This is seen on the version of avr-gcc 4.3.3 that gets built by the script that
comes with FemtoOS 0.88.
I'm compiling like this:
avr-gcc -mmcu=atmega128 -O0 small_preprocessed.c -o small.elf
And observing the result of a run like this:
java -server avrora.Main -platform=mica2 -simulation=sensor-network
-monitors=break -colors=false -seconds=15 small.elf
Of course you need Avrora installed to do this.
The program computes a checksum over its globals before terminating, this is
found in the Avrora output as:
r30:r31 = 0x5DAD
It can be seen that the checksum computed at -O0 is different from higher
optimization levels, which give 0xDBFA. My belief is that the -O0 result is
wrong, and here's why: deleting almost any line of code from the program causes
it to have the same checksum at all optimization levels. To see this, delete
for example the line "int16_t l_46 = 1;" in func_43(). This line obviously has
no effect on the computation. This changes the checksum to 0xDBFA, which is in
agreement with higher optimization levels.
The test code is obviously nonsense. However, I cannot give a smaller testcase
since deleting code makes the problem go away.
My belief is that this problem in not the result of a stack overflow: my stack
analysis tool estimates that maximum RAM usage (including stack) is 2496 bytes,
leaving plenty of free space on the mega128.
My believe is that this problem is no due to undefined behavior in the C code.
--
Summary: apparent bizarre miscompilation on AVR
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: regehr at cs dot utah dot edu
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: avr
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39232
