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a60335ba SB |
1 | /* |
2 | * Use DWARF Debug information to skip unnecessary callchain entries. | |
3 | * | |
4 | * Copyright (C) 2014 Sukadev Bhattiprolu, IBM Corporation. | |
5 | * Copyright (C) 2014 Ulrich Weigand, IBM Corporation. | |
6 | * | |
7 | * This program is free software; you can redistribute it and/or | |
8 | * modify it under the terms of the GNU General Public License | |
9 | * as published by the Free Software Foundation; either version | |
10 | * 2 of the License, or (at your option) any later version. | |
11 | */ | |
12 | #include <inttypes.h> | |
13 | #include <dwarf.h> | |
14 | #include <elfutils/libdwfl.h> | |
15 | ||
16 | #include "util/thread.h" | |
17 | #include "util/callchain.h" | |
ad7e767a | 18 | #include "util/debug.h" |
a60335ba SB |
19 | |
20 | /* | |
21 | * When saving the callchain on Power, the kernel conservatively saves | |
22 | * excess entries in the callchain. A few of these entries are needed | |
23 | * in some cases but not others. If the unnecessary entries are not | |
24 | * ignored, we end up with duplicate arcs in the call-graphs. Use | |
25 | * DWARF debug information to skip over any unnecessary callchain | |
26 | * entries. | |
27 | * | |
28 | * See function header for arch_adjust_callchain() below for more details. | |
29 | * | |
30 | * The libdwfl code in this file is based on code from elfutils | |
31 | * (libdwfl/argp-std.c, libdwfl/tests/addrcfi.c, etc). | |
32 | */ | |
33 | static char *debuginfo_path; | |
34 | ||
35 | static const Dwfl_Callbacks offline_callbacks = { | |
36 | .debuginfo_path = &debuginfo_path, | |
37 | .find_debuginfo = dwfl_standard_find_debuginfo, | |
38 | .section_address = dwfl_offline_section_address, | |
39 | }; | |
40 | ||
41 | ||
42 | /* | |
43 | * Use the DWARF expression for the Call-frame-address and determine | |
44 | * if return address is in LR and if a new frame was allocated. | |
45 | */ | |
46 | static int check_return_reg(int ra_regno, Dwarf_Frame *frame) | |
47 | { | |
48 | Dwarf_Op ops_mem[2]; | |
49 | Dwarf_Op dummy; | |
50 | Dwarf_Op *ops = &dummy; | |
51 | size_t nops; | |
52 | int result; | |
53 | ||
54 | result = dwarf_frame_register(frame, ra_regno, ops_mem, &ops, &nops); | |
55 | if (result < 0) { | |
56 | pr_debug("dwarf_frame_register() %s\n", dwarf_errmsg(-1)); | |
57 | return -1; | |
58 | } | |
59 | ||
60 | /* | |
61 | * Check if return address is on the stack. | |
62 | */ | |
63 | if (nops != 0 || ops != NULL) | |
64 | return 0; | |
65 | ||
66 | /* | |
67 | * Return address is in LR. Check if a frame was allocated | |
68 | * but not-yet used. | |
69 | */ | |
70 | result = dwarf_frame_cfa(frame, &ops, &nops); | |
71 | if (result < 0) { | |
72 | pr_debug("dwarf_frame_cfa() returns %d, %s\n", result, | |
73 | dwarf_errmsg(-1)); | |
74 | return -1; | |
75 | } | |
76 | ||
77 | /* | |
78 | * If call frame address is in r1, no new frame was allocated. | |
79 | */ | |
80 | if (nops == 1 && ops[0].atom == DW_OP_bregx && ops[0].number == 1 && | |
81 | ops[0].number2 == 0) | |
82 | return 1; | |
83 | ||
84 | /* | |
85 | * A new frame was allocated but has not yet been used. | |
86 | */ | |
87 | return 2; | |
88 | } | |
89 | ||
90 | /* | |
91 | * Get the DWARF frame from the .eh_frame section. | |
92 | */ | |
93 | static Dwarf_Frame *get_eh_frame(Dwfl_Module *mod, Dwarf_Addr pc) | |
94 | { | |
95 | int result; | |
96 | Dwarf_Addr bias; | |
97 | Dwarf_CFI *cfi; | |
98 | Dwarf_Frame *frame; | |
99 | ||
100 | cfi = dwfl_module_eh_cfi(mod, &bias); | |
101 | if (!cfi) { | |
102 | pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1)); | |
103 | return NULL; | |
104 | } | |
105 | ||
106 | result = dwarf_cfi_addrframe(cfi, pc, &frame); | |
107 | if (result) { | |
108 | pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1)); | |
109 | return NULL; | |
110 | } | |
111 | ||
112 | return frame; | |
113 | } | |
114 | ||
115 | /* | |
116 | * Get the DWARF frame from the .debug_frame section. | |
117 | */ | |
118 | static Dwarf_Frame *get_dwarf_frame(Dwfl_Module *mod, Dwarf_Addr pc) | |
119 | { | |
120 | Dwarf_CFI *cfi; | |
121 | Dwarf_Addr bias; | |
122 | Dwarf_Frame *frame; | |
123 | int result; | |
124 | ||
125 | cfi = dwfl_module_dwarf_cfi(mod, &bias); | |
126 | if (!cfi) { | |
127 | pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1)); | |
128 | return NULL; | |
129 | } | |
130 | ||
131 | result = dwarf_cfi_addrframe(cfi, pc, &frame); | |
132 | if (result) { | |
133 | pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1)); | |
134 | return NULL; | |
135 | } | |
136 | ||
137 | return frame; | |
138 | } | |
139 | ||
140 | /* | |
141 | * Return: | |
142 | * 0 if return address for the program counter @pc is on stack | |
143 | * 1 if return address is in LR and no new stack frame was allocated | |
144 | * 2 if return address is in LR and a new frame was allocated (but not | |
145 | * yet used) | |
146 | * -1 in case of errors | |
147 | */ | |
7d073b33 | 148 | static int check_return_addr(struct dso *dso, Dwarf_Addr pc) |
a60335ba SB |
149 | { |
150 | int rc = -1; | |
151 | Dwfl *dwfl; | |
152 | Dwfl_Module *mod; | |
153 | Dwarf_Frame *frame; | |
154 | int ra_regno; | |
155 | Dwarf_Addr start = pc; | |
156 | Dwarf_Addr end = pc; | |
157 | bool signalp; | |
158 | ||
7d073b33 | 159 | dwfl = dso->dwfl; |
a60335ba | 160 | |
7d073b33 SB |
161 | if (!dwfl) { |
162 | dwfl = dwfl_begin(&offline_callbacks); | |
163 | if (!dwfl) { | |
164 | pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1)); | |
165 | return -1; | |
166 | } | |
167 | ||
168 | if (dwfl_report_offline(dwfl, "", dso->long_name, -1) == NULL) { | |
169 | pr_debug("dwfl_report_offline() failed %s\n", | |
170 | dwarf_errmsg(-1)); | |
171 | /* | |
172 | * We normally cache the DWARF debug info and never | |
173 | * call dwfl_end(). But to prevent fd leak, free in | |
174 | * case of error. | |
175 | */ | |
176 | dwfl_end(dwfl); | |
177 | goto out; | |
178 | } | |
179 | dso->dwfl = dwfl; | |
a60335ba SB |
180 | } |
181 | ||
182 | mod = dwfl_addrmodule(dwfl, pc); | |
183 | if (!mod) { | |
184 | pr_debug("dwfl_addrmodule() failed, %s\n", dwarf_errmsg(-1)); | |
185 | goto out; | |
186 | } | |
187 | ||
188 | /* | |
189 | * To work with split debug info files (eg: glibc), check both | |
190 | * .eh_frame and .debug_frame sections of the ELF header. | |
191 | */ | |
192 | frame = get_eh_frame(mod, pc); | |
193 | if (!frame) { | |
194 | frame = get_dwarf_frame(mod, pc); | |
195 | if (!frame) | |
196 | goto out; | |
197 | } | |
198 | ||
199 | ra_regno = dwarf_frame_info(frame, &start, &end, &signalp); | |
200 | if (ra_regno < 0) { | |
201 | pr_debug("Return address register unavailable: %s\n", | |
202 | dwarf_errmsg(-1)); | |
203 | goto out; | |
204 | } | |
205 | ||
206 | rc = check_return_reg(ra_regno, frame); | |
207 | ||
208 | out: | |
a60335ba SB |
209 | return rc; |
210 | } | |
211 | ||
212 | /* | |
213 | * The callchain saved by the kernel always includes the link register (LR). | |
214 | * | |
215 | * 0: PERF_CONTEXT_USER | |
216 | * 1: Program counter (Next instruction pointer) | |
217 | * 2: LR value | |
218 | * 3: Caller's caller | |
219 | * 4: ... | |
220 | * | |
221 | * The value in LR is only needed when it holds a return address. If the | |
222 | * return address is on the stack, we should ignore the LR value. | |
223 | * | |
224 | * Further, when the return address is in the LR, if a new frame was just | |
225 | * allocated but the LR was not saved into it, then the LR contains the | |
226 | * caller, slot 4: contains the caller's caller and the contents of slot 3: | |
227 | * (chain->ips[3]) is undefined and must be ignored. | |
228 | * | |
229 | * Use DWARF debug information to determine if any entries need to be skipped. | |
230 | * | |
231 | * Return: | |
232 | * index: of callchain entry that needs to be ignored (if any) | |
233 | * -1 if no entry needs to be ignored or in case of errors | |
234 | */ | |
bb871a9c | 235 | int arch_skip_callchain_idx(struct thread *thread, struct ip_callchain *chain) |
a60335ba SB |
236 | { |
237 | struct addr_location al; | |
238 | struct dso *dso = NULL; | |
239 | int rc; | |
240 | u64 ip; | |
241 | u64 skip_slot = -1; | |
242 | ||
243 | if (chain->nr < 3) | |
244 | return skip_slot; | |
245 | ||
246 | ip = chain->ips[2]; | |
247 | ||
bb871a9c | 248 | thread__find_addr_location(thread, PERF_RECORD_MISC_USER, |
a60335ba SB |
249 | MAP__FUNCTION, ip, &al); |
250 | ||
251 | if (al.map) | |
252 | dso = al.map->dso; | |
253 | ||
254 | if (!dso) { | |
255 | pr_debug("%" PRIx64 " dso is NULL\n", ip); | |
256 | return skip_slot; | |
257 | } | |
258 | ||
7d073b33 | 259 | rc = check_return_addr(dso, ip); |
a60335ba SB |
260 | |
261 | pr_debug("DSO %s, nr %" PRIx64 ", ip 0x%" PRIx64 "rc %d\n", | |
262 | dso->long_name, chain->nr, ip, rc); | |
263 | ||
264 | if (rc == 0) { | |
265 | /* | |
266 | * Return address on stack. Ignore LR value in callchain | |
267 | */ | |
268 | skip_slot = 2; | |
269 | } else if (rc == 2) { | |
270 | /* | |
271 | * New frame allocated but return address still in LR. | |
272 | * Ignore the caller's caller entry in callchain. | |
273 | */ | |
274 | skip_slot = 3; | |
275 | } | |
276 | return skip_slot; | |
277 | } |