diff options
Diffstat (limited to 'gdb/solib-svr4.c')
| -rw-r--r-- | gdb/solib-svr4.c | 212 |
1 files changed, 208 insertions, 4 deletions
diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c index 2a2745d..458c4ba 100644 --- a/gdb/solib-svr4.c +++ b/gdb/solib-svr4.c @@ -431,6 +431,14 @@ struct svr4_info /* This identifies which namespaces are active. A namespace is considered active when there is at least one shared object loaded into it. */ std::set<size_t> active_namespaces; + + /* This flag indicates whether initializations related to the + GLIBC TLS module id tracking code have been performed. */ + bool glibc_tls_slots_inited = false; + + /* A vector of link map addresses for GLIBC TLS slots. See comment + for tls_maybe_fill_slot for more information. */ + std::vector<CORE_ADDR> glibc_tls_slots; }; /* Per-program-space data key. */ @@ -635,10 +643,10 @@ read_program_header (int type, int *p_arch_size, CORE_ADDR *base_addr) return buf; } +/* See solib-svr4.h. */ -/* Return program interpreter string. */ -static std::optional<gdb::byte_vector> -find_program_interpreter (void) +std::optional<gdb::byte_vector> +svr4_find_program_interpreter () { /* If we have a current exec_bfd, use its section table. */ if (current_program_space->exec_bfd () @@ -1580,6 +1588,198 @@ svr4_fetch_objfile_link_map (struct objfile *objfile) return 0; } +/* Return true if bfd section BFD_SECT is a thread local section + (i.e. either named ".tdata" or ".tbss"), and false otherwise. */ + +static bool +is_thread_local_section (struct bfd_section *bfd_sect) +{ + return ((strcmp (bfd_sect->name, ".tdata") == 0 + || strcmp (bfd_sect->name, ".tbss") == 0) + && bfd_sect->size != 0); +} + +/* Return true if objfile OBJF contains a thread local section, and + false otherwise. */ + +static bool +has_thread_local_section (const objfile *objf) +{ + for (obj_section *objsec : objf->sections ()) + if (is_thread_local_section (objsec->the_bfd_section)) + return true; + return false; +} + +/* Return true if solib SO contains a thread local section, and false + otherwise. */ + +static bool +has_thread_local_section (const solib &so) +{ + for (const target_section &p : so.sections) + if (is_thread_local_section (p.the_bfd_section)) + return true; + return false; +} + +/* For the MUSL C library, given link map address LM_ADDR, return the + corresponding TLS module id, or 0 if not found. + + Background: Unlike the mechanism used by glibc (see below), the + scheme used by the MUSL C library is pretty simple. If the + executable contains TLS variables it gets module id 1. Otherwise, + the first shared object loaded which contains TLS variables is + assigned to module id 1. TLS-containing shared objects are then + assigned consecutive module ids, based on the order that they are + loaded. When unloaded via dlclose, module ids are reassigned as if + that module had never been loaded. */ + +int +musl_link_map_to_tls_module_id (CORE_ADDR lm_addr) +{ + /* When lm_addr is zero, the program is statically linked. Any TLS + variables will be in module id 1. */ + if (lm_addr == 0) + return 1; + + int mod_id = 0; + if (has_thread_local_section (current_program_space->symfile_object_file)) + mod_id++; + + struct svr4_info *info = get_svr4_info (current_program_space); + + /* Cause svr4_current_sos() to be run if it hasn't been already. */ + if (info->main_lm_addr == 0) + solib_add (NULL, 0, auto_solib_add); + + /* Handle case where lm_addr corresponds to the main program. + Return value is either 0, when there are no TLS variables, or 1, + when there are. */ + if (lm_addr == info->main_lm_addr) + return mod_id; + + /* Iterate through the shared objects, possibly incrementing the + module id, and returning mod_id should a match be found. */ + for (const solib &so : current_program_space->solibs ()) + { + if (has_thread_local_section (so)) + mod_id++; + + auto *li = gdb::checked_static_cast<lm_info_svr4 *> (so.lm_info.get ()); + if (li->lm_addr == lm_addr) + return mod_id; + } + return 0; +} + +/* For GLIBC, given link map address LM_ADDR, return the corresponding TLS + module id, or 0 if not found. */ + +int +glibc_link_map_to_tls_module_id (CORE_ADDR lm_addr) +{ + /* When lm_addr is zero, the program is statically linked. Any TLS + variables will be in module id 1. */ + if (lm_addr == 0) + return 1; + + /* Look up lm_addr in the TLS slot data structure. */ + struct svr4_info *info = get_svr4_info (current_program_space); + auto it = std::find (info->glibc_tls_slots.begin (), + info->glibc_tls_slots.end (), + lm_addr); + if (it == info->glibc_tls_slots.end ()) + return 0; + else + return 1 + it - info->glibc_tls_slots.begin (); +} + +/* Conditionally, based on whether the shared object, SO, contains TLS + variables, assign a link map address to a TLS module id slot. This + code is GLIBC-specific and may only work for specific GLIBC + versions. That said, it is known to work for (at least) GLIBC + versions 2.27 thru 2.40. + + Background: In order to implement internal TLS address lookup + code, it is necessary to find the module id that has been + associated with a specific link map address. In GLIBC, the TLS + module id is stored in struct link_map, in the member + 'l_tls_modid'. While the first several members of struct link_map + are part of the SVR4 ABI, the offset to l_tls_modid definitely is + not. Therefore, since we don't know the offset to l_tls_modid, we + cannot simply look it up - which is a shame, because things would + be so much more easy and obviously accurate, if we could access + l_tls_modid. + + GLIBC has a concept of TLS module id slots. These slots are + allocated consecutively as shared objects containing TLS variables + are loaded. When unloaded (e.g. via dlclose()), the corresponding + slot is marked as unused, but may be used again when later loading + a shared object. + + The functions tls_maybe_fill_slot and tls_maybe_erase_slot are + associated with the observers 'solib_loaded' and 'solib_unloaded'. + They (attempt to) track use of TLS module id slots in the same way + that GLIBC does, which will hopefully provide an accurate module id + when asked to provide it via glibc_link_map_to_tls_module_id(), + above. */ + +static void +tls_maybe_fill_slot (solib &so) +{ + struct svr4_info *info = get_svr4_info (current_program_space); + if (!info->glibc_tls_slots_inited) + { + /* Cause svr4_current_sos() to be run if it hasn't been already. */ + if (info->main_lm_addr == 0) + svr4_current_sos_direct (info); + + /* Quit early when main_lm_addr is still 0. */ + if (info->main_lm_addr == 0) + return; + + /* Also quit early when symfile_object_file is not yet known. */ + if (current_program_space->symfile_object_file == nullptr) + return; + + if (has_thread_local_section (current_program_space->symfile_object_file)) + info->glibc_tls_slots.push_back (info->main_lm_addr); + info->glibc_tls_slots_inited = true; + } + + if (has_thread_local_section (so)) + { + auto it = std::find (info->glibc_tls_slots.begin (), + info->glibc_tls_slots.end (), + 0); + auto *li = gdb::checked_static_cast<lm_info_svr4 *> (so.lm_info.get ()); + if (it == info->glibc_tls_slots.end ()) + info->glibc_tls_slots.push_back (li->lm_addr); + else + *it = li->lm_addr; + } +} + +/* Remove a link map address from the TLS module slot data structure. + As noted above, this code is GLIBC-specific. */ + +static void +tls_maybe_erase_slot (program_space *pspace, const solib &so, + bool still_in_use, bool silent) +{ + if (still_in_use) + return; + + struct svr4_info *info = get_svr4_info (pspace); + auto *li = gdb::checked_static_cast<lm_info_svr4 *> (so.lm_info.get ()); + auto it = std::find (info->glibc_tls_slots.begin (), + info->glibc_tls_slots.end (), + li->lm_addr); + if (it != info->glibc_tls_slots.end ()) + *it = 0; +} + /* On some systems, the only way to recognize the link map entry for the main executable file is by looking at its name. Return non-zero iff SONAME matches one of the known main executable names. */ @@ -2377,7 +2577,7 @@ enable_break (struct svr4_info *info, int from_tty) /* Find the program interpreter; if not found, warn the user and drop into the old breakpoint at symbol code. */ std::optional<gdb::byte_vector> interp_name_holder - = find_program_interpreter (); + = svr4_find_program_interpreter (); if (interp_name_holder) { const char *interp_name = (const char *) interp_name_holder->data (); @@ -3632,4 +3832,8 @@ _initialize_svr4_solib () { gdb::observers::free_objfile.attach (svr4_free_objfile_observer, "solib-svr4"); + + /* Set up observers for tracking GLIBC TLS module id slots. */ + gdb::observers::solib_loaded.attach (tls_maybe_fill_slot, "solib-svr4"); + gdb::observers::solib_unloaded.attach (tls_maybe_erase_slot, "solib-svr4"); } |