Adding the testcase... On 10/7/20 4:08 PM, Jeff Law wrote: > On 9/17/20 1:03 PM, Jakub Jelinek wrote: > [ ... Big snip, starting over ... ] > > I may have not explained things too well. So I've put together a small > example that folks can play with to show the underlying issue. > > > There's a static library libfu.a. In this static library we have a hunk > of local static data (utf8_sb_map) and two functions. One function puts > the address utf8_sb_map into a structure (rpl_regcomp), the other > verifies that the address stored in the structure is the same as the > address of utf8_sb_map (rpl_regfree). > > > That static library is linked into DSO libdso.so. The DSO sources > define a single function xregcomp which calls rpl_regcomp, but > references nothing else from the static library. Since libfu.a was > linked into the library we actually get a *copy* of rpl_regcomp in the > DSO. In fact, we get a copy of the entire .o file from libfu.a, which > matches traditional linkage models where the .o file is an atomic unit > for linking. > > > The main program calls xregcomp which is defined in the DSO and calls > rpl_regfree. The main program links against libdso.so and libfu.a. > Because it links libfu.a, it gets a copy of rpl_regfree, but *only* > rpl_regfree. That copy of rpl_regfree references a new and distinct > copy of utf8_sb_map. Naturally the address of utf8_sb_map in the main > program is different from the one in libdso.so and the test aborts. > > > Without LTO the main program would still reference rpl_regfree, but the > main program would not have its own copy. rpl_regfree and rpl_regcomp > would both be satisfied by the DSO (which remember has a complete copy > of the .o file from libfu.a). Thus there would be only one utf8_sb_map > as well and naturally the program will exit normally. > > > So I've got a bunch of thoughts here, but will defer sharing them > immediately so as not to unduly influence anyone. > > > I don't have a sense of how pervasive this issue is. I know it affects > man-db, but there could well be others. > > > > > jeff >
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