fix(regsort): drop self-assignments through register aliases (#2795)

* fix(regsort): drop self-assignments through register aliases

The self-assignment drop compared register names only (k != v), so an
assignment through an alias (e.g. {'ax': 'eax'} with registers.native32)
was not recognized as a no-op.  It then surfaced as a spurious
1-register dependency cycle, which either raised PwnlibException with
xchg=False or emitted a useless 'mov' of a register into its own alias.

With xchg=False and other registers present, the bogus cycle also
forced the temporary-register code path, reordering unrelated moves and
silently leaving registers with wrong values (see the linked issue).

Compare the mapped names instead, like the rest of the function.

Fixes #2794

Co-authored-by: rahul05ranjan <[email protected]>

* docs(changelog): add regsort register-alias self-assignment fix entry

---------

Co-authored-by: Rahul Ranjan <[email protected]>

CHANGELOG.md

@@ -137,6 +137,7 @@ The table below shows which release corresponds to each branch, and what date th
 - [#2773][2773] Disable debuginfod doctests in libcdb.unstrip_libc
 - [#2772][2772] fix(packing): `dd()` no longer crashes on a `bytearray` destination
 - [#2787][2787] gdb.corefile: Run gdb directly to prevent detach race
+- [#2795][2795] regsort: Fix self-assignment detection through register aliases
 
 [2694]: https://github.com/Gallopsled/pwntools/pull/2694
 [2701]: https://github.com/Gallopsled/pwntools/pull/2701
@@ -144,6 +145,7 @@ The table below shows which release corresponds to each branch, and what date th
 [2773]: https://github.com/Gallopsled/pwntools/pull/2773
 [2772]: https://github.com/Gallopsled/pwntools/pull/2772
 [2787]: https://github.com/Gallopsled/pwntools/pull/2787
+[2795]: https://github.com/Gallopsled/pwntools/pull/2795
 
 ## 4.15.0 (`stable`)
 

pwnlib/regsort.py

@@ -190,6 +190,15 @@ def regsort(in_out, all_regs, mapping = None, tmp = None, xchg = True, randomize
 
         >>> regsort({'a': 1, 'b': 2}, R)
         [('mov', 'a', 1), ('mov', 'b', 2)]
+        >>> M = {'ax': 'eax', 'eax': 'eax', 'ebx': 'ebx'}
+
+        Registers which are assigned one of their own aliases
+        are dropped, like same-name self-assignments.
+
+        >>> regsort({'ax': 'eax'}, M)
+        []
+        >>> regsort({'ax': 'eax'}, M, xchg=False)
+        []
         >>> regsort({'a': 'b', 'b': 'a'}, R)
         [('xchg', 'a', 'b')]
         >>> regsort({'a': 'b', 'b': 'a'}, R, tmp='X') #doctest: +NORMALIZE_WHITESPACE
@@ -253,7 +262,9 @@ def regsort(in_out, all_regs, mapping = None, tmp = None, xchg = True, randomize
     # Drop all registers which will be set to themselves.
     #
     # For example, {'eax': 'eax'}
-    in_out = {k:v for k,v in in_out.items() if k != v}
+    # This must go through the mapping, so that {'ax': 'eax'} is
+    # recognized as a self-assignment as well.
+    in_out = {k:v for k,v in in_out.items() if mapping.get(k, k) != mapping.get(v, v)}
 
     # Collapse constant values
     #