Fix asm() instruction consistency (#2144)

* sets p2align header to 0 for x86-32 x86-64 and thumb * updates changelog * adds PR link to changelog * Update pwnlib/asm.py Co-authored-by: Arusekk <[email protected]> Co-authored-by: Arusekk <[email protected]>
Gallopsled · Dec 28, 2022 · b771fc5 · b771fc5
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -70,11 +70,13 @@ The table below shows which release corresponds to each branch, and what date th
 - [#2092][2092] shellcraft: dup() is now called dupio() consistently across all supported arches
 - [#2093][2093] setresuid() in shellcraft uses current euid by default
 - [#2125][2125] Allow tube.recvregex to return capture groups
+- [#2144][2144] Removes `p2align 2` `asm()` headers from `x86-32`, `x86-64` and `mips` architectures to avoid inconsistent instruction length when patching binaries
 
 [2062]: https://github.com/Gallopsled/pwntools/pull/2062
 [2092]: https://github.com/Gallopsled/pwntools/pull/2092
 [2093]: https://github.com/Gallopsled/pwntools/pull/2093
 [2125]: https://github.com/Gallopsled/pwntools/pull/2125
+[2144]: https://github.com/Gallopsled/pwntools/pull/2144
 
 ## 4.9.0 (`beta`)
 

diff --git a/pwnlib/asm.py b/pwnlib/asm.py
@@ -320,20 +320,23 @@ def _arch_header():
     prefix  = ['.section .shellcode,"awx"',
                 '.global _start',
                 '.global __start',
-                '.p2align 2',
                 '_start:',
                 '__start:']
     headers = {
-        'i386'  :  ['.intel_syntax noprefix'],
-        'amd64' :  ['.intel_syntax noprefix'],
+        'i386'  :  ['.intel_syntax noprefix', '.p2align 0'],
+        'amd64' :  ['.intel_syntax noprefix', '.p2align 0'],
         'arm'   : ['.syntax unified',
                    '.arch armv7-a',
-                   '.arm'],
+                   '.arm',
+                   '.p2align 2'],
         'thumb' : ['.syntax unified',
                    '.arch armv7-a',
-                   '.thumb'],
+                   '.thumb',
+                   '.p2align 1'
+                   ],
         'mips'  : ['.set mips2',
                    '.set noreorder',
+                   '.p2align 2'
                    ],
     }