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POHow does creating a replacement memset trigger duplicate symbol errors in specific circumstances?
 

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  1. POHow does creating a replacement memset trigger duplicate symbol errors in specific circumstances?
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    <p>I recently wrote a few replacements for string routines (memcpy, memset, and memmove). It is my understanding that if the library containing these routines is specified on the compile / link line, these will take precedence over system standard library routines of the same name. If I'm wrong already, please let me know!</p> <p>This works correctly in all testing I did (verified by disassembly that the correct routines are there and glibc routines don't exist), but further testing discovered an odd break caused by this:</p> <p>1) build another file in the same library with -g (I had been building -O2)</p> <p>2) this file has an explicit call to memset</p> <p>3a) if the compile time options work in such a way that this memset is inlined by gcc, everything is OK</p> <p>3b) if, however, the options disable the inlining of a memset call <em>which would have been inlined otherwise</em>, the library will build but using the library to statically link an application causes a duplicate symbol linker error - the other instance of the symbol is the system library's memset.</p> <p>Basically I can build two versions of my library (100's of source files), and by changing the make CFLAGS in one directory from -O1 -g to just -g I can trigger the linker error when this library is used.</p> <p>I can take the working version, run it through nm, and see that it has many undefined references to memset including in routines which are linked into my test case - so I know it should be trying to resolve memset in the working case. When I diff this against the nm output for the broken library, all I see is a few extra undefined memcpy and memset references. If memset resolved in the first case (to my routine), it should in the second.</p> <p>I have also looked at the verbose compiler output and verified that the link lines are exactly the same in both cases, except for the path to this one library.</p> <p>There are two super puzzling things here (among a myriad of other issues):</p> <p>1) Why would a file in a library built -O1 -g link any differently than -g</p> <p>2) Why would a replacement memset, in a user library, conflict with the system memset</p> <p>And for the grand prize, how does 1) cause 2)</p>
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