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gdb/gdb-pie-3of6-relocate-once.patch
Jan Kratochvil 7b8bd72d9a - Drop obsoleted `gdb-archer-pie-0315-breakpoint_address_match.patch'. 
- Do not consider memory error on reading _r_debug->r_map as fatal (BZ
    576742).
- PIE: Attach binary even after re-prelinked underneath.
- PIE: Attach binary even after ld.so re-prelinked underneath.
- PIE: Fix occasional error attaching i686 binary (BZ 576742).
- testsuite: Fix unstable results of gdb.base/prelink.exp.
2010-03-29 17:54:39 +00:00

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http://sourceware.org/ml/gdb-patches/2010-03/msg01001.html
Subject: [patch 3/6] PIE: Fix occasional error attaching i686 binary
[ Testcase diff backported. ]
Hi,
this is the real bugreport which started this patch series.
gdb "Cannot access memory" on a running process
https://bugzilla.redhat.com/show_bug.cgi?id=576742
Offsets on i686 cause that while attaching to an unprelinked running PIE
scan_dyntag will incorrectly get a successful read in scan_dyntag from DT_DEBUG
it expects is from the mani executable but in fact it is from some ld.so or
libc.so (located low for --exec-shield). Another issue is that scan_dyntag
could verify more that the target memory matches the .dynamic section it is
reading from exec_bfd. It could also complain when the read failed (as always
failed so for for PIE attaches first, succeeded later so nobody has noticed
anything).
The successful read reads a bogus DT_DEBUG value and GDB errors on it later.
This is again a non-fatal error after the patch by Joel Brobecker above but it
was not so before and it is incorrect anyway.
The svr4_relocate_main_executable call in svr4_special_symbol_handling was
there before delayed that way for svr4_static_exec_displacement.
But svr4_static_exec_displacement has been removed in the meantime by:
Re: RFC: Verify AT_ENTRY before using it
http://sourceware.org/ml/gdb-patches/2010-03/msg00030.html
So it can be simplified + corrected now. Moreover GDB will now finally print
exactly "Using PIE (Position Independent Executable) displacement" exactly
once.
The reproducer depends on various offsets which may be distro dependent but it
was made so that it is hopefully reproducible everywhere. Reproduced + fixed
on Fedora 12 x86_64 and i686.
No regressions on {x86_64,x86_64-m32,i686}-fedora12-linux-gnu for the whole
patch series together.
Thanks,
Jan
gdb/
2010-03-29 Jan Kratochvil <jan.kratochvil@redhat.com>
* auxv.c (memory_xfer_auxv): Update attach comment.
* solib-svr4.c (svr4_special_symbol_handling): Remove the call to
svr4_relocate_main_executable.
(svr4_solib_create_inferior_hook): Make the call to
svr4_relocate_main_executable unconditional.
gdb/testsuite/
2010-03-29 Jan Kratochvil <jan.kratochvil@redhat.com>
* gdb.base/attach-pie-misread.exp, gdb.base/attach-pie-misread.c: New.
--- a/gdb/auxv.c
+++ b/gdb/auxv.c
@@ -198,7 +198,8 @@ memory_xfer_auxv (struct target_ops *ops,
/* ld_so_xfer_auxv is the only function safe for virtual executables being
executed by valgrind's memcheck. As using ld_so_xfer_auxv is problematic
- during inferior startup GDB does call it only for attached processes. */
+ during inferior startup as ld.so symbol tables are not yet relocated GDB
+ calls ld_so_xfer_auxv only for attached processes. */
if (current_inferior ()->attach_flag != 0)
{
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -1628,7 +1628,6 @@ enable_break (struct svr4_info *info, int from_tty)
static void
svr4_special_symbol_handling (void)
{
- svr4_relocate_main_executable ();
}
/* Read the ELF program headers from ABFD. Return the contents and
@@ -2065,8 +2064,7 @@ svr4_solib_create_inferior_hook (int from_tty)
info = get_svr4_info ();
/* Relocate the main executable if necessary. */
- if (current_inferior ()->attach_flag == 0)
- svr4_relocate_main_executable ();
+ svr4_relocate_main_executable ();
if (!svr4_have_link_map_offsets ())
return;
--- /dev/null
+++ b/gdb/testsuite/gdb.base/attach-pie-misread.c
@@ -0,0 +1,47 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2010 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 <stdio.h>
+#include <unistd.h>
+
+const char stub[] = {
+#ifdef GEN
+# include GEN
+#endif
+};
+
+int
+main (int argc, char **argv)
+{
+ /* Generator of GEN written in Python takes about 15s for x86_64's 4MB. */
+ if (argc == 2)
+ {
+ long count = strtol (argv[1], NULL, 0);
+
+ while (count-- > 0)
+ puts ("0x55,");
+
+ return 0;
+ }
+ if (argc != 1)
+ return 1;
+
+ puts ("sleeping");
+ fflush (stdout);
+
+ return sleep (60);
+}
--- /dev/null
+++ b/gdb/testsuite/gdb.base/attach-pie-misread.exp
@@ -0,0 +1,209 @@
+# Copyright 2010 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/>.
+
+# This test only works on GNU/Linux.
+if { ![isnative] || [is_remote host] || ![istarget *-linux*] || [skip_shlib_tests]} {
+ continue
+}
+
+set test "attach-pie-misread"
+set srcfile ${test}.c
+set genfile ${objdir}/${subdir}/${test}-gen.h
+set executable ${test}
+set binfile ${objdir}/${subdir}/${executable}
+
+if {[build_executable ${test}.exp $executable $srcfile [list "additional_flags=-fPIE -pie"]] == -1} {
+ return -1
+}
+
+# Program Headers:
+# Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
+# LOAD 0x000000 0x0000000000400000 0x0000000000400000 0x134f5ec 0x134f5ec R E 0x200000
+# LOAD 0x134f5f0 0x000000000194f5f0 0x000000000194f5f0 0x1dbc60 0x214088 RW 0x200000
+# DYNAMIC 0x134f618 0x000000000194f618 0x000000000194f618 0x000200 0x000200 RW 0x8
+#
+proc read_phdr {binfile test} {
+ set readelf_program [transform readelf]
+ set command "exec $readelf_program -Wl $binfile"
+ verbose -log "command is $command"
+ set result [catch $command output]
+ verbose -log "result is $result"
+ verbose -log "output is $output"
+ if {$result != 0} {
+ fail $test
+ return
+ }
+ if ![regexp {\nProgram Headers:\n *Type [^\n]* Align\n(.*?)\n\n} $output trash phdr] {
+ fail "$test (no Program Headers)"
+ return
+ }
+ if ![regexp -line {^ *DYNAMIC +0x[0-9a-f]+ +(0x[0-9a-f]+) } $phdr trash dynamic_vaddr] {
+ fail "$test (no DYNAMIC found)"
+ return
+ }
+ verbose -log "dynamic_vaddr is $dynamic_vaddr"
+ set align_max -1
+ foreach {trash align} [regexp -line -all -inline {^ *LOAD .* (0x[0-9]+)$} $phdr] {
+ if {$align_max < $align} {
+ set align_max $align
+ }
+ }
+ verbose -log "align_max is $align_max"
+ if {$align_max == -1} {
+ fail "$test (no LOAD found)"
+ return
+ }
+ pass $test
+ return [list $dynamic_vaddr $align_max]
+}
+
+set phdr [read_phdr $binfile "readelf initial scan"]
+set dynamic_vaddr [lindex $phdr 0]
+set align_max [lindex $phdr 1]
+
+set stub_size [format 0x%x [expr "2 * $align_max - ($dynamic_vaddr & ($align_max - 1))"]]
+verbose -log "stub_size is $stub_size"
+
+# On x86_64 it is commonly about 4MB.
+if {$stub_size > 25000000} {
+ xfail "stub size $stub_size is too large"
+ return
+}
+
+set test "generate stub"
+set command "exec $binfile $stub_size >$genfile"
+verbose -log "command is $command"
+set result [catch $command output]
+verbose -log "result is $result"
+verbose -log "output is $output"
+if {$result == 0} {
+ pass $test
+} else {
+ fail $test
+}
+
+if {[build_executable ${test}.exp $executable $srcfile [list "additional_flags=-fPIE -pie -DGEN=\"$genfile\""]] == -1} {
+ return -1
+}
+
+# x86_64 file has 25MB, no need to keep it.
+file delete -- $genfile
+
+set phdr [read_phdr $binfile "readelf rebuilt with stub_size"]
+set dynamic_vaddr_prelinkno [lindex $phdr 0]
+
+set command "exec /usr/sbin/prelink -q -N --no-exec-shield -R $binfile"
+verbose -log "command is $command"
+set result [catch $command output]
+verbose -log "result is $result"
+verbose -log "output is $output"
+
+set test "prelink -R"
+if {$result == 0 && $output == ""} {
+ pass $test
+} elseif {$result == 1 && [regexp {^(couldn't execute "/usr/sbin/prelink[^\r\n]*": no such file or directory\n?)*$} $output]} {
+ untested attach-pie-misread.exp
+ return -1
+} else {
+ fail $test
+}
+
+set phdr [read_phdr $binfile "readelf with prelink -R"]
+set dynamic_vaddr_prelinkyes [lindex $phdr 0]
+
+set first_offset [format 0x%x [expr $dynamic_vaddr_prelinkyes - $dynamic_vaddr_prelinkno]]
+verbose -log "first_offset is $first_offset"
+
+set test "first offset is non-zero"
+if {$first_offset == 0} {
+ fail "$test (-fPIE -pie in effect?)"
+} else {
+ pass $test
+}
+
+set test "start inferior"
+gdb_exit
+
+set res [remote_spawn host $binfile];
+if { $res < 0 || $res == "" } {
+ perror "Spawning $binfile failed."
+ fail $test
+ return
+}
+set pid [exp_pid -i $res]
+gdb_expect {
+ -re "sleeping\r\n" {
+ pass $test
+ }
+ eof {
+ fail "$test (eof)"
+ remote_exec host "kill -9 $pid"
+ return
+ }
+ timeout {
+ fail "$test (timeout)"
+ remote_exec host "kill -9 $pid"
+ return
+ }
+}
+
+# Due to alignments it was reproducible with 1 on x86_64 but 2 on i686.
+foreach align_mult {1 2} {
+ set old_ldprefix $pf_prefix
+ lappend pf_prefix "shift-by-$align_mult:"
+
+ # FIXME: We believe there is enough room under FIRST_OFFSET.
+ set shifted_offset [format 0x%x [expr "$first_offset - $align_mult * $align_max"]]
+ verbose -log "shifted_offset is $shifted_offset"
+
+ set command "exec /usr/sbin/prelink -q -N --no-exec-shield -r $shifted_offset $binfile"
+ verbose -log "command is $command"
+ set result [catch $command output]
+ verbose -log "result is $result"
+ verbose -log "output is $output"
+
+ set test "prelink -r"
+ if {$result == 0 && $output == ""} {
+ pass $test
+ } else {
+ fail $test
+ }
+
+ clean_restart $executable
+
+ set test "attach"
+ gdb_test_multiple "attach $pid" $test {
+ -re "Attaching to program: .*, process $pid\r\n" {
+ # Missing "$gdb_prompt $" is intentional.
+ pass $test
+ }
+ }
+
+ set test "error on Cannot access memory at address"
+ gdb_test_multiple "" $test {
+ -re "\r\nCannot access memory at address .*$gdb_prompt $" {
+ fail $test
+ }
+ -re "$gdb_prompt $" {
+ pass $test
+ }
+ }
+
+ gdb_test "detach" "Detaching from program: .*"
+
+ set pf_prefix $old_ldprefix
+}
+
+remote_exec host "kill -9 $pid"
--- a/gdb/testsuite/gdb.base/break-interp.exp
+++ b/gdb/testsuite/gdb.base/break-interp.exp
@@ -248,9 +248,8 @@ proc reach {func command displacement} {
}
if {$displacement == $case} {
pass $test_displacement
- # Permit multiple such messages.
set displacement "FOUND-$displacement"
- } elseif {$displacement != "FOUND-$case"} {
+ } else {
fail $test_displacement
}
exp_continue
@@ -304,9 +303,8 @@ proc test_core {file displacement} {
}
if {$displacement == $case} {
pass $test_displacement
- # Permit multiple such messages.
set displacement "FOUND-$displacement"
- } elseif {$displacement != "FOUND-$case"} {
+ } else {
fail $test_displacement
}
exp_continue
@@ -362,9 +360,8 @@ proc test_attach_gdb {file pid displacement prefix} {
}
if {$displacement == $case} {
pass $test_displacement
- # Permit multiple such messages.
set displacement "FOUND-$displacement"
- } elseif {$displacement != "FOUND-$case"} {
+ } else {
fail $test_displacement
}
exp_continue
@@ -451,9 +448,7 @@
gdb_test "bt" "#0 +\[^\r\n\]*\\mdl_main\\M.*" "dl bt"
if $ifmain {
- # Displacement message will be printed the second time on initializing
- # the linker from svr4_special_symbol_handling.
- reach "main" continue $displacement
+ reach "main" continue "NONE"
reach "libfunc" continue "NONE"
@@ -528,9 +517,8 @@ proc test_ld {file ifmain trynosym displacement} {
}
if {$displacement == $case} {
pass $test_displacement
- # Permit multiple such messages.
set displacement "FOUND-$displacement"
- } elseif {$displacement != "FOUND-$case"} {
+ } else {
fail $test_displacement
}
exp_continue
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