https://llvm.org/bugs/show_bug.cgi?id=27508
Bug ID: 27508
Summary: [MC] X86 intel syntax: push immediate misassembled to
a 16 bit push
Product: libraries
Version: 3.8
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: teeem...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
When assembling with intel syntax for i386, pushing an immediate which has a
value between -128 and 127 causes a pushw instruction to be emitted (decrements
esp by 2 bytes) instead of the correct pushl (decrements by 4 bytes). pushw is
selected by the 0x66 prefix.
> echo 'push 0' | llvm-mc -triple i386-unknown-unknown
--x86-asm-syntax=intel -filetype obj | llvm-objdump -d -
...
0: 66 6a 00 pushw $0
(Outputting -filetype asm directly shows the same result)
Each of pushw and pushl has two different opcodes, 0x6a for 8 bit immediate,
and 0x68 for a 16 or 32bit immediate.
If the value doesn't fit in 8 bits, the correct opcode is emitted:
> echo 'push 128' | llvm-mc -triple i386-unknown-unknown
--x86-asm-syntax=intel -filetype obj | llvm-objdump -d -
...
0: 68 80 00 00 00 pushl $128
There's no problem when using at&t syntax:
> echo 'push $0' | llvm-mc -triple i386-unknown-unknown
--x86-asm-syntax=att -filetype obj | llvm-objdump -d -
...
0: 6a 00 pushl $0
Nor when targetting x86_64:
> echo 'push 0' | llvm-mc -triple x86_64-unknown-unknown
--x86-asm-syntax=intel -filetype obj | llvm-objdump -d -
...
0: 6a 00 pushq $0
llvm-mc is latest stable:
LLVM (http://llvm.org/):
LLVM version 3.8.0
Optimized build.
Built Mar 8 2016 (17:36:36).
Default target: x86_64-unknown-linux-gnu
Host CPU: amdfam10
I actually couldn't figure out what the intel syntax equivalent for pushw is,
if any exists. Anyone know? It doesn't appear to be very popular on
i386/x86_64.
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