[llvm-dev] [BUG] Mismatch between assembler & disassembler of X86 RIP-relative instruction

[Jun Koi via llvm-dev]

On Mon, May 23, 2016 at 2:44 PM, Jun Koi <junkoi2004 at gmail.com> wrote:

> Hi,
>
> I found a mismatch between assembler & disassembler of X86: I assembled an
> instruction, then disassembled the output, but the result is not the same
> as the first original code: "add qword ptr [205163983024656], 1" vs " add
> qword ptr [1985229328], 1"
>
> Anybody knows what is wrong?
>
> Thanks.
>
>
> $ echo "ADD QWORD PTR [0xba9876543210], 0x1"|llvm-mc -assemble
> -triple=x86_64 -x86-asm-syntax=intel -output-asm-variant=1
> --show-encoding
>     add    qword ptr [205163983024656], 1 #
> encoding:[0x48,0x83,0x04,0x25,0x10,0x32,0x54,0x76,0x01]
>
> $ echo "0x48,0x83,0x04,0x25,0x10,0x32,0x54,0x76,0x01"|llvm-mc -disassemble
> -triple=x86_64 -x86-asm-syntax=intel -output-asm-variant=1 --show-encoding
>     add    qword ptr [1985229328], 1 # encoding:
> [0x48,0x83,0x04,0x25,0x10,0x32,0x54,0x76,0x01]
>

To make it more clear, here is the same thing again, but with hexa
immediate. You can see the difference in memory address: 0xba9876543210 vs
0x76543210.


$ echo "ADD QWORD PTR [0xba9876543210], 0x1"|llvm-mc -assemble
-triple=x86_64 -x86-asm-syntax=intel -output-asm-variant=1 --show-encoding
-print-imm-hex
    .text
    add    qword ptr [0xba9876543210], 0x1 # encoding:
[0x48,0x83,0x04,0x25,0x10,0x32,0x54,0x76,0x01]


$ echo "0x48,0x83,0x04,0x25,0x10,0x32,0x54,0x76,0x01"|llvm-mc -disassemble
-triple=x86_64 -x86-asm-syntax=intel -output-asm-variant=1 --show-encoding
-print-imm-hex
    .text
    add    qword ptr [0x76543210], 0x1 # encoding:
[0x48,0x83,0x04,0x25,0x10,0x32,0x54,0x76,0x01]
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