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Fix/follow-up to commit 17ee85fc2a ("Share DWARF partial symtabs"). In the non-index case, where GDB builds partial symbols from scratch, two objfiles around the same BFD correctly share partial symtabs. The first objfile, which has to do all the work, saves a reference to the created partial symtabs in the shared per_bfd object (at the end of dwarf2_build_psymtabs). The second objfile, when it reaches dwarf2_build_psymtabs, sees that there are already partial symtabs built for this BFD and just uses it. However, that commit missed implementing the same sharing for cases where GDB uses .gdb_index or .debug_names to build the partial symtabs. This patch fixes it by having the first objfile to use the BFD set per_bfd->partial_symtabs at the end of dwarf2_read_gdb_index / dwarf2_read_debug_names. For the subsequent objfiles using that BFD, the partial symtabs are then picked up in dwarf2_initialize_objfile. This patch adds a test that mimics how the issue was originally triggered: 1. Load the test file twice, such that the second objfile re-uses the per_bfd object created for the first objfile. 2. Run to some point where in the backtrace there is a frame for a function that's in a CU that's not yet read in. 3. Check that this frame's information is complete in the "backtrace" output. Step 2 requires an address -> symbol lookup which uses the addrmap at objfile->partial_symtabs->psymtabs_addrmap. If the objfile->partial_symtabs link is not properly setup (as is the case before this patch), the symbol for that frame won't be found and we'll get a frame with incomplete information. The test fails without the fix when using boards "cc-with-gdb-index" and "cc-with-debug-names". gdb/ChangeLog: * dwarf2/read.c (dwarf2_read_gdb_index): Save partial_symtabs in the per_bfd object. (dwarf2_read_debug_names): Likewise. (dwarf2_initialize_objfile): Use partial_symtabs from per_bfd object when re-using a per_bfd object with an index. gdb/testsuite/ChangeLog: * gdb.dwarf2/share-psymtabs-bt.exp: New file. * gdb.dwarf2/share-psymtabs-bt.c: New file. * gdb.dwarf2/share-psymtabs-bt-2.c: New file. Change-Id: Ibb26210e2dfc03b80ba9fa56b875ba4cc58c0352