Add skipi command to skip N instructions (#964)

docs/commands/skipi.md

@@ -0,0 +1,18 @@
+## Command `skipi`
+
+The `skipi` command allows you to easily skip instructions execution.
+
+```
+skipi [LOCATION] [--n NUM_INSTRUCTIONS]
+```
+
+`LOCATION` address/symbol from where to skip (default is `$pc`)
+
+`--n NUM_INSTRUCTIONS` Skip the specified number of instructions instead of the default 1.
+
+```bash
+gef➤ 	skipi
+gef➤ 	skipi --n 3
+gef➤ 	skipi 0x69696969
+gef➤ 	skipi 0x69696969 --n 6
+```

gef.py

@@ -5985,6 +5985,40 @@ def do_invoke(self, _: List[str], **kwargs: Any) -> None:
         return
 
 
+@register
+class SkipiCommand(GenericCommand):
+    """Skip N instruction(s) execution"""
+
+    _cmdline_ = "skipi"
+    _syntax_  = ("{_cmdline_} [LOCATION] [--n NUM_INSTRUCTIONS]"
+                "\n\tLOCATION\taddress/symbol from where to skip"
+                 "\t--n NUM_INSTRUCTIONS\tSkip the specified number of instructions instead of the default 1.")
+
+    _example_ = [f"{_cmdline_}",
+                 f"{_cmdline_} --n 3",
+                 f"{_cmdline_} 0x69696969",
+                 f"{_cmdline_} 0x69696969 --n 6",]
+
+    def __init__(self) -> None:
+        super().__init__(complete=gdb.COMPLETE_LOCATION)
+        return
+
+    @only_if_gdb_running
+    @parse_arguments({"address": "$pc"}, {"--n": 1})
+    def do_invoke(self, _: List[str], **kwargs: Any) -> None:
+        args : argparse.Namespace = kwargs["arguments"]
+        address = parse_address(args.address)
+        num_instructions = args.n
+
+        last_addr = gdb_get_nth_next_instruction_address(address, num_instructions)
+        total_bytes = (last_addr - address) + gef_get_instruction_at(last_addr).size()
+        target_addr  = address + total_bytes
+
+        info(f"skipping {num_instructions} instructions ({total_bytes} bytes) from {address:#x} to {target_addr:#x}")
+        gdb.execute(f"set $pc = {target_addr:#x}")
+        return
+
+
 @register
 class NopCommand(GenericCommand):
     """Patch the instruction(s) pointed by parameters with NOP. Note: this command is architecture

tests/commands/skipi.py

@@ -0,0 +1,63 @@
+"""
+`skipi` command test module
+"""
+
+import pytest
+
+from tests.utils import (ARCH, GefUnitTestGeneric, _target, findlines,
+                         gdb_run_cmd, gdb_run_silent_cmd, gdb_start_silent_cmd)
+
+
+class SkipiCommand(GefUnitTestGeneric):
+    """`skipi` command test module"""
+
+
+    cmd = "skipi"
+
+
+    def test_cmd_nop_inactive(self):
+        res = gdb_run_cmd(f"{self.cmd}")
+        self.assertFailIfInactiveSession(res)
+
+
+    @pytest.mark.skipif(ARCH not in ("i686", "x86_64"), reason=f"Skipped for {ARCH}")
+    def test_cmd_skipi_no_arg(self):
+
+        res = gdb_start_silent_cmd(
+            "pi gef.memory.write(gef.arch.pc, p32(0x9090feeb))", # 1 short jumps to pc + 2 nops
+            after=(
+                self.cmd,
+                "pi print(gef.memory.read(gef.arch.pc, 2))", # read 2 bytes
+            )
+        )
+        self.assertNoException(res)
+        self.assertIn(r"\x90\x90", res) # 2 nops
+
+
+    @pytest.mark.skipif(ARCH not in ("i686", "x86_64"), reason=f"Skipped for {ARCH}")
+    def test_cmd_skipi_skip_two_instructions(self):
+
+        res = gdb_start_silent_cmd(
+            "pi gef.memory.write(gef.arch.pc, p64(0x90909090feebfeeb))", # 2 short jumps to pc + 4 nops
+            after=(
+                f"{self.cmd} --n 2",
+                "pi print(gef.memory.read(gef.arch.pc, 4))", # read 4 bytes
+            )
+        )
+        self.assertNoException(res)
+        self.assertIn(r"\x90\x90\x90\x90", res) # 4 nops
+
+
+    @pytest.mark.skipif(ARCH not in ("i686", "x86_64"), reason=f"Skipped for {ARCH}")
+    def test_cmd_skipi_two_instructions_from_location(self):
+
+        res = gdb_start_silent_cmd(
+            "pi gef.memory.write(gef.arch.pc, p64(0x9090feebfeebfeeb))", # 2 short jumps to pc + 2 nops
+            after=(
+                f"{self.cmd} $pc+2 --n 2", # from the second short jump
+                "pi print(gef.memory.read(gef.arch.pc, 2))", # read 2 bytes
+            )
+        )
+        self.assertNoException(res)
+        self.assertIn(r"\x90\x90", res) # 2 nops
+