I read this page containing a good list of differences between Intel and AT&T

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Asked: June 2, 20262026-06-02T06:25:48+00:00 2026-06-02T06:25:48+00:00

I read this page containing a good list of differences between Intel and AT&T

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I read this page containing a good list of differences between Intel and AT&T syntax for GAS but it did not cover the case of specifying an address with a displacement only.

Here I’ve assembled four lines with AT&T syntax:

                         .text
0000 48C7C008000000      mov    $8, %rax
0007 488B042508000000    mov    (8), %rax
000f 4889F0              mov    %rsi, %rax
0012 488B06              mov    (%rsi), %rax

The first two lines are different, as expected. The first moves the immediate value 8 into rax and the second moves the contents of address 8 into rax. But with Intel syntax I get the following odd behavior:

                         .text
                         .intel_syntax
0000 48C7C008000000      mov    %rax, 8
0007 48C7C008000000      mov    %rax, [8]
000e 4889F0              mov    %rax, %rsi
0011 488B06              mov    %rax, [%rsi]

Here the first and second lines assembled to the same machine code! First I thought the square brackets were wrong, so I added the third and fourth lines to the test, and the square brackets do work for memory addressing at least when registers are involved.

All of the documentation I have read show memory addressing examples with at least a base or index register, and sometimes a scale and displacement, but never a displacement only.

I do have experience with the Intel syntax using the NASM assembler, which does distinguish mov rax, 8 and mov rax, [8].

Is this a bug in GAS? Or if not, how do I specify the equivalent of NASM’s mov rax, [8]?

I realize it is probably uncommon to specify a displacement-only address but I would like to get a complete understanding of all of the memory addressing forms with this syntax.