What's difference between number with $ or without $ symbol in at&t assembly syntax?

Question

Let's say .data section has following item:

0x1234 00010203 04050607 08090a0b 0c0d0e0f
0x1238 10000000

And in code,

mov $0x1234, %eax
mov 0x1238, %ebx

I believe with $ symbol, it would be constant number, so %eax will have memory address, but what about %ebx?

What exactly different between two instruction?

phuclv · Accepted Answer · 2021-04-07 09:10:26Z

11

The difference is that with $ it's the numeric value while without $ it's the contents of memory at that address

If argument of instruction is without any special marker (such as % for register or $ for numeric constant), then it is memory access. So following:
movl 10, %eax
movl foo, %eax
Corresponds to intel syntax:
mov eax, [10]
mov eax, [foo]
To use numeric constant, or use address of label, there is $ operator:
movl $10, %eax
movl $foo, %eax
In Intel syntax:
mov eax, 10
mov eax, offset foo
http://x86asm.net/articles/what-i-dislike-about-gas/

edited Apr 7, 2021 at 9:10

answered Sep 25, 2013 at 7:01

phuclv

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2 Comments

REALFREE Over a year ago

So are you saying mov $0x1238, %ebx is just numeric constant and not memory access even though 0x1238 address is present in memory ?

phuclv Over a year ago

Memory access here is data, not instruction

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