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(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><db>: Abbrev Number: 5 (DW_TAG_subprogram) <dc> DW_AT_name : (indirect string, offset: 0x111): func <e0> DW_AT_decl_file : 1 <e1> DW_AT_decl_line : 27 <e2> DW_AT_prototyped : 1 <e2> DW_AT_type : <0xf8> <e6> DW_AT_low_pc : 0x4005ae <ee> DW_AT_high_pc : 0xb <f6> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa) <f8> 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 = {<text variable, no debug info>} 0x4005ae <func> (gdb) ptype func_alias type = int () (gdb) p func $2 = {struct S *(void)} 0x4005ae <func> (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 <func> (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: 2017-08-21 Pedro Alves <palves@redhat.com> 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: 2017-08-21 Pedro Alves <palves@redhat.com> PR gdb/19487 * gdb.base/symbol-alias.c: New. * gdb.base/symbol-alias2.c: New. * gdb.base/symbol-alias.exp: New. |
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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.