the callsite x0-x8 and x19-x30 were live. Any C code will have preserved
+ * x19-x29 per the AAPCS, and we created frame records upon entry, so we need
+ * to restore x0-x8, x29, and x30.
+ */
+ /* Restore function arguments */
+ ldp x0, x1, [sp]
+ ldp x2, x3, [sp, #S_X2]
+ ldp x4, x5, [sp, #S_X4]
+ ldp x6, x7, [sp, #S_X6]
+ ldr x8, [sp, #S_X8]
+
+ /* Restore the callsite's FP, LR, PC */
+ ldr x29, [sp, #S_FP]
+ ldr x30, [sp, #S_LR]
+ ldr x9, [sp, #S_PC]
+
+ /* Restore the callsite's SP */
+ add sp, sp, #PT_REGS_SIZE + 16
+
+ ret x9
+SYM_CODE_END(ftrace_common)
+
+#else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
+
+/*
+ * Gcc with -pg will put the following code in the beginning of each function:
+ * mov x0, x30
+ * bl _mcount
+ * [function's body ...]
+ * "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
+ * ftrace is enabled.
+ *
+ * Please note that x0 as an argument will not be used here because we can
+ * get lr(x30) of instrumented function at any time by winding up call stack
+ * as long as the kernel is compiled without -fomit-frame-pointer.
+ * (or CONFIG_FRAME_POINTER, this is forced on arm64)
+ *
+ * stack layout after mcount_enter in _mcount():
+ *
+ * current sp/fp => 0:+-----+
+ * in _mcount() | x29 | -> instrumented function's fp
+ * +-----+
+ * | x30 | -> _mcount()'s lr (= instrumented function's pc)
+ * old sp => +16:+-----+
+ * when instrumented | |
+ * function calls | ... |
+ * _mcount() | |
+ * | |
+ * instrumented => +xx:+-----+
+ * function's fp | x29 | -> parent's fp
+ * +-----+
+ * | x30 | -> instrumented function's lr (= parent's pc)
+ * +-----+
+ * | ... |
+ */
+
+ .macro mcount_enter
+ stp x29, x30, [sp, #-16]!
+ mov x29, sp
+ .endm
+
+ .macro mcount_exit
+ ldp x29, x30, [sp], #16
+ ret
+ .endm
+
+ .macro mcount_adjust_addr rd, rn
+ sub \rd, \rn, #AARCH64_INSN_SIZE
+ .endm
+
+ /* for instrumented function's parent */
+ .macro mcount_get_parent_fp reg
+ ldr \reg, [x29]
+ ldr \reg, [\reg]
+ .endm
+
+ /* for instrumented function */
+ .macro mcount_get_pc0 reg
+ mcount_adjust_addr \reg, x30
+ .endm
+
+ .macro mcount_get_pc reg
+ ldr \reg, [x29, #8]
+ mcount_adjust_addr \reg, \reg
+ .endm
+
+ .macro mcount_get_lr reg
+ ldr \reg, [x29]
+ ldr \reg, [\reg, #8]
+ .endm
+
+ .macro mcount_get_lr_addr reg
+ ldr \reg, [x29]
+ add \reg, \reg, #8
+ .endm
+
+#ifndef CONFIG_DYNAMIC_FTRACE
+/*
+ * void _mcount(unsigned long return_address)
+ * @return_address: return address to instrumented function
+ *
+ * This function makes calls, if enabled, to:
+ * - tracer function to probe instrumented function's entry,
+ * - ftrace_graph_caller to set up an exit hook
+ */
+SYM_FUNC_START(_mcount)
+ mcount_enter
+
+ ldr_l x2, ftrace_trace_function
+ adr x0, ftrace_stub
+ cmp x0, x2 // if (ftrace_trace_function
+ b.eq skip_ftrace_call // != ftrace_stub) {
+
+ mcount_get_pc x0 // function's pc
+ mcount_get_lr x1 // function's lr (= parent's pc)
+ blr x2 // (*ftrace_trace_function)(pc, lr);
+
+skip_ftrace_call: // }
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ ldr_l x2, ftrace_graph_return
+ cmp x0, x2 // if ((ftrace_graph_return
+ b.ne ftrace_graph_caller // != ftrace_stub)
+
+ ldr_l x2, ftrace_graph_entry // || (ftrace_graph_entry
+ adr_l x0, ftrace_graph_entry_stub // != ftrace_graph_entry_stub))
+ cmp x0, x2
+ b.ne ftrace_graph_caller // ftrace_graph_caller();
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+ mcount_exit
+SYM_FUNC_END(_mcount)
+EXPORT_SYMBOL(_mcount)
+NOKPROBE(_mcount)
+
+#else /* CONFIG_DYNAMIC_FTRACE */
+/*
+ * _mcount() is used to build the kernel with -pg option, but all the branch
+ * instructions to _mcount() are replaced to NOP initially at kernel start up,
+ * and later on, NOP to branch to ftrace_caller() when enabled or branch to
+ * NOP when disabled per-function base.
+ */
+SYM_FUNC_START(_mcount)
+ ret
+SYM_FUNC_END(_mcount)
+EXPORT_SYMBOL(_mcount)
+NOKPROBE(_mcount)
+
+/*
+ * void ftrace_caller(unsigned long return_address)
+ * @return_address: return address to instrumented function
+ *
+ * This function is a counterpart of _mcount() in 'static' ftrace, and
+ * makes calls to:
+ * - tracer function to probe instrumented function's entry,
+ * - ftrace_graph_caller to set up an exit hook
+ */
+SYM_FUNC_START(ftrace_caller)
+ mcount_enter
+
+ mcount_get_pc0 x0 // function's pc
+ mcount_get_lr x1 // function's lr
+
+SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) // tracer(pc, lr);
+ nop // This will be replaced with "bl xxx"
+ // where xxx can be any kind of tracer.
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
+ nop // If enabled, this will be replaced
+ // "b ftrace_graph_caller"
+#endif
+
+ mcount_exit
+SYM_FUNC_END(ftrace_caller)
+#endif /* CONFIG_DYNAMIC_FTRACE */
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+/*
+ * void ftrace_graph_caller(void)
+ *
+ * Called from _mcount() or ftrace_caller() when function_graph tracer is
+ * selected.
+ * This function w/ prepare_ftrace_return() fakes link register's value on
+ * the call stack in order to intercept instrumented function's return path
+ * and run return_to_handler() later on its exit.
+ */
+SYM_FUNC_START(ftrace_graph_caller)
+ mcount_get_pc x0 // function's pc
+ mcount_get_lr_addr x1 // pointer to function's saved lr
+ mcount_get_parent_fp x2 // parent's fp
+ bl prepare_ftrace_return // prepare_ftrace_return(pc, &lr, fp)
+
+ mcount_exit
+SYM_FUNC_END(ftrace_graph_caller)
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
+
+SYM_TYPED_FUNC_START(ftrace_stub)
+ ret
+SYM_FUNC_END(ftrace_stub)
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+SYM_TYPED_FUNC_START(ftrace_stub_graph)
+ ret
+SYM_FUNC_END(ftrace_stub_graph)
+
+/*
+ * void return_to_handler(void)
+ *
+ * Run ftrace_return_to_handler() before going back to parent.
+ * @fp is checked against the value passed by ftrace_graph_caller().
+ */
+SYM_CODE_START(return_to_handler)
+ /* save return value regs */
+ sub sp, sp, #64
+ stp x0, x1, [sp]
+ stp x2, x3, [sp, #16]
+ stp x4, x5, [sp, #32]
+ stp x6, x7, [sp, #48]
+
+ mov x0, x29 // parent's fp
+ bl ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
+ mov x30, x0 // restore the original return address
+
+ /* restore return value regs */
+ ldp x0, x1, [sp]
+ ldp x2, x3, [sp, #16]
+ ldp x4, x5, [sp, #32]
+ ldp x6, x7, [sp, #48]
+ add sp, sp, #64
+
+ ret
+SYM_CODE_END(return_to_handler)
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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