ARM Cortex-M detection (#2381)

* Fix detection of Arm Cortex-M

* lint

* order of operations

* add comment for cortex-m

pwndbg/gdblib/arch.py

@@ -96,7 +96,13 @@ def _get_arch(ptrsize: int):
     for match in ARCHS:
         if match in arch:
             # Distinguish between Cortex-M and other ARM
-            if match == "arm" and "-m" in arch:
+            # When GDB detects correctly Cortex-M processes, it will label them with `arm*-m`, such as armv7e-m
+            # However, GDB will sometimes fail to correctly label Cortex-M binaries properly, and says it's simply 'arm'.
+            # Internally, GDB still detects the processes as Cortex-M, as it can access .xpsr, but it doesn't
+            # appear to expose this in information through any command/API. Since Cortex-M has the .xpsr flags register
+            # instead of .cpsr, we will check if it's present.
+            # See: https://github.com/pwndbg/pwndbg/issues/2153
+            if match == "arm" and ("-m" in arch or pwndbg.gdblib.regs.xpsr is not None):
                 match = "armcm"
             elif match.startswith("riscv:"):
                 match = match[6:]