https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83244
Bug ID: 83244
Summary: inline assembly does not verify input operands
allocation
Product: gcc
Version: 6.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: unjello at gmail dot com
Target Milestone: ---
Created attachment 42767
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42767&action=edit
zip file with all the files to reproduce
on x86 `int` instruction needs to receive `imm8`. g++ allows to pass an input
operand in inline assembly as "register" too. Example:
template<unsigned char int_no> void int_test_pass() {
asm("int %0"
:
: "N"(int_no)
:);
}
called with:
int_test_pass<10>();
results in assembly (cutting out garbage):
_Z13int_test_passILh10EEvv:
int $10
but:
template<unsigned char int_no> void int_test_fail() {
asm("int %0"
:
: "r"(int_no)
:);
}
quietly results in assembly like this. no errors:
_Z13int_test_failILh10EEvv:
movl $10, %eax
int %al
which is illigal. I've tested this on:
g++-7 (Ubuntu 7.2.0-1ubuntu1~16.04) 7.2.0
g++-6 (Ubuntu/Linaro 6.3.0-18ubuntu2~16.04) 6.3.0 20170519
g++-5 (Ubuntu 5.4.1-2ubuntu1~16.04) 5.4.1 20160904
g++-4.9 (Ubuntu 4.9.4-2ubuntu1~16.04) 4.9.4
g++-4.8 (Ubuntu 4.8.5-4ubuntu2) 4.8.5
g++-4.7 (Ubuntu/Linaro 4.7.4-3ubuntu12) 4.7.4
g++-4.6 (Ubuntu/Linaro 4.6.4-6ubuntu6) 4.6.4
on all above, this program compiles with no errors on -Wall -Werror.
Clang on the other hands breaks compilation with an error:
gcc_imm8_bug.cpp:9:7: error: invalid operand for instruction
asm("int %0"
^
<inline asm>:1:6: note: instantiated into assembly here
int %al
^~~
1 error generated.
