[commit: ghc] ghc-8.0: rts: Limit maximum backtrace depth (b963f07)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : ghc-8.0
Link       : http://ghc.haskell.org/trac/ghc/changeset/b963f07f2ab6ca2209e0e295a3f570e2c25ff440/ghc

>---------------------------------------------------------------

commit b963f07f2ab6ca2209e0e295a3f570e2c25ff440
Author: Ben Gamari <ben at smart-cactus.org>
Date:   Mon Apr 11 00:49:06 2016 +0200

    rts: Limit maximum backtrace depth
    
    This prevents us from entering an infinite loop in the event of a
    hitting bad unwinding information.
    
    (cherry picked from commit 350ffc3e4c6b3aefd6ae621991564cc28f585d46)


>---------------------------------------------------------------

b963f07f2ab6ca2209e0e295a3f570e2c25ff440
 rts/Libdw.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/rts/Libdw.c b/rts/Libdw.c
index 8c3c581..e796840 100644
--- a/rts/Libdw.c
+++ b/rts/Libdw.c
@@ -16,6 +16,8 @@
 #include <dwarf.h>
 #include <unistd.h>
 
+const int max_backtrace_depth = 5000;
+
 static BacktraceChunk *backtraceAllocChunk(BacktraceChunk *next) {
     BacktraceChunk *chunk = stgMallocBytes(sizeof(BacktraceChunk),
                                            "backtraceAllocChunk");
@@ -57,7 +59,10 @@ void backtraceFree(Backtrace *bt) {
 
 struct LibdwSession_ {
     Dwfl *dwfl;
-    Backtrace *cur_bt; // The current backtrace we are collecting (if any)
+
+    // The current backtrace we are collecting (if any)
+    Backtrace *cur_bt;
+    int max_depth;
 };
 
 static const Dwfl_Thread_Callbacks thread_cbs;
@@ -230,8 +235,12 @@ static int getBacktraceFrameCb(Dwfl_Frame *frame, void *arg) {
             pc -= 1; // TODO: is this right?
         backtracePush(session->cur_bt, (StgPtr) (uintptr_t) pc);
     }
-
-    return DWARF_CB_OK;
+    session->max_depth--;
+    if (session->max_depth == 0) {
+        return DWARF_CB_ABORT;
+    } else {
+        return DWARF_CB_OK;
+    }
 }
 
 Backtrace *libdwGetBacktrace(LibdwSession *session) {
@@ -242,6 +251,7 @@ Backtrace *libdwGetBacktrace(LibdwSession *session) {
 
     Backtrace *bt = backtraceAlloc();
     session->cur_bt = bt;
+    session->max_depth = max_backtrace_depth;
 
     int pid = getpid();
     int ret = dwfl_getthread_frames(session->dwfl, pid,