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Diffstat (limited to 'gdb/doc')
| -rw-r--r-- | gdb/doc/ChangeLog | 4 | ||||
| -rw-r--r-- | gdb/doc/gdb.texinfo | 51 |
2 files changed, 55 insertions, 0 deletions
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog index 8d7041f..182b9dc 100644 --- a/gdb/doc/ChangeLog +++ b/gdb/doc/ChangeLog @@ -1,3 +1,7 @@ +2008-07-10 Jan Kratochvil <jan.kratochvil@redhat.com> + + * gdb.texinfo (Starting): Document "set disable-randomization". + 2008-07-07 Andreas Schwab <schwab@suse.de> * gdb.texinfo (GDB/MI Target Manipulation): Fix last change. diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo index bbbcd04..710b96b 100644 --- a/gdb/doc/gdb.texinfo +++ b/gdb/doc/gdb.texinfo @@ -1999,6 +1999,57 @@ environment: This command is available when debugging locally on most targets, excluding @sc{djgpp}, Cygwin, MS Windows, and QNX Neutrino. +@kindex set disable-randomization +@item set disable-randomization +@itemx set disable-randomization on +This option (enabled by default in @value{GDBN}) will turn off the native +randomization of the virtual address space of the started program. This option +is useful for multiple debugging sessions to make the execution better +reproducible and memory addresses reusable across debugging sessions. + +This feature is implemented only on @sc{gnu}/Linux. You can get the same +behavior using + +@smallexample +(@value{GDBP}) set exec-wrapper setarch `uname -m` -R +@end smallexample + +@item set disable-randomization off +Leave the behavior of the started executable unchanged. Some bugs rear their +ugly heads only when the program is loaded at certain addresses. If your bug +disappears when you run the program under @value{GDBN}, that might be because +@value{GDBN} by default disables the address randomization on platforms, such +as @sc{gnu}/Linux, which do that for stand-alone programs. Use @kbd{set +disable-randomization off} to try to reproduce such elusive bugs. + +The virtual address space randomization is implemented only on @sc{gnu}/Linux. +It protects the programs against some kinds of security attacks. In these +cases the attacker needs to know the exact location of a concrete executable +code. Randomizing its location makes it impossible to inject jumps misusing +a code at its expected addresses. + +Prelinking shared libraries provides a startup performance advantage but it +makes addresses in these libraries predictable for privileged processes by +having just unprivileged access at the target system. Reading the shared +library binary gives enough information for assembling the malicious code +misusing it. Still even a prelinked shared library can get loaded at a new +random address just requiring the regular relocation process during the +startup. Shared libraries not already prelinked are always loaded at +a randomly chosen address. + +Position independent executables (PIE) contain position independent code +similar to the shared libraries and therefore such executables get loaded at +a randomly chosen address upon startup. PIE executables always load even +already prelinked shared libraries at a random address. You can build such +executable using @command{gcc -fPIE -pie}. + +Heap (malloc storage), stack and custom mmap areas are always placed randomly +(as long as the randomization is enabled). + +@item show disable-randomization +Show the current setting of the explicit disable of the native randomization of +the virtual address space of the started program. + @end table @node Arguments |