From: Pedro Alves Date: Thu, 26 Apr 2018 12:01:26 +0000 (+0100) Subject: Calling ifunc functions when resolver has debug info, user symbol same name X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=ca31ab1d675c1e20cee5f8cb213c52e3d7352496;p=binutils-gdb.git Calling ifunc functions when resolver has debug info, user symbol same name If the GNU ifunc resolver has the same name as the user visible symbol, and the resolver has debug info, then the DWARF info for the resolver masks the ifunc minsym. In that scenario, if you try calling the ifunc from GDB, you call the resolver instead. With the gnu-ifunc.exp testcase added in a following patch, you'd see: (gdb) p gnu_ifunc (3) $1 = (int (*)(int)) 0x400753 (gdb) FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=1: resolved_debug=0: p gnu_ifunc (3) ^^^^^^^^^^^^^^^^ That is, we called the ifunc resolver manually, which returned a pointer to the ifunc target function ("final"). The "final" symbol is the function that GDB should have called automatically, ~~~~~~~~~~~~ int final (int arg) { return arg + 1; } ~~~~~~~~~ which is what happens if you don't have debug info for the resolver: (gdb) p gnu_ifunc (3) $1 = 4 (gdb) PASS: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=0: resolved_debug=1: p gnu_ifunc (3) ^^^^^^^^^^^^^^^^ or if the resolver's symbol has a different name from the ifunc (as is the case with modern uses of ifunc via __attribute__ ifunc, such as glibc uses): (gdb) p gnu_ifunc (3) $1 = 4 (gdb) PASS: gdb.base/gnu-ifunc.exp: resolver_attr=1: resolver_debug=1: resolved_debug=0: p gnu_ifunc (3) ^^^^^^^^^^^^^^^ in which case after this patch, you can still call the resolver directly if you want: (gdb) p gnu_ifunc_resolver (3) $1 = (int (*)(int)) 0x400753 gdb/ChangeLog: 2018-04-26 Pedro Alves * c-exp.y (variable production): Prefer ifunc minsyms over regular function symbols. * symtab.c (find_gnu_ifunc): New function. * minsyms.h (lookup_msym_prefer): New enum. (lookup_minimal_symbol_by_pc_section): Replace 'want_trampoline' parameter by a lookup_msym_prefer parameter. * symtab.h (find_gnu_ifunc): New declaration. --- diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 8db2d8aeb6d..67e1babcba2 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,13 @@ +2018-04-26 Pedro Alves + + * c-exp.y (variable production): Prefer ifunc minsyms over + regular function symbols. + * symtab.c (find_gnu_ifunc): New function. + * minsyms.h (lookup_msym_prefer): New enum. + (lookup_minimal_symbol_by_pc_section): Replace 'want_trampoline' + parameter by a lookup_msym_prefer parameter. + * symtab.h (find_gnu_ifunc): New declaration. + 2018-04-26 Pedro Alves * blockframe.c (find_gnu_ifunc_target_type): New function. diff --git a/gdb/c-exp.y b/gdb/c-exp.y index e2ea07cd792..723249c1f58 100644 --- a/gdb/c-exp.y +++ b/gdb/c-exp.y @@ -1041,10 +1041,22 @@ variable: name_not_typename if (symbol_read_needs_frame (sym.symbol)) innermost_block.update (sym); - write_exp_elt_opcode (pstate, OP_VAR_VALUE); - write_exp_elt_block (pstate, sym.block); - write_exp_elt_sym (pstate, sym.symbol); - write_exp_elt_opcode (pstate, OP_VAR_VALUE); + /* If we found a function, see if it's + an ifunc resolver that has the same + address as the ifunc symbol itself. + If so, prefer the ifunc symbol. */ + + bound_minimal_symbol resolver + = find_gnu_ifunc (sym.symbol); + if (resolver.minsym != NULL) + write_exp_msymbol (pstate, resolver); + else + { + write_exp_elt_opcode (pstate, OP_VAR_VALUE); + write_exp_elt_block (pstate, sym.block); + write_exp_elt_sym (pstate, sym.symbol); + write_exp_elt_opcode (pstate, OP_VAR_VALUE); + } } else if ($1.is_a_field_of_this) { diff --git a/gdb/linespec.c b/gdb/linespec.c index 7ef8012ab56..8951c1e8c47 100644 --- a/gdb/linespec.c +++ b/gdb/linespec.c @@ -4343,6 +4343,7 @@ add_minsym (struct minimal_symbol *minsym, struct objfile *objfile, struct bound_minimal_symbol mo = {minsym, objfile}; msyms->push_back (mo); + return; } /* Search for minimal symbols called NAME. If SEARCH_PSPACE @@ -4383,6 +4384,7 @@ search_minsyms_for_name (struct collect_info *info, add_minsym (msym, objfile, nullptr, info->state->list_mode, &minsyms); + return false; }); } } @@ -4398,6 +4400,7 @@ search_minsyms_for_name (struct collect_info *info, { add_minsym (msym, SYMTAB_OBJFILE (symtab), symtab, info->state->list_mode, &minsyms); + return false; }); } } diff --git a/gdb/minsyms.c b/gdb/minsyms.c index 9d23c4fd4fd..7ca3fcccbea 100644 --- a/gdb/minsyms.c +++ b/gdb/minsyms.c @@ -471,7 +471,7 @@ linkage_name_str (const lookup_name_info &lookup_name) void iterate_over_minimal_symbols (struct objfile *objf, const lookup_name_info &lookup_name, - gdb::function_view callback) + gdb::function_view callback) { /* The first pass is over the ordinary hash table. */ { @@ -487,7 +487,8 @@ iterate_over_minimal_symbols iter = iter->hash_next) { if (mangled_cmp (MSYMBOL_LINKAGE_NAME (iter), name) == 0) - callback (iter); + if (callback (iter)) + return; } } @@ -506,7 +507,8 @@ iterate_over_minimal_symbols iter != NULL; iter = iter->demangled_hash_next) if (name_match (MSYMBOL_SEARCH_NAME (iter), lookup_name, NULL)) - callback (iter); + if (callback (iter)) + return; } } diff --git a/gdb/minsyms.h b/gdb/minsyms.h index a2b7ddd7035..29d8283c214 100644 --- a/gdb/minsyms.h +++ b/gdb/minsyms.h @@ -269,7 +269,7 @@ struct bound_minimal_symbol lookup_minimal_symbol_by_pc (CORE_ADDR); void iterate_over_minimal_symbols (struct objfile *objf, const lookup_name_info &name, - gdb::function_view callback); + gdb::function_view callback); /* Compute the upper bound of MINSYM. The upper bound is the last address thought to be part of the symbol. If the symbol has a diff --git a/gdb/symtab.c b/gdb/symtab.c index c1ead701ece..92b7ed7538c 100644 --- a/gdb/symtab.c +++ b/gdb/symtab.c @@ -4953,6 +4953,38 @@ symbol_is_function_or_method (minimal_symbol *msymbol) } } +/* See symtab.h. */ + +bound_minimal_symbol +find_gnu_ifunc (const symbol *sym) +{ + if (SYMBOL_CLASS (sym) != LOC_BLOCK) + return {}; + + lookup_name_info lookup_name (SYMBOL_SEARCH_NAME (sym), + symbol_name_match_type::SEARCH_NAME); + struct objfile *objfile = symbol_objfile (sym); + + CORE_ADDR address = BLOCK_START (SYMBOL_BLOCK_VALUE (sym)); + minimal_symbol *ifunc = NULL; + + iterate_over_minimal_symbols (objfile, lookup_name, + [&] (minimal_symbol *minsym) + { + if (MSYMBOL_TYPE (minsym) == mst_text_gnu_ifunc + && MSYMBOL_VALUE_ADDRESS (objfile, minsym) == address) + { + ifunc = minsym; + return true; + } + return false; + }); + + if (ifunc != NULL) + return {ifunc, objfile}; + return {}; +} + /* Add matching symbols from SYMTAB to the current completion list. */ static void diff --git a/gdb/symtab.h b/gdb/symtab.h index 83ff6f226d8..94b6b24bd5d 100644 --- a/gdb/symtab.h +++ b/gdb/symtab.h @@ -1686,6 +1686,9 @@ extern struct type *find_function_type (CORE_ADDR pc); extern struct type *find_gnu_ifunc_target_type (CORE_ADDR resolver_funaddr); +/* Find the GNU ifunc minimal symbol that matches SYM. */ +extern bound_minimal_symbol find_gnu_ifunc (const symbol *sym); + extern void clear_pc_function_cache (void); /* Expand symtab containing PC, SECTION if not already expanded. */