1 /* GNU/Linux on ARM target support.
2 Copyright 1999, 2000 Free Software Foundation, Inc.
4 This file is part of GDB.
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.
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.
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. */
25 #include "floatformat.h"
27 /* For arm_linux_skip_solib_resolver. */
32 #ifdef GET_LONGJMP_TARGET
34 /* Figure out where the longjmp will land. We expect that we have
35 just entered longjmp and haven't yet altered r0, r1, so the
36 arguments are still in the registers. (A1_REGNUM) points at the
37 jmp_buf structure from which we extract the pc (JB_PC) that we will
38 land at. The pc is copied into ADDR. This routine returns true on
41 #define LONGJMP_TARGET_SIZE sizeof(int)
42 #define JB_ELEMENT_SIZE sizeof(int)
49 arm_get_longjmp_target (CORE_ADDR
* pc
)
52 char buf
[LONGJMP_TARGET_SIZE
];
54 jb_addr
= read_register (A1_REGNUM
);
56 if (target_read_memory (jb_addr
+ JB_PC
* JB_ELEMENT_SIZE
, buf
,
60 *pc
= extract_address (buf
, LONGJMP_TARGET_SIZE
);
64 #endif /* GET_LONGJMP_TARGET */
66 /* Extract from an array REGBUF containing the (raw) register state
67 a function return value of type TYPE, and copy that, in virtual format,
71 arm_linux_extract_return_value (struct type
*type
,
72 char regbuf
[REGISTER_BYTES
],
75 /* ScottB: This needs to be looked at to handle the different
76 floating point emulators on ARM Linux. Right now the code
77 assumes that fetch inferior registers does the right thing for
78 GDB. I suspect this won't handle NWFPE registers correctly, nor
79 will the default ARM version (arm_extract_return_value()). */
81 int regnum
= (TYPE_CODE_FLT
== TYPE_CODE (type
)) ? F0_REGNUM
: A1_REGNUM
;
82 memcpy (valbuf
, ®buf
[REGISTER_BYTE (regnum
)], TYPE_LENGTH (type
));
87 This function does not support passing parameters using the FPA
88 variant of the APCS. It passes any floating point arguments in the
89 general registers and/or on the stack.
91 FIXME: This and arm_push_arguments should be merged. However this
92 function breaks on a little endian host, big endian target
93 using the COFF file format. ELF is ok.
97 /* Addresses for calling Thumb functions have the bit 0 set.
98 Here are some macros to test, set, or clear bit 0 of addresses. */
99 #define IS_THUMB_ADDR(addr) ((addr) & 1)
100 #define MAKE_THUMB_ADDR(addr) ((addr) | 1)
101 #define UNMAKE_THUMB_ADDR(addr) ((addr) & ~1)
104 arm_linux_push_arguments (int nargs
, value_ptr
* args
, CORE_ADDR sp
,
105 int struct_return
, CORE_ADDR struct_addr
)
108 int argnum
, argreg
, nstack_size
;
110 /* Walk through the list of args and determine how large a temporary
111 stack is required. Need to take care here as structs may be
112 passed on the stack, and we have to to push them. */
113 nstack_size
= -4 * REGISTER_SIZE
; /* Some arguments go into A1-A4. */
115 if (struct_return
) /* The struct address goes in A1. */
116 nstack_size
+= REGISTER_SIZE
;
118 /* Walk through the arguments and add their size to nstack_size. */
119 for (argnum
= 0; argnum
< nargs
; argnum
++)
122 struct type
*arg_type
;
124 arg_type
= check_typedef (VALUE_TYPE (args
[argnum
]));
125 len
= TYPE_LENGTH (arg_type
);
127 /* ANSI C code passes float arguments as integers, K&R code
128 passes float arguments as doubles. Correct for this here. */
129 if (TYPE_CODE_FLT
== TYPE_CODE (arg_type
) && REGISTER_SIZE
== len
)
130 nstack_size
+= FP_REGISTER_VIRTUAL_SIZE
;
135 /* Allocate room on the stack, and initialize our stack frame
144 /* Initialize the integer argument register pointer. */
147 /* The struct_return pointer occupies the first parameter passing
150 write_register (argreg
++, struct_addr
);
152 /* Process arguments from left to right. Store as many as allowed
153 in the parameter passing registers (A1-A4), and save the rest on
154 the temporary stack. */
155 for (argnum
= 0; argnum
< nargs
; argnum
++)
161 enum type_code typecode
;
162 struct type
*arg_type
, *target_type
;
164 arg_type
= check_typedef (VALUE_TYPE (args
[argnum
]));
165 target_type
= TYPE_TARGET_TYPE (arg_type
);
166 len
= TYPE_LENGTH (arg_type
);
167 typecode
= TYPE_CODE (arg_type
);
168 val
= (char *) VALUE_CONTENTS (args
[argnum
]);
170 /* ANSI C code passes float arguments as integers, K&R code
171 passes float arguments as doubles. The .stabs record for
172 for ANSI prototype floating point arguments records the
173 type as FP_INTEGER, while a K&R style (no prototype)
174 .stabs records the type as FP_FLOAT. In this latter case
175 the compiler converts the float arguments to double before
176 calling the function. */
177 if (TYPE_CODE_FLT
== typecode
&& REGISTER_SIZE
== len
)
179 /* Float argument in buffer is in host format. Read it and
180 convert to DOUBLEST, and store it in target double. */
183 len
= TARGET_DOUBLE_BIT
/ TARGET_CHAR_BIT
;
184 floatformat_to_doublest (HOST_FLOAT_FORMAT
, val
, &dblval
);
185 store_floating (&dbl_arg
, len
, dblval
);
186 val
= (char *) &dbl_arg
;
189 /* If the argument is a pointer to a function, and it is a Thumb
190 function, set the low bit of the pointer. */
191 if (TYPE_CODE_PTR
== typecode
192 && NULL
!= target_type
193 && TYPE_CODE_FUNC
== TYPE_CODE (target_type
))
195 CORE_ADDR regval
= extract_address (val
, len
);
196 if (arm_pc_is_thumb (regval
))
197 store_address (val
, len
, MAKE_THUMB_ADDR (regval
));
200 /* Copy the argument to general registers or the stack in
201 register-sized pieces. Large arguments are split between
202 registers and stack. */
205 int partial_len
= len
< REGISTER_SIZE
? len
: REGISTER_SIZE
;
207 if (argreg
<= ARM_LAST_ARG_REGNUM
)
209 /* It's an argument being passed in a general register. */
210 regval
= extract_address (val
, partial_len
);
211 write_register (argreg
++, regval
);
215 /* Push the arguments onto the stack. */
216 write_memory ((CORE_ADDR
) fp
, val
, REGISTER_SIZE
);
225 /* Return adjusted stack pointer. */
230 Dynamic Linking on ARM Linux
231 ----------------------------
233 Note: PLT = procedure linkage table
234 GOT = global offset table
236 As much as possible, ELF dynamic linking defers the resolution of
237 jump/call addresses until the last minute. The technique used is
238 inspired by the i386 ELF design, and is based on the following
241 1) The calling technique should not force a change in the assembly
242 code produced for apps; it MAY cause changes in the way assembly
243 code is produced for position independent code (i.e. shared
246 2) The technique must be such that all executable areas must not be
247 modified; and any modified areas must not be executed.
249 To do this, there are three steps involved in a typical jump:
253 3) using a pointer from the GOT
255 When the executable or library is first loaded, each GOT entry is
256 initialized to point to the code which implements dynamic name
257 resolution and code finding. This is normally a function in the
258 program interpreter (on ARM Linux this is usually ld-linux.so.2,
259 but it does not have to be). On the first invocation, the function
260 is located and the GOT entry is replaced with the real function
261 address. Subsequent calls go through steps 1, 2 and 3 and end up
262 calling the real code.
269 This is typical ARM code using the 26 bit relative branch or branch
270 and link instructions. The target of the instruction
271 (function_call is usually the address of the function to be called.
272 In position independent code, the target of the instruction is
273 actually an entry in the PLT when calling functions in a shared
274 library. Note that this call is identical to a normal function
275 call, only the target differs.
279 The PLT is a synthetic area, created by the linker. It exists in
280 both executables and libraries. It is an array of stubs, one per
281 imported function call. It looks like this:
284 str lr, [sp, #-4]! @push the return address (lr)
285 ldr lr, [pc, #16] @load from 6 words ahead
286 add lr, pc, lr @form an address for GOT[0]
287 ldr pc, [lr, #8]! @jump to the contents of that addr
289 The return address (lr) is pushed on the stack and used for
290 calculations. The load on the second line loads the lr with
291 &GOT[3] - . - 20. The addition on the third leaves:
293 lr = (&GOT[3] - . - 20) + (. + 8)
297 On the fourth line, the pc and lr are both updated, so that:
303 NOTE: PLT[0] borrows an offset .word from PLT[1]. This is a little
304 "tight", but allows us to keep all the PLT entries the same size.
307 ldr ip, [pc, #4] @load offset from gotoff
308 add ip, pc, ip @add the offset to the pc
309 ldr pc, [ip] @jump to that address
310 gotoff: .word GOT[n+3] - .
312 The load on the first line, gets an offset from the fourth word of
313 the PLT entry. The add on the second line makes ip = &GOT[n+3],
314 which contains either a pointer to PLT[0] (the fixup trampoline) or
315 a pointer to the actual code.
319 The GOT contains helper pointers for both code (PLT) fixups and
320 data fixups. The first 3 entries of the GOT are special. The next
321 M entries (where M is the number of entries in the PLT) belong to
322 the PLT fixups. The next D (all remaining) entries belong to
323 various data fixups. The actual size of the GOT is 3 + M + D.
325 The GOT is also a synthetic area, created by the linker. It exists
326 in both executables and libraries. When the GOT is first
327 initialized , all the GOT entries relating to PLT fixups are
328 pointing to code back at PLT[0].
330 The special entries in the GOT are:
332 GOT[0] = linked list pointer used by the dynamic loader
333 GOT[1] = pointer to the reloc table for this module
334 GOT[2] = pointer to the fixup/resolver code
336 The first invocation of function call comes through and uses the
337 fixup/resolver code. On the entry to the fixup/resolver code:
341 stack[0] = return address (lr) of the function call
342 [r0, r1, r2, r3] are still the arguments to the function call
344 This is enough information for the fixup/resolver code to work
345 with. Before the fixup/resolver code returns, it actually calls
346 the requested function and repairs &GOT[n+3]. */
348 /* Find the minimal symbol named NAME, and return both the minsym
349 struct and its objfile. This probably ought to be in minsym.c, but
350 everything there is trying to deal with things like C++ and
351 SOFUN_ADDRESS_MAYBE_TURQUOISE, ... Since this is so simple, it may
352 be considered too special-purpose for general consumption. */
354 static struct minimal_symbol
*
355 find_minsym_and_objfile (char *name
, struct objfile
**objfile_p
)
357 struct objfile
*objfile
;
359 ALL_OBJFILES (objfile
)
361 struct minimal_symbol
*msym
;
363 ALL_OBJFILE_MSYMBOLS (objfile
, msym
)
365 if (SYMBOL_NAME (msym
)
366 && STREQ (SYMBOL_NAME (msym
), name
))
368 *objfile_p
= objfile
;
379 skip_hurd_resolver (CORE_ADDR pc
)
381 /* The HURD dynamic linker is part of the GNU C library, so many
382 GNU/Linux distributions use it. (All ELF versions, as far as I
383 know.) An unresolved PLT entry points to "_dl_runtime_resolve",
384 which calls "fixup" to patch the PLT, and then passes control to
387 We look for the symbol `_dl_runtime_resolve', and find `fixup' in
388 the same objfile. If we are at the entry point of `fixup', then
389 we set a breakpoint at the return address (at the top of the
390 stack), and continue.
392 It's kind of gross to do all these checks every time we're
393 called, since they don't change once the executable has gotten
394 started. But this is only a temporary hack --- upcoming versions
395 of Linux will provide a portable, efficient interface for
396 debugging programs that use shared libraries. */
398 struct objfile
*objfile
;
399 struct minimal_symbol
*resolver
400 = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile
);
404 struct minimal_symbol
*fixup
405 = lookup_minimal_symbol ("fixup", 0, objfile
);
407 if (fixup
&& SYMBOL_VALUE_ADDRESS (fixup
) == pc
)
408 return (SAVED_PC_AFTER_CALL (get_current_frame ()));
414 /* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c.
416 1) decides whether a PLT has sent us into the linker to resolve
417 a function reference, and
418 2) if so, tells us where to set a temporary breakpoint that will
419 trigger when the dynamic linker is done. */
422 arm_linux_skip_solib_resolver (CORE_ADDR pc
)
426 /* Plug in functions for other kinds of resolvers here. */
427 result
= skip_hurd_resolver (pc
);
428 printf ("Result = 0x%08x\n");
437 _initialize_arm_linux_tdep (void)
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