C++: __asm on static method
Georg-Johann Lay
avr@gjlay.de
Thu Aug 1 09:45:00 GMT 2019
Hi,
suppose the following GNU C++ code:
class C
{
__attribute((used))
static void method() __asm ("__vector_1")
{
__asm ("; method1");
}
static void method2() __asm ("__vector_2");
};
void C::method2()
{
__asm ("; method2");
}
Similar code is used on bare metal when you want an interrupt
service routine (ISR) be defined as a class method that can
access private (static) members.
The generated assembly for method2 is as expected
(here with avr-g++ v8):
.text
.global __vector_2
.type __vector_2, @function
__vector_2:
/* #APP */
; method2
/* #NOAPP */
ret
The ISR must have this specific name to be recognized as
interrupt vector and to be inserted into the vector table.
method1 however reads as follows:
.text
.section .text._ZN1C7method1Ev,"axG",@progbits,_ZN1C7method1Ev,comdat
.weak _ZN1C7method1Ev
.type _ZN1C7method1Ev, @function
_ZN1C7method1Ev:
/* #APP */
; method1
/* #NOAPP */
ret
As far as I understand the semantics of __asm, the assembler
name of method1 should be __vector_1. For the comdat group
name, both __vector_1 and _ZN1C7method1Ev should be okay
provided it is consistent across units.
IMO method1 is not compiled correctly; it would be pointless
to specify __asm if it was supposed to have to effect.
Presumably, this is some glitch / bug in varasm.c?
Thanks,
Johann
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