d0b00e74bf
The CTF format cannot differentiate between a non-defining extern variable declaration vs. a defining variable declaration (unlike DWARF). So, the correct behaviour wrt the compiler generating CTF for such extern variables (i.e., when both the defining and non-defining decl are present in the same CU) is to simply emit the CTF variable correspoding to the defining declaration. To carry out the above, following changes are introduced via the patch: 1. The CTF container (ctfc.h) now keeps track of the non-defining declarations (by noting the DWARF attribute DW_AT_specification) in a new ctfc_ignore_vars hashtable. Such book-keeping is necessary because the CTF container should not rely on the order of DWARF DIEs presented to it at generation time. 2. At the time of ctf_add_variable (), the DW_AT_specification DIE if present is added in the ctfc_ignore_vars hashtable. The CTF variable generation for the defining declaration continues as normal. 3. If the ctf_add_variable () is asked to generate CTF variable for a DIE present in the ctfc_ignore_vars, it skips generating CTF for it. 4. Recall that CTF variables are pre-processed before emission. Till now, the only pre-processing that was being done was to sort them in order of their names. Now an additional step is added: If the CTF variable which corresponds to the non-defining declaration is indeed present in the ctfc_vars hashtable (because the corresponding DWARF DIE was encountered first by the CTF generation engine), skip that CTF variable from output. An important side effect of such a workflow above is that CTF for the C type of the non-defining decl will remain in the CTF dictionary (and will be emitted in the output section as well). This type can be pruned by the link-time de-duplicator as usual, if deemed unused. 2022-04-14 Indu Bhagat <indu.bhagat@oracle.com> gcc/ChangeLog: PR debug/105089 * ctfc.cc (ctf_dvd_ignore_insert): New function. (ctf_dvd_ignore_lookup): Likewise. (ctf_add_variable): Keep track of non-defining decl DIEs. (new_ctf_container): Initialize the new hash-table. (ctfc_delete_container): Empty hash-table. * ctfc.h (struct ctf_container): Add new hash-table. (ctf_dvd_ignore_lookup): New declaration. (ctf_add_variable): Add additional argument. * ctfout.cc (ctf_dvd_preprocess_cb): Skip adding CTF variable record for non-defining decl for which a defining decl exists in the same TU. (ctf_preprocess): Defer updating the number of global objts until here. (output_ctf_header): Use ctfc_vars_list_count as some CTF variables may not make it to the final output. (output_ctf_vars): Likewise. * dwarf2ctf.cc (gen_ctf_variable): Skip generating CTF variable if this is known to be a non-defining decl DIE. |
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