| /* GNU/Linux on ARM target support. |
| |
| Copyright 1999, 2000, 2001, 2002, 2003, 2005 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" |
| #include "gdbcore.h" |
| #include "frame.h" |
| #include "regcache.h" |
| #include "doublest.h" |
| #include "solib-svr4.h" |
| #include "osabi.h" |
| |
| #include "arm-tdep.h" |
| #include "glibc-tdep.h" |
| |
| /* Under ARM GNU/Linux the traditional way of performing a breakpoint |
| is to execute a particular software interrupt, rather than use a |
| particular undefined instruction to provoke a trap. Upon exection |
| of the software interrupt the kernel stops the inferior with a |
| SIGTRAP, and wakes the debugger. */ |
| |
| static const char arm_linux_arm_le_breakpoint[] = { 0x01, 0x00, 0x9f, 0xef }; |
| |
| static const char arm_linux_arm_be_breakpoint[] = { 0xef, 0x9f, 0x00, 0x01 }; |
| |
| static const char arm_linux_thumb_be_breakpoint[] = {0xde, 0x01}; |
| |
| static const char arm_linux_thumb_le_breakpoint[] = {0x01, 0xde}; |
| |
| /* Description of the longjmp buffer. */ |
| #define ARM_LINUX_JB_ELEMENT_SIZE INT_REGISTER_SIZE |
| #define ARM_LINUX_JB_PC 21 |
| |
| /* 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. */ |
| /* FIXME rearnsha/2002-02-23: This function shouldn't be necessary. |
| The ARM generic one should be able to handle the model used by |
| linux and the low-level formatting of the registers should be |
| hidden behind the regcache abstraction. */ |
| static void |
| arm_linux_extract_return_value (struct type *type, |
| char regbuf[], |
| char *valbuf) |
| { |
| /* ScottB: This needs to be looked at to handle the different |
| floating point emulators on ARM GNU/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)) |
| ? ARM_F0_REGNUM : ARM_A1_REGNUM); |
| memcpy (valbuf, ®buf[DEPRECATED_REGISTER_BYTE (regnum)], TYPE_LENGTH (type)); |
| } |
| |
| /* |
| Dynamic Linking on ARM GNU/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 GNU/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]. */ |
| |
| /* Fetch, and possibly build, an appropriate link_map_offsets structure |
| for ARM linux targets using the struct offsets defined in <link.h>. |
| Note, however, that link.h is not actually referred to in this file. |
| Instead, the relevant structs offsets were obtained from examining |
| link.h. (We can't refer to link.h from this file because the host |
| system won't necessarily have it, or if it does, the structs which |
| it defines will refer to the host system, not the target). */ |
| |
| static struct link_map_offsets * |
| arm_linux_svr4_fetch_link_map_offsets (void) |
| { |
| static struct link_map_offsets lmo; |
| static struct link_map_offsets *lmp = 0; |
| |
| if (lmp == 0) |
| { |
| lmp = &lmo; |
| |
| lmo.r_debug_size = 8; /* Actual size is 20, but this is all we |
| need. */ |
| |
| lmo.r_map_offset = 4; |
| lmo.r_map_size = 4; |
| |
| lmo.link_map_size = 20; /* Actual size is 552, but this is all we |
| need. */ |
| |
| lmo.l_addr_offset = 0; |
| lmo.l_addr_size = 4; |
| |
| lmo.l_name_offset = 4; |
| lmo.l_name_size = 4; |
| |
| lmo.l_next_offset = 12; |
| lmo.l_next_size = 4; |
| |
| lmo.l_prev_offset = 16; |
| lmo.l_prev_size = 4; |
| } |
| |
| return lmp; |
| } |
| |
| /* The constants below were determined by examining the following files |
| in the linux kernel sources: |
| |
| arch/arm/kernel/signal.c |
| - see SWI_SYS_SIGRETURN and SWI_SYS_RT_SIGRETURN |
| include/asm-arm/unistd.h |
| - see __NR_sigreturn, __NR_rt_sigreturn, and __NR_SYSCALL_BASE */ |
| |
| #define ARM_LINUX_SIGRETURN_INSTR 0xef900077 |
| #define ARM_LINUX_RT_SIGRETURN_INSTR 0xef9000ad |
| |
| /* arm_linux_in_sigtramp determines if PC points at one of the |
| instructions which cause control to return to the Linux kernel upon |
| return from a signal handler. FUNC_NAME is unused. */ |
| |
| int |
| arm_linux_in_sigtramp (CORE_ADDR pc, char *func_name) |
| { |
| unsigned long inst; |
| |
| inst = read_memory_integer (pc, 4); |
| |
| return (inst == ARM_LINUX_SIGRETURN_INSTR |
| || inst == ARM_LINUX_RT_SIGRETURN_INSTR); |
| |
| } |
| |
| /* arm_linux_sigcontext_register_address returns the address in the |
| sigcontext of register REGNO given a stack pointer value SP and |
| program counter value PC. The value 0 is returned if PC is not |
| pointing at one of the signal return instructions or if REGNO is |
| not saved in the sigcontext struct. */ |
| |
| CORE_ADDR |
| arm_linux_sigcontext_register_address (CORE_ADDR sp, CORE_ADDR pc, int regno) |
| { |
| unsigned long inst; |
| CORE_ADDR reg_addr = 0; |
| |
| inst = read_memory_integer (pc, 4); |
| |
| if (inst == ARM_LINUX_SIGRETURN_INSTR |
| || inst == ARM_LINUX_RT_SIGRETURN_INSTR) |
| { |
| CORE_ADDR sigcontext_addr; |
| |
| /* The sigcontext structure is at different places for the two |
| signal return instructions. For ARM_LINUX_SIGRETURN_INSTR, |
| it starts at the SP value. For ARM_LINUX_RT_SIGRETURN_INSTR, |
| it is at SP+8. For the latter instruction, it may also be |
| the case that the address of this structure may be determined |
| by reading the 4 bytes at SP, but I'm not convinced this is |
| reliable. |
| |
| In any event, these magic constants (0 and 8) may be |
| determined by examining struct sigframe and struct |
| rt_sigframe in arch/arm/kernel/signal.c in the Linux kernel |
| sources. */ |
| |
| if (inst == ARM_LINUX_RT_SIGRETURN_INSTR) |
| sigcontext_addr = sp + 8; |
| else /* inst == ARM_LINUX_SIGRETURN_INSTR */ |
| sigcontext_addr = sp + 0; |
| |
| /* The layout of the sigcontext structure for ARM GNU/Linux is |
| in include/asm-arm/sigcontext.h in the Linux kernel sources. |
| |
| There are three 4-byte fields which precede the saved r0 |
| field. (This accounts for the 12 in the code below.) The |
| sixteen registers (4 bytes per field) follow in order. The |
| PSR value follows the sixteen registers which accounts for |
| the constant 19 below. */ |
| |
| if (0 <= regno && regno <= ARM_PC_REGNUM) |
| reg_addr = sigcontext_addr + 12 + (4 * regno); |
| else if (regno == ARM_PS_REGNUM) |
| reg_addr = sigcontext_addr + 19 * 4; |
| } |
| |
| return reg_addr; |
| } |
| |
| static void |
| arm_linux_init_abi (struct gdbarch_info info, |
| struct gdbarch *gdbarch) |
| { |
| struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch); |
| |
| tdep->lowest_pc = 0x8000; |
| if (info.byte_order == BFD_ENDIAN_BIG) |
| { |
| tdep->arm_breakpoint = arm_linux_arm_be_breakpoint; |
| tdep->thumb_breakpoint = arm_linux_thumb_be_breakpoint; |
| } |
| else |
| { |
| tdep->arm_breakpoint = arm_linux_arm_le_breakpoint; |
| tdep->thumb_breakpoint = arm_linux_thumb_le_breakpoint; |
| } |
| tdep->arm_breakpoint_size = sizeof (arm_linux_arm_le_breakpoint); |
| tdep->thumb_breakpoint_size = sizeof (arm_linux_thumb_le_breakpoint); |
| |
| if (tdep->fp_model == ARM_FLOAT_AUTO) |
| tdep->fp_model = ARM_FLOAT_FPA; |
| |
| tdep->jb_pc = ARM_LINUX_JB_PC; |
| tdep->jb_elt_size = ARM_LINUX_JB_ELEMENT_SIZE; |
| |
| set_solib_svr4_fetch_link_map_offsets |
| (gdbarch, arm_linux_svr4_fetch_link_map_offsets); |
| |
| /* The following override shouldn't be needed. */ |
| set_gdbarch_deprecated_extract_return_value (gdbarch, arm_linux_extract_return_value); |
| |
| /* Shared library handling. */ |
| set_gdbarch_skip_trampoline_code (gdbarch, find_solib_trampoline_target); |
| set_gdbarch_skip_solib_resolver (gdbarch, glibc_skip_solib_resolver); |
| |
| /* Enable TLS support. */ |
| set_gdbarch_fetch_tls_load_module_address (gdbarch, |
| svr4_fetch_objfile_link_map); |
| } |
| |
| void |
| _initialize_arm_linux_tdep (void) |
| { |
| gdbarch_register_osabi (bfd_arch_arm, 0, GDB_OSABI_LINUX, |
| arm_linux_init_abi); |
| } |
