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faf5f7ad SB |
1 | /* GNU/Linux on ARM target support. |
2 | Copyright 1999, 2000 Free Software Foundation, Inc. | |
3 | ||
4 | This file is part of GDB. | |
5 | ||
6 | This program is free software; you can redistribute it and/or modify | |
7 | it under the terms of the GNU General Public License as published by | |
8 | the Free Software Foundation; either version 2 of the License, or | |
9 | (at your option) any later version. | |
10 | ||
11 | This program is distributed in the hope that it will be useful, | |
12 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | GNU General Public License for more details. | |
15 | ||
16 | You should have received a copy of the GNU General Public License | |
17 | along with this program; if not, write to the Free Software | |
18 | Foundation, Inc., 59 Temple Place - Suite 330, | |
19 | Boston, MA 02111-1307, USA. */ | |
20 | ||
21 | #include "defs.h" | |
c20f6dea SB |
22 | #include "target.h" |
23 | #include "value.h" | |
faf5f7ad | 24 | #include "gdbtypes.h" |
134e61c4 | 25 | #include "floatformat.h" |
2a451106 KB |
26 | #include "gdbcore.h" |
27 | #include "frame.h" | |
faf5f7ad | 28 | |
a52e6aac SB |
29 | /* For arm_linux_skip_solib_resolver. */ |
30 | #include "symtab.h" | |
31 | #include "symfile.h" | |
32 | #include "objfiles.h" | |
33 | ||
2a451106 KB |
34 | /* FIXME: Put in common header file shared between arm-tdep.c and |
35 | arm-linux-tdep.c */ | |
36 | int arm_pc_is_thumb (CORE_ADDR memaddr); | |
37 | ||
faf5f7ad SB |
38 | #ifdef GET_LONGJMP_TARGET |
39 | ||
40 | /* Figure out where the longjmp will land. We expect that we have | |
41 | just entered longjmp and haven't yet altered r0, r1, so the | |
42 | arguments are still in the registers. (A1_REGNUM) points at the | |
43 | jmp_buf structure from which we extract the pc (JB_PC) that we will | |
44 | land at. The pc is copied into ADDR. This routine returns true on | |
45 | success. */ | |
46 | ||
47 | #define LONGJMP_TARGET_SIZE sizeof(int) | |
48 | #define JB_ELEMENT_SIZE sizeof(int) | |
49 | #define JB_SL 18 | |
50 | #define JB_FP 19 | |
51 | #define JB_SP 20 | |
52 | #define JB_PC 21 | |
53 | ||
54 | int | |
55 | arm_get_longjmp_target (CORE_ADDR * pc) | |
56 | { | |
57 | CORE_ADDR jb_addr; | |
58 | char buf[LONGJMP_TARGET_SIZE]; | |
59 | ||
60 | jb_addr = read_register (A1_REGNUM); | |
61 | ||
62 | if (target_read_memory (jb_addr + JB_PC * JB_ELEMENT_SIZE, buf, | |
63 | LONGJMP_TARGET_SIZE)) | |
64 | return 0; | |
65 | ||
66 | *pc = extract_address (buf, LONGJMP_TARGET_SIZE); | |
67 | return 1; | |
68 | } | |
69 | ||
70 | #endif /* GET_LONGJMP_TARGET */ | |
71 | ||
72 | /* Extract from an array REGBUF containing the (raw) register state | |
73 | a function return value of type TYPE, and copy that, in virtual format, | |
74 | into VALBUF. */ | |
75 | ||
76 | void | |
77 | arm_linux_extract_return_value (struct type *type, | |
78 | char regbuf[REGISTER_BYTES], | |
79 | char *valbuf) | |
80 | { | |
81 | /* ScottB: This needs to be looked at to handle the different | |
82 | floating point emulators on ARM Linux. Right now the code | |
83 | assumes that fetch inferior registers does the right thing for | |
84 | GDB. I suspect this won't handle NWFPE registers correctly, nor | |
85 | will the default ARM version (arm_extract_return_value()). */ | |
86 | ||
87 | int regnum = (TYPE_CODE_FLT == TYPE_CODE (type)) ? F0_REGNUM : A1_REGNUM; | |
88 | memcpy (valbuf, ®buf[REGISTER_BYTE (regnum)], TYPE_LENGTH (type)); | |
89 | } | |
90 | ||
134e61c4 SB |
91 | /* Note: ScottB |
92 | ||
93 | This function does not support passing parameters using the FPA | |
94 | variant of the APCS. It passes any floating point arguments in the | |
95 | general registers and/or on the stack. | |
96 | ||
97 | FIXME: This and arm_push_arguments should be merged. However this | |
98 | function breaks on a little endian host, big endian target | |
99 | using the COFF file format. ELF is ok. | |
100 | ||
101 | ScottB. */ | |
102 | ||
103 | /* Addresses for calling Thumb functions have the bit 0 set. | |
104 | Here are some macros to test, set, or clear bit 0 of addresses. */ | |
105 | #define IS_THUMB_ADDR(addr) ((addr) & 1) | |
106 | #define MAKE_THUMB_ADDR(addr) ((addr) | 1) | |
107 | #define UNMAKE_THUMB_ADDR(addr) ((addr) & ~1) | |
108 | ||
109 | CORE_ADDR | |
110 | arm_linux_push_arguments (int nargs, value_ptr * args, CORE_ADDR sp, | |
111 | int struct_return, CORE_ADDR struct_addr) | |
112 | { | |
113 | char *fp; | |
114 | int argnum, argreg, nstack_size; | |
115 | ||
116 | /* Walk through the list of args and determine how large a temporary | |
117 | stack is required. Need to take care here as structs may be | |
118 | passed on the stack, and we have to to push them. */ | |
119 | nstack_size = -4 * REGISTER_SIZE; /* Some arguments go into A1-A4. */ | |
120 | ||
121 | if (struct_return) /* The struct address goes in A1. */ | |
122 | nstack_size += REGISTER_SIZE; | |
123 | ||
124 | /* Walk through the arguments and add their size to nstack_size. */ | |
125 | for (argnum = 0; argnum < nargs; argnum++) | |
126 | { | |
127 | int len; | |
128 | struct type *arg_type; | |
129 | ||
130 | arg_type = check_typedef (VALUE_TYPE (args[argnum])); | |
131 | len = TYPE_LENGTH (arg_type); | |
132 | ||
133 | /* ANSI C code passes float arguments as integers, K&R code | |
134 | passes float arguments as doubles. Correct for this here. */ | |
135 | if (TYPE_CODE_FLT == TYPE_CODE (arg_type) && REGISTER_SIZE == len) | |
136 | nstack_size += FP_REGISTER_VIRTUAL_SIZE; | |
137 | else | |
138 | nstack_size += len; | |
139 | } | |
140 | ||
141 | /* Allocate room on the stack, and initialize our stack frame | |
142 | pointer. */ | |
143 | fp = NULL; | |
144 | if (nstack_size > 0) | |
145 | { | |
146 | sp -= nstack_size; | |
147 | fp = (char *) sp; | |
148 | } | |
149 | ||
150 | /* Initialize the integer argument register pointer. */ | |
151 | argreg = A1_REGNUM; | |
152 | ||
153 | /* The struct_return pointer occupies the first parameter passing | |
154 | register. */ | |
155 | if (struct_return) | |
156 | write_register (argreg++, struct_addr); | |
157 | ||
158 | /* Process arguments from left to right. Store as many as allowed | |
159 | in the parameter passing registers (A1-A4), and save the rest on | |
160 | the temporary stack. */ | |
161 | for (argnum = 0; argnum < nargs; argnum++) | |
162 | { | |
163 | int len; | |
164 | char *val; | |
165 | double dbl_arg; | |
166 | CORE_ADDR regval; | |
167 | enum type_code typecode; | |
168 | struct type *arg_type, *target_type; | |
169 | ||
170 | arg_type = check_typedef (VALUE_TYPE (args[argnum])); | |
171 | target_type = TYPE_TARGET_TYPE (arg_type); | |
172 | len = TYPE_LENGTH (arg_type); | |
173 | typecode = TYPE_CODE (arg_type); | |
174 | val = (char *) VALUE_CONTENTS (args[argnum]); | |
175 | ||
176 | /* ANSI C code passes float arguments as integers, K&R code | |
177 | passes float arguments as doubles. The .stabs record for | |
178 | for ANSI prototype floating point arguments records the | |
179 | type as FP_INTEGER, while a K&R style (no prototype) | |
180 | .stabs records the type as FP_FLOAT. In this latter case | |
181 | the compiler converts the float arguments to double before | |
182 | calling the function. */ | |
183 | if (TYPE_CODE_FLT == typecode && REGISTER_SIZE == len) | |
184 | { | |
185 | /* Float argument in buffer is in host format. Read it and | |
186 | convert to DOUBLEST, and store it in target double. */ | |
187 | DOUBLEST dblval; | |
188 | ||
189 | len = TARGET_DOUBLE_BIT / TARGET_CHAR_BIT; | |
190 | floatformat_to_doublest (HOST_FLOAT_FORMAT, val, &dblval); | |
191 | store_floating (&dbl_arg, len, dblval); | |
192 | val = (char *) &dbl_arg; | |
193 | } | |
194 | ||
195 | /* If the argument is a pointer to a function, and it is a Thumb | |
196 | function, set the low bit of the pointer. */ | |
197 | if (TYPE_CODE_PTR == typecode | |
198 | && NULL != target_type | |
199 | && TYPE_CODE_FUNC == TYPE_CODE (target_type)) | |
200 | { | |
201 | CORE_ADDR regval = extract_address (val, len); | |
202 | if (arm_pc_is_thumb (regval)) | |
203 | store_address (val, len, MAKE_THUMB_ADDR (regval)); | |
204 | } | |
205 | ||
206 | /* Copy the argument to general registers or the stack in | |
207 | register-sized pieces. Large arguments are split between | |
208 | registers and stack. */ | |
209 | while (len > 0) | |
210 | { | |
211 | int partial_len = len < REGISTER_SIZE ? len : REGISTER_SIZE; | |
212 | ||
213 | if (argreg <= ARM_LAST_ARG_REGNUM) | |
214 | { | |
215 | /* It's an argument being passed in a general register. */ | |
216 | regval = extract_address (val, partial_len); | |
217 | write_register (argreg++, regval); | |
218 | } | |
219 | else | |
220 | { | |
221 | /* Push the arguments onto the stack. */ | |
222 | write_memory ((CORE_ADDR) fp, val, REGISTER_SIZE); | |
223 | fp += REGISTER_SIZE; | |
224 | } | |
225 | ||
226 | len -= partial_len; | |
227 | val += partial_len; | |
228 | } | |
229 | } | |
230 | ||
231 | /* Return adjusted stack pointer. */ | |
232 | return sp; | |
233 | } | |
234 | ||
f38e884d SB |
235 | /* |
236 | Dynamic Linking on ARM Linux | |
237 | ---------------------------- | |
238 | ||
239 | Note: PLT = procedure linkage table | |
240 | GOT = global offset table | |
241 | ||
242 | As much as possible, ELF dynamic linking defers the resolution of | |
243 | jump/call addresses until the last minute. The technique used is | |
244 | inspired by the i386 ELF design, and is based on the following | |
245 | constraints. | |
246 | ||
247 | 1) The calling technique should not force a change in the assembly | |
248 | code produced for apps; it MAY cause changes in the way assembly | |
249 | code is produced for position independent code (i.e. shared | |
250 | libraries). | |
251 | ||
252 | 2) The technique must be such that all executable areas must not be | |
253 | modified; and any modified areas must not be executed. | |
254 | ||
255 | To do this, there are three steps involved in a typical jump: | |
256 | ||
257 | 1) in the code | |
258 | 2) through the PLT | |
259 | 3) using a pointer from the GOT | |
260 | ||
261 | When the executable or library is first loaded, each GOT entry is | |
262 | initialized to point to the code which implements dynamic name | |
263 | resolution and code finding. This is normally a function in the | |
264 | program interpreter (on ARM Linux this is usually ld-linux.so.2, | |
265 | but it does not have to be). On the first invocation, the function | |
266 | is located and the GOT entry is replaced with the real function | |
267 | address. Subsequent calls go through steps 1, 2 and 3 and end up | |
268 | calling the real code. | |
269 | ||
270 | 1) In the code: | |
271 | ||
272 | b function_call | |
273 | bl function_call | |
274 | ||
275 | This is typical ARM code using the 26 bit relative branch or branch | |
276 | and link instructions. The target of the instruction | |
277 | (function_call is usually the address of the function to be called. | |
278 | In position independent code, the target of the instruction is | |
279 | actually an entry in the PLT when calling functions in a shared | |
280 | library. Note that this call is identical to a normal function | |
281 | call, only the target differs. | |
282 | ||
283 | 2) In the PLT: | |
284 | ||
285 | The PLT is a synthetic area, created by the linker. It exists in | |
286 | both executables and libraries. It is an array of stubs, one per | |
287 | imported function call. It looks like this: | |
288 | ||
289 | PLT[0]: | |
290 | str lr, [sp, #-4]! @push the return address (lr) | |
291 | ldr lr, [pc, #16] @load from 6 words ahead | |
292 | add lr, pc, lr @form an address for GOT[0] | |
293 | ldr pc, [lr, #8]! @jump to the contents of that addr | |
294 | ||
295 | The return address (lr) is pushed on the stack and used for | |
296 | calculations. The load on the second line loads the lr with | |
297 | &GOT[3] - . - 20. The addition on the third leaves: | |
298 | ||
299 | lr = (&GOT[3] - . - 20) + (. + 8) | |
300 | lr = (&GOT[3] - 12) | |
301 | lr = &GOT[0] | |
302 | ||
303 | On the fourth line, the pc and lr are both updated, so that: | |
304 | ||
305 | pc = GOT[2] | |
306 | lr = &GOT[0] + 8 | |
307 | = &GOT[2] | |
308 | ||
309 | NOTE: PLT[0] borrows an offset .word from PLT[1]. This is a little | |
310 | "tight", but allows us to keep all the PLT entries the same size. | |
311 | ||
312 | PLT[n+1]: | |
313 | ldr ip, [pc, #4] @load offset from gotoff | |
314 | add ip, pc, ip @add the offset to the pc | |
315 | ldr pc, [ip] @jump to that address | |
316 | gotoff: .word GOT[n+3] - . | |
317 | ||
318 | The load on the first line, gets an offset from the fourth word of | |
319 | the PLT entry. The add on the second line makes ip = &GOT[n+3], | |
320 | which contains either a pointer to PLT[0] (the fixup trampoline) or | |
321 | a pointer to the actual code. | |
322 | ||
323 | 3) In the GOT: | |
324 | ||
325 | The GOT contains helper pointers for both code (PLT) fixups and | |
326 | data fixups. The first 3 entries of the GOT are special. The next | |
327 | M entries (where M is the number of entries in the PLT) belong to | |
328 | the PLT fixups. The next D (all remaining) entries belong to | |
329 | various data fixups. The actual size of the GOT is 3 + M + D. | |
330 | ||
331 | The GOT is also a synthetic area, created by the linker. It exists | |
332 | in both executables and libraries. When the GOT is first | |
333 | initialized , all the GOT entries relating to PLT fixups are | |
334 | pointing to code back at PLT[0]. | |
335 | ||
336 | The special entries in the GOT are: | |
337 | ||
338 | GOT[0] = linked list pointer used by the dynamic loader | |
339 | GOT[1] = pointer to the reloc table for this module | |
340 | GOT[2] = pointer to the fixup/resolver code | |
341 | ||
342 | The first invocation of function call comes through and uses the | |
343 | fixup/resolver code. On the entry to the fixup/resolver code: | |
344 | ||
345 | ip = &GOT[n+3] | |
346 | lr = &GOT[2] | |
347 | stack[0] = return address (lr) of the function call | |
348 | [r0, r1, r2, r3] are still the arguments to the function call | |
349 | ||
350 | This is enough information for the fixup/resolver code to work | |
351 | with. Before the fixup/resolver code returns, it actually calls | |
352 | the requested function and repairs &GOT[n+3]. */ | |
353 | ||
a52e6aac SB |
354 | /* Find the minimal symbol named NAME, and return both the minsym |
355 | struct and its objfile. This probably ought to be in minsym.c, but | |
356 | everything there is trying to deal with things like C++ and | |
357 | SOFUN_ADDRESS_MAYBE_TURQUOISE, ... Since this is so simple, it may | |
358 | be considered too special-purpose for general consumption. */ | |
359 | ||
360 | static struct minimal_symbol * | |
361 | find_minsym_and_objfile (char *name, struct objfile **objfile_p) | |
362 | { | |
363 | struct objfile *objfile; | |
364 | ||
365 | ALL_OBJFILES (objfile) | |
366 | { | |
367 | struct minimal_symbol *msym; | |
368 | ||
369 | ALL_OBJFILE_MSYMBOLS (objfile, msym) | |
370 | { | |
371 | if (SYMBOL_NAME (msym) | |
372 | && STREQ (SYMBOL_NAME (msym), name)) | |
373 | { | |
374 | *objfile_p = objfile; | |
375 | return msym; | |
376 | } | |
377 | } | |
378 | } | |
379 | ||
380 | return 0; | |
381 | } | |
382 | ||
383 | ||
384 | static CORE_ADDR | |
385 | skip_hurd_resolver (CORE_ADDR pc) | |
386 | { | |
387 | /* The HURD dynamic linker is part of the GNU C library, so many | |
388 | GNU/Linux distributions use it. (All ELF versions, as far as I | |
389 | know.) An unresolved PLT entry points to "_dl_runtime_resolve", | |
390 | which calls "fixup" to patch the PLT, and then passes control to | |
391 | the function. | |
392 | ||
393 | We look for the symbol `_dl_runtime_resolve', and find `fixup' in | |
394 | the same objfile. If we are at the entry point of `fixup', then | |
395 | we set a breakpoint at the return address (at the top of the | |
396 | stack), and continue. | |
397 | ||
398 | It's kind of gross to do all these checks every time we're | |
399 | called, since they don't change once the executable has gotten | |
400 | started. But this is only a temporary hack --- upcoming versions | |
401 | of Linux will provide a portable, efficient interface for | |
402 | debugging programs that use shared libraries. */ | |
403 | ||
404 | struct objfile *objfile; | |
405 | struct minimal_symbol *resolver | |
406 | = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile); | |
407 | ||
408 | if (resolver) | |
409 | { | |
410 | struct minimal_symbol *fixup | |
411 | = lookup_minimal_symbol ("fixup", 0, objfile); | |
412 | ||
413 | if (fixup && SYMBOL_VALUE_ADDRESS (fixup) == pc) | |
414 | return (SAVED_PC_AFTER_CALL (get_current_frame ())); | |
415 | } | |
416 | ||
417 | return 0; | |
418 | } | |
419 | ||
420 | /* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c. | |
421 | This function: | |
422 | 1) decides whether a PLT has sent us into the linker to resolve | |
423 | a function reference, and | |
424 | 2) if so, tells us where to set a temporary breakpoint that will | |
425 | trigger when the dynamic linker is done. */ | |
426 | ||
f38e884d | 427 | CORE_ADDR |
a52e6aac | 428 | arm_linux_skip_solib_resolver (CORE_ADDR pc) |
f38e884d | 429 | { |
a52e6aac SB |
430 | CORE_ADDR result; |
431 | ||
432 | /* Plug in functions for other kinds of resolvers here. */ | |
433 | result = skip_hurd_resolver (pc); | |
2a451106 | 434 | printf ("Result = 0x%08lx\n", result); |
a52e6aac SB |
435 | if (result) |
436 | return result; | |
437 | ||
438 | ||
f38e884d SB |
439 | return 0; |
440 | } | |
441 | ||
2a451106 KB |
442 | /* The constants below were determined by examining the following files |
443 | in the linux kernel sources: | |
444 | ||
445 | arch/arm/kernel/signal.c | |
446 | - see SWI_SYS_SIGRETURN and SWI_SYS_RT_SIGRETURN | |
447 | include/asm-arm/unistd.h | |
448 | - see __NR_sigreturn, __NR_rt_sigreturn, and __NR_SYSCALL_BASE */ | |
449 | ||
450 | #define ARM_LINUX_SIGRETURN_INSTR 0xef900077 | |
451 | #define ARM_LINUX_RT_SIGRETURN_INSTR 0xef9000ad | |
452 | ||
453 | /* arm_linux_in_sigtramp determines if PC points at one of the | |
454 | instructions which cause control to return to the Linux kernel upon | |
455 | return from a signal handler. FUNC_NAME is unused. */ | |
456 | ||
457 | int | |
458 | arm_linux_in_sigtramp (CORE_ADDR pc, char *func_name) | |
459 | { | |
460 | unsigned long inst; | |
461 | ||
462 | inst = read_memory_integer (pc, 4); | |
463 | ||
464 | return (inst == ARM_LINUX_SIGRETURN_INSTR | |
465 | || inst == ARM_LINUX_RT_SIGRETURN_INSTR); | |
466 | ||
467 | } | |
468 | ||
469 | /* arm_linux_sigcontext_register_address returns the address in the | |
470 | sigcontext of register REGNO given a stack pointer value SP and | |
471 | program counter value PC. The value 0 is returned if PC is not | |
472 | pointing at one of the signal return instructions or if REGNO is | |
473 | not saved in the sigcontext struct. */ | |
474 | ||
475 | CORE_ADDR | |
476 | arm_linux_sigcontext_register_address (CORE_ADDR sp, CORE_ADDR pc, int regno) | |
477 | { | |
478 | unsigned long inst; | |
479 | CORE_ADDR reg_addr = 0; | |
480 | ||
481 | inst = read_memory_integer (pc, 4); | |
482 | ||
483 | if (inst == ARM_LINUX_SIGRETURN_INSTR || inst == ARM_LINUX_RT_SIGRETURN_INSTR) | |
484 | { | |
485 | CORE_ADDR sigcontext_addr; | |
486 | ||
487 | /* The sigcontext structure is at different places for the two | |
488 | signal return instructions. For ARM_LINUX_SIGRETURN_INSTR, | |
489 | it starts at the SP value. For ARM_LINUX_RT_SIGRETURN_INSTR, | |
490 | it is at SP+8. For the latter instruction, it may also be | |
491 | the case that the address of this structure may be determined | |
492 | by reading the 4 bytes at SP, but I'm not convinced this is | |
493 | reliable. | |
494 | ||
495 | In any event, these magic constants (0 and 8) may be | |
496 | determined by examining struct sigframe and struct | |
497 | rt_sigframe in arch/arm/kernel/signal.c in the Linux kernel | |
498 | sources. */ | |
499 | ||
500 | if (inst == ARM_LINUX_RT_SIGRETURN_INSTR) | |
501 | sigcontext_addr = sp + 8; | |
502 | else /* inst == ARM_LINUX_SIGRETURN_INSTR */ | |
503 | sigcontext_addr = sp + 0; | |
504 | ||
505 | /* The layout of the sigcontext structure for ARM GNU/Linux is | |
506 | in include/asm-arm/sigcontext.h in the Linux kernel sources. | |
507 | ||
508 | There are three 4-byte fields which precede the saved r0 | |
509 | field. (This accounts for the 12 in the code below.) The | |
510 | sixteen registers (4 bytes per field) follow in order. The | |
511 | PSR value follows the sixteen registers which accounts for | |
512 | the constant 19 below. */ | |
513 | ||
514 | if (0 <= regno && regno <= PC_REGNUM) | |
515 | reg_addr = sigcontext_addr + 12 + (4 * regno); | |
516 | else if (regno == PS_REGNUM) | |
517 | reg_addr = sigcontext_addr + 19 * 4; | |
518 | } | |
519 | ||
520 | return reg_addr; | |
521 | } | |
522 | ||
faf5f7ad SB |
523 | void |
524 | _initialize_arm_linux_tdep (void) | |
525 | { | |
526 | } |