[ping][PATCH] symlookup: improves symbol lookup when a file is specified.

Tedeschi, Walfred
2017-09-20T15:22:22Z

Any feedback?

On 09/06/2017 10:46 AM, Walfred Tedeschi wrote:
> The provided patch adds a global lookup with higher priority for the
> provided file.
>
> Usual symbol lookup from GDB follows linker logic. This is what is
> desired most of the time. In the usage case a file is provided as
> scope, so the lookup has to follow this priority. Failing in finding
> the symbol at this scope usual path is followed.
>
> As test case it is presented two shared objects having a global variable
> with the same name but comming from different source files. Without the
> patch accessing them via the file scope returns the value seen in the
> first loaded shared object. Using the patch the value defined in the file
> scope is the one returned.
>
> One of the already existing test cases in print-file-var.exp starts to
> fail after using this patch. In fact the value that the linker sees is
> different then the one debugger can read from the shared object. In
> this sense it looks like to me that the test has to be changed.
> The fail is in the call:
> print 'print-file-var-lib2.c'::this_version_id == v2
>
> In this case there also in both libraries the symbol this_version_id.
> During load of the libraries linker resolves the symbol as the first one
> loaded and independent of the scope symbol will have the same value, as
> defined in the first library loaded.
> However, when defining the scope the value should represent the value
> in that context. Diferent evaluations of the same symbols might also better
> spot the issue in users code.
>
> - I haven't changed the test because I wanted to hear the community
> thought on the subject.
>
>
>
> 2017-07-13 Walfred Tedeschi <walfred.tedeschi@intel.com>
>
> gdb/ChangeLog:
>
> * symtab.c (lookup_global_symbol): Add new lookup to ensure
> priority on given block.
>
> gdb/testsuite/ChangeLog:
>
> * gdb.base/print-file-var-dlopen-main.c: New file.
> * gdb.base/print-file-var-dlopen.exp: New test based on
> print-file-var.exp.
>
> ---
> gdb/symtab.c | 4 +
> .../gdb.base/print-file-var-dlopen-main.c | 62 +++++++++++++
> gdb/testsuite/gdb.base/print-file-var-dlopen.exp | 101 +++++++++++++++++++++
> 3 files changed, 167 insertions(+)
> create mode 100644 gdb/testsuite/gdb.base/print-file-var-dlopen-main.c
> create mode 100644 gdb/testsuite/gdb.base/print-file-var-dlopen.exp
>
> diff --git a/gdb/symtab.c b/gdb/symtab.c
> index 8492315..920461f 100644
> --- a/gdb/symtab.c
> +++ b/gdb/symtab.c
> @@ -2590,6 +2590,10 @@ lookup_global_symbol (const char *name,
> if (objfile != NULL)
> result = solib_global_lookup (objfile, name, domain);
>
> + /* We still need to look on the global scope of current object file. */
> + if (result.symbol == NULL && objfile != NULL)
> + result = lookup_symbol_in_objfile (objfile, GLOBAL_BLOCK, name, domain);
> +
> /* If that didn't work go a global search (of global blocks, heh). */
> if (result.symbol == NULL)
> {
> diff --git a/gdb/testsuite/gdb.base/print-file-var-dlopen-main.c b/gdb/testsuite/gdb.base/print-file-var-dlopen-main.c
> new file mode 100644
> index 0000000..98cfd97
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/print-file-var-dlopen-main.c
> @@ -0,0 +1,62 @@
> +/* This testcase 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 <http://www.gnu.org/licenses/>. */
> +
> +#include <dlfcn.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +
> +int
> +dummy (void)
> +{
> + return 1;
> +}
> +
> +int
> +main (void)
> +{
> + int (*get_version1) (void);
> + int (*get_version2) (void);
> + int v1, v2;
> +
> + dummy ();
> + void *lib1 = dlopen ("print-file-var-dlopen-lib1.so", RTLD_LAZY);
> + void *lib2 = dlopen ("print-file-var-dlopen-lib2.so", RTLD_LAZY);
> +
> + if (lib1 == NULL || lib2 == NULL)
> + return 1;
> +
> + *(int **) (&get_version1) = dlsym (lib1, "get_version");
> + *(int **) (&get_version2) = dlsym (lib2, "get_version");
> +
> + if (get_version1 != NULL
> + && get_version2 != NULL)
> + {
> + v1 = get_version1();
> + v2 = get_version2();
> + }
> +
> + dummy (); /* STOP */
> + dlclose (lib1);
> + dlclose (lib2);
> + if (v1 != 104)
> + return 1;
> + /* The value returned by get_version_2 depends on the target system. */
> + if (v2 != 104 || v2 != 203)
> + return 2;
> +
> + return 0;
> +}
> +
> diff --git a/gdb/testsuite/gdb.base/print-file-var-dlopen.exp b/gdb/testsuite/gdb.base/print-file-var-dlopen.exp
> new file mode 100644
> index 0000000..87f89f2
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/print-file-var-dlopen.exp
> @@ -0,0 +1,101 @@
> +# 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 <http://www.gnu.org/licenses/>. */
> +
> +if {[skip_shlib_tests]} {
> + return -1
> +}
> +
> +set executable print-file-var-dlopen-main
> +
> +set lib1 "print-file-var-lib1"
> +set lib2 "print-file-var-lib2"
> +
> +set libobj1 [standard_output_file ${lib1}.so]
> +set libobj2 [standard_output_file ${lib2}.so]
> +
> +set lib_opts { debug additional_flags=-fPIC additional_flags=-shared}
> +
> +if { [gdb_compile_shlib ${srcdir}/${subdir}/${lib1}.c \
> + ${libobj1} \
> + ${lib_opts} ] != "" } {
> + return -1
> +}
> +if { [gdb_compile_shlib ${srcdir}/${subdir}/${lib2}.c \
> + ${libobj2} \
> + ${lib_opts} ] != "" } {
> + return -1
> +}
> +if { [gdb_compile "${srcdir}/${subdir}/${executable}.c" \
> + [standard_output_file ${executable}] \
> + executable \
> + [list debug shlib=-ldl]]
> + != ""} {
> + return -1
> +}
> +
> +clean_restart $executable
> +
> +set outdir [file dirname $libobj1]
> +
> +gdb_test_no_output "set env LD_LIBRARY_PATH=${outdir}/:"
> +
> +if ![runto_main] {
> + untested "could not run to main"
> + return -1
> +}
> +
> +# Try printing "this_version_num" qualified with the name of the file
> +# where the variables are defined. There are two global variables
> +# with that name, and some systems such as GNU/Linux merge them
> +# into one single entity, while some other systems such as Windows
> +# keep them separate. In the first situation, we have to verify
> +# that GDB does not randomly select the wrong instance, even when
> +# a specific filename is used to qualified the lookup. And in the
> +# second case, we have to verify that GDB does select the instance
> +# defined in the given filename.
> +#
> +# To avoid adding target-specific code in this testcase, the program
> +# sets two local variable named 'v1' and 'v2' with the value of
> +# our global variables. This allows us to compare the value that
> +# GDB returns for each query against the actual value seen by
> +# the program itself.
> +
> +# Get past the initialization of variables 'v1' and 'v2'.
> +
> +set bp_location \
> + [gdb_get_line_number "STOP" "${executable}.c"]
> +gdb_test "break $executable.c:$bp_location" \
> + "Breakpoint \[0-9\]+ at 0x\[0-9a-fA-F\]+: .*" \
> + "breapoint past v1 & v2 initialization"
> +
> +gdb_test "continue" \
> + "Breakpoint \[0-9\]+, main \\(\\) at.*" \
> + "continue to STOP marker"
> +
> +# Now check the value of this_version_id in both print-file-var-lib1.c
> +# and print-file-var-lib2.c.
> +
> +gdb_test "print 'print-file-var-dlopen-lib1.c'::this_version_id == v1" \
> + " = 1"
> +
> +gdb_test "print 'print-file-var-dlopen-lib2.c'::this_version_id == v2" \
> + " = 1"
> +
> +gdb_test "print 'print-file-var-dlopen-lib2.c'::get_version::test == v2" \
> + " = 1"
> +
> +gdb_test "print 'print-file-var-dlopen-lib1.c'::get_version::test" \
> + " = 100"
> +

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