On 18/06/13 07:47, Ian Lance Taylor wrote: > On Mon, Jun 17, 2013 at 10:21 PM, Gene Smith <gds@xxxxxxxxxxxxx> wrote: >> 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. > > 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/ . Thanks. > > Ian > I did not think that was the case. As I understood it, "-g" /may/ cause to the code to improve debugging. I can't say that I have ever noticed any code changes, but I've always assumed it is possible especially with more advanced optimisations. I certainly don't see anything in the documentation that suggests "-g" cannot change the code - only that "-g -O" will generate optimised and debugable code (though possibly with confusing debugging).
