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c877c8e6 | 1 | /* Target-dependent code for GDB, the GNU debugger. |
4e052eda | 2 | |
ca557f44 | 3 | Copyright 1986, 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, |
4be87837 | 4 | 1997, 2000, 2001, 2002, 2003 Free Software Foundation, Inc. |
c877c8e6 KB |
5 | |
6 | This file is part of GDB. | |
7 | ||
8 | This program is free software; you can redistribute it and/or modify | |
9 | it under the terms of the GNU General Public License as published by | |
10 | the Free Software Foundation; either version 2 of the License, or | |
11 | (at your option) any later version. | |
12 | ||
13 | This program is distributed in the hope that it will be useful, | |
14 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
15 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
16 | GNU General Public License for more details. | |
17 | ||
18 | You should have received a copy of the GNU General Public License | |
19 | along with this program; if not, write to the Free Software | |
20 | Foundation, Inc., 59 Temple Place - Suite 330, | |
21 | Boston, MA 02111-1307, USA. */ | |
22 | ||
23 | #include "defs.h" | |
24 | #include "frame.h" | |
25 | #include "inferior.h" | |
26 | #include "symtab.h" | |
27 | #include "target.h" | |
28 | #include "gdbcore.h" | |
29 | #include "gdbcmd.h" | |
30 | #include "symfile.h" | |
31 | #include "objfiles.h" | |
4e052eda | 32 | #include "regcache.h" |
fd0407d6 | 33 | #include "value.h" |
4be87837 | 34 | #include "osabi.h" |
c877c8e6 | 35 | |
6ded7999 | 36 | #include "solib-svr4.h" |
9aa1e687 KB |
37 | #include "ppc-tdep.h" |
38 | ||
c877c8e6 | 39 | /* The following two instructions are used in the signal trampoline |
ca557f44 | 40 | code on GNU/Linux PPC. */ |
c877c8e6 KB |
41 | #define INSTR_LI_R0_0x7777 0x38007777 |
42 | #define INSTR_SC 0x44000002 | |
43 | ||
44 | /* Since the *-tdep.c files are platform independent (i.e, they may be | |
45 | used to build cross platform debuggers), we can't include system | |
46 | headers. Therefore, details concerning the sigcontext structure | |
47 | must be painstakingly rerecorded. What's worse, if these details | |
48 | ever change in the header files, they'll have to be changed here | |
49 | as well. */ | |
50 | ||
51 | /* __SIGNAL_FRAMESIZE from <asm/ptrace.h> */ | |
52 | #define PPC_LINUX_SIGNAL_FRAMESIZE 64 | |
53 | ||
54 | /* From <asm/sigcontext.h>, offsetof(struct sigcontext_struct, regs) == 0x1c */ | |
55 | #define PPC_LINUX_REGS_PTR_OFFSET (PPC_LINUX_SIGNAL_FRAMESIZE + 0x1c) | |
56 | ||
57 | /* From <asm/sigcontext.h>, | |
58 | offsetof(struct sigcontext_struct, handler) == 0x14 */ | |
59 | #define PPC_LINUX_HANDLER_PTR_OFFSET (PPC_LINUX_SIGNAL_FRAMESIZE + 0x14) | |
60 | ||
61 | /* From <asm/ptrace.h>, values for PT_NIP, PT_R1, and PT_LNK */ | |
62 | #define PPC_LINUX_PT_R0 0 | |
63 | #define PPC_LINUX_PT_R1 1 | |
64 | #define PPC_LINUX_PT_R2 2 | |
65 | #define PPC_LINUX_PT_R3 3 | |
66 | #define PPC_LINUX_PT_R4 4 | |
67 | #define PPC_LINUX_PT_R5 5 | |
68 | #define PPC_LINUX_PT_R6 6 | |
69 | #define PPC_LINUX_PT_R7 7 | |
70 | #define PPC_LINUX_PT_R8 8 | |
71 | #define PPC_LINUX_PT_R9 9 | |
72 | #define PPC_LINUX_PT_R10 10 | |
73 | #define PPC_LINUX_PT_R11 11 | |
74 | #define PPC_LINUX_PT_R12 12 | |
75 | #define PPC_LINUX_PT_R13 13 | |
76 | #define PPC_LINUX_PT_R14 14 | |
77 | #define PPC_LINUX_PT_R15 15 | |
78 | #define PPC_LINUX_PT_R16 16 | |
79 | #define PPC_LINUX_PT_R17 17 | |
80 | #define PPC_LINUX_PT_R18 18 | |
81 | #define PPC_LINUX_PT_R19 19 | |
82 | #define PPC_LINUX_PT_R20 20 | |
83 | #define PPC_LINUX_PT_R21 21 | |
84 | #define PPC_LINUX_PT_R22 22 | |
85 | #define PPC_LINUX_PT_R23 23 | |
86 | #define PPC_LINUX_PT_R24 24 | |
87 | #define PPC_LINUX_PT_R25 25 | |
88 | #define PPC_LINUX_PT_R26 26 | |
89 | #define PPC_LINUX_PT_R27 27 | |
90 | #define PPC_LINUX_PT_R28 28 | |
91 | #define PPC_LINUX_PT_R29 29 | |
92 | #define PPC_LINUX_PT_R30 30 | |
93 | #define PPC_LINUX_PT_R31 31 | |
94 | #define PPC_LINUX_PT_NIP 32 | |
95 | #define PPC_LINUX_PT_MSR 33 | |
96 | #define PPC_LINUX_PT_CTR 35 | |
97 | #define PPC_LINUX_PT_LNK 36 | |
98 | #define PPC_LINUX_PT_XER 37 | |
99 | #define PPC_LINUX_PT_CCR 38 | |
100 | #define PPC_LINUX_PT_MQ 39 | |
101 | #define PPC_LINUX_PT_FPR0 48 /* each FP reg occupies 2 slots in this space */ | |
102 | #define PPC_LINUX_PT_FPR31 (PPC_LINUX_PT_FPR0 + 2*31) | |
103 | #define PPC_LINUX_PT_FPSCR (PPC_LINUX_PT_FPR0 + 2*32 + 1) | |
104 | ||
9aa1e687 | 105 | static int ppc_linux_at_sigtramp_return_path (CORE_ADDR pc); |
50c9bd31 | 106 | |
c877c8e6 KB |
107 | /* Determine if pc is in a signal trampoline... |
108 | ||
ca557f44 | 109 | Ha! That's not what this does at all. wait_for_inferior in |
d7bd68ca AC |
110 | infrun.c calls PC_IN_SIGTRAMP in order to detect entry into a |
111 | signal trampoline just after delivery of a signal. But on | |
112 | GNU/Linux, signal trampolines are used for the return path only. | |
113 | The kernel sets things up so that the signal handler is called | |
114 | directly. | |
c877c8e6 KB |
115 | |
116 | If we use in_sigtramp2() in place of in_sigtramp() (see below) | |
117 | we'll (often) end up with stop_pc in the trampoline and prev_pc in | |
118 | the (now exited) handler. The code there will cause a temporary | |
119 | breakpoint to be set on prev_pc which is not very likely to get hit | |
120 | again. | |
121 | ||
122 | If this is confusing, think of it this way... the code in | |
123 | wait_for_inferior() needs to be able to detect entry into a signal | |
124 | trampoline just after a signal is delivered, not after the handler | |
125 | has been run. | |
126 | ||
127 | So, we define in_sigtramp() below to return 1 if the following is | |
128 | true: | |
129 | ||
130 | 1) The previous frame is a real signal trampoline. | |
131 | ||
132 | - and - | |
133 | ||
134 | 2) pc is at the first or second instruction of the corresponding | |
135 | handler. | |
136 | ||
137 | Why the second instruction? It seems that wait_for_inferior() | |
138 | never sees the first instruction when single stepping. When a | |
139 | signal is delivered while stepping, the next instruction that | |
140 | would've been stepped over isn't, instead a signal is delivered and | |
141 | the first instruction of the handler is stepped over instead. That | |
142 | puts us on the second instruction. (I added the test for the | |
143 | first instruction long after the fact, just in case the observed | |
144 | behavior is ever fixed.) | |
145 | ||
d7bd68ca | 146 | PC_IN_SIGTRAMP is called from blockframe.c as well in order to set |
5a203e44 AC |
147 | the frame's type (if a SIGTRAMP_FRAME). Because of our strange |
148 | definition of in_sigtramp below, we can't rely on the frame's type | |
d7bd68ca | 149 | getting set correctly from within blockframe.c. This is why we |
5a203e44 AC |
150 | take pains to set it in init_extra_frame_info(). |
151 | ||
152 | NOTE: cagney/2002-11-10: I suspect the real problem here is that | |
153 | the get_prev_frame() only initializes the frame's type after the | |
154 | call to INIT_FRAME_INFO. get_prev_frame() should be fixed, this | |
155 | code shouldn't be working its way around a bug :-(. */ | |
c877c8e6 KB |
156 | |
157 | int | |
158 | ppc_linux_in_sigtramp (CORE_ADDR pc, char *func_name) | |
159 | { | |
160 | CORE_ADDR lr; | |
161 | CORE_ADDR sp; | |
162 | CORE_ADDR tramp_sp; | |
163 | char buf[4]; | |
164 | CORE_ADDR handler; | |
165 | ||
2188cbdd | 166 | lr = read_register (gdbarch_tdep (current_gdbarch)->ppc_lr_regnum); |
c877c8e6 KB |
167 | if (!ppc_linux_at_sigtramp_return_path (lr)) |
168 | return 0; | |
169 | ||
170 | sp = read_register (SP_REGNUM); | |
171 | ||
172 | if (target_read_memory (sp, buf, sizeof (buf)) != 0) | |
173 | return 0; | |
174 | ||
175 | tramp_sp = extract_unsigned_integer (buf, 4); | |
176 | ||
177 | if (target_read_memory (tramp_sp + PPC_LINUX_HANDLER_PTR_OFFSET, buf, | |
178 | sizeof (buf)) != 0) | |
179 | return 0; | |
180 | ||
181 | handler = extract_unsigned_integer (buf, 4); | |
182 | ||
183 | return (pc == handler || pc == handler + 4); | |
184 | } | |
185 | ||
186 | /* | |
187 | * The signal handler trampoline is on the stack and consists of exactly | |
188 | * two instructions. The easiest and most accurate way of determining | |
189 | * whether the pc is in one of these trampolines is by inspecting the | |
190 | * instructions. It'd be faster though if we could find a way to do this | |
191 | * via some simple address comparisons. | |
192 | */ | |
9aa1e687 | 193 | static int |
c877c8e6 KB |
194 | ppc_linux_at_sigtramp_return_path (CORE_ADDR pc) |
195 | { | |
196 | char buf[12]; | |
197 | unsigned long pcinsn; | |
198 | if (target_read_memory (pc - 4, buf, sizeof (buf)) != 0) | |
199 | return 0; | |
200 | ||
201 | /* extract the instruction at the pc */ | |
202 | pcinsn = extract_unsigned_integer (buf + 4, 4); | |
203 | ||
204 | return ( | |
205 | (pcinsn == INSTR_LI_R0_0x7777 | |
206 | && extract_unsigned_integer (buf + 8, 4) == INSTR_SC) | |
207 | || | |
208 | (pcinsn == INSTR_SC | |
209 | && extract_unsigned_integer (buf, 4) == INSTR_LI_R0_0x7777)); | |
210 | } | |
211 | ||
212 | CORE_ADDR | |
213 | ppc_linux_skip_trampoline_code (CORE_ADDR pc) | |
214 | { | |
215 | char buf[4]; | |
216 | struct obj_section *sect; | |
217 | struct objfile *objfile; | |
218 | unsigned long insn; | |
219 | CORE_ADDR plt_start = 0; | |
220 | CORE_ADDR symtab = 0; | |
221 | CORE_ADDR strtab = 0; | |
222 | int num_slots = -1; | |
223 | int reloc_index = -1; | |
224 | CORE_ADDR plt_table; | |
225 | CORE_ADDR reloc; | |
226 | CORE_ADDR sym; | |
227 | long symidx; | |
228 | char symname[1024]; | |
229 | struct minimal_symbol *msymbol; | |
230 | ||
231 | /* Find the section pc is in; return if not in .plt */ | |
232 | sect = find_pc_section (pc); | |
233 | if (!sect || strcmp (sect->the_bfd_section->name, ".plt") != 0) | |
234 | return 0; | |
235 | ||
236 | objfile = sect->objfile; | |
237 | ||
238 | /* Pick up the instruction at pc. It had better be of the | |
239 | form | |
240 | li r11, IDX | |
241 | ||
242 | where IDX is an index into the plt_table. */ | |
243 | ||
244 | if (target_read_memory (pc, buf, 4) != 0) | |
245 | return 0; | |
246 | insn = extract_unsigned_integer (buf, 4); | |
247 | ||
248 | if ((insn & 0xffff0000) != 0x39600000 /* li r11, VAL */ ) | |
249 | return 0; | |
250 | ||
251 | reloc_index = (insn << 16) >> 16; | |
252 | ||
253 | /* Find the objfile that pc is in and obtain the information | |
254 | necessary for finding the symbol name. */ | |
255 | for (sect = objfile->sections; sect < objfile->sections_end; ++sect) | |
256 | { | |
257 | const char *secname = sect->the_bfd_section->name; | |
258 | if (strcmp (secname, ".plt") == 0) | |
259 | plt_start = sect->addr; | |
260 | else if (strcmp (secname, ".rela.plt") == 0) | |
261 | num_slots = ((int) sect->endaddr - (int) sect->addr) / 12; | |
262 | else if (strcmp (secname, ".dynsym") == 0) | |
263 | symtab = sect->addr; | |
264 | else if (strcmp (secname, ".dynstr") == 0) | |
265 | strtab = sect->addr; | |
266 | } | |
267 | ||
268 | /* Make sure we have all the information we need. */ | |
269 | if (plt_start == 0 || num_slots == -1 || symtab == 0 || strtab == 0) | |
270 | return 0; | |
271 | ||
272 | /* Compute the value of the plt table */ | |
273 | plt_table = plt_start + 72 + 8 * num_slots; | |
274 | ||
275 | /* Get address of the relocation entry (Elf32_Rela) */ | |
276 | if (target_read_memory (plt_table + reloc_index, buf, 4) != 0) | |
277 | return 0; | |
278 | reloc = extract_address (buf, 4); | |
279 | ||
280 | sect = find_pc_section (reloc); | |
281 | if (!sect) | |
282 | return 0; | |
283 | ||
284 | if (strcmp (sect->the_bfd_section->name, ".text") == 0) | |
285 | return reloc; | |
286 | ||
287 | /* Now get the r_info field which is the relocation type and symbol | |
288 | index. */ | |
289 | if (target_read_memory (reloc + 4, buf, 4) != 0) | |
290 | return 0; | |
291 | symidx = extract_unsigned_integer (buf, 4); | |
292 | ||
293 | /* Shift out the relocation type leaving just the symbol index */ | |
294 | /* symidx = ELF32_R_SYM(symidx); */ | |
295 | symidx = symidx >> 8; | |
296 | ||
297 | /* compute the address of the symbol */ | |
298 | sym = symtab + symidx * 4; | |
299 | ||
300 | /* Fetch the string table index */ | |
301 | if (target_read_memory (sym, buf, 4) != 0) | |
302 | return 0; | |
303 | symidx = extract_unsigned_integer (buf, 4); | |
304 | ||
305 | /* Fetch the string; we don't know how long it is. Is it possible | |
306 | that the following will fail because we're trying to fetch too | |
307 | much? */ | |
308 | if (target_read_memory (strtab + symidx, symname, sizeof (symname)) != 0) | |
309 | return 0; | |
310 | ||
311 | /* This might not work right if we have multiple symbols with the | |
312 | same name; the only way to really get it right is to perform | |
313 | the same sort of lookup as the dynamic linker. */ | |
314 | msymbol = lookup_minimal_symbol_text (symname, NULL, NULL); | |
315 | if (!msymbol) | |
316 | return 0; | |
317 | ||
318 | return SYMBOL_VALUE_ADDRESS (msymbol); | |
319 | } | |
320 | ||
321 | /* The rs6000 version of FRAME_SAVED_PC will almost work for us. The | |
322 | signal handler details are different, so we'll handle those here | |
323 | and call the rs6000 version to do the rest. */ | |
9aa1e687 | 324 | CORE_ADDR |
c877c8e6 KB |
325 | ppc_linux_frame_saved_pc (struct frame_info *fi) |
326 | { | |
5a203e44 | 327 | if ((get_frame_type (fi) == SIGTRAMP_FRAME)) |
c877c8e6 KB |
328 | { |
329 | CORE_ADDR regs_addr = | |
50c9bd31 | 330 | read_memory_integer (fi->frame + PPC_LINUX_REGS_PTR_OFFSET, 4); |
c877c8e6 KB |
331 | /* return the NIP in the regs array */ |
332 | return read_memory_integer (regs_addr + 4 * PPC_LINUX_PT_NIP, 4); | |
333 | } | |
5a203e44 | 334 | else if (fi->next && (get_frame_type (fi->next) == SIGTRAMP_FRAME)) |
50c9bd31 KB |
335 | { |
336 | CORE_ADDR regs_addr = | |
337 | read_memory_integer (fi->next->frame + PPC_LINUX_REGS_PTR_OFFSET, 4); | |
338 | /* return LNK in the regs array */ | |
339 | return read_memory_integer (regs_addr + 4 * PPC_LINUX_PT_LNK, 4); | |
340 | } | |
341 | else | |
342 | return rs6000_frame_saved_pc (fi); | |
c877c8e6 KB |
343 | } |
344 | ||
345 | void | |
346 | ppc_linux_init_extra_frame_info (int fromleaf, struct frame_info *fi) | |
347 | { | |
348 | rs6000_init_extra_frame_info (fromleaf, fi); | |
349 | ||
350 | if (fi->next != 0) | |
351 | { | |
352 | /* We're called from get_prev_frame_info; check to see if | |
353 | this is a signal frame by looking to see if the pc points | |
354 | at trampoline code */ | |
355 | if (ppc_linux_at_sigtramp_return_path (fi->pc)) | |
5a203e44 | 356 | deprecated_set_frame_type (fi, SIGTRAMP_FRAME); |
c877c8e6 | 357 | else |
5a203e44 AC |
358 | /* FIXME: cagney/2002-11-10: Is this double bogus? What |
359 | happens if the frame has previously been marked as a dummy? */ | |
360 | deprecated_set_frame_type (fi, NORMAL_FRAME); | |
c877c8e6 KB |
361 | } |
362 | } | |
363 | ||
364 | int | |
365 | ppc_linux_frameless_function_invocation (struct frame_info *fi) | |
366 | { | |
367 | /* We'll find the wrong thing if we let | |
368 | rs6000_frameless_function_invocation () search for a signal trampoline */ | |
369 | if (ppc_linux_at_sigtramp_return_path (fi->pc)) | |
370 | return 0; | |
371 | else | |
372 | return rs6000_frameless_function_invocation (fi); | |
373 | } | |
374 | ||
375 | void | |
376 | ppc_linux_frame_init_saved_regs (struct frame_info *fi) | |
377 | { | |
5a203e44 | 378 | if ((get_frame_type (fi) == SIGTRAMP_FRAME)) |
c877c8e6 KB |
379 | { |
380 | CORE_ADDR regs_addr; | |
381 | int i; | |
382 | if (fi->saved_regs) | |
383 | return; | |
384 | ||
385 | frame_saved_regs_zalloc (fi); | |
386 | ||
387 | regs_addr = | |
388 | read_memory_integer (fi->frame + PPC_LINUX_REGS_PTR_OFFSET, 4); | |
389 | fi->saved_regs[PC_REGNUM] = regs_addr + 4 * PPC_LINUX_PT_NIP; | |
2188cbdd EZ |
390 | fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_ps_regnum] = |
391 | regs_addr + 4 * PPC_LINUX_PT_MSR; | |
392 | fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_cr_regnum] = | |
393 | regs_addr + 4 * PPC_LINUX_PT_CCR; | |
394 | fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_lr_regnum] = | |
395 | regs_addr + 4 * PPC_LINUX_PT_LNK; | |
396 | fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_ctr_regnum] = | |
397 | regs_addr + 4 * PPC_LINUX_PT_CTR; | |
398 | fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_xer_regnum] = | |
399 | regs_addr + 4 * PPC_LINUX_PT_XER; | |
400 | fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_mq_regnum] = | |
401 | regs_addr + 4 * PPC_LINUX_PT_MQ; | |
c877c8e6 | 402 | for (i = 0; i < 32; i++) |
2188cbdd EZ |
403 | fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_gp0_regnum + i] = |
404 | regs_addr + 4 * PPC_LINUX_PT_R0 + 4 * i; | |
c877c8e6 KB |
405 | for (i = 0; i < 32; i++) |
406 | fi->saved_regs[FP0_REGNUM + i] = regs_addr + 4 * PPC_LINUX_PT_FPR0 + 8 * i; | |
407 | } | |
408 | else | |
409 | rs6000_frame_init_saved_regs (fi); | |
410 | } | |
411 | ||
412 | CORE_ADDR | |
413 | ppc_linux_frame_chain (struct frame_info *thisframe) | |
414 | { | |
415 | /* Kernel properly constructs the frame chain for the handler */ | |
5a203e44 | 416 | if ((get_frame_type (thisframe) == SIGTRAMP_FRAME)) |
c877c8e6 KB |
417 | return read_memory_integer ((thisframe)->frame, 4); |
418 | else | |
419 | return rs6000_frame_chain (thisframe); | |
420 | } | |
421 | ||
122a33de KB |
422 | /* ppc_linux_memory_remove_breakpoints attempts to remove a breakpoint |
423 | in much the same fashion as memory_remove_breakpoint in mem-break.c, | |
424 | but is careful not to write back the previous contents if the code | |
425 | in question has changed in between inserting the breakpoint and | |
426 | removing it. | |
427 | ||
428 | Here is the problem that we're trying to solve... | |
429 | ||
430 | Once upon a time, before introducing this function to remove | |
431 | breakpoints from the inferior, setting a breakpoint on a shared | |
432 | library function prior to running the program would not work | |
433 | properly. In order to understand the problem, it is first | |
434 | necessary to understand a little bit about dynamic linking on | |
435 | this platform. | |
436 | ||
437 | A call to a shared library function is accomplished via a bl | |
438 | (branch-and-link) instruction whose branch target is an entry | |
439 | in the procedure linkage table (PLT). The PLT in the object | |
440 | file is uninitialized. To gdb, prior to running the program, the | |
441 | entries in the PLT are all zeros. | |
442 | ||
443 | Once the program starts running, the shared libraries are loaded | |
444 | and the procedure linkage table is initialized, but the entries in | |
445 | the table are not (necessarily) resolved. Once a function is | |
446 | actually called, the code in the PLT is hit and the function is | |
447 | resolved. In order to better illustrate this, an example is in | |
448 | order; the following example is from the gdb testsuite. | |
449 | ||
450 | We start the program shmain. | |
451 | ||
452 | [kev@arroyo testsuite]$ ../gdb gdb.base/shmain | |
453 | [...] | |
454 | ||
455 | We place two breakpoints, one on shr1 and the other on main. | |
456 | ||
457 | (gdb) b shr1 | |
458 | Breakpoint 1 at 0x100409d4 | |
459 | (gdb) b main | |
460 | Breakpoint 2 at 0x100006a0: file gdb.base/shmain.c, line 44. | |
461 | ||
462 | Examine the instruction (and the immediatly following instruction) | |
463 | upon which the breakpoint was placed. Note that the PLT entry | |
464 | for shr1 contains zeros. | |
465 | ||
466 | (gdb) x/2i 0x100409d4 | |
467 | 0x100409d4 <shr1>: .long 0x0 | |
468 | 0x100409d8 <shr1+4>: .long 0x0 | |
469 | ||
470 | Now run 'til main. | |
471 | ||
472 | (gdb) r | |
473 | Starting program: gdb.base/shmain | |
474 | Breakpoint 1 at 0xffaf790: file gdb.base/shr1.c, line 19. | |
475 | ||
476 | Breakpoint 2, main () | |
477 | at gdb.base/shmain.c:44 | |
478 | 44 g = 1; | |
479 | ||
480 | Examine the PLT again. Note that the loading of the shared | |
481 | library has initialized the PLT to code which loads a constant | |
482 | (which I think is an index into the GOT) into r11 and then | |
483 | branchs a short distance to the code which actually does the | |
484 | resolving. | |
485 | ||
486 | (gdb) x/2i 0x100409d4 | |
487 | 0x100409d4 <shr1>: li r11,4 | |
488 | 0x100409d8 <shr1+4>: b 0x10040984 <sg+4> | |
489 | (gdb) c | |
490 | Continuing. | |
491 | ||
492 | Breakpoint 1, shr1 (x=1) | |
493 | at gdb.base/shr1.c:19 | |
494 | 19 l = 1; | |
495 | ||
496 | Now we've hit the breakpoint at shr1. (The breakpoint was | |
497 | reset from the PLT entry to the actual shr1 function after the | |
498 | shared library was loaded.) Note that the PLT entry has been | |
499 | resolved to contain a branch that takes us directly to shr1. | |
500 | (The real one, not the PLT entry.) | |
501 | ||
502 | (gdb) x/2i 0x100409d4 | |
503 | 0x100409d4 <shr1>: b 0xffaf76c <shr1> | |
504 | 0x100409d8 <shr1+4>: b 0x10040984 <sg+4> | |
505 | ||
506 | The thing to note here is that the PLT entry for shr1 has been | |
507 | changed twice. | |
508 | ||
509 | Now the problem should be obvious. GDB places a breakpoint (a | |
510 | trap instruction) on the zero value of the PLT entry for shr1. | |
511 | Later on, after the shared library had been loaded and the PLT | |
512 | initialized, GDB gets a signal indicating this fact and attempts | |
513 | (as it always does when it stops) to remove all the breakpoints. | |
514 | ||
515 | The breakpoint removal was causing the former contents (a zero | |
516 | word) to be written back to the now initialized PLT entry thus | |
517 | destroying a portion of the initialization that had occurred only a | |
518 | short time ago. When execution continued, the zero word would be | |
519 | executed as an instruction an an illegal instruction trap was | |
520 | generated instead. (0 is not a legal instruction.) | |
521 | ||
522 | The fix for this problem was fairly straightforward. The function | |
523 | memory_remove_breakpoint from mem-break.c was copied to this file, | |
524 | modified slightly, and renamed to ppc_linux_memory_remove_breakpoint. | |
525 | In tm-linux.h, MEMORY_REMOVE_BREAKPOINT is defined to call this new | |
526 | function. | |
527 | ||
528 | The differences between ppc_linux_memory_remove_breakpoint () and | |
529 | memory_remove_breakpoint () are minor. All that the former does | |
530 | that the latter does not is check to make sure that the breakpoint | |
531 | location actually contains a breakpoint (trap instruction) prior | |
532 | to attempting to write back the old contents. If it does contain | |
533 | a trap instruction, we allow the old contents to be written back. | |
534 | Otherwise, we silently do nothing. | |
535 | ||
536 | The big question is whether memory_remove_breakpoint () should be | |
537 | changed to have the same functionality. The downside is that more | |
538 | traffic is generated for remote targets since we'll have an extra | |
539 | fetch of a memory word each time a breakpoint is removed. | |
540 | ||
541 | For the time being, we'll leave this self-modifying-code-friendly | |
542 | version in ppc-linux-tdep.c, but it ought to be migrated somewhere | |
543 | else in the event that some other platform has similar needs with | |
544 | regard to removing breakpoints in some potentially self modifying | |
545 | code. */ | |
482ca3f5 KB |
546 | int |
547 | ppc_linux_memory_remove_breakpoint (CORE_ADDR addr, char *contents_cache) | |
548 | { | |
f4f9705a | 549 | const unsigned char *bp; |
482ca3f5 KB |
550 | int val; |
551 | int bplen; | |
552 | char old_contents[BREAKPOINT_MAX]; | |
553 | ||
554 | /* Determine appropriate breakpoint contents and size for this address. */ | |
555 | bp = BREAKPOINT_FROM_PC (&addr, &bplen); | |
556 | if (bp == NULL) | |
557 | error ("Software breakpoints not implemented for this target."); | |
558 | ||
559 | val = target_read_memory (addr, old_contents, bplen); | |
560 | ||
561 | /* If our breakpoint is no longer at the address, this means that the | |
562 | program modified the code on us, so it is wrong to put back the | |
563 | old value */ | |
564 | if (val == 0 && memcmp (bp, old_contents, bplen) == 0) | |
565 | val = target_write_memory (addr, contents_cache, bplen); | |
566 | ||
567 | return val; | |
568 | } | |
6ded7999 KB |
569 | |
570 | /* Fetch (and possibly build) an appropriate link_map_offsets | |
ca557f44 | 571 | structure for GNU/Linux PPC targets using the struct offsets |
6ded7999 KB |
572 | defined in link.h (but without actual reference to that file). |
573 | ||
ca557f44 AC |
574 | This makes it possible to access GNU/Linux PPC shared libraries |
575 | from a GDB that was not built on an GNU/Linux PPC host (for cross | |
576 | debugging). */ | |
6ded7999 KB |
577 | |
578 | struct link_map_offsets * | |
579 | ppc_linux_svr4_fetch_link_map_offsets (void) | |
580 | { | |
581 | static struct link_map_offsets lmo; | |
582 | static struct link_map_offsets *lmp = NULL; | |
583 | ||
584 | if (lmp == NULL) | |
585 | { | |
586 | lmp = &lmo; | |
587 | ||
588 | lmo.r_debug_size = 8; /* The actual size is 20 bytes, but | |
589 | this is all we need. */ | |
590 | lmo.r_map_offset = 4; | |
591 | lmo.r_map_size = 4; | |
592 | ||
593 | lmo.link_map_size = 20; /* The actual size is 560 bytes, but | |
594 | this is all we need. */ | |
595 | lmo.l_addr_offset = 0; | |
596 | lmo.l_addr_size = 4; | |
597 | ||
598 | lmo.l_name_offset = 4; | |
599 | lmo.l_name_size = 4; | |
600 | ||
601 | lmo.l_next_offset = 12; | |
602 | lmo.l_next_size = 4; | |
603 | ||
604 | lmo.l_prev_offset = 16; | |
605 | lmo.l_prev_size = 4; | |
606 | } | |
607 | ||
608 | return lmp; | |
609 | } | |
7b112f9c | 610 | |
2fda4977 DJ |
611 | enum { |
612 | ELF_NGREG = 48, | |
613 | ELF_NFPREG = 33, | |
614 | ELF_NVRREG = 33 | |
615 | }; | |
616 | ||
617 | enum { | |
618 | ELF_GREGSET_SIZE = (ELF_NGREG * 4), | |
619 | ELF_FPREGSET_SIZE = (ELF_NFPREG * 8) | |
620 | }; | |
621 | ||
622 | void | |
623 | ppc_linux_supply_gregset (char *buf) | |
624 | { | |
625 | int regi; | |
626 | struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch); | |
627 | ||
628 | for (regi = 0; regi < 32; regi++) | |
629 | supply_register (regi, buf + 4 * regi); | |
630 | ||
631 | supply_register (PC_REGNUM, buf + 4 * PPC_LINUX_PT_NIP); | |
632 | supply_register (tdep->ppc_lr_regnum, buf + 4 * PPC_LINUX_PT_LNK); | |
633 | supply_register (tdep->ppc_cr_regnum, buf + 4 * PPC_LINUX_PT_CCR); | |
634 | supply_register (tdep->ppc_xer_regnum, buf + 4 * PPC_LINUX_PT_XER); | |
635 | supply_register (tdep->ppc_ctr_regnum, buf + 4 * PPC_LINUX_PT_CTR); | |
636 | if (tdep->ppc_mq_regnum != -1) | |
637 | supply_register (tdep->ppc_mq_regnum, buf + 4 * PPC_LINUX_PT_MQ); | |
638 | supply_register (tdep->ppc_ps_regnum, buf + 4 * PPC_LINUX_PT_MSR); | |
639 | } | |
640 | ||
641 | void | |
642 | ppc_linux_supply_fpregset (char *buf) | |
643 | { | |
644 | int regi; | |
645 | struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch); | |
646 | ||
647 | for (regi = 0; regi < 32; regi++) | |
648 | supply_register (FP0_REGNUM + regi, buf + 8 * regi); | |
649 | ||
650 | /* The FPSCR is stored in the low order word of the last doubleword in the | |
651 | fpregset. */ | |
652 | supply_register (tdep->ppc_fpscr_regnum, buf + 8 * 32 + 4); | |
653 | } | |
654 | ||
655 | /* | |
656 | Use a local version of this function to get the correct types for regsets. | |
657 | */ | |
658 | ||
659 | static void | |
660 | fetch_core_registers (char *core_reg_sect, | |
661 | unsigned core_reg_size, | |
662 | int which, | |
663 | CORE_ADDR reg_addr) | |
664 | { | |
665 | if (which == 0) | |
666 | { | |
667 | if (core_reg_size == ELF_GREGSET_SIZE) | |
668 | ppc_linux_supply_gregset (core_reg_sect); | |
669 | else | |
670 | warning ("wrong size gregset struct in core file"); | |
671 | } | |
672 | else if (which == 2) | |
673 | { | |
674 | if (core_reg_size == ELF_FPREGSET_SIZE) | |
675 | ppc_linux_supply_fpregset (core_reg_sect); | |
676 | else | |
677 | warning ("wrong size fpregset struct in core file"); | |
678 | } | |
679 | } | |
680 | ||
681 | /* Register that we are able to handle ELF file formats using standard | |
682 | procfs "regset" structures. */ | |
683 | ||
684 | static struct core_fns ppc_linux_regset_core_fns = | |
685 | { | |
686 | bfd_target_elf_flavour, /* core_flavour */ | |
687 | default_check_format, /* check_format */ | |
688 | default_core_sniffer, /* core_sniffer */ | |
689 | fetch_core_registers, /* core_read_registers */ | |
690 | NULL /* next */ | |
691 | }; | |
692 | ||
7b112f9c JT |
693 | static void |
694 | ppc_linux_init_abi (struct gdbarch_info info, | |
695 | struct gdbarch *gdbarch) | |
696 | { | |
697 | struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch); | |
698 | ||
699 | /* Until November 2001, gcc was not complying to the SYSV ABI for | |
700 | returning structures less than or equal to 8 bytes in size. It was | |
701 | returning everything in memory. When this was corrected, it wasn't | |
702 | fixed for native platforms. */ | |
703 | set_gdbarch_use_struct_convention (gdbarch, | |
704 | ppc_sysv_abi_broken_use_struct_convention); | |
705 | ||
706 | if (tdep->wordsize == 4) | |
707 | { | |
708 | /* Note: kevinb/2002-04-12: See note in rs6000_gdbarch_init regarding | |
709 | *_push_arguments(). The same remarks hold for the methods below. */ | |
710 | set_gdbarch_frameless_function_invocation (gdbarch, | |
711 | ppc_linux_frameless_function_invocation); | |
712 | set_gdbarch_frame_chain (gdbarch, ppc_linux_frame_chain); | |
713 | set_gdbarch_frame_saved_pc (gdbarch, ppc_linux_frame_saved_pc); | |
714 | ||
715 | set_gdbarch_frame_init_saved_regs (gdbarch, | |
716 | ppc_linux_frame_init_saved_regs); | |
717 | set_gdbarch_init_extra_frame_info (gdbarch, | |
718 | ppc_linux_init_extra_frame_info); | |
719 | ||
720 | set_gdbarch_memory_remove_breakpoint (gdbarch, | |
721 | ppc_linux_memory_remove_breakpoint); | |
722 | set_solib_svr4_fetch_link_map_offsets | |
723 | (gdbarch, ppc_linux_svr4_fetch_link_map_offsets); | |
724 | } | |
725 | } | |
726 | ||
727 | void | |
728 | _initialize_ppc_linux_tdep (void) | |
729 | { | |
05816f70 | 730 | gdbarch_register_osabi (bfd_arch_powerpc, 0, GDB_OSABI_LINUX, |
7b112f9c | 731 | ppc_linux_init_abi); |
2fda4977 | 732 | add_core_fns (&ppc_linux_regset_core_fns); |
7b112f9c | 733 | } |