http://sourceware.org/ml/gdb-patches/2010-09/msg00519.html Subject: [patch] Fix inferior execl of new PIE x86_64 Hi, gcc -o 1 1.c -Wall -g -fPIE -pie; gdb -nx ./1 -ex 'b main' -ex r -ex c Starting program: .../gdb/1 Breakpoint 1, main (argc=1, argv=0x7fffffffdff8) at 1.c:7 7 setbuf (stdout, NULL); Continuing. re-exec process 28056 is executing new program: .../gdb/1 Error in re-setting breakpoint 1: Cannot access memory at address 0x80c exit Program exited normally. (gdb) _ while it should be: re-exec process 28095 is executing new program: .../gdb/1 Breakpoint 1, main (argc=2, argv=0x7fffffffe008) at 1.c:7 7 setbuf (stdout, NULL); (gdb) _ The error comes from: throw_error <- memory_error <- read_memory <- read_memory_unsigned_integer <- amd64_analyze_prologue <- amd64_skip_prologue <- gdbarch_skip_prologue <- skip_prologue_sal <- find_function_start_sal <- symbol_found <- decode_variable <- decode_line_1 <- breakpoint_re_set_one <- catch_errors <- breakpoint_re_set <- clear_symtab_users <- new_symfile_objfile <- symbol_file_add_with_addrs_or_offsets <- symbol_file_add_from_bfd <- symbol_file_add <- symbol_file_add_main_1 <- symbol_file_add_main <- follow_exec I understand this hack is not nice, the correct way would be to unify more follow_exec with post_create_inferior. But I could break it for non-GNU/Linux targets a lot. No regressions on {x86_64,x86_64-m32,i686}-fedora14snapshot-linux-gnu. Thanks, Jan for the demo above: ------------------------------------------------------------------------------ #include #include #include int main (int argc, char **argv) { setbuf (stdout, NULL); if (argc == 1) { puts ("re-exec"); execl ("/proc/self/exe", argv[0], "foo", NULL); assert (0); } puts ("exit"); return 0; } ------------------------------------------------------------------------------ gdb/ 2010-09-30 Jan Kratochvil * infrun.c (follow_exec): Replace symbol_file_add_main by symbol_file_add with SYMFILE_DEFER_BP_RESET, set_initial_language and breakpoint_re_set. * m32r-rom.c (m32r_load, m32r_upload_command): Use parameter 0 for clear_symtab_users. * objfiles.c (free_all_objfiles): Likewise. * remote-m32r-sdi.c (m32r_load): Likewise. * solib-som.c (som_solib_create_inferior_hook): Likewise. * symfile.c (new_symfile_objfile): New comment for add_flags. Call clear_symtab_users with ADD_FLAGS. (reread_symbols): Use parameter 0 for clear_symtab_users. (clear_symtab_users): New parameter add_flags. Do not call breakpoint_re_set if SYMFILE_DEFER_BP_RESET. (clear_symtab_users_cleanup): Use parameter 0 for clear_symtab_users. * symtab.h (clear_symtab_users): New parameter add_flags. gdb/testsuite/ 2010-09-30 Jan Kratochvil * gdb.base/pie-execl.exp: New file. * gdb.base/pie-execl.c: New file. Index: gdb-7.2/gdb/infrun.c =================================================================== --- gdb-7.2.orig/gdb/infrun.c 2010-10-12 18:27:58.000000000 +0200 +++ gdb-7.2/gdb/infrun.c 2010-10-12 18:29:24.000000000 +0200 @@ -840,8 +840,15 @@ follow_exec (ptid_t pid, char *execd_pat /* That a.out is now the one to use. */ exec_file_attach (execd_pathname, 0); - /* Load the main file's symbols. */ - symbol_file_add_main (execd_pathname, 0); + /* SYMFILE_DEFER_BP_RESET is used as the proper displacement for PIE + (Position Independent Executable) main symbol file will get applied by + solib_create_inferior_hook below. breakpoint_re_set would fail to insert + the breakpoints with the zero displacement. */ + + symbol_file_add (execd_pathname, SYMFILE_MAINLINE | SYMFILE_DEFER_BP_RESET, + NULL, 0); + + set_initial_language (); #ifdef SOLIB_CREATE_INFERIOR_HOOK SOLIB_CREATE_INFERIOR_HOOK (PIDGET (inferior_ptid)); @@ -851,6 +858,8 @@ follow_exec (ptid_t pid, char *execd_pat jit_inferior_created_hook (); + breakpoint_re_set (); + /* Reinsert all breakpoints. (Those which were symbolic have been reset to the proper address in the new a.out, thanks to symbol_file_command...) */ Index: gdb-7.2/gdb/m32r-rom.c =================================================================== --- gdb-7.2.orig/gdb/m32r-rom.c 2010-01-01 08:31:37.000000000 +0100 +++ gdb-7.2/gdb/m32r-rom.c 2010-10-12 18:29:24.000000000 +0200 @@ -188,7 +188,7 @@ m32r_load (char *filename, int from_tty) the stack may not be valid, and things would get horribly confused... */ - clear_symtab_users (); + clear_symtab_users (0); } static void @@ -551,7 +551,7 @@ m32r_upload_command (char *args, int fro the stack may not be valid, and things would get horribly confused... */ - clear_symtab_users (); + clear_symtab_users (0); } /* Provide a prototype to silence -Wmissing-prototypes. */ Index: gdb-7.2/gdb/objfiles.c =================================================================== --- gdb-7.2.orig/gdb/objfiles.c 2010-10-12 18:27:56.000000000 +0200 +++ gdb-7.2/gdb/objfiles.c 2010-10-12 18:29:39.000000000 +0200 @@ -699,7 +699,7 @@ free_all_objfiles (void) { free_objfile (objfile); } - clear_symtab_users (); + clear_symtab_users (0); } /* Relocate OBJFILE to NEW_OFFSETS. There should be OBJFILE->NUM_SECTIONS Index: gdb-7.2/gdb/remote-m32r-sdi.c =================================================================== --- gdb-7.2.orig/gdb/remote-m32r-sdi.c 2010-07-07 18:15:16.000000000 +0200 +++ gdb-7.2/gdb/remote-m32r-sdi.c 2010-10-12 18:29:24.000000000 +0200 @@ -1377,7 +1377,7 @@ m32r_load (char *args, int from_tty) might be to call normal_stop, except that the stack may not be valid, and things would get horribly confused... */ - clear_symtab_users (); + clear_symtab_users (0); if (!nostart) { Index: gdb-7.2/gdb/solib-som.c =================================================================== --- gdb-7.2.orig/gdb/solib-som.c 2010-05-17 01:49:58.000000000 +0200 +++ gdb-7.2/gdb/solib-som.c 2010-10-12 18:29:24.000000000 +0200 @@ -354,7 +354,7 @@ keep_going: /* Make the breakpoint at "_start" a shared library event breakpoint. */ create_solib_event_breakpoint (target_gdbarch, anaddr); - clear_symtab_users (); + clear_symtab_users (0); } static void Index: gdb-7.2/gdb/symfile.c =================================================================== --- gdb-7.2.orig/gdb/symfile.c 2010-10-12 18:27:57.000000000 +0200 +++ gdb-7.2/gdb/symfile.c 2010-10-12 18:29:24.000000000 +0200 @@ -1036,7 +1036,7 @@ syms_from_objfile (struct objfile *objfi /* Perform required actions after either reading in the initial symbols for a new objfile, or mapping in the symbols from a reusable - objfile. */ + objfile. ADD_FLAGS is a bitmask of enum symfile_add_flags. */ void new_symfile_objfile (struct objfile *objfile, int add_flags) @@ -1049,7 +1049,7 @@ new_symfile_objfile (struct objfile *obj /* OK, make it the "real" symbol file. */ symfile_objfile = objfile; - clear_symtab_users (); + clear_symtab_users (add_flags); } else if ((add_flags & SYMFILE_DEFER_BP_RESET) == 0) { @@ -2527,7 +2527,7 @@ reread_symbols (void) /* Notify objfiles that we've modified objfile sections. */ objfiles_changed (); - clear_symtab_users (); + clear_symtab_users (0); /* At least one objfile has changed, so we can consider that the executable we're debugging has changed too. */ observer_notify_executable_changed (); @@ -2745,10 +2745,10 @@ allocate_symtab (char *filename, struct /* Reset all data structures in gdb which may contain references to symbol - table data. */ + table data. ADD_FLAGS is a bitmask of enum symfile_add_flags. */ void -clear_symtab_users (void) +clear_symtab_users (int add_flags) { /* Someday, we should do better than this, by only blowing away the things that really need to be blown. */ @@ -2758,7 +2758,8 @@ clear_symtab_users (void) clear_current_source_symtab_and_line (); clear_displays (); - breakpoint_re_set (); + if ((add_flags & SYMFILE_DEFER_BP_RESET) == 0) + breakpoint_re_set (); set_default_breakpoint (0, NULL, 0, 0, 0); clear_pc_function_cache (); observer_notify_new_objfile (NULL); @@ -2777,7 +2778,7 @@ clear_symtab_users (void) static void clear_symtab_users_cleanup (void *ignore) { - clear_symtab_users (); + clear_symtab_users (0); } /* OVERLAYS: Index: gdb-7.2/gdb/symtab.h =================================================================== --- gdb-7.2.orig/gdb/symtab.h 2010-10-12 18:27:56.000000000 +0200 +++ gdb-7.2/gdb/symtab.h 2010-10-12 18:29:24.000000000 +0200 @@ -1170,7 +1170,7 @@ extern void skip_prologue_sal (struct sy /* symfile.c */ -extern void clear_symtab_users (void); +extern void clear_symtab_users (int add_flags); extern enum language deduce_language_from_filename (const char *); Index: gdb-7.2/gdb/testsuite/gdb.base/pie-execl.c =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ gdb-7.2/gdb/testsuite/gdb.base/pie-execl.c 2010-10-12 18:29:24.000000000 +0200 @@ -0,0 +1,51 @@ +/* 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 . */ + +#include +#include +#include + +static void pie_execl_marker (void); + +int +main (int argc, char **argv) +{ + setbuf (stdout, NULL); + +#if BIN == 1 + if (argc == 2) + { + printf ("pie-execl: re-exec: %s\n", argv[1]); + execl (argv[1], argv[1], NULL); + assert (0); + } +#endif + + pie_execl_marker (); + + return 0; +} + +/* pie_execl_marker must be on a different address than in `pie-execl2.c'. */ + +volatile int v; + +static void +pie_execl_marker (void) +{ + v = 1; +} Index: gdb-7.2/gdb/testsuite/gdb.base/pie-execl.exp =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ gdb-7.2/gdb/testsuite/gdb.base/pie-execl.exp 2010-10-12 18:29:24.000000000 +0200 @@ -0,0 +1,94 @@ +# 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 . + +# The problem was due to amd64_skip_prologue attempting to access inferior +# memory before the PIE (Position Independent Executable) gets relocated. + +if { ![istarget *-linux*]} { + continue +} + +set testfile "pie-execl" +set srcfile ${testfile}.c +set executable1 ${testfile}1 +set executable2 ${testfile}2 +set binfile1 ${objdir}/${subdir}/${executable1} +set binfile2 ${objdir}/${subdir}/${executable2} + +# Use conditional compilation according to `BIN' as GDB remembers the source +# file name of the breakpoint. + +set opts [list debug {additional_flags=-fPIE -pie}] +if {[build_executable ${testfile}.exp $executable1 $srcfile [concat $opts {additional_flags=-DBIN=1}]] == "" + || [build_executable ${testfile}.exp $executable2 $srcfile [concat $opts {additional_flags=-DBIN=2}]] == ""} { + return -1 +} + +clean_restart ${executable1} + +gdb_test_no_output "set args ${binfile2}" + +if ![runto_main] { + return -1 +} + +# Do not stop on `main' after re-exec. +delete_breakpoints + +gdb_breakpoint "pie_execl_marker" +gdb_test "info breakpoints" ".*" "" + +set addr1 "" +set test "pie_execl_marker address first" +gdb_test_multiple "p/x &pie_execl_marker" $test { + -re " = (0x\[0-9a-f\]+)\r\n$gdb_prompt $" { + set addr1 $expect_out(1,string) + pass $test + } +} +verbose -log "addr1 is $addr1" + +set test "continue" +gdb_test_multiple $test $test { + -re "Error in re-setting breakpoint" { + fail $test + } + -re "Cannot access memory" { + fail $test + } + -re "pie-execl: re-exec.*executing new program.*\r\nBreakpoint \[0-9\]+,\[^\r\n\]* pie_execl_marker .*\r\n$gdb_prompt $" { + pass $test + } +} + +gdb_test "info breakpoints" ".*" "" + +set addr2 "" +set test "pie_execl_marker address second" +gdb_test_multiple "p/x &pie_execl_marker" $test { + -re " = (0x\[0-9a-f\]+)\r\n$gdb_prompt $" { + set addr2 $expect_out(1,string) + pass $test + } +} +verbose -log "addr2 is $addr2" + +# Ensure we cannot get a false PASS and the inferior has really changed. +set test "pie_execl_marker address has changed" +if [string equal $addr1 $addr2] { + fail $test +} else { + pass $test +}