+\f
+/* Displaced instruction handling. */
+
+
+static int
+i386_absolute_jmp_p (gdb_byte *insn)
+{
+ /* jmp far (absolute address in operand) */
+ if (insn[0] == 0xea)
+ return 1;
+
+ if (insn[0] == 0xff)
+ {
+ /* jump near, absolute indirect (/4) */
+ if ((insn[1] & 0x38) == 0x20)
+ return 1;
+
+ /* jump far, absolute indirect (/5) */
+ if ((insn[1] & 0x38) == 0x28)
+ return 1;
+ }
+
+ return 0;
+}
+
+static int
+i386_absolute_call_p (gdb_byte *insn)
+{
+ /* call far, absolute */
+ if (insn[0] == 0x9a)
+ return 1;
+
+ if (insn[0] == 0xff)
+ {
+ /* Call near, absolute indirect (/2) */
+ if ((insn[1] & 0x38) == 0x10)
+ return 1;
+
+ /* Call far, absolute indirect (/3) */
+ if ((insn[1] & 0x38) == 0x18)
+ return 1;
+ }
+
+ return 0;
+}
+
+static int
+i386_ret_p (gdb_byte *insn)
+{
+ switch (insn[0])
+ {
+ case 0xc2: /* ret near, pop N bytes */
+ case 0xc3: /* ret near */
+ case 0xca: /* ret far, pop N bytes */
+ case 0xcb: /* ret far */
+ case 0xcf: /* iret */
+ return 1;
+
+ default:
+ return 0;
+ }
+}
+
+static int
+i386_call_p (gdb_byte *insn)
+{
+ if (i386_absolute_call_p (insn))
+ return 1;
+
+ /* call near, relative */
+ if (insn[0] == 0xe8)
+ return 1;
+
+ return 0;
+}
+
+static int
+i386_breakpoint_p (gdb_byte *insn)
+{
+ return insn[0] == 0xcc; /* int 3 */
+}
+
+/* Return non-zero if INSN is a system call, and set *LENGTHP to its
+ length in bytes. Otherwise, return zero. */
+static int
+i386_syscall_p (gdb_byte *insn, ULONGEST *lengthp)
+{
+ if (insn[0] == 0xcd)
+ {
+ *lengthp = 2;
+ return 1;
+ }
+
+ return 0;
+}
+
+/* Fix up the state of registers and memory after having single-stepped
+ a displaced instruction. */
+void
+i386_displaced_step_fixup (struct gdbarch *gdbarch,
+ struct displaced_step_closure *closure,
+ CORE_ADDR from, CORE_ADDR to,
+ struct regcache *regs)
+{
+ /* The offset we applied to the instruction's address.
+ This could well be negative (when viewed as a signed 32-bit
+ value), but ULONGEST won't reflect that, so take care when
+ applying it. */
+ ULONGEST insn_offset = to - from;
+
+ /* Since we use simple_displaced_step_copy_insn, our closure is a
+ copy of the instruction. */
+ gdb_byte *insn = (gdb_byte *) closure;
+
+ if (debug_displaced)
+ fprintf_unfiltered (gdb_stdlog,
+ "displaced: fixup (0x%s, 0x%s), "
+ "insn = 0x%02x 0x%02x ...\n",
+ paddr_nz (from), paddr_nz (to), insn[0], insn[1]);
+
+ /* The list of issues to contend with here is taken from
+ resume_execution in arch/i386/kernel/kprobes.c, Linux 2.6.20.
+ Yay for Free Software! */
+
+ /* Relocate the %eip, if necessary. */
+
+ /* Except in the case of absolute or indirect jump or call
+ instructions, or a return instruction, the new eip is relative to
+ the displaced instruction; make it relative. Well, signal
+ handler returns don't need relocation either, but we use the
+ value of %eip to recognize those; see below. */
+ if (! i386_absolute_jmp_p (insn)
+ && ! i386_absolute_call_p (insn)
+ && ! i386_ret_p (insn))
+ {
+ ULONGEST orig_eip;
+ ULONGEST insn_len;
+
+ regcache_cooked_read_unsigned (regs, I386_EIP_REGNUM, &orig_eip);
+
+ /* A signal trampoline system call changes the %eip, resuming
+ execution of the main program after the signal handler has
+ returned. That makes them like 'return' instructions; we
+ shouldn't relocate %eip.
+
+ But most system calls don't, and we do need to relocate %eip.
+
+ Our heuristic for distinguishing these cases: if stepping
+ over the system call instruction left control directly after
+ the instruction, the we relocate --- control almost certainly
+ doesn't belong in the displaced copy. Otherwise, we assume
+ the instruction has put control where it belongs, and leave
+ it unrelocated. Goodness help us if there are PC-relative
+ system calls. */
+ if (i386_syscall_p (insn, &insn_len)
+ && orig_eip != to + insn_len)
+ {
+ if (debug_displaced)
+ fprintf_unfiltered (gdb_stdlog,
+ "displaced: syscall changed %%eip; "
+ "not relocating\n");
+ }
+ else
+ {
+ ULONGEST eip = (orig_eip - insn_offset) & 0xffffffffUL;
+
+ /* If we have stepped over a breakpoint, set the %eip to
+ point at the breakpoint instruction itself.
+
+ (gdbarch_decr_pc_after_break was never something the core
+ of GDB should have been concerned with; arch-specific
+ code should be making PC values consistent before
+ presenting them to GDB.) */
+ if (i386_breakpoint_p (insn))
+ {
+ if (debug_displaced)
+ fprintf_unfiltered (gdb_stdlog,
+ "displaced: stepped breakpoint\n");
+ eip--;
+ }
+
+ regcache_cooked_write_unsigned (regs, I386_EIP_REGNUM, eip);
+
+ if (debug_displaced)
+ fprintf_unfiltered (gdb_stdlog,
+ "displaced: "
+ "relocated %%eip from 0x%s to 0x%s\n",
+ paddr_nz (orig_eip), paddr_nz (eip));
+ }
+ }
+
+ /* If the instruction was PUSHFL, then the TF bit will be set in the
+ pushed value, and should be cleared. We'll leave this for later,
+ since GDB already messes up the TF flag when stepping over a
+ pushfl. */
+
+ /* If the instruction was a call, the return address now atop the
+ stack is the address following the copied instruction. We need
+ to make it the address following the original instruction. */
+ if (i386_call_p (insn))
+ {
+ ULONGEST esp;
+ ULONGEST retaddr;
+ const ULONGEST retaddr_len = 4;
+
+ regcache_cooked_read_unsigned (regs, I386_ESP_REGNUM, &esp);
+ retaddr = read_memory_unsigned_integer (esp, retaddr_len);
+ retaddr = (retaddr - insn_offset) & 0xffffffffUL;
+ write_memory_unsigned_integer (esp, retaddr_len, retaddr);
+
+ if (debug_displaced)
+ fprintf_unfiltered (gdb_stdlog,
+ "displaced: relocated return addr at 0x%s "
+ "to 0x%s\n",
+ paddr_nz (esp),
+ paddr_nz (retaddr));
+ }
+}
+
+
projects / binutils-gdb.git / blobdiff