| /* GNU/Linux on ARM target support. |
| Copyright 1999, 2000 Free Software Foundation, Inc. |
| |
| This file is part of GDB. |
| |
| This program is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2 of the License, or |
| (at your option) any later version. |
| |
| This program is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| GNU General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with this program; if not, write to the Free Software |
| Foundation, Inc., 59 Temple Place - Suite 330, |
| Boston, MA 02111-1307, USA. */ |
| |
| #include "defs.h" |
| #include "target.h" |
| #include "value.h" |
| #include "gdbtypes.h" |
| #include "floatformat.h" |
| |
| /* For arm_linux_skip_solib_resolver. */ |
| #include "symtab.h" |
| #include "symfile.h" |
| #include "objfiles.h" |
| |
| #ifdef GET_LONGJMP_TARGET |
| |
| /* Figure out where the longjmp will land. We expect that we have |
| just entered longjmp and haven't yet altered r0, r1, so the |
| arguments are still in the registers. (A1_REGNUM) points at the |
| jmp_buf structure from which we extract the pc (JB_PC) that we will |
| land at. The pc is copied into ADDR. This routine returns true on |
| success. */ |
| |
| #define LONGJMP_TARGET_SIZE sizeof(int) |
| #define JB_ELEMENT_SIZE sizeof(int) |
| #define JB_SL 18 |
| #define JB_FP 19 |
| #define JB_SP 20 |
| #define JB_PC 21 |
| |
| int |
| arm_get_longjmp_target (CORE_ADDR * pc) |
| { |
| CORE_ADDR jb_addr; |
| char buf[LONGJMP_TARGET_SIZE]; |
| |
| jb_addr = read_register (A1_REGNUM); |
| |
| if (target_read_memory (jb_addr + JB_PC * JB_ELEMENT_SIZE, buf, |
| LONGJMP_TARGET_SIZE)) |
| return 0; |
| |
| *pc = extract_address (buf, LONGJMP_TARGET_SIZE); |
| return 1; |
| } |
| |
| #endif /* GET_LONGJMP_TARGET */ |
| |
| /* Extract from an array REGBUF containing the (raw) register state |
| a function return value of type TYPE, and copy that, in virtual format, |
| into VALBUF. */ |
| |
| void |
| arm_linux_extract_return_value (struct type *type, |
| char regbuf[REGISTER_BYTES], |
| char *valbuf) |
| { |
| /* ScottB: This needs to be looked at to handle the different |
| floating point emulators on ARM Linux. Right now the code |
| assumes that fetch inferior registers does the right thing for |
| GDB. I suspect this won't handle NWFPE registers correctly, nor |
| will the default ARM version (arm_extract_return_value()). */ |
| |
| int regnum = (TYPE_CODE_FLT == TYPE_CODE (type)) ? F0_REGNUM : A1_REGNUM; |
| memcpy (valbuf, ®buf[REGISTER_BYTE (regnum)], TYPE_LENGTH (type)); |
| } |
| |
| /* Note: ScottB |
| |
| This function does not support passing parameters using the FPA |
| variant of the APCS. It passes any floating point arguments in the |
| general registers and/or on the stack. |
| |
| FIXME: This and arm_push_arguments should be merged. However this |
| function breaks on a little endian host, big endian target |
| using the COFF file format. ELF is ok. |
| |
| ScottB. */ |
| |
| /* Addresses for calling Thumb functions have the bit 0 set. |
| Here are some macros to test, set, or clear bit 0 of addresses. */ |
| #define IS_THUMB_ADDR(addr) ((addr) & 1) |
| #define MAKE_THUMB_ADDR(addr) ((addr) | 1) |
| #define UNMAKE_THUMB_ADDR(addr) ((addr) & ~1) |
| |
| CORE_ADDR |
| arm_linux_push_arguments (int nargs, value_ptr * args, CORE_ADDR sp, |
| int struct_return, CORE_ADDR struct_addr) |
| { |
| char *fp; |
| int argnum, argreg, nstack_size; |
| |
| /* Walk through the list of args and determine how large a temporary |
| stack is required. Need to take care here as structs may be |
| passed on the stack, and we have to to push them. */ |
| nstack_size = -4 * REGISTER_SIZE; /* Some arguments go into A1-A4. */ |
| |
| if (struct_return) /* The struct address goes in A1. */ |
| nstack_size += REGISTER_SIZE; |
| |
| /* Walk through the arguments and add their size to nstack_size. */ |
| for (argnum = 0; argnum < nargs; argnum++) |
| { |
| int len; |
| struct type *arg_type; |
| |
| arg_type = check_typedef (VALUE_TYPE (args[argnum])); |
| len = TYPE_LENGTH (arg_type); |
| |
| /* ANSI C code passes float arguments as integers, K&R code |
| passes float arguments as doubles. Correct for this here. */ |
| if (TYPE_CODE_FLT == TYPE_CODE (arg_type) && REGISTER_SIZE == len) |
| nstack_size += FP_REGISTER_VIRTUAL_SIZE; |
| else |
| nstack_size += len; |
| } |
| |
| /* Allocate room on the stack, and initialize our stack frame |
| pointer. */ |
| fp = NULL; |
| if (nstack_size > 0) |
| { |
| sp -= nstack_size; |
| fp = (char *) sp; |
| } |
| |
| /* Initialize the integer argument register pointer. */ |
| argreg = A1_REGNUM; |
| |
| /* The struct_return pointer occupies the first parameter passing |
| register. */ |
| if (struct_return) |
| write_register (argreg++, struct_addr); |
| |
| /* Process arguments from left to right. Store as many as allowed |
| in the parameter passing registers (A1-A4), and save the rest on |
| the temporary stack. */ |
| for (argnum = 0; argnum < nargs; argnum++) |
| { |
| int len; |
| char *val; |
| double dbl_arg; |
| CORE_ADDR regval; |
| enum type_code typecode; |
| struct type *arg_type, *target_type; |
| |
| arg_type = check_typedef (VALUE_TYPE (args[argnum])); |
| target_type = TYPE_TARGET_TYPE (arg_type); |
| len = TYPE_LENGTH (arg_type); |
| typecode = TYPE_CODE (arg_type); |
| val = (char *) VALUE_CONTENTS (args[argnum]); |
| |
| /* ANSI C code passes float arguments as integers, K&R code |
| passes float arguments as doubles. The .stabs record for |
| for ANSI prototype floating point arguments records the |
| type as FP_INTEGER, while a K&R style (no prototype) |
| .stabs records the type as FP_FLOAT. In this latter case |
| the compiler converts the float arguments to double before |
| calling the function. */ |
| if (TYPE_CODE_FLT == typecode && REGISTER_SIZE == len) |
| { |
| /* Float argument in buffer is in host format. Read it and |
| convert to DOUBLEST, and store it in target double. */ |
| DOUBLEST dblval; |
| |
| len = TARGET_DOUBLE_BIT / TARGET_CHAR_BIT; |
| floatformat_to_doublest (HOST_FLOAT_FORMAT, val, &dblval); |
| store_floating (&dbl_arg, len, dblval); |
| val = (char *) &dbl_arg; |
| } |
| |
| /* If the argument is a pointer to a function, and it is a Thumb |
| function, set the low bit of the pointer. */ |
| if (TYPE_CODE_PTR == typecode |
| && NULL != target_type |
| && TYPE_CODE_FUNC == TYPE_CODE (target_type)) |
| { |
| CORE_ADDR regval = extract_address (val, len); |
| if (arm_pc_is_thumb (regval)) |
| store_address (val, len, MAKE_THUMB_ADDR (regval)); |
| } |
| |
| /* Copy the argument to general registers or the stack in |
| register-sized pieces. Large arguments are split between |
| registers and stack. */ |
| while (len > 0) |
| { |
| int partial_len = len < REGISTER_SIZE ? len : REGISTER_SIZE; |
| |
| if (argreg <= ARM_LAST_ARG_REGNUM) |
| { |
| /* It's an argument being passed in a general register. */ |
| regval = extract_address (val, partial_len); |
| write_register (argreg++, regval); |
| } |
| else |
| { |
| /* Push the arguments onto the stack. */ |
| write_memory ((CORE_ADDR) fp, val, REGISTER_SIZE); |
| fp += REGISTER_SIZE; |
| } |
| |
| len -= partial_len; |
| val += partial_len; |
| } |
| } |
| |
| /* Return adjusted stack pointer. */ |
| return sp; |
| } |
| |
| /* |
| Dynamic Linking on ARM Linux |
| ---------------------------- |
| |
| Note: PLT = procedure linkage table |
| GOT = global offset table |
| |
| As much as possible, ELF dynamic linking defers the resolution of |
| jump/call addresses until the last minute. The technique used is |
| inspired by the i386 ELF design, and is based on the following |
| constraints. |
| |
| 1) The calling technique should not force a change in the assembly |
| code produced for apps; it MAY cause changes in the way assembly |
| code is produced for position independent code (i.e. shared |
| libraries). |
| |
| 2) The technique must be such that all executable areas must not be |
| modified; and any modified areas must not be executed. |
| |
| To do this, there are three steps involved in a typical jump: |
| |
| 1) in the code |
| 2) through the PLT |
| 3) using a pointer from the GOT |
| |
| When the executable or library is first loaded, each GOT entry is |
| initialized to point to the code which implements dynamic name |
| resolution and code finding. This is normally a function in the |
| program interpreter (on ARM Linux this is usually ld-linux.so.2, |
| but it does not have to be). On the first invocation, the function |
| is located and the GOT entry is replaced with the real function |
| address. Subsequent calls go through steps 1, 2 and 3 and end up |
| calling the real code. |
| |
| 1) In the code: |
| |
| b function_call |
| bl function_call |
| |
| This is typical ARM code using the 26 bit relative branch or branch |
| and link instructions. The target of the instruction |
| (function_call is usually the address of the function to be called. |
| In position independent code, the target of the instruction is |
| actually an entry in the PLT when calling functions in a shared |
| library. Note that this call is identical to a normal function |
| call, only the target differs. |
| |
| 2) In the PLT: |
| |
| The PLT is a synthetic area, created by the linker. It exists in |
| both executables and libraries. It is an array of stubs, one per |
| imported function call. It looks like this: |
| |
| PLT[0]: |
| str lr, [sp, #-4]! @push the return address (lr) |
| ldr lr, [pc, #16] @load from 6 words ahead |
| add lr, pc, lr @form an address for GOT[0] |
| ldr pc, [lr, #8]! @jump to the contents of that addr |
| |
| The return address (lr) is pushed on the stack and used for |
| calculations. The load on the second line loads the lr with |
| &GOT[3] - . - 20. The addition on the third leaves: |
| |
| lr = (&GOT[3] - . - 20) + (. + 8) |
| lr = (&GOT[3] - 12) |
| lr = &GOT[0] |
| |
| On the fourth line, the pc and lr are both updated, so that: |
| |
| pc = GOT[2] |
| lr = &GOT[0] + 8 |
| = &GOT[2] |
| |
| NOTE: PLT[0] borrows an offset .word from PLT[1]. This is a little |
| "tight", but allows us to keep all the PLT entries the same size. |
| |
| PLT[n+1]: |
| ldr ip, [pc, #4] @load offset from gotoff |
| add ip, pc, ip @add the offset to the pc |
| ldr pc, [ip] @jump to that address |
| gotoff: .word GOT[n+3] - . |
| |
| The load on the first line, gets an offset from the fourth word of |
| the PLT entry. The add on the second line makes ip = &GOT[n+3], |
| which contains either a pointer to PLT[0] (the fixup trampoline) or |
| a pointer to the actual code. |
| |
| 3) In the GOT: |
| |
| The GOT contains helper pointers for both code (PLT) fixups and |
| data fixups. The first 3 entries of the GOT are special. The next |
| M entries (where M is the number of entries in the PLT) belong to |
| the PLT fixups. The next D (all remaining) entries belong to |
| various data fixups. The actual size of the GOT is 3 + M + D. |
| |
| The GOT is also a synthetic area, created by the linker. It exists |
| in both executables and libraries. When the GOT is first |
| initialized , all the GOT entries relating to PLT fixups are |
| pointing to code back at PLT[0]. |
| |
| The special entries in the GOT are: |
| |
| GOT[0] = linked list pointer used by the dynamic loader |
| GOT[1] = pointer to the reloc table for this module |
| GOT[2] = pointer to the fixup/resolver code |
| |
| The first invocation of function call comes through and uses the |
| fixup/resolver code. On the entry to the fixup/resolver code: |
| |
| ip = &GOT[n+3] |
| lr = &GOT[2] |
| stack[0] = return address (lr) of the function call |
| [r0, r1, r2, r3] are still the arguments to the function call |
| |
| This is enough information for the fixup/resolver code to work |
| with. Before the fixup/resolver code returns, it actually calls |
| the requested function and repairs &GOT[n+3]. */ |
| |
| /* Find the minimal symbol named NAME, and return both the minsym |
| struct and its objfile. This probably ought to be in minsym.c, but |
| everything there is trying to deal with things like C++ and |
| SOFUN_ADDRESS_MAYBE_TURQUOISE, ... Since this is so simple, it may |
| be considered too special-purpose for general consumption. */ |
| |
| static struct minimal_symbol * |
| find_minsym_and_objfile (char *name, struct objfile **objfile_p) |
| { |
| struct objfile *objfile; |
| |
| ALL_OBJFILES (objfile) |
| { |
| struct minimal_symbol *msym; |
| |
| ALL_OBJFILE_MSYMBOLS (objfile, msym) |
| { |
| if (SYMBOL_NAME (msym) |
| && STREQ (SYMBOL_NAME (msym), name)) |
| { |
| *objfile_p = objfile; |
| return msym; |
| } |
| } |
| } |
| |
| return 0; |
| } |
| |
| |
| static CORE_ADDR |
| skip_hurd_resolver (CORE_ADDR pc) |
| { |
| /* The HURD dynamic linker is part of the GNU C library, so many |
| GNU/Linux distributions use it. (All ELF versions, as far as I |
| know.) An unresolved PLT entry points to "_dl_runtime_resolve", |
| which calls "fixup" to patch the PLT, and then passes control to |
| the function. |
| |
| We look for the symbol `_dl_runtime_resolve', and find `fixup' in |
| the same objfile. If we are at the entry point of `fixup', then |
| we set a breakpoint at the return address (at the top of the |
| stack), and continue. |
| |
| It's kind of gross to do all these checks every time we're |
| called, since they don't change once the executable has gotten |
| started. But this is only a temporary hack --- upcoming versions |
| of Linux will provide a portable, efficient interface for |
| debugging programs that use shared libraries. */ |
| |
| struct objfile *objfile; |
| struct minimal_symbol *resolver |
| = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile); |
| |
| if (resolver) |
| { |
| struct minimal_symbol *fixup |
| = lookup_minimal_symbol ("fixup", 0, objfile); |
| |
| if (fixup && SYMBOL_VALUE_ADDRESS (fixup) == pc) |
| return (SAVED_PC_AFTER_CALL (get_current_frame ())); |
| } |
| |
| return 0; |
| } |
| |
| /* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c. |
| This function: |
| 1) decides whether a PLT has sent us into the linker to resolve |
| a function reference, and |
| 2) if so, tells us where to set a temporary breakpoint that will |
| trigger when the dynamic linker is done. */ |
| |
| CORE_ADDR |
| arm_linux_skip_solib_resolver (CORE_ADDR pc) |
| { |
| CORE_ADDR result; |
| |
| /* Plug in functions for other kinds of resolvers here. */ |
| result = skip_hurd_resolver (pc); |
| printf ("Result = 0x%08x\n"); |
| if (result) |
| return result; |
| |
| |
| return 0; |
| } |
| |
| void |
| _initialize_arm_linux_tdep (void) |
| { |
| } |