Add support for telescope to show previous addresses #1047 (#1094)

* Added -r argument to telescope command (#1047)

* Added tests for telescope command (#1047)

pwndbg/commands/telescope.py

@@ -36,14 +36,18 @@ parser = argparse.ArgumentParser(description="""
     """)
 parser.add_argument("address", nargs="?", default=None, type=int, help="The address to telescope at.")
 parser.add_argument("count", nargs="?", default=telescope_lines, type=int, help="The number of lines to show.")
+parser.add_argument("-r", "--reverse", dest="reverse", action='store_true', default=False,
+                    help='Show <count> previous addresses instead of next ones')
+
+
 @pwndbg.commands.ArgparsedCommand(parser)
 @pwndbg.commands.OnlyWhenRunning
-def telescope(address=None, count=telescope_lines, to_string=False):
+def telescope(address=None, count=telescope_lines, to_string=False, reverse=False):
     """
     Recursively dereferences pointers starting at the specified address
     ($sp by default)
     """
-    ptrsize   = pwndbg.typeinfo.ptrsize
+    ptrsize = pwndbg.typeinfo.ptrsize
     if telescope.repeat:
         address = telescope.last_address + ptrsize
         telescope.offset += 1
@@ -51,10 +55,14 @@ def telescope(address=None, count=telescope_lines, to_string=False):
         telescope.offset = 0
 
     address = int(address if address else pwndbg.regs.sp) & pwndbg.arch.ptrmask
-    count   = max(int(count), 1) & pwndbg.arch.ptrmask
+    count = max(int(count), 1) & pwndbg.arch.ptrmask
     delimiter = T.delimiter(offset_delimiter)
     separator = T.separator(offset_separator)
 
+    # Allow invocation of telescope -r to dump previous addresses
+    if reverse:
+        address -= (count - 1) * ptrsize
+
     # Allow invocation of "telescope 20" to dump 20 bytes at the stack pointer
     if address < pwndbg.memory.MMAP_MIN_ADDR and not pwndbg.memory.peek(address):
         count   = address

tests/binaries/telescope_binary.c

@@ -0,0 +1,22 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct A {
+    void* func_ptr;
+    void* stack_ptr;
+    void* heap_ptr;
+    char buf[16];
+    char gap[128];
+};
+
+void break_here() {}
+
+int main() {
+    struct A a = {};
+    a.func_ptr = (void*)main;
+    a.stack_ptr = (void*) &a;
+    a.heap_ptr = malloc(10);
+    strcpy(a.buf, "aaa");
+    break_here();
+}

tests/test_command_telescope.py

@@ -0,0 +1,59 @@
+import gdb
+
+import tests
+
+TELESCOPE_BINARY = tests.binaries.get('telescope_binary.out')
+
+
+def test_command_telescope(start_binary):
+    """
+    Tests simple telescope
+    """
+    start_binary(TELESCOPE_BINARY)
+
+    gdb.execute('break break_here')
+    gdb.execute('run')
+    gdb.execute('up')
+
+    expected_str = gdb.execute('print a', to_string=True)
+    expected_lines = expected_str.split('\n')
+
+    result_str = gdb.execute('telescope &a', to_string=True)
+    result_lines = result_str.split('\n')
+
+    for i in range(4):
+        expected_addr = expected_lines[i+1].split(' ')[4].strip(',"')
+        assert expected_addr in result_lines[i]
+
+
+def test_command_telescope_reverse(start_binary):
+    """
+    Tests reversed telescope
+    """
+    start_binary(TELESCOPE_BINARY)
+
+    gdb.execute('break break_here')
+    gdb.execute('run')
+    gdb.execute('up')
+
+    expected_str = gdb.execute('print a', to_string=True)
+    expected_lines = expected_str.split('\n')
+
+    result_str = gdb.execute('telescope ((uint8_t*)&a)+0x38 -r', to_string=True)
+    result_lines = result_str.split('\n')
+
+    for i in range(4):
+        expected_addr = expected_lines[i+1].split(' ')[4].strip(',"')
+        assert expected_addr in result_lines[i]
+
+
+def test_command_telescope_n_records(start_binary):
+    """
+    Tests telescope defined number of records
+    """
+    start_binary(TELESCOPE_BINARY)
+
+    n = 3
+    gdb.execute('entry')
+    result_str = gdb.execute('telescope $rsp {}'.format(n), to_string=True)
+    assert len(result_str.strip('\n').split('\n')) == n