/* GNU/Linux on ARM target support.
- Copyright 1999, 2000 Free Software Foundation, Inc.
+ Copyright 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
This file is part of GDB.
#include "value.h"
#include "gdbtypes.h"
#include "floatformat.h"
+#include "gdbcore.h"
+#include "frame.h"
+#include "regcache.h"
+#include "doublest.h"
-#ifdef GET_LONGJMP_TARGET
+#include "arm-tdep.h"
-/* 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. */
+/* For shared library handling. */
+#include "symtab.h"
+#include "symfile.h"
+#include "objfiles.h"
-#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
+/* 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. Since ARM GNU/Linux is little
+ endian, and doesn't support Thumb at the moment we only override
+ the ARM little-endian breakpoint. */
-int
-arm_get_longjmp_target (CORE_ADDR * pc)
-{
- CORE_ADDR jb_addr;
- char buf[LONGJMP_TARGET_SIZE];
+static const char arm_linux_arm_le_breakpoint[] = {0x01,0x00,0x9f,0xef};
- jb_addr = read_register (A1_REGNUM);
+/* CALL_DUMMY_WORDS:
+ This sequence of words is the instructions
- if (target_read_memory (jb_addr + JB_PC * JB_ELEMENT_SIZE, buf,
- LONGJMP_TARGET_SIZE))
- return 0;
+ mov lr, pc
+ mov pc, r4
+ swi bkpt_swi
- *pc = extract_address (buf, LONGJMP_TARGET_SIZE);
- return 1;
-}
+ Note this is 12 bytes. */
+
+LONGEST arm_linux_call_dummy_words[] =
+{
+ 0xe1a0e00f, 0xe1a0f004, 0xef9f001
+};
-#endif /* GET_LONGJMP_TARGET */
+/* Description of the longjmp buffer. */
+#define ARM_LINUX_JB_ELEMENT_SIZE INT_REGISTER_RAW_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. */
-
-void
+/* 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[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
+ 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)) ? F0_REGNUM : A1_REGNUM;
+ int regnum = ((TYPE_CODE_FLT == TYPE_CODE (type))
+ ? ARM_F0_REGNUM : ARM_A1_REGNUM);
memcpy (valbuf, ®buf[REGISTER_BYTE (regnum)], TYPE_LENGTH (type));
}
#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,
+static CORE_ADDR
+arm_linux_push_arguments (int nargs, struct value **args, CORE_ADDR sp,
int struct_return, CORE_ADDR struct_addr)
{
char *fp;
}
/* Initialize the integer argument register pointer. */
- argreg = A1_REGNUM;
+ argreg = ARM_A1_REGNUM;
/* The struct_return pointer occupies the first parameter passing
register. */
{
int len;
char *val;
- double dbl_arg;
CORE_ADDR regval;
enum type_code typecode;
struct type *arg_type, *target_type;
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;
-
+ dblval = extract_floating (val, len);
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;
+ val = alloca (len);
+ store_floating (val, len, dblval);
}
/* If the argument is a pointer to a function, and it is a Thumb
return sp;
}
+/*
+ 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]. */
+
+/* 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)
+ && strcmp (SYMBOL_NAME (msym), name) == 0)
+ {
+ *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
+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);
+
+ if (result)
+ return result;
+
+ return 0;
+}
+
+/* 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;
+ tdep->arm_breakpoint = arm_linux_arm_le_breakpoint;
+ tdep->arm_breakpoint_size = sizeof (arm_linux_arm_le_breakpoint);
+
+ tdep->jb_pc = ARM_LINUX_JB_PC;
+ tdep->jb_elt_size = ARM_LINUX_JB_ELEMENT_SIZE;
+
+ set_gdbarch_call_dummy_words (gdbarch, arm_linux_call_dummy_words);
+ set_gdbarch_sizeof_call_dummy_words (gdbarch,
+ sizeof (arm_linux_call_dummy_words));
+
+ /* The following two overrides shouldn't be needed. */
+ set_gdbarch_extract_return_value (gdbarch, arm_linux_extract_return_value);
+ set_gdbarch_push_arguments (gdbarch, arm_linux_push_arguments);
+
+ /* Shared library handling. */
+ set_gdbarch_in_solib_call_trampoline (gdbarch, in_plt_section);
+ set_gdbarch_skip_trampoline_code (gdbarch, find_solib_trampoline_target);
+}
+
void
_initialize_arm_linux_tdep (void)
{
+ gdbarch_register_osabi (bfd_arch_arm, GDB_OSABI_LINUX, arm_linux_init_abi);
}