short: shorten the shorter prestub

Author: byeongkeunahn

scripts/static-pie-prestub-amd64-shorter.asm

@@ -56,11 +56,9 @@ _decode_output:
     jnz     _decode_output
     jmp     _decode_loop
 _decode_zeros:
-    xchg    eax, edx
     movzx   ecx, byte [rdi-1]
     dec     rdi
-    rep     stosb
-    xchg    eax, edx
+    rep     stosb                   ; the fact we jumped to here ensures al=0
     jmp     _decode_loop_2
 
 ; Jump to entrypoint

scripts/static-pie-prestub-amd64-shorter.bin

@@ -1 +1 @@
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^�j"AZj�AX^H�����,#�r%t�Ȓ�,$k�[
Ъ����u��ߒ�O�H�����H+���
+j	X�E1�V1�j
^�j"AZj�AX^H�����,#�r#t�Ȓ�,$k�[
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scripts/static-pie-template-amd64-shorter.rs

@@ -5,4 +5,4 @@
 $$$$solution_src$$$$
 }
 // SOLUTION END
-#[no_link]extern crate std;#[no_mangle]unsafe fn _start(){std::arch::asm!(".quad 56c931459958096ah,6a07b25e016aff31h,0f5841ff6a5a4122h,0e0c11fb097485e05h,74257299232cac0dh,6b242cac92c8fe16h,8e8c1aad0015bc0h,92dfebf77510c4f6h,0f3cfff48ff4fb60fh,0f87f2b48d5eb92aah,59391",in("rsi")r$$$$binary_raw_base91$$$$.as_ptr())}
+#[no_link]extern crate std;#[no_mangle]unsafe fn _start(){std::arch::asm!(".quad 56c931459958096ah,6a07b25e016aff31h,0f5841ff6a5a4122h,0e0c11fb097485e05h,74237299232cac0dh,6b242cac92c8fe16h,8e8c1aad0015bc0h,0fdfebf77510c4f6h,0aaf3cfff48ff4fb6h,0e7fff87f2b48d7ebh",in("rsi")r$$$$binary_raw_base91$$$$.as_ptr())}