Hi.
This patch add "OS_main" and 'OS_task' attributes in GCC 4.2.1. Function with
"OS_main" and 'OS_task' attributes do not save any "call-saved" registers.
1. "OS_main" attribute used when there IS guarantee that interrupts are
disabled at that time when function is called. For example "main" function in
avr-libc. If this function has local variables that a prologue will look so:
in r28, 0x3d ; 61
in r29, 0x3e ; 62
sbiw r28, 0x08 ; 8
out 0x3e, r29 ; 62
out 0x3d, r28 ; 61
No save/clear/restore "I" flag.
2. "OS_task" attribute used when there is NO guarantee that interrupts are
disabled at that time when function is called. For example task functions
multi-threading operating systems. In this case save/clear/restore "I" flag is
need for changing SP register. Prologue (if this function has local variables)
will look so:
in r28, 0x3d ; 61
in r29, 0x3e ; 62
sbiw r28, 0x08 ; 8
in r0, 0x3f ; 63
cli
out 0x3e, r29 ; 62
out 0x3f, r0 ; 63
out 0x3d, r28 ; 61
Testcase:
__attribute__ ((noinline))
int fn0(long a1, long a2, long a3, long a4, long a5)
{
return 0;
}
__attribute__ ((OS_main))
int main(void)
{
volatile long long a; // local var, need function frame
a = 1;
return fn0(1, 2, 3, 4, 5); // use call-saved regs
}
PS: At this moment, I have not found a simple way to add "OS_main" attribute
in the avr-gcc 4.3. So presence of this attribute in GCC 4.3 in doubt.
Anatoly.
begin 666 gcc-4.2.1-os_main_os_task.txt
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end
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