[2/4] Handle copy relocations
Commit Message
On 6/27/19 3:52 PM, Tom Tromey wrote:
> In ELF, if a data symbol is defined in a shared library and used by
> the main program, it will be subject to a "copy relocation".
To be more correct, this depends on ABI, or how you compile your
binary. Compiling the main binary as PIC/PIE may or may not use
copy relocations and use GOT accesses instead, for example.
> In this
> scenario, the main program has a copy of the symbol in question, and a
> relocation that tells ld.so to copy the data from the shared library.
> Then the symbol in the main program is used to satisfy all references.
>
> This patch changes gdb to handle this scenario. Data symbols coming
> from ELF shared libraries get a special flag that indicates that the
> symbol's address may be subject to copy relocation.
>
> I looked briefly into handling copy relocations by looking at the
> actual relocations in the main program, but this seemed difficult to
> do with BFD.
>
> Note that no caching is done here. Perhaps this could be changed if
> need be; I wanted to avoid possible problems with either objfile
> lifetimes and changes, or conflicts with the long-term (vapor-ware)
> objfile splitting project.
I'm surprised to find no tests in this patch?
I'm not sure whether this is the right approach, since it seems to assume
that interposition/preemption happens, while it may not, given
possibility of attribute visibility hidden/protected. Ideally whatever
design we take considers how no-preemption would be addressed.
This came up earlier here:
https://sourceware.org/ml/gdb-patches/2017-10/msg00710.html
I've taken the examples from that email and converted them to
a proper testcase today. See below.
With current master, we get:
FAIL: gdb.base/print-file-var.exp: hidden=1: dlopen=0: version_id_main=0: 'print-file-var-lib2.c'::this_version_id == v2
FAIL: gdb.base/print-file-var.exp: hidden=1: dlopen=0: version_id_main=1: 'print-file-var-lib1.c'::this_version_id == v1
FAIL: gdb.base/print-file-var.exp: hidden=1: dlopen=0: version_id_main=1: 'print-file-var-lib2.c'::this_version_id == v2
FAIL: gdb.base/print-file-var.exp: hidden=1: dlopen=1: version_id_main=0: 'print-file-var-lib2.c'::this_version_id == v2
FAIL: gdb.base/print-file-var.exp: hidden=1: dlopen=1: version_id_main=1: 'print-file-var-lib1.c'::this_version_id == v1
FAIL: gdb.base/print-file-var.exp: hidden=1: dlopen=1: version_id_main=1: 'print-file-var-lib2.c'::this_version_id == v2
Your patch curiously doesn't make a difference here. Could we add
something here to show what your patch improves?
But I'm wondering whether fixing the hidden=1 cases would fit
with the design of your patch, or does that scenario require
thinking about all this differently?
From ffe918c15e9dc10540ed1590d9d37fee3fcea844 Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Sat, 20 Jul 2019 01:20:35 +0100
Subject: [PATCH] Make print-file-var.exp test attribute visibility hidden,
dlopen, and main symbol
Make gdb.base/print-file-var.exp test all combinations of:
- attribute hidden in the this_version_id symbols or not
- dlopen or not
- this_version_id symbol in main file or not
I did not reindent the body of "test" in order to keep the patch
readable. To be reindended before pushing.
gdb/ChangeLog:
yyyy-mm-dd Pedro Alves <palves@redhat.com>
* gdb.base/print-file-var-lib1.c: Include <stdio.h> and
"print-file-var.h".
(this_version_id) Use ATTRIBUTE_VISIBILITY.
(get_version_1): Print this_version_id and its address.
* gdb.base/print-file-var-lib2.c: Include <stdio.h> and
"print-file-var.h".
(this_version_id) Use ATTRIBUTE_VISIBILITY.
(get_version_2): Print this_version_id and its address.
* gdb.base/print-file-var-main.c: Include <dlfcn.h>, <assert.h>,
<stddef.h> and "print-file-var.h".
[VERSION_ID_MAIN] (this_version_id): Define.
(main): Define v0. Use dlopen if SHLIB_NAME is defined.
* gdb.base/print-file-var.exp (test): New, factored out from top
level.
(top level): Test all combinations of attribute hidden or not,
dlopen or not, and this_version_id symbol in main file or not.
---
gdb/testsuite/gdb.base/print-file-var-lib1.c | 7 ++-
gdb/testsuite/gdb.base/print-file-var-lib2.c | 6 ++-
gdb/testsuite/gdb.base/print-file-var-main.c | 38 +++++++++++---
gdb/testsuite/gdb.base/print-file-var.exp | 76 +++++++++++++++++++++-------
gdb/testsuite/gdb.base/print-file-var.h | 26 ++++++++++
5 files changed, 127 insertions(+), 26 deletions(-)
create mode 100644 gdb/testsuite/gdb.base/print-file-var.h
@@ -14,10 +14,15 @@
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
-int this_version_id = 104;
+#include <stdio.h>
+#include "print-file-var.h"
+
+ATTRIBUTE_VISIBILITY int this_version_id = 104;
int
get_version_1 (void)
{
+ printf ("get_version_1: &this_version_id=%p, this_version_id=%d\n", &this_version_id, this_version_id);
+
return this_version_id;
}
@@ -14,10 +14,14 @@
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
-int this_version_id = 203;
+#include <stdio.h>
+#include "print-file-var.h"
+
+ATTRIBUTE_VISIBILITY int this_version_id = 203;
int
get_version_2 (void)
{
+ printf ("get_version_2: &this_version_id=%p, this_version_id=%d\n", &this_version_id, this_version_id);
return this_version_id;
}
@@ -14,21 +14,45 @@
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
+#ifdef SHLIB_NAME
+# include <dlfcn.h>
+#endif
+
+#include <assert.h>
+#include <stddef.h>
+
+#include "print-file-var.h"
+
extern int get_version_1 (void);
extern int get_version_2 (void);
+#if VERSION_ID_MAIN
+ATTRIBUTE_VISIBILITY int this_version_id = 55;
+#endif
+
int
main (void)
{
+#if VERSION_ID_MAIN
+ int vm = this_version_id;
+#endif
int v1 = get_version_1 ();
- int v2 = get_version_2 ();
+ int v2;
- if (v1 != 104)
- return 1;
- /* The value returned by get_version_2 depends on the target system. */
- if (v2 != 104 && v2 != 203)
- return 2;
+#ifdef SHLIB_NAME
+ {
+ void *handle = dlopen (SHLIB_NAME, RTLD_LAZY);
+ int (*getver2) (void);
+
+ assert (handle != NULL);
+
+ getver2 = (int (*)(void)) dlsym (handle, "get_version_2");
+
+ v2 = getver2 ();
+ }
+#else
+ v2 = get_version_2 ();
+#endif
return 0; /* STOP */
}
-
@@ -17,15 +17,23 @@ if {[skip_shlib_tests]} {
return -1
}
-set executable print-file-var-main
+proc test {hidden dlopen version_id_main} {
+ global srcdir subdir
+
+set main "print-file-var-main"
+
+set suffix "-hidden$hidden-dlopen$dlopen-version_id_main$version_id_main"
+
+set executable $main$suffix
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 libobj1 [standard_output_file ${lib1}$suffix.so]
+set libobj2 [standard_output_file ${lib2}$suffix.so]
set lib_opts { debug additional_flags=-fPIC }
+lappend lib_opts "additional_flags=-DHIDDEN=$hidden"
if { [gdb_compile_shlib ${srcdir}/${subdir}/${lib1}.c \
${libobj1} \
@@ -37,10 +45,21 @@ if { [gdb_compile_shlib ${srcdir}/${subdir}/${lib2}.c \
${lib_opts} ] != "" } {
return -1
}
-if { [gdb_compile "${srcdir}/${subdir}/${executable}.c" \
+
+set main_opts [list debug shlib=${libobj1}]
+
+if {$dlopen} {
+ lappend main_opts "shlib_load" "additional_flags=-DSHLIB_NAME=\"$libobj2\""
+} else {
+ lappend main_opts "shlib=${libobj2}"
+}
+
+lappend main_opts "additional_flags=-DVERSION_ID_MAIN=$version_id_main"
+
+if { [gdb_compile "${srcdir}/${subdir}/${main}.c" \
[standard_output_file ${executable}] \
executable \
- [list debug shlib=${libobj1} shlib=${libobj2}]]
+ $main_opts]
!= ""} {
return -1
}
@@ -55,7 +74,7 @@ if ![runto_main] {
}
# Try printing "this_version_num" qualified with the name of the file
-# where the variables are defined. There are two global variables
+# where the variables are defined. There are three global variables
# with that name, and some systems such as GNU/Linux merge them
# into one single entity, while some other systems such as Windows
# keep them separate. In the first situation, we have to verify
@@ -65,28 +84,51 @@ if ![runto_main] {
# defined in the given filename.
#
# To avoid adding target-specific code in this testcase, the program
-# sets two local variable named 'v1' and 'v2' with the value of
+# sets three local variables named 'vm', 'v1' and 'v2' with the value of
# our global variables. This allows us to compare the value that
# GDB returns for each query against the actual value seen by
# the program itself.
-# Get past the initialization of variables 'v1' and 'v2'.
+# Get past the initialization of the v* variables.
set bp_location \
- [gdb_get_line_number "STOP" "${executable}.c"]
-gdb_test "break $executable.c:$bp_location" \
+ [gdb_get_line_number "STOP" "${main}.c"]
+gdb_test "break $main.c:$bp_location" \
"Breakpoint \[0-9\]+ at 0x\[0-9a-fA-F\]+: .*" \
- "breapoint past v1 & v2 initialization"
+ "breapoint at STOP marker"
gdb_test "continue" \
"Breakpoint \[0-9\]+, main \\(\\) at.*STOP.*" \
"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.
+# Now check the value of this_version_id in all of
+# print-file-var-main.c, print-file-var-lib1.c and
+# print-file-var-lib2.c.
+
+# Compare the values of $sym1 and $sym2.
+proc compare {sym1 sym2} {
+ # Done this way instead of comparing the symbols with "print $sym1
+ # == sym2" in GDB directly so that the values of the symbols end
+ # up visible in the logs, for debug purposes.
+ set vsym1 [get_integer_valueof $sym1 -1]
+ set vsym2 [get_integer_valueof $sym2 -1]
+ gdb_assert {$vsym1 == $vsym2} "$sym1 == $sym2"
+}
+
+if $version_id_main {
+ compare "'print-file-var-main.c'::this_version_id" "vm"
+ compare "this_version_id" "vm"
+}
-gdb_test "print 'print-file-var-lib1.c'::this_version_id == v1" \
- " = 1"
+compare "'print-file-var-lib1.c'::this_version_id" "v1"
+compare "'print-file-var-lib2.c'::this_version_id" "v2"
-gdb_test "print 'print-file-var-lib2.c'::this_version_id == v2" \
- " = 1"
+}
+
+foreach_with_prefix hidden {0 1} {
+ foreach_with_prefix dlopen {0 1} {
+ foreach_with_prefix version_id_main {0 1} {
+ test $hidden $dlopen $version_id_main
+ }
+ }
+}
new file mode 100644
@@ -0,0 +1,26 @@
+/* This testcase is part of GDB, the GNU debugger.
+ Copyright 2019 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/>. */
+
+#ifndef PRINT_FILE_VAR_H
+#define PRINT_FILE_VAR_H
+
+#if HIDDEN
+# define ATTRIBUTE_VISIBILITY __attribute__((visibility ("hidden")))
+#else
+# define ATTRIBUTE_VISIBILITY
+#endif
+
+#endif /* PRINT_FILE_VAR_H */