1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Copyright (C) 2014 Steven Rostedt, Red Hat Inc
4 */
5
6#include <linux/export.h>
7#include <linux/cfi_types.h>
8#include <linux/linkage.h>
9#include <asm/asm-offsets.h>
10#include <asm/ptrace.h>
11#include <asm/ftrace.h>
12#include <asm/nospec-branch.h>
13#include <asm/unwind_hints.h>
14#include <asm/frame.h>
15
16 .code64
17 .section .text, "ax"
18
19#ifdef CONFIG_FRAME_POINTER
20/* Save parent and function stack frames (rip and rbp) */
21# define MCOUNT_FRAME_SIZE (8+16*2)
22#else
23/* No need to save a stack frame */
24# define MCOUNT_FRAME_SIZE 0
25#endif /* CONFIG_FRAME_POINTER */
26
27/* Size of stack used to save mcount regs in save_mcount_regs */
28#define MCOUNT_REG_SIZE (FRAME_SIZE + MCOUNT_FRAME_SIZE)
29
30/*
31 * gcc -pg option adds a call to 'mcount' in most functions.
32 * When -mfentry is used, the call is to 'fentry' and not 'mcount'
33 * and is done before the function's stack frame is set up.
34 * They both require a set of regs to be saved before calling
35 * any C code and restored before returning back to the function.
36 *
37 * On boot up, all these calls are converted into nops. When tracing
38 * is enabled, the call can jump to either ftrace_caller or
39 * ftrace_regs_caller. Callbacks (tracing functions) that require
40 * ftrace_regs_caller (like kprobes) need to have pt_regs passed to
41 * it. For this reason, the size of the pt_regs structure will be
42 * allocated on the stack and the required mcount registers will
43 * be saved in the locations that pt_regs has them in.
44 */
45
46/*
47 * @added: the amount of stack added before calling this
48 *
49 * After this is called, the following registers contain:
50 *
51 * %rdi - holds the address that called the trampoline
52 * %rsi - holds the parent function (traced function's return address)
53 * %rdx - holds the original %rbp
54 */
55.macro save_mcount_regs added=0
56
57#ifdef CONFIG_FRAME_POINTER
58 /* Save the original rbp */
59 pushq %rbp
60
61 /*
62 * Stack traces will stop at the ftrace trampoline if the frame pointer
63 * is not set up properly. If fentry is used, we need to save a frame
64 * pointer for the parent as well as the function traced, because the
65 * fentry is called before the stack frame is set up, where as mcount
66 * is called afterward.
67 */
68
69 /* Save the parent pointer (skip orig rbp and our return address) */
70 pushq \added+8*2(%rsp)
71 pushq %rbp
72 movq %rsp, %rbp
73 /* Save the return address (now skip orig rbp, rbp and parent) */
74 pushq \added+8*3(%rsp)
75 pushq %rbp
76 movq %rsp, %rbp
77#endif /* CONFIG_FRAME_POINTER */
78
79 /*
80 * We add enough stack to save all regs.
81 */
82 subq $(FRAME_SIZE), %rsp
83 movq %rax, RAX(%rsp)
84 movq %rcx, RCX(%rsp)
85 movq %rdx, RDX(%rsp)
86 movq %rsi, RSI(%rsp)
87 movq %rdi, RDI(%rsp)
88 movq %r8, R8(%rsp)
89 movq %r9, R9(%rsp)
90 movq $0, ORIG_RAX(%rsp)
91 /*
92 * Save the original RBP. Even though the mcount ABI does not
93 * require this, it helps out callers.
94 */
95#ifdef CONFIG_FRAME_POINTER
96 movq MCOUNT_REG_SIZE-8(%rsp), %rdx
97#else
98 movq %rbp, %rdx
99#endif
100 movq %rdx, RBP(%rsp)
101
102 /* Copy the parent address into %rsi (second parameter) */
103 movq MCOUNT_REG_SIZE+8+\added(%rsp), %rsi
104
105 /* Move RIP to its proper location */
106 movq MCOUNT_REG_SIZE+\added(%rsp), %rdi
107 movq %rdi, RIP(%rsp)
108
109 /*
110 * Now %rdi (the first parameter) has the return address of
111 * where ftrace_call returns. But the callbacks expect the
112 * address of the call itself.
113 */
114 subq $MCOUNT_INSN_SIZE, %rdi
115 .endm
116
117.macro restore_mcount_regs save=0
118
119 /* ftrace_regs_caller or frame pointers require this */
120 movq RBP(%rsp), %rbp
121
122 movq R9(%rsp), %r9
123 movq R8(%rsp), %r8
124 movq RDI(%rsp), %rdi
125 movq RSI(%rsp), %rsi
126 movq RDX(%rsp), %rdx
127 movq RCX(%rsp), %rcx
128 movq RAX(%rsp), %rax
129
130 addq $MCOUNT_REG_SIZE-\save, %rsp
131
132 .endm
133
134SYM_TYPED_FUNC_START(ftrace_stub)
135 CALL_DEPTH_ACCOUNT
136 RET
137SYM_FUNC_END(ftrace_stub)
138
139#ifdef CONFIG_FUNCTION_GRAPH_TRACER
140SYM_TYPED_FUNC_START(ftrace_stub_graph)
141 CALL_DEPTH_ACCOUNT
142 RET
143SYM_FUNC_END(ftrace_stub_graph)
144#endif
145
146#ifdef CONFIG_DYNAMIC_FTRACE
147
148SYM_FUNC_START(__fentry__)
149 CALL_DEPTH_ACCOUNT
150 RET
151SYM_FUNC_END(__fentry__)
152EXPORT_SYMBOL(__fentry__)
153
154SYM_FUNC_START(ftrace_caller)
155 /* save_mcount_regs fills in first two parameters */
156 save_mcount_regs
157
158 CALL_DEPTH_ACCOUNT
159
160 /* Stack - skipping return address of ftrace_caller */
161 leaq MCOUNT_REG_SIZE+8(%rsp), %rcx
162 movq %rcx, RSP(%rsp)
163
164SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL)
165 ANNOTATE_NOENDBR
166 /* Load the ftrace_ops into the 3rd parameter */
167 movq function_trace_op(%rip), %rdx
168
169 /* regs go into 4th parameter */
170 leaq (%rsp), %rcx
171
172 /* Only ops with REGS flag set should have CS register set */
173 movq $0, CS(%rsp)
174
175 /* Account for the function call below */
176 CALL_DEPTH_ACCOUNT
177
178SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
179 ANNOTATE_NOENDBR
180 call ftrace_stub
181
182 /* Handlers can change the RIP */
183 movq RIP(%rsp), %rax
184 movq %rax, MCOUNT_REG_SIZE(%rsp)
185
186 restore_mcount_regs
187
188 /*
189 * The code up to this label is copied into trampolines so
190 * think twice before adding any new code or changing the
191 * layout here.
192 */
193SYM_INNER_LABEL(ftrace_caller_end, SYM_L_GLOBAL)
194 ANNOTATE_NOENDBR
195 RET
196SYM_FUNC_END(ftrace_caller);
197STACK_FRAME_NON_STANDARD_FP(ftrace_caller)
198
199SYM_FUNC_START(ftrace_regs_caller)
200 /* Save the current flags before any operations that can change them */
201 pushfq
202
203 /* added 8 bytes to save flags */
204 save_mcount_regs 8
205 /* save_mcount_regs fills in first two parameters */
206
207 CALL_DEPTH_ACCOUNT
208
209SYM_INNER_LABEL(ftrace_regs_caller_op_ptr, SYM_L_GLOBAL)
210 ANNOTATE_NOENDBR
211 /* Load the ftrace_ops into the 3rd parameter */
212 movq function_trace_op(%rip), %rdx
213
214 /* Save the rest of pt_regs */
215 movq %r15, R15(%rsp)
216 movq %r14, R14(%rsp)
217 movq %r13, R13(%rsp)
218 movq %r12, R12(%rsp)
219 movq %r11, R11(%rsp)
220 movq %r10, R10(%rsp)
221 movq %rbx, RBX(%rsp)
222 /* Copy saved flags */
223 movq MCOUNT_REG_SIZE(%rsp), %rcx
224 movq %rcx, EFLAGS(%rsp)
225 /* Kernel segments */
226 movq $__KERNEL_DS, %rcx
227 movq %rcx, SS(%rsp)
228 movq $__KERNEL_CS, %rcx
229 movq %rcx, CS(%rsp)
230 /* Stack - skipping return address and flags */
231 leaq MCOUNT_REG_SIZE+8*2(%rsp), %rcx
232 movq %rcx, RSP(%rsp)
233
234 ENCODE_FRAME_POINTER
235
236 /* regs go into 4th parameter */
237 leaq (%rsp), %rcx
238
239 /* Account for the function call below */
240 CALL_DEPTH_ACCOUNT
241
242SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
243 ANNOTATE_NOENDBR
244 call ftrace_stub
245
246 /* Copy flags back to SS, to restore them */
247 movq EFLAGS(%rsp), %rax
248 movq %rax, MCOUNT_REG_SIZE(%rsp)
249
250 /* Handlers can change the RIP */
251 movq RIP(%rsp), %rax
252 movq %rax, MCOUNT_REG_SIZE+8(%rsp)
253
254 /* restore the rest of pt_regs */
255 movq R15(%rsp), %r15
256 movq R14(%rsp), %r14
257 movq R13(%rsp), %r13
258 movq R12(%rsp), %r12
259 movq R10(%rsp), %r10
260 movq RBX(%rsp), %rbx
261
262 movq ORIG_RAX(%rsp), %rax
263 movq %rax, MCOUNT_REG_SIZE-8(%rsp)
264
265 /*
266 * If ORIG_RAX is anything but zero, make this a call to that.
267 * See arch_ftrace_set_direct_caller().
268 */
269 testq %rax, %rax
270SYM_INNER_LABEL(ftrace_regs_caller_jmp, SYM_L_GLOBAL)
271 ANNOTATE_NOENDBR
272 jnz 1f
273
274 restore_mcount_regs
275 /* Restore flags */
276 popfq
277
278 /*
279 * The trampoline will add the return.
280 */
281SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
282 ANNOTATE_NOENDBR
283 RET
284
285 /* Swap the flags with orig_rax */
2861: movq MCOUNT_REG_SIZE(%rsp), %rdi
287 movq %rdi, MCOUNT_REG_SIZE-8(%rsp)
288 movq %rax, MCOUNT_REG_SIZE(%rsp)
289
290 restore_mcount_regs 8
291 /* Restore flags */
292 popfq
293 UNWIND_HINT_FUNC
294
295 /*
296 * The above left an extra return value on the stack; effectively
297 * doing a tail-call without using a register. This PUSH;RET
298 * pattern unbalances the RSB, inject a pointless CALL to rebalance.
299 */
300 ANNOTATE_INTRA_FUNCTION_CALL
301 CALL .Ldo_rebalance
302 int3
303.Ldo_rebalance:
304 add $8, %rsp
305 ALTERNATIVE __stringify(RET), \
306 __stringify(ANNOTATE_UNRET_SAFE; ret; int3), \
307 X86_FEATURE_CALL_DEPTH
308
309SYM_FUNC_END(ftrace_regs_caller)
310STACK_FRAME_NON_STANDARD_FP(ftrace_regs_caller)
311
312SYM_FUNC_START(ftrace_stub_direct_tramp)
313 CALL_DEPTH_ACCOUNT
314 RET
315SYM_FUNC_END(ftrace_stub_direct_tramp)
316
317#else /* ! CONFIG_DYNAMIC_FTRACE */
318
319SYM_FUNC_START(__fentry__)
320 CALL_DEPTH_ACCOUNT
321
322 cmpq $ftrace_stub, ftrace_trace_function
323 jnz trace
324 RET
325
326trace:
327 /* save_mcount_regs fills in first two parameters */
328 save_mcount_regs
329
330 /*
331 * When DYNAMIC_FTRACE is not defined, ARCH_SUPPORTS_FTRACE_OPS is not
332 * set (see include/asm/ftrace.h and include/linux/ftrace.h). Only the
333 * ip and parent ip are used and the list function is called when
334 * function tracing is enabled.
335 */
336 movq ftrace_trace_function, %r8
337 CALL_NOSPEC r8
338 restore_mcount_regs
339
340 jmp ftrace_stub
341SYM_FUNC_END(__fentry__)
342EXPORT_SYMBOL(__fentry__)
343STACK_FRAME_NON_STANDARD_FP(__fentry__)
344
345#endif /* CONFIG_DYNAMIC_FTRACE */
346
347#ifdef CONFIG_FUNCTION_GRAPH_TRACER
348SYM_CODE_START(return_to_handler)
349 UNWIND_HINT_UNDEFINED
350 ANNOTATE_NOENDBR
351 subq $24, %rsp
352
353 /* Save the return values */
354 movq %rax, (%rsp)
355 movq %rdx, 8(%rsp)
356 movq %rbp, 16(%rsp)
357 movq %rsp, %rdi
358
359 call ftrace_return_to_handler
360
361 movq %rax, %rdi
362 movq 8(%rsp), %rdx
363 movq (%rsp), %rax
364
365 addq $24, %rsp
366 /*
367 * Jump back to the old return address. This cannot be JMP_NOSPEC rdi
368 * since IBT would demand that contain ENDBR, which simply isn't so for
369 * return addresses. Use a retpoline here to keep the RSB balanced.
370 */
371 ANNOTATE_INTRA_FUNCTION_CALL
372 call .Ldo_rop
373 int3
374.Ldo_rop:
375 mov %rdi, (%rsp)
376 ALTERNATIVE __stringify(RET), \
377 __stringify(ANNOTATE_UNRET_SAFE; ret; int3), \
378 X86_FEATURE_CALL_DEPTH
379SYM_CODE_END(return_to_handler)
380#endif
381

source code of linux/arch/x86/kernel/ftrace_64.S