https://sourceware.org/bugzilla/show_bug.cgi?id=30849
Bug ID: 30849
Summary: gas x86-64: Operand size prefix incorrectly parsed as
operand in `prefetch` Instruction
Product: binutils
Version: 2.41
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: gas
Assignee: unassigned at sourceware dot org
Reporter: jwlee2217 at softsec dot kaist.ac.kr
Target Milestone: ---
```
$ cat examples/bug3_1.s
.intel_syntax noprefix
prefetch WORD PTR [R11]
$ ./as examples/bug3_1.s -o bug3_1.o
$ ./objdump -d -M intel bug3_1.o
bug3_1.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <.text>:
0: 41 0f 0d 03 prefetch BYTE PTR [r11]
```
It seems GAS ignores memory operand prefixes for Intel `prefetch` instruction.
I guess this behavior is because `prefetch` only accepts an 8-bit width memory
operand.
```
$ cat examples/bug3_2.s
.intel_syntax noprefix
prefetch DUMMYDUMMYDUMMY [R11]
prefetch [R11] [R11]
$ ./as examples/bug3_2.s -o bug3_2.o
$ ./objdump -d -M intel bug3_2.o
bug3_2.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <.text>:
0: 41 0f 0d 83 00 00 00 prefetch BYTE PTR [r11+0x0]
7: 00
8: 43 0f 0d 04 1b prefetch BYTE PTR [r11+r11*1]
$ ./readelf -r bug3_2.o
Relocation section '.rela.text' at offset 0xc8 contains 1 entry:
Offset Info Type Sym. Value Sym. Name +
Addend
000000000004 00010000000b R_X86_64_32S 0000000000000000 DUMMYDUMMYDUMMY +
0
```
More interesting behaviors can be observed when we give an arbitrary token
instead of a memory operand prefix. If we put a symbol or an additional memory
operand, then two memory operands are treated as a single memory operand.
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