From patchwork Tue Jul 4 15:49:10 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Pedro Alves X-Patchwork-Id: 21406 Received: (qmail 26490 invoked by alias); 4 Jul 2017 15:49:17 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Delivered-To: mailing list gdb-patches@sourceware.org Received: (qmail 26383 invoked by uid 89); 4 Jul 2017 15:49:16 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-26.8 required=5.0 tests=BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KAM_STOCKGEN, RP_MATCHES_RCVD, SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=Those X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Tue, 04 Jul 2017 15:49:13 +0000 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B1C664E4CB; Tue, 4 Jul 2017 15:49:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com B1C664E4CB Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=palves@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com B1C664E4CB Received: from cascais.lan (ovpn04.gateway.prod.ext.ams2.redhat.com [10.39.146.4]) by smtp.corp.redhat.com (Postfix) with ESMTP id C08F16292A; Tue, 4 Jul 2017 15:49:11 +0000 (UTC) From: Pedro Alves To: gdb-patches@sourceware.org Cc: Zack Weinberg Subject: [PATCH] Handle function aliases better (PR gdb/19487, errno printing) Date: Tue, 4 Jul 2017 16:49:10 +0100 Message-Id: <1499183350-23666-1-git-send-email-palves@redhat.com> (Ref: https://sourceware.org/ml/gdb/2017-06/msg00048.html) This patch improves GDB support for function aliases defined with __attribute__ alias. For example, in the test added by this commit, there is no reference to "func_alias" in the debug info at all, only to "func"'s definition: $ nm ./testsuite/outputs/gdb.base/symbol-alias/symbol-alias | grep " func" 00000000004005ae t func 00000000004005ae T func_alias $ readelf -w ./testsuite/outputs/gdb.base/symbol-alias/symbol-alias | grep func -B 1 -A 8 <1>: Abbrev Number: 5 (DW_TAG_subprogram) DW_AT_name : (indirect string, offset: 0x111): func DW_AT_decl_file : 1 DW_AT_decl_line : 27 DW_AT_prototyped : 1 DW_AT_type : <0xf8> DW_AT_low_pc : 0x4005ae DW_AT_high_pc : 0xb DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa) DW_AT_GNU_all_call_sites: 1 So all GDB knows about "func_alias" is from the minsym (elf symbol): (gdb) p func_alias $1 = {} 0x4005ae (gdb) ptype func_alias type = int () (gdb) p func $2 = {struct S *(void)} 0x4005ae (gdb) ptype func type = struct S { int field1; int field2; } *(void) The result is that calling func_alias from the command line produces incorrect results. This is similar (though not exactly the same) to the glibc errno/__errno_location/__GI___errno_location situation. On glibc, errno is defined like this: extern int *__errno_location (void); #define errno (*__errno_location ()) with __GI___errno_location being an internal alias for __errno_location. On my system's libc (F23), I do see debug info for __errno_location, in the form of name vs linkage name: <1><95a5>: Abbrev Number: 18 (DW_TAG_subprogram) <95a6> DW_AT_external : 1 <95a6> DW_AT_name : (indirect string, offset: 0x2c26): __errno_location <95aa> DW_AT_decl_file : 1 <95ab> DW_AT_decl_line : 24 <95ac> DW_AT_linkage_name: (indirect string, offset: 0x2c21): __GI___errno_location <95b0> DW_AT_prototyped : 1 <95b0> DW_AT_type : <0x9206> <95b4> DW_AT_low_pc : 0x20f40 <95bc> DW_AT_high_pc : 0x11 <95c4> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa) <95c6> DW_AT_GNU_all_call_sites: 1 however that doesn't matter in practice, because GDB doesn't record demangled names anyway, and so we end up with the exact same situation covered by the testcase. So the fix is to make the expression parser find a debug symbol for the same address as the just-found minsym, when a lookup by name didn't find a debug symbol by name. We now get: (gdb) p func_alias $1 = {struct S *(void)} 0x4005ae (gdb) p __errno_location $2 = {int *(void)} 0x7ffff6e92830 <__errno_location> I've made the test exercise variable aliases too, for completeness. Those already work correctly, because unlike for function aliases, GCC emits debug information for variable aliases. Tested on GNU/Linux. gdb/ChangeLog: yyyy-mm-dd Pedro Alves PR gdb/19487 * c-exp.y (variable production): Handle function aliases. * minsyms.c (msymbol_is_text): New function. * minsyms.h (msymbol_is_text): Declare. * symtab.c (find_function_alias_target): New function. * symtab.h (find_function_alias_target): Declare. gdb/testsuite/ChangeLog: yyyy-mm-dd Pedro Alves PR gdb/19487 * gdb.base/symbol-alias.c: New. * gdb.base/symbol-alias2.c: New. * gdb.base/symbol-alias.exp: New. --- gdb/c-exp.y | 35 ++++++++++++++++++++++++------- gdb/minsyms.c | 17 +++++++++++++++ gdb/minsyms.h | 4 ++++ gdb/symtab.c | 19 +++++++++++++++++ gdb/symtab.h | 7 +++++++ gdb/testsuite/gdb.base/symbol-alias.c | 31 +++++++++++++++++++++++++++ gdb/testsuite/gdb.base/symbol-alias.exp | 37 +++++++++++++++++++++++++++++++++ gdb/testsuite/gdb.base/symbol-alias2.c | 34 ++++++++++++++++++++++++++++++ 8 files changed, 176 insertions(+), 8 deletions(-) create mode 100644 gdb/testsuite/gdb.base/symbol-alias.c create mode 100644 gdb/testsuite/gdb.base/symbol-alias.exp create mode 100644 gdb/testsuite/gdb.base/symbol-alias2.c diff --git a/gdb/c-exp.y b/gdb/c-exp.y index bdcd51f..650ae10 100644 --- a/gdb/c-exp.y +++ b/gdb/c-exp.y @@ -1041,15 +1041,34 @@ variable: name_not_typename struct bound_minimal_symbol msymbol; char *arg = copy_name ($1.stoken); - msymbol = - lookup_bound_minimal_symbol (arg); - if (msymbol.minsym != NULL) - write_exp_msymbol (pstate, msymbol); - else if (!have_full_symbols () && !have_partial_symbols ()) - error (_("No symbol table is loaded. Use the \"file\" command.")); + msymbol = lookup_bound_minimal_symbol (arg); + if (msymbol.minsym == NULL) + { + if (!have_full_symbols () && !have_partial_symbols ()) + error (_("No symbol table is loaded. Use the \"file\" command.")); + else + error (_("No symbol \"%s\" in current context."), + copy_name ($1.stoken)); + } + + /* This minsym might be an alias for + another function. See if we can find + the debug symbol for the target, and + if so, use it instead, since it has + prototype info. This is important + for example for "p *__errno_location()". */ + symbol *alias_target + = find_function_alias_target (msymbol); + if (alias_target != NULL) + { + write_exp_elt_opcode (pstate, OP_VAR_VALUE); + write_exp_elt_block + (pstate, SYMBOL_BLOCK_VALUE (alias_target)); + write_exp_elt_sym (pstate, alias_target); + write_exp_elt_opcode (pstate, OP_VAR_VALUE); + } else - error (_("No symbol \"%s\" in current context."), - copy_name ($1.stoken)); + write_exp_msymbol (pstate, msymbol); } } ; diff --git a/gdb/minsyms.c b/gdb/minsyms.c index c93eaa3..69b9e40 100644 --- a/gdb/minsyms.c +++ b/gdb/minsyms.c @@ -52,6 +52,23 @@ #include "cli/cli-utils.h" #include "symbol.h" +/* See minsyms.h. */ + +bool +msymbol_is_text (minimal_symbol *msymbol) +{ + switch (MSYMBOL_TYPE (msymbol)) + { + case mst_text: + case mst_text_gnu_ifunc: + case mst_solib_trampoline: + case mst_file_text: + return true; + default: + return false; + } +} + /* Accumulate the minimal symbols for each objfile in bunches of BUNCH_SIZE. At the end, copy them all into one newly allocated location on an objfile's per-BFD storage obstack. */ diff --git a/gdb/minsyms.h b/gdb/minsyms.h index b82a22a..e763f62 100644 --- a/gdb/minsyms.h +++ b/gdb/minsyms.h @@ -157,6 +157,10 @@ void terminate_minimal_symbol_table (struct objfile *objfile); +/* Return whether MSYMBOL is a function/method. */ + +bool msymbol_is_text (minimal_symbol *msymbol); + /* Compute a hash code for the string argument. */ unsigned int msymbol_hash (const char *); diff --git a/gdb/symtab.c b/gdb/symtab.c index 497d520..4269267 100644 --- a/gdb/symtab.c +++ b/gdb/symtab.c @@ -3827,6 +3827,25 @@ skip_prologue_using_sal (struct gdbarch *gdbarch, CORE_ADDR func_addr) /* Don't return END_PC, which is past the end of the function. */ return prologue_sal.pc; } + +/* See symtab.h. */ + +symbol * +find_function_alias_target (bound_minimal_symbol msymbol) +{ + if (!msymbol_is_text (msymbol.minsym)) + return NULL; + + CORE_ADDR addr = BMSYMBOL_VALUE_ADDRESS (msymbol); + symbol *sym = find_pc_function (addr); + if (sym != NULL + && SYMBOL_CLASS (sym) == LOC_BLOCK + && BLOCK_START (SYMBOL_BLOCK_VALUE (sym)) == addr) + return sym; + + return NULL; +} + /* If P is of the form "operator[ \t]+..." where `...' is some legitimate operator text, return a pointer to the diff --git a/gdb/symtab.h b/gdb/symtab.h index 341deca..1b48611 100644 --- a/gdb/symtab.h +++ b/gdb/symtab.h @@ -1537,6 +1537,13 @@ extern CORE_ADDR skip_prologue_using_sal (struct gdbarch *gdbarch, extern struct symbol *fixup_symbol_section (struct symbol *, struct objfile *); +/* If MSYMBOL is an text symbol, look for a function debug symbol with + the same address. Returns NULL if not found. This is necessary in + case a function is an alias to some other function, because debug + information is only emitted for the alias target function's + definition, not for the alias. */ +extern symbol *find_function_alias_target (bound_minimal_symbol msymbol); + /* Symbol searching */ /* Note: struct symbol_search, search_symbols, et.al. are declared here, instead of making them local to symtab.c, for gdbtk's sake. */ diff --git a/gdb/testsuite/gdb.base/symbol-alias.c b/gdb/testsuite/gdb.base/symbol-alias.c new file mode 100644 index 0000000..cc5d104 --- /dev/null +++ b/gdb/testsuite/gdb.base/symbol-alias.c @@ -0,0 +1,31 @@ +/* This test is part of GDB, the GNU debugger. + + Copyright 2017 Free Software Foundation, Inc. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see . */ + +struct S +{ + int field1; + int field2; +}; + +extern struct S *func_alias (void); + +int +main (void) +{ + struct S *s = func_alias (); + return s->field1 - s->field1; +} diff --git a/gdb/testsuite/gdb.base/symbol-alias.exp b/gdb/testsuite/gdb.base/symbol-alias.exp new file mode 100644 index 0000000..dc63eb1 --- /dev/null +++ b/gdb/testsuite/gdb.base/symbol-alias.exp @@ -0,0 +1,37 @@ +# Test for printing alias symbols. +# Copyright 2017 Free Software Foundation, Inc. + +# This program is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 3 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program. If not, see . + +standard_testfile symbol-alias.c symbol-alias2.c + +if { [prepare_for_testing "failed to prepare" ${testfile} [list $srcfile $srcfile2]] } { + return -1 +} + +if ![runto_main] then { + fail "can't run to main" + continue +} + +# Functions. +foreach f {"func" "func_alias"} { + gdb_test "p $f" " = {struct S \\*\\(void\\)} $hex " + gdb_test "p *${f}()" "= {field1 = 1, field2 = 2}" +} + +# Variables. +foreach v {"g_var_s" "g_var_s_alias"} { + gdb_test "p $v" "= {field1 = 1, field2 = 2}" +} diff --git a/gdb/testsuite/gdb.base/symbol-alias2.c b/gdb/testsuite/gdb.base/symbol-alias2.c new file mode 100644 index 0000000..aedd520 --- /dev/null +++ b/gdb/testsuite/gdb.base/symbol-alias2.c @@ -0,0 +1,34 @@ +/* This test is part of GDB, the GNU debugger. + + Copyright 2017 Free Software Foundation, Inc. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see . */ + +struct S +{ + int field1; + int field2; +}; + +struct S g_var_s = { 1, 2 }; + +static struct S * +func (void) +{ + return &g_var_s; +} + +struct S *func_alias (void) __attribute__ ((alias ("func"))); + +extern struct S g_var_s_alias __attribute__ ((alias ("g_var_s")));