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gcc: difference -g -O1 vs. -O1

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If I compile my embedded program with options "-g -O1" I obtain an elf file with debug information. I can objcopy the elf file to a binary or hex file that can be loaded to flash, effectively striping out the debug
information leaving only the optimized code in ROM.

But if I re-build with options the same except omit the -g option, obviously I will have no symbols in the elf file making debugging impossible or at least more difficult. However, when I object copy this elf to a binary or hex file they are different somewhat than the binary or hex produced with options -g present. At least with 4.7.3 the main difference, as seen with objdump, is in the prologue to certain function calls with only a few bytes different in total code length on a fairly large embedded application (arm). So -g has some effect on the actual code produced it appears.

Is this difference expected? Should -g cause changes in the actual code generated and not just add debug symbols to the elf? Possibly it is related to the optimization level? I have not checked to see if the
results differ with higher or lower levels than -O1.

I have seen several opinions regarding this but no authoritative answer. The gcc manual also does not really answer this.

posted Jun 18, 2013 by anonymous

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1 Answer

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If the only change in the command line options is whether you use -g, you should get exactly the same code. Any difference in code generation is a bug. Please try to file a bug report according to the guidelines at http://gcc.gnu.org/bugs/ .

answer Jun 18, 2013 by anonymous
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