[RFA] Fix GDB 8.3 regression crash when registers cannot be modified.

Philippe Waroquiers
2019-04-13T08:28:29Z

This crash was detected when using GDB with the valgrind gdbserver.
To reproduce:

valgrind sleep 10000

In another window:
gdb
target remote | vgdb
p printf("make sleep print something\n")
=>
terminate called after throwing an instance of 'gdb_exception_RETURN_MASK_ERROR'
Aborted

The problem is that the valgrind gdbserver does not allow to change
registers when the inferior is blocked in a system call.
GDB then raises an exception. The exception causes the destructor
of
typedef std::unique_ptr<infcall_suspend_state, infcall_suspend_state_deleter>
infcall_suspend_state_up;
to be called. This destructor itself tries to restore the value of
the registers, and fails similarly. We must catch the exception in
the destructor to avoid crashing GDB.
If the destructor encounters a problem, no warning is produced if
there is an uncaught exception, as in this case, the user will already
be informed of a problem via this exception.

With this change, no crash anymore, and all the valgrind 3.15 tests
pass succesfully.

Note: when this patch is approved, I will push an equivalent patch
on master, but with TRY/CATCH/e.message () replaced by
try/catch/e.what ().

gdb/ChangeLog

struct infcall_suspend_state_deleter
2019-04-13 Philippe Waroquiers <philippe.waroquiers@skynet.be>

* inferior.h (struct infcall_suspend_state_deleter):
Catch exception in destructor to avoid crash.
---
gdb/inferior.h | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/gdb/inferior.h b/gdb/inferior.h
index 2d1bb97a28..4d84afac6a 100644
--- a/gdb/inferior.h
+++ b/gdb/inferior.h
@@ -68,7 +68,19 @@ struct infcall_suspend_state_deleter
{
void operator() (struct infcall_suspend_state *state) const
{
- restore_infcall_suspend_state (state);
+ TRY
+ {
+ restore_infcall_suspend_state (state);
+ }
+ CATCH (e, RETURN_MASK_ALL)
+ {
+ /* If we are restoring the inferior state due to an exception,
+ some error message will be printed. So, only warn the user
+ when we cannot restore during normal execution. */
+ if (!std::uncaught_exception ())
+ warning (_("Failed to restore inferior state: %s"), e.message);
+ }
+ END_CATCH
}
};

--
2.20.1