The following code throws a warning which I do not understand.
Purpose is to save and restore SREG, which is a special function
register (SFR) defined by its hardware address as:
#define SREG (*(volatile uint8_t*) (0x3F + __AVR_SFR_OFFSET__))
which is the common C idiom to define such an SFR. The C code is:
<code>
typedef __UINT8_TYPE__ uint8_t;
#define SREG (*(volatile uint8_t*) (0x3F + __AVR_SFR_OFFSET__))
static __inline__ uint8_t __iCliRetVal (void)
{
__asm__ __volatile__ ("cli" ::: "memory");
return 1;
}
static __inline__ void __iRestore (const uint8_t *__s)
{
SREG = *__s;
__asm__ volatile ("" ::: "memory");
}
void foo (void)
{
for (uint8_t sreg_save __attribute__((__cleanup__(__iRestore))) = SREG,
__ToDo = __iCliRetVal();
__ToDo ;
__ToDo = 0 )
{
__asm ("nop");
}
}
</code>
The documentation of attribute cleanup says that the function provided
to cleanup (__iRestore) must take a pointer type that is compatible with
the attributed variable, which is the case. The warning is:
avr-gcc-13 -c foo-i.c -mmcu=atmega8 -Os -Wall -save-temps -dumpbase ""
foo-i.c: In function 'foo':
foo-i.c:20:71: warning: array subscript 0 is outside array bounds of
'volatile uint8_t[0]' {aka 'volatile unsigned char[]'} [-Warray-bounds]
20 | for (uint8_t sreg_save
__attribute__((__cleanup__(__iRestore))) = SREG,
|
~^~~~
In function '__iRestore',
inlined from 'foo' at foo-i.c:20:17:
foo-i.c:13:42: warning: array subscript 0 is outside array bounds of
'volatile uint8_t[0]' {aka 'volatile unsigned char[]'} [-Warray-bounds]
13 | SREG = *__s;
| ~~~~~~~~~~~~ ^
To me this looks like a GCC problem, and older versions of the compiler
don't complain. Or is there actually an issue with that code? Purpose
of the code is to save / restore SREG around a block of code, "nop" in
the example.
The warning complains about the places that are using SREG, so it that
macro definition wrong?
Thanks in advance,
Johann
> avr-gcc-13 -v
Using built-in specs.
Reading specs from
/home/DATA/gnu/install/gcc-master-avr/bin/../lib/gcc/avr/13.0.0/device-specs/specs-avr2
COLLECT_GCC=avr-gcc-13
COLLECT_LTO_WRAPPER=/home/DATA/gnu/install/gcc-master-avr/bin/../libexec/gcc/avr/13.0.0/lto-wrapper
Target: avr
Configured with: ../../source/gcc-master/configure --target=avr
--disable-nls --with-dwarf2 --enable-languages=c,c++ --with-gnu-as
--with-gnu-ld --disable-shared --with-fixed-point=no
--prefix=/home/john/gnu/install/gcc-master-avr --enable-checking=release
Thread model: single
Supported LTO compression algorithms: zlib
gcc version 13.0.0 20221103 (experimental) (GCC)
