Comment 6 for bug 1843394

Quoting a post of a ipxe related developer that did a nice check realizing that e.g. disassembly always lists pushq (and opcode stays the same) - thanks to Valentine for these checks!:

AFAIU, segment registers
are 16-bit long, however, "pushl" and "pushq" should also be valid and
produce the same opcode.

Quite interesting that obdump -S always shows "pushq" even when
"push" or "pushl" is used in the original source.

Please, take a look at the following log:

<email address hidden>:/tmp$ cat push.S
 push %gs
 push %fs
<email address hidden>:/tmp$ as --64 push.S -o push.out
<email address hidden>:/tmp$ objdump -S push.out

push.out: file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <.text>:
   0: 0f a8 pushq %gs
   2: 0f a0 pushq %fs
<email address hidden>:/tmp$ cat pushl.S
 pushl %gs
 pushl %fs
<email address hidden>:/tmp$ as --64 pushl.S -o pushl.out
<email address hidden>:/tmp$ objdump -S pushl.out

pushl.out: file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <.text>:
   0: 0f a8 pushq %gs
   2: 0f a0 pushq %fs
<email address hidden>:/tmp$ cat pushq.S
 pushq %gs
 pushq %fs
<email address hidden>:/tmp$ as --64 pushq.S -o pushq.out
pushq.S: Assembler messages:
pushq.S:1: Error: operand type mismatch for `push'
pushq.S:2: Error: operand type mismatch for `push'