diff options
| author | Arun Sharma <arun.sharma@google.com> | 2008-06-16 14:35:53 -0600 |
|---|---|---|
| committer | David Mosberger-Tang <davidm@koala.mostang.com> | 2008-06-16 14:35:53 -0600 |
| commit | 649f1fb3449a65dd0626a709432d8b02a7c56bbc (patch) | |
| tree | 61b412e9938a8ebfa870a4cf202e1697cff22383 /src/x86_64/Gstep.c | |
| parent | 183d28a0668f100a181cc665ea702985d2ee717e (diff) | |
| download | libunwind-649f1fb3449a65dd0626a709432d8b02a7c56bbc.tar.gz | |
[X86-64] For local unwinding, we have a defence mechanism against
bad/missing unwind information, which could result in libunwind
dereferencing bad pointers. This mechanism is based on msync(2) system
call and significantly reduces the chances of a bad pointer
dereference in libunwind.
The original idea was to turn this mechanism on only when necessary
i.e. libunwind didn't find proper unwind information for a IP.
There are a couple of problems in the current implementation.
* The flag is global and is modified without locking
* The flag isn't reset when starting a new unwind
The attached patch makes ->validate a per-thread setting by moving it
into struct cursor from unw_local_addr_space and resets it to false
when starting a new unwind. As a result, cursor->as_arg points to the
cursor itself instead of the ucontext (for the local case).
This was found to reduce the number of msync() system calls from an
application using libunwind significantly.
Signed-off-by: Paul Pluzhnikov <ppluzhnikov@google.com>
Signed-off-by: Arun Sharma <arun.sharma@google.com>
Diffstat (limited to 'src/x86_64/Gstep.c')
| -rw-r--r-- | src/x86_64/Gstep.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/src/x86_64/Gstep.c b/src/x86_64/Gstep.c index 75f796f5..2da1c25d 100644 --- a/src/x86_64/Gstep.c +++ b/src/x86_64/Gstep.c @@ -71,6 +71,10 @@ unw_step (unw_cursor_t *cursor) unw_word_t prev_ip = c->dwarf.ip, prev_cfa = c->dwarf.cfa; struct dwarf_loc rbp_loc, rsp_loc, rip_loc; + /* We could get here because of missing/bad unwind information. + Validate all addresses before dereferencing. */ + c->validate = 1; + Debug (13, "dwarf_step() failed (ret=%d), trying frame-chain\n", ret); if (unw_is_signal_frame (cursor)) |