Hello, I seem to have found a bug in GNU as, when using the intel syntax on x86_64, for some mov instructions, as explained below. I looked into the archive, and could not find a mention of this bug. You'll find two source files attached.
Best regards, Sébastien Dusuel ----------------------------------------------------------------------------- The att syntax has no problem: # cat mov_att.s /* as -o mov_att.o mov_att.s && ld -o mov_att mov_att.o */ .global _start _start: mov %rax, 0x10(%rbp) mov %ebx, 0x20(%rbx) mov %ax, 0x30(%rcx) mov %cl, 0x40(%rdx) # as -o mov_att.o mov_att.s && ld -o mov_att mov_att.o # gdb -q mov_att Reading symbols from mov_att...(no debugging symbols found)...done. (gdb) disassemble _start Dump of assembler code for function _start: 0x0000000000400078 <+0>: mov %rax,0x10(%rbp) 0x000000000040007c <+4>: mov %ebx,0x20(%rbx) 0x000000000040007f <+7>: mov %ax,0x30(%rcx) 0x0000000000400083 <+11>: mov %cl,0x40(%rdx) End of assembler dump. ----------------------------------------------------------------------------- But the intel syntax has a problem: # cat mov_intel.s /* as -o mov_intel.o mov_intel.s && ld -o mov_intel mov_intel.o */ .intel_syntax noprefix .global _start _start: mov qword [rbp + 0x10], rax mov dword [rbx + 0x20], ebx mov word [rcx + 0x30], ax mov byte [rdx + 0x40], cl # as -o mov_intel.o mov_intel.s && ld -o mov_intel mov_intel.o # gdb -q mov_intel Reading symbols from mov_intel...(no debugging symbols found)...done. (gdb) disassemble _start Dump of assembler code for function _start: 0x0000000000400078 <+0>: mov %rax,0x18(%rbp) 0x000000000040007c <+4>: mov %ebx,0x24(%rbx) 0x000000000040007f <+7>: mov %ax,0x32(%rcx) 0x0000000000400083 <+11>: mov %cl,0x41(%rdx) End of assembler dump. As you can see, the numerical shifts are not properly treated when using the intel syntax. ----------------------------------------------------------------------------- The above has been tested on the three following setups: ############################################################################# setup 1: # uname -a Linux kali 4.9.0-kali3-amd64 #1 SMP Debian 4.9.18-1kali1 (2017-04-04) x86_64 GNU/Linux # as --version GNU assembler (GNU Binutils for Debian) 2.28 Copyright (C) 2017 Free Software Foundation, Inc. This program is free software; you may redistribute it under the terms of the GNU General Public License version 3 or later. This program has absolutely no warranty. This assembler was configured for a target of `x86_64-linux-gnu'. ############################################################################# setup 2: $ uname -a Linux *** 4.4.0-72-generic #93-Ubuntu SMP Fri Mar 31 14:07:41 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux $ as --version GNU assembler (GNU Binutils for Ubuntu) 2.26.1 Copyright (C) 2015 Free Software Foundation, Inc. This program is free software; you may redistribute it under the terms of the GNU General Public License version 3 or later. This program has absolutely no warranty. This assembler was configured for a target of `x86_64-linux-gnu'. ############################################################################# setup 3: # uname -a Linux *** 4.4.8-hardened-r1 #4 SMP Sat Oct 22 13:48:12 CEST 2016 x86_64 GNU/Linux # as --version GNU assembler (GNU Binutils for Debian) 2.25 Copyright (C) 2014 Free Software Foundation, Inc. This program is free software; you may redistribute it under the terms of the GNU General Public License version 3 or later. This program has absolutely no warranty. This assembler was configured for a target of `x86_64-linux-gnu'.
mov_att.s
Description: Binary data
mov_intel.s
Description: Binary data
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