35a01a0454
The variable section in a CTF dict is meant to contain the types of variables that do not appear in the symbol table (mostly file-scope static declarations). We implement this by having the compiler emit all potential data symbols into both sections, then delete those symbols from the variable section that correspond to data symbols the linker has reported. Unfortunately, the check for this in ctf_serialize is wrong: rather than checking the set of linker-reported symbols, we check the set of names in the data object symtypetab section: if the linker has reported no symbols at all (usually if ld -r has been run, or if a non-linker program that does not use symbol tables is calling ctf_link) this will include every single symbol, emptying the variable section completely. Worse, when ld -r is in use, we want to force writeout of every symtypetab entry on the inputs, in an indexed section, whether or not the linker has reported them, since this isn't a final link yet and the symbol table is not finalized (and may grow more symbols than the linker has yet reported). But the check for this is flawed too: we were relying on ctf_link_shuffle_syms not having been called if no symbols exist, but that function is *always* called by ld even when ld -r is in use: ctf_link_add_linker_symbol is the one that's not called when there are no symbols. We clearly need to rethink this. Using the emptiness of the set of reported symbols as a test for ld -r is just ugly: the linker already knows if ld -r is underway and can just tell us. So add a new linker flag CTF_LINK_NO_FILTER_REPORTED_SYMS that is set to stop the linker filtering the symbols in the symtypetab sections using the set that the linker has reported: use the presence or absence of this flag to determine whether to emit unindexed symtabs: we only remove entries from the variable section when filtering symbols, and we only remove them if they are in the reported symbol set, fixing the case where no symbols are reported by the linker at all. (The negative sense of the new CTF_LINK flag is intentional: the common case, both for ld and for simple tools that want to do a ctf_link with no ELF symbol table in sight, is probably to filter out symbols that no linker has reported: i.e., for the simple tools, all of them.) There's another wrinkle, though. It is quite possible for a non-linker to add symbols to a dict via ctf_add_*_sym and then write it out via the ctf_write APIs: perhaps it's preparing a dict for a later linker invocation. Right now this would not lead to anything terribly meaningful happening: ctf_serialize just assumes it was called via ctf_link if symbols are present. So add an (internal-to-libctf) flag that indicates that a writeout is happening via ctf_link_write, and set it there (propagating it to child dicts as needed). ctf_serialize can then spot when it is not being called by a linker, and arrange to always write out an indexed, sorted symtypetab for fastest possible future symbol lookup by name in that case. (The writeouts done by ld -r are unsorted, because the only thing likely to use those symtabs is the linker, which doesn't benefit from symtypetab sorting.) Tests added for all three linking cases (ld -r, ld -shared, ld), with a bit of testsuite framework enhancement to stop it unconditionally linking the CTF to be checked by the lookup program with -shared, so tests can now examine CTF linked with -r or indeed with no flags at all, though the output filename is still foo.so even in this case. Another test added for the non-linker case that endeavours to determine whether the symtypetab is sorted by examining the order of entries returned from ctf_symbol_next: nobody outside libctf should rely on this ordering, but this test is not outside libctf :) include/ChangeLog 2021-01-26 Nick Alcock <nick.alcock@oracle.com> * ctf-api.h (CTF_LINK_NO_FILTER_REPORTED_SYMS): New. ld/ChangeLog 2021-01-26 Nick Alcock <nick.alcock@oracle.com> * ldlang.c (lang_merge_ctf): Set CTF_LINK_NO_FILTER_REPORTED_SYMS when appropriate. libctf/ChangeLog 2021-01-27 Nick Alcock <nick.alcock@oracle.com> * ctf-impl.c (_libctf_nonnull_): Add parameters. (LCTF_LINKING): New flag. (ctf_dict_t) <ctf_link_flags>: Mention it. * ctf-link.c (ctf_link): Keep LCTF_LINKING set across call. (ctf_write): Likewise, including in child dictionaries. (ctf_link_shuffle_syms): Make sure ctf_dynsyms is NULL if there are no reported symbols. * ctf-create.c (symtypetab_delete_nonstatic_vars): Make sure the variable has been reported as a symbol by the linker. (symtypetab_skippable): Mention relationship between SYMFP and the flags. (symtypetab_density): Adjust nonnullity. Exit early if no symbols were reported and force-indexing is off (i.e., we are doing a final link). (ctf_serialize): Handle the !LCTF_LINKING case by writing out an indexed, sorted symtypetab (and allow SYMFP to be NULL in this case). Turn sorting off if this is a non-final link. Only delete nonstatic vars if we are filtering symbols and the linker has reported some. * testsuite/libctf-regression/nonstatic-var-section-ld-r*: New test of variable and symtypetab section population when ld -r is used. * testsuite/libctf-regression/nonstatic-var-section-ld-executable.lk: Likewise, when ld of an executable is used. * testsuite/libctf-regression/nonstatic-var-section-ld.lk: Likewise, when ld -shared alone is used. * testsuite/libctf-regression/nonstatic-var-section-ld*.c: Lookup programs for the above. * testsuite/libctf-writable/symtypetab-nonlinker-writeout.*: New test, testing survival of symbols across ctf_write paths. * testsuite/lib/ctf-lib.exp (run_lookup_test): New option, nonshared, suppressing linking of the SOURCE with -shared. |
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README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.