| /* Target-dependent code for GNU/Linux running on i386's, for GDB. |
| |
| Copyright 2000, 2001, 2002 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 "gdbcore.h" |
| #include "frame.h" |
| #include "value.h" |
| #include "regcache.h" |
| #include "inferior.h" |
| |
| /* For i386_linux_skip_solib_resolver. */ |
| #include "symtab.h" |
| #include "symfile.h" |
| #include "objfiles.h" |
| |
| #include "solib-svr4.h" /* For struct link_map_offsets. */ |
| |
| /* Return the name of register REG. */ |
| |
| char * |
| i386_linux_register_name (int reg) |
| { |
| /* Deal with the extra "orig_eax" pseudo register. */ |
| if (reg == I386_LINUX_ORIG_EAX_REGNUM) |
| return "orig_eax"; |
| |
| return i386_register_name (reg); |
| } |
| |
| int |
| i386_linux_register_byte (int reg) |
| { |
| /* Deal with the extra "orig_eax" pseudo register. */ |
| if (reg == I386_LINUX_ORIG_EAX_REGNUM) |
| return (i386_register_byte (I386_LINUX_ORIG_EAX_REGNUM - 1) |
| + i386_register_raw_size (I386_LINUX_ORIG_EAX_REGNUM - 1)); |
| |
| return i386_register_byte (reg); |
| } |
| |
| int |
| i386_linux_register_raw_size (int reg) |
| { |
| /* Deal with the extra "orig_eax" pseudo register. */ |
| if (reg == I386_LINUX_ORIG_EAX_REGNUM) |
| return 4; |
| |
| return i386_register_raw_size (reg); |
| } |
| |
| /* Recognizing signal handler frames. */ |
| |
| /* GNU/Linux has two flavors of signals. Normal signal handlers, and |
| "realtime" (RT) signals. The RT signals can provide additional |
| information to the signal handler if the SA_SIGINFO flag is set |
| when establishing a signal handler using `sigaction'. It is not |
| unlikely that future versions of GNU/Linux will support SA_SIGINFO |
| for normal signals too. */ |
| |
| /* When the i386 Linux kernel calls a signal handler and the |
| SA_RESTORER flag isn't set, the return address points to a bit of |
| code on the stack. This function returns whether the PC appears to |
| be within this bit of code. |
| |
| The instruction sequence for normal signals is |
| pop %eax |
| mov $0x77,%eax |
| int $0x80 |
| or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80. |
| |
| Checking for the code sequence should be somewhat reliable, because |
| the effect is to call the system call sigreturn. This is unlikely |
| to occur anywhere other than a signal trampoline. |
| |
| It kind of sucks that we have to read memory from the process in |
| order to identify a signal trampoline, but there doesn't seem to be |
| any other way. The PC_IN_SIGTRAMP macro in tm-linux.h arranges to |
| only call us if no function name could be identified, which should |
| be the case since the code is on the stack. |
| |
| Detection of signal trampolines for handlers that set the |
| SA_RESTORER flag is in general not possible. Unfortunately this is |
| what the GNU C Library has been doing for quite some time now. |
| However, as of version 2.1.2, the GNU C Library uses signal |
| trampolines (named __restore and __restore_rt) that are identical |
| to the ones used by the kernel. Therefore, these trampolines are |
| supported too. */ |
| |
| #define LINUX_SIGTRAMP_INSN0 (0x58) /* pop %eax */ |
| #define LINUX_SIGTRAMP_OFFSET0 (0) |
| #define LINUX_SIGTRAMP_INSN1 (0xb8) /* mov $NNNN,%eax */ |
| #define LINUX_SIGTRAMP_OFFSET1 (1) |
| #define LINUX_SIGTRAMP_INSN2 (0xcd) /* int */ |
| #define LINUX_SIGTRAMP_OFFSET2 (6) |
| |
| static const unsigned char linux_sigtramp_code[] = |
| { |
| LINUX_SIGTRAMP_INSN0, /* pop %eax */ |
| LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00, /* mov $0x77,%eax */ |
| LINUX_SIGTRAMP_INSN2, 0x80 /* int $0x80 */ |
| }; |
| |
| #define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code) |
| |
| /* If PC is in a sigtramp routine, return the address of the start of |
| the routine. Otherwise, return 0. */ |
| |
| static CORE_ADDR |
| i386_linux_sigtramp_start (CORE_ADDR pc) |
| { |
| unsigned char buf[LINUX_SIGTRAMP_LEN]; |
| |
| /* We only recognize a signal trampoline if PC is at the start of |
| one of the three instructions. We optimize for finding the PC at |
| the start, as will be the case when the trampoline is not the |
| first frame on the stack. We assume that in the case where the |
| PC is not at the start of the instruction sequence, there will be |
| a few trailing readable bytes on the stack. */ |
| |
| if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) |
| return 0; |
| |
| if (buf[0] != LINUX_SIGTRAMP_INSN0) |
| { |
| int adjust; |
| |
| switch (buf[0]) |
| { |
| case LINUX_SIGTRAMP_INSN1: |
| adjust = LINUX_SIGTRAMP_OFFSET1; |
| break; |
| case LINUX_SIGTRAMP_INSN2: |
| adjust = LINUX_SIGTRAMP_OFFSET2; |
| break; |
| default: |
| return 0; |
| } |
| |
| pc -= adjust; |
| |
| if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) |
| return 0; |
| } |
| |
| if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0) |
| return 0; |
| |
| return pc; |
| } |
| |
| /* This function does the same for RT signals. Here the instruction |
| sequence is |
| mov $0xad,%eax |
| int $0x80 |
| or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80. |
| |
| The effect is to call the system call rt_sigreturn. */ |
| |
| #define LINUX_RT_SIGTRAMP_INSN0 (0xb8) /* mov $NNNN,%eax */ |
| #define LINUX_RT_SIGTRAMP_OFFSET0 (0) |
| #define LINUX_RT_SIGTRAMP_INSN1 (0xcd) /* int */ |
| #define LINUX_RT_SIGTRAMP_OFFSET1 (5) |
| |
| static const unsigned char linux_rt_sigtramp_code[] = |
| { |
| LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00, /* mov $0xad,%eax */ |
| LINUX_RT_SIGTRAMP_INSN1, 0x80 /* int $0x80 */ |
| }; |
| |
| #define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code) |
| |
| /* If PC is in a RT sigtramp routine, return the address of the start |
| of the routine. Otherwise, return 0. */ |
| |
| static CORE_ADDR |
| i386_linux_rt_sigtramp_start (CORE_ADDR pc) |
| { |
| unsigned char buf[LINUX_RT_SIGTRAMP_LEN]; |
| |
| /* We only recognize a signal trampoline if PC is at the start of |
| one of the two instructions. We optimize for finding the PC at |
| the start, as will be the case when the trampoline is not the |
| first frame on the stack. We assume that in the case where the |
| PC is not at the start of the instruction sequence, there will be |
| a few trailing readable bytes on the stack. */ |
| |
| if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) |
| return 0; |
| |
| if (buf[0] != LINUX_RT_SIGTRAMP_INSN0) |
| { |
| if (buf[0] != LINUX_RT_SIGTRAMP_INSN1) |
| return 0; |
| |
| pc -= LINUX_RT_SIGTRAMP_OFFSET1; |
| |
| if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) |
| return 0; |
| } |
| |
| if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0) |
| return 0; |
| |
| return pc; |
| } |
| |
| /* Return whether PC is in a GNU/Linux sigtramp routine. */ |
| |
| int |
| i386_linux_in_sigtramp (CORE_ADDR pc, char *name) |
| { |
| if (name) |
| return STREQ ("__restore", name) || STREQ ("__restore_rt", name); |
| |
| return (i386_linux_sigtramp_start (pc) != 0 |
| || i386_linux_rt_sigtramp_start (pc) != 0); |
| } |
| |
| /* Assuming FRAME is for a GNU/Linux sigtramp routine, return the |
| address of the associated sigcontext structure. */ |
| |
| CORE_ADDR |
| i386_linux_sigcontext_addr (struct frame_info *frame) |
| { |
| CORE_ADDR pc; |
| |
| pc = i386_linux_sigtramp_start (frame->pc); |
| if (pc) |
| { |
| CORE_ADDR sp; |
| |
| if (frame->next) |
| /* If this isn't the top frame, the next frame must be for the |
| signal handler itself. The sigcontext structure lives on |
| the stack, right after the signum argument. */ |
| return frame->next->frame + 12; |
| |
| /* This is the top frame. We'll have to find the address of the |
| sigcontext structure by looking at the stack pointer. Keep |
| in mind that the first instruction of the sigtramp code is |
| "pop %eax". If the PC is at this instruction, adjust the |
| returned value accordingly. */ |
| sp = read_register (SP_REGNUM); |
| if (pc == frame->pc) |
| return sp + 4; |
| return sp; |
| } |
| |
| pc = i386_linux_rt_sigtramp_start (frame->pc); |
| if (pc) |
| { |
| if (frame->next) |
| /* If this isn't the top frame, the next frame must be for the |
| signal handler itself. The sigcontext structure is part of |
| the user context. A pointer to the user context is passed |
| as the third argument to the signal handler. */ |
| return read_memory_integer (frame->next->frame + 16, 4) + 20; |
| |
| /* This is the top frame. Again, use the stack pointer to find |
| the address of the sigcontext structure. */ |
| return read_memory_integer (read_register (SP_REGNUM) + 8, 4) + 20; |
| } |
| |
| error ("Couldn't recognize signal trampoline."); |
| return 0; |
| } |
| |
| /* Offset to saved PC in sigcontext, from <asm/sigcontext.h>. */ |
| #define LINUX_SIGCONTEXT_PC_OFFSET (56) |
| |
| /* Assuming FRAME is for a GNU/Linux sigtramp routine, return the |
| saved program counter. */ |
| |
| static CORE_ADDR |
| i386_linux_sigtramp_saved_pc (struct frame_info *frame) |
| { |
| CORE_ADDR addr; |
| addr = i386_linux_sigcontext_addr (frame); |
| return read_memory_integer (addr + LINUX_SIGCONTEXT_PC_OFFSET, 4); |
| } |
| |
| /* Offset to saved SP in sigcontext, from <asm/sigcontext.h>. */ |
| #define LINUX_SIGCONTEXT_SP_OFFSET (28) |
| |
| /* Assuming FRAME is for a GNU/Linux sigtramp routine, return the |
| saved stack pointer. */ |
| |
| static CORE_ADDR |
| i386_linux_sigtramp_saved_sp (struct frame_info *frame) |
| { |
| CORE_ADDR addr; |
| addr = i386_linux_sigcontext_addr (frame); |
| return read_memory_integer (addr + LINUX_SIGCONTEXT_SP_OFFSET, 4); |
| } |
| |
| /* Signal trampolines don't have a meaningful frame. As in |
| "i386/tm-i386.h", the frame pointer value we use is actually the |
| frame pointer of the calling frame -- that is, the frame which was |
| in progress when the signal trampoline was entered. GDB mostly |
| treats this frame pointer value as a magic cookie. We detect the |
| case of a signal trampoline by looking at the SIGNAL_HANDLER_CALLER |
| field, which is set based on PC_IN_SIGTRAMP. |
| |
| When a signal trampoline is invoked from a frameless function, we |
| essentially have two frameless functions in a row. In this case, |
| we use the same magic cookie for three frames in a row. We detect |
| this case by seeing whether the next frame has |
| SIGNAL_HANDLER_CALLER set, and, if it does, checking whether the |
| current frame is actually frameless. In this case, we need to get |
| the PC by looking at the SP register value stored in the signal |
| context. |
| |
| This should work in most cases except in horrible situations where |
| a signal occurs just as we enter a function but before the frame |
| has been set up. */ |
| |
| #define FRAMELESS_SIGNAL(frame) \ |
| ((frame)->next != NULL \ |
| && (frame)->next->signal_handler_caller \ |
| && frameless_look_for_prologue (frame)) |
| |
| CORE_ADDR |
| i386_linux_frame_chain (struct frame_info *frame) |
| { |
| if (frame->signal_handler_caller || FRAMELESS_SIGNAL (frame)) |
| return frame->frame; |
| |
| if (! inside_entry_file (frame->pc)) |
| return read_memory_unsigned_integer (frame->frame, 4); |
| |
| return 0; |
| } |
| |
| /* Return the saved program counter for FRAME. */ |
| |
| CORE_ADDR |
| i386_linux_frame_saved_pc (struct frame_info *frame) |
| { |
| if (frame->signal_handler_caller) |
| return i386_linux_sigtramp_saved_pc (frame); |
| |
| if (FRAMELESS_SIGNAL (frame)) |
| { |
| CORE_ADDR sp = i386_linux_sigtramp_saved_sp (frame->next); |
| return read_memory_unsigned_integer (sp, 4); |
| } |
| |
| return read_memory_unsigned_integer (frame->frame + 4, 4); |
| } |
| |
| /* Immediately after a function call, return the saved pc. */ |
| |
| CORE_ADDR |
| i386_linux_saved_pc_after_call (struct frame_info *frame) |
| { |
| if (frame->signal_handler_caller) |
| return i386_linux_sigtramp_saved_pc (frame); |
| |
| return read_memory_unsigned_integer (read_register (SP_REGNUM), 4); |
| } |
| |
| /* Set the program counter for process PTID to PC. */ |
| |
| void |
| i386_linux_write_pc (CORE_ADDR pc, ptid_t ptid) |
| { |
| write_register_pid (PC_REGNUM, pc, ptid); |
| |
| /* We must be careful with modifying the program counter. If we |
| just interrupted a system call, the kernel might try to restart |
| it when we resume the inferior. On restarting the system call, |
| the kernel will try backing up the program counter even though it |
| no longer points at the system call. This typically results in a |
| SIGSEGV or SIGILL. We can prevent this by writing `-1' in the |
| "orig_eax" pseudo-register. |
| |
| Note that "orig_eax" is saved when setting up a dummy call frame. |
| This means that it is properly restored when that frame is |
| popped, and that the interrupted system call will be restarted |
| when we resume the inferior on return from a function call from |
| within GDB. In all other cases the system call will not be |
| restarted. */ |
| write_register_pid (I386_LINUX_ORIG_EAX_REGNUM, -1, ptid); |
| } |
| |
| /* Calling functions in shared libraries. */ |
| |
| /* 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 GNU/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", NULL, 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 |
| i386_linux_skip_solib_resolver (CORE_ADDR pc) |
| { |
| CORE_ADDR result; |
| |
| /* Plug in functions for other kinds of resolvers here. */ |
| result = skip_hurd_resolver (pc); |
| if (result) |
| return result; |
| |
| return 0; |
| } |
| |
| /* Fetch (and possibly build) an appropriate link_map_offsets |
| structure for native GNU/Linux x86 targets using the struct offsets |
| defined in link.h (but without actual reference to that file). |
| |
| This makes it possible to access GNU/Linux x86 shared libraries |
| from a GDB that was not built on an GNU/Linux x86 host (for cross |
| debugging). */ |
| |
| struct link_map_offsets * |
| i386_linux_svr4_fetch_link_map_offsets (void) |
| { |
| static struct link_map_offsets lmo; |
| static struct link_map_offsets *lmp = NULL; |
| |
| if (lmp == NULL) |
| { |
| lmp = &lmo; |
| |
| lmo.r_debug_size = 8; /* The actual size is 20 bytes, but |
| this is all we need. */ |
| lmo.r_map_offset = 4; |
| lmo.r_map_size = 4; |
| |
| lmo.link_map_size = 20; /* The actual size is 552 bytes, 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; |
| } |