...plus, I updated the documentation: -mno-call-main
asserts that main() does not return.
Johann
index 0aef2abf05b..af41d7b9ad3 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -24457,6 +24457,24 @@ Do not save registers in @code{main}. The
effect is the same like
attaching attribute @ref{AVR Function Attributes,,@code{OS_task}}
to @code{main}. It is activated per default if optimization is on.
+@opindex mno-call-main
+@opindex mcall-main
+@item -mno-call-main
+Don't run @code{main} by means of
+@example
+XCALL main
+XJMP exit
+@end example
+Instead, put @code{main} in section
+@w{@uref{https://avrdudes.github.io/avr-libc/avr-libc-user-manual/mem_sections.html#sec_dot_init,@code{.init9}}}
+so that no call is required.
+By setting this options the user asserts that @code{main} will not return.
+
+This option can be used for devices with very limited resources in order
+to save a few bytes of code and stack space. It will work as expected
since
+@w{@uref{https://github.com/avrdudes/avr-libc/issues/1012,AVR-LibC v2.3}}.
+With older versions, there will be no performance gain.
+
@opindex mno-interrupts
@item -mno-interrupts
Generated code is not compatible with hardware interrupts.
@@ -24535,7 +24553,19 @@ Allow to use truncation instead of rounding
towards zero for fractional fixed-po
@opindex nodevicelib
@item -nodevicelib
-Don't link against AVR-LibC's device specific library
Am 09.02.25 um 11:26 schrieb Georg-Johann Lay:
On devices with very limited resources, it may be desirable to run
main in a more efficient way than provided by the startup code
XCALL main
XJMP exit
from section .init9. In AVR-LibC v2.3, that code has been moved to
libmcu.a, hence symbol __call_main can be satisfied so that the
respective code is no more pulled in from that library.
Instead, main can be run by putting it in section .init9.
The patch adds attributes noreturn and section(".init9"), and
sets __call_main=0 when it encounters main().
Ok for trunk?
Johann
--
AVR: target/118806 - Add -mno-call-main to tweak running main().
On devices with very limited resources, it may be desirable to run
main in a more efficient way than provided by the startup code
XCALL main
XJMP exit
from section .init9. In AVR-LibC v2.3, that code has been moved to
libmcu.a, hence symbol __call_main can be satisfied so that the
respective code is no more pulled in from that library.
Instead, main can be run by putting it in section .init9.
The patch adds attributes noreturn and section(".init9"), and
sets __call_main=0 when it encounters main().
gcc/
PR target/118806
* config/avr/avr.opt (-mcall-main): New option and...
(avropt_call_main): ...variable.
* config/avr/avr.cc (avr_no_call_main_p): New variable.
(avr_insert_attributes) [-mno-call-main, main]: Add attributes
noreturn and section(".init9") to main. Set avr_no_call_main_p.
(avr_file_end) [avr_no_call_main_p]: Define symbol __call_main.
* doc/invoke.texi (AVR Options) <-mno-call-main>: Document.
<-mnodevicelib>: Extend explanation.
