I have just installed the recent Windows x64 4.2.0-rc1 release and tried
updating one of my projects to use '__sdcccall(0)' for existing STM8
assembly code, and was puzzled to find that it had no effect - some
functions marked with that attribute were still being called with the
new ABI!
After doing some digging, I discovered that functions where the new
attribute had no effect were functions that were also declared with
'__naked'.
Here is a short test program illustrating the problem:
#include <stdint.h>
static uint8_t test_1(const uint8_t foo) __sdcccall(0) {
(void)foo;
return 255;
}
static uint8_t test_2(const uint8_t foo) __naked __sdcccall(0) {
(void)foo;
__asm
ld a, 255
retf
__endasm;
}
void main(void) {
volatile uint8_t foo = test_1(0);
volatile uint8_t bar = test_2(0);
while(1);
}
The generated assembly is as follows:
_test_1:
ld a, #0xff
retf
_test_2:
ld a, 255
retf
_main:
; ...snip...
push #0x00
callf _test_1
addw sp, #1
ld (0x01, sp), a
clr a
callf _test_2
ld (0x02, sp), a
; ...snip...
You can see that test_1() has its argument pushed to the stack before
being called, as per the old ABI, but test_2() does not - its argument
is incorrectly passed in the A register, as per the new ABI.
Is this a bug? I don't believe '__naked' should be changing anything
about how a function is *called*, only whether prologue and epilogue
code inside that function is generated.
Regards,
Basil Hussain
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