Fix vmmap coredump test (#1391)

* fix shlint

* Fix crash when unable to get ehdr and fix vmmap coredump test

This commit fixes two issues and test them.

1. It changes the reads in `get_ehdr` to partial reads so that inability
   to read the `vmmap.start` address there will not crash Pwndbg with
`gdb.error` but instead we will simply return `None` as expected from
this function. This crash could happen on Debian 10 (GDB 8.2.1) and
Ubuntu 18.04 (not sure which GDB) when you did:
- gdb ./binary-that-crashes
- `run`
- `generate-core-file /tmp/core`
- `file` - to unload the binary
- `core-file /tmp/core` - to load the generated core

At this point I think we may have preserved the old vmmap info and use
it in `get_ehdr` maybe, which then crashed? I am not sure, but this fix
here works.

To test this behavior properly I also added the `unload_file`
parametrization to the
`test_command_vmmap_on_coredump_on_crash_simple_binary` test.

2. We fix the vmmap coredump test case when the `info proc mappings` returns nothing on core
   dumps on old GDBs. In such case we are missing the vmmap info about
the binary mapping, so now we properly remove it in the test.

pwndbg/gdblib/elf.py

@@ -249,7 +249,7 @@ def get_ehdr(pointer):
         return None, None
 
     # We first check if the beginning of the page contains the ELF magic
-    if pwndbg.gdblib.memory.read(vmmap.start, 4) == b"\x7fELF":
+    if pwndbg.gdblib.memory.read(vmmap.start, 4, partial=True) == b"\x7fELF":
         base = vmmap.start
 
     # The page did not have ELF magic; it may be that .text and binary start are split
@@ -260,7 +260,7 @@ def get_ehdr(pointer):
                 vmmap = v
                 break
 
-        if pwndbg.gdblib.memory.read(vmmap.start, 4) == b"\x7fELF":
+        if pwndbg.gdblib.memory.read(vmmap.start, 4, partial=True) == b"\x7fELF":
             base = vmmap.start
 
     if base is None:

setup-dev.sh

@@ -92,7 +92,7 @@ install_apt() {
         build-essential \
         gdb \
         parallel \
-	netcat-openbsd
+        netcat-openbsd
 
     if [[ "$1" == "22.04" ]]; then
         sudo apt install shfmt
@@ -107,7 +107,7 @@ install_pacman() {
     set_zigpath "$(pwd)/.zig"
 
     # add debug repo for glibc-debug
-    cat <<EOF | sudo tee -a /etc/pacman.conf
+    cat << EOF | sudo tee -a /etc/pacman.conf
 [core-debug]
 Include = /etc/pacman.d/mirrorlist
 

tests/gdb-tests/tests/test_command_vmmap.py

@@ -1,6 +1,7 @@
 import tempfile
 
 import gdb
+import pytest
 
 import pwndbg
 import tests
@@ -40,7 +41,8 @@ def get_proc_maps():
     return maps
 
 
-def test_command_vmmap_on_coredump_on_crash_simple_binary(start_binary):
+@pytest.mark.parametrize("unload_file", (False, True))
+def test_command_vmmap_on_coredump_on_crash_simple_binary(start_binary, unload_file):
     """
     Example vmmap when debugging binary:
         LEGEND: STACK | HEAP | CODE | DATA | RWX | RODATA
@@ -84,6 +86,10 @@ def test_command_vmmap_on_coredump_on_crash_simple_binary(start_binary):
     core = tempfile.mktemp()
     gdb.execute("generate-core-file %s" % core)
 
+    # The test should work fine even if we unload the original binary
+    if unload_file:
+        gdb.execute("file")
+
     #### TEST COREDUMP VMMAP
     # Now, let's load the generated core file
     gdb.execute("core-file %s" % core)
@@ -94,7 +100,18 @@ def test_command_vmmap_on_coredump_on_crash_simple_binary(start_binary):
     # Note: we will now see one less vmmap page as [vvar] will be missing
     assert vmmaps[0] == "LEGEND: STACK | HEAP | CODE | DATA | RWX | RODATA"
     vmmaps = [i.split() for i in vmmaps[2:]]
-    assert len(vmmaps) == old_len_vmmaps - 1
+
+    has_proc_maps = "warning: unable to find mappings in core file" not in gdb.execute(
+        "info proc mappings", to_string=True
+    )
+
+    if has_proc_maps:
+        assert len(vmmaps) == old_len_vmmaps - 1
+    else:
+        # E.g. on Debian 10 with GDB 8.2.1 the core dump does not contain mappings info
+        assert len(vmmaps) == old_len_vmmaps - 2
+        binary_map = next(i for i in expected_maps if CRASH_SIMPLE_BINARY in i[-1])
+        expected_maps.remove(binary_map)
 
     # Fix up expected maps
     next(i for i in expected_maps if i[-1] == "[vdso]")[-1] = "load2"