ARM64: differences between "ldr w0,label" & "ldr w0,[label]"

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Index > Non-x86 architectures > ARM64: differences between "ldr w0,label" & "ldr w0,[label]"

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alorent

Joined: 05 Dec 2005
Posts: 221

alorent 16 Mar 2023, 12:50

I'm starting with ARM64 using FASMARM (thanks revolution!) and with FASMG with "aarch64.inc" (thanks tthsqe!)

The following instructions assemble correctly with FASMARM:

Code:

label_ldr:
    ldr x0,label_ldr
    ldr x0,[label_ldr]

But with tthsqe's inc, the following is not accepted:

Code:

label_ldr:
    ldr x0,label_ldr    ; ACCEPTED
    ldr x0,[label_ldr]  ; NOT ACCEPTED!

1) In any case, what's the difference between those 2 instructions?

2) Am I using an incorrect format for "ldr x0, [label_ldr]" on tthsqe's inc?

Thanks!

16 Mar 2023, 12:50

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20298
Location: In your JS exploiting you and your system

revolution 16 Mar 2023, 16:18

They are the same instruction.

The bracketed version is the programmer friendly version that is less confusing to the reader. The un-bracketed version is how it is defined it officially.

16 Mar 2023, 16:18

alorent

Joined: 05 Dec 2005
Posts: 221

alorent 16 Mar 2023, 18:41

Thanks revolution!

16 Mar 2023, 18:41

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20298
Location: In your JS exploiting you and your system

revolution 16 Mar 2023, 19:12

The output binary values can be seen here.

Code:

~ cat ldr.asm
processor cpu64_v8
use64
ldr x0,[$]
ldr x0,$

~ fasmarm -s ldr.fas ldr.asm
flat assembler for ARM  version 1.43 (built on fasm 1.73.02)  (2359008 kilobytes memory)
1 passes, 8 bytes.

~ listing -b 4 ldr.fas ldr.lst

~ cat ldr.lst
                        processor cpu64_v8
                        use64
00000000: 00 00 00 58   ldr x0,[$]
00000004: 00 00 00 58   ldr x0,$

Last edited by revolution on 17 Mar 2023, 19:00; edited 1 time in total

16 Mar 2023, 19:12

alorent

Joined: 05 Dec 2005
Posts: 221

alorent 17 Mar 2023, 10:19

Great! Good commands for quick check Wink

17 Mar 2023, 10:19

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