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Created attachment 545277 [details] Test case showing the problem Description of problem: I'm trying to build stuff for my Arduino board, but the compiler occasionally clobbers the return value of a function it just called. This is notable in the Arduino Ethernet library where the interactions with the W5100 chipset go interestingly wrong. I opened a bug on this in the gcc bugzilla: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51445 but the problem appears fixed in gcc-4.6.2 (I found that by building that for myself and trying it). Version-Release number of selected component (if applicable): avr-gcc-4.6.1-3 and -4. How reproducible: 100%. Steps to Reproduce: 1. Build the attached test case using: avr-gcc -g -Os -w -mmcu=atmega328p -ffunction-sections -fdata-sections -o tmp.o -c tmp.cpp 2. Use avr-objdump -d to disassemble the resulting tmp.o and look for the send_data_processing method. 3. Find the first CALL instruction. The result of this function call is returned in the R24 register. Actual results: With the #if set to 1 in the test case, it can be seen that the return value from the function call is clobbered immediately after the return: 26: 0e 94 00 00 call 0 ; 0x0 <W5100Class::send_data_processing(unsigned char, unsigned char*, unsigned int)> 2a: 81 2f mov r24, r17 (data moves right to left in the MOV instruction). Expected results: R24 should be saved as it's needed later. Flipping the #if to 0 in the test case shows this instead: 24: 0e 94 00 00 call 0 ; 0x0 <W5100Class::send_data_processing(unsigned char, unsigned char*, unsigned int)> 28: e8 2e mov r14, r24 2a: 81 2f mov r24, r17 Additional info: This seems to be fixed in 4.6.2: 24: 0e 94 00 00 call 0 ; 0x0 <W5100Class::send_data_processing(unsigned char, unsigned char*, unsigned int)> 28: a8 2e mov r10, r24 2a: 81 2f mov r24, r17 I tested this by substituting the 4.6.2 gcc in the spec file and dropping the progmem patch.
Hello, Thanks for your report. Indeed I have to update to 4.6.2. Will do ASAP.
avr-gcc-4.6.2-1.fc16 has been submitted as an update for Fedora 16. https://admin.fedoraproject.org/updates/avr-gcc-4.6.2-1.fc16
Package avr-gcc-4.6.2-1.fc16: * should fix your issue, * was pushed to the Fedora 16 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=updates-testing avr-gcc-4.6.2-1.fc16' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-2011-16971/avr-gcc-4.6.2-1.fc16 then log in and leave karma (feedback).
Works for me.
avr-gcc-4.6.2-1.fc16 has been pushed to the Fedora 16 stable repository. If problems still persist, please make note of it in this bug report.