[PATCH][BZ #18508] S390: Fix "backtrace() returns infinitely deep stack frames with makecontext()".

[Stefan Liebler]

On 06/12/2015 05:40 PM, Andreas Schwab wrote:
> Stefan Liebler <stli@linux.vnet.ibm.com> writes:
>
>> Is there a way to load the correct libgcc_s.so on all architectures?
>
> #include <gnu/lib-names.h>
> dlopen(LIBGCC_S_SO, ...)
>
> Andreas.
>
Thanks.
Here is the patch with the enhanced tst-makecontext testcase.
It calls _Unwind_Backtrace within cf() function, which is called in a 
makecontext context and check if the callback function is not called 
infinitely times.

Tested on s390/s390x before and after this patch.
Before: Test fails; After: Test succeeds.

Ok to commit?

Bye Stefan

---
2015-06-15  Stefan Liebler  <stli@linux.vnet.ibm.com>

	[BZ #18508]
	* stdlib/Makefile ($(objpfx)tst-makecontext3):
	Depend on $(libdl).
	* stdlib/tst-makecontext.c (cf): Test if _Unwind_Backtrace
	is not called infinitely times.
	(backtrace_helper): New function.
	(trace_arg): New struct.
	(st1): Enlarge stack size.
	* sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S:
	(__makecontext_ret): Omit cfi_startproc and cfi_endproc.
	* sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S:
	Likewise.
-------------- next part --------------
diff --git a/stdlib/Makefile b/stdlib/Makefile
index 3300dd2..7fc5a80 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -164,3 +164,5 @@ $(objpfx)tst-setcontext3.out: tst-setcontext3.sh $(objpfx)tst-setcontext3
 		 '$(run-program-env)' '$(test-program-prefix-after-env)' \
 		 $(common-objpfx)stdlib/; \
 	$(evaluate-test)
+
+$(objpfx)tst-makecontext: $(libdl)
diff --git a/stdlib/tst-makecontext.c b/stdlib/tst-makecontext.c
index 29a588e..8170e8a 100644
--- a/stdlib/tst-makecontext.c
+++ b/stdlib/tst-makecontext.c
@@ -19,23 +19,62 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <ucontext.h>
+#include <assert.h>
+#include <unwind.h>
+#include <dlfcn.h>
+#include <gnu/lib-names.h>
 
 ucontext_t ucp;
-char st1[8192];
+char st1[16384];
 __thread int thr;
 
 int somevar = -76;
 long othervar = -78L;
 
+struct trace_arg
+{
+  int cnt, size;
+};
+
+static _Unwind_Reason_Code
+backtrace_helper (struct _Unwind_Context *ctx, void *a)
+{
+  struct trace_arg *arg = a;
+  if (++arg->cnt == arg->size)
+    return _URC_END_OF_STACK;
+  return _URC_NO_REASON;
+}
+
 void
 cf (int i)
 {
+  struct trace_arg arg = { .size = 100, .cnt = -1 };
+  void *handle;
+  _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
+
   if (i != othervar || thr != 94)
     {
       printf ("i %d thr %d\n", i, thr);
       exit (1);
     }
 
+  /* Test if callback function of _Unwind_Backtrace is not called infinitely
+     times. See Bug 18508 or gcc bug "Bug 66303 - runtime.Caller() returns
+     infinitely deep stack frames on s390x.".
+     The go runtime calls backtrace_full() in
+     <gcc-src>/libbacktrace/backtrace.c, which uses _Unwind_Backtrace().  */
+  handle = dlopen (LIBGCC_S_SO, RTLD_LAZY);
+  if (handle != NULL)
+    {
+      unwind_backtrace = dlsym (handle, "_Unwind_Backtrace");
+      if (unwind_backtrace != NULL)
+	{
+	  unwind_backtrace (backtrace_helper, &arg);
+	  assert (arg.cnt != -1 && arg.cnt < 100);
+	}
+      dlclose (handle);
+    }
+
   /* Since uc_link below has been set to NULL, setcontext is supposed to
      terminate the process normally after this function returns.  */
 }
diff --git a/sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S b/sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S
index e1f9347..8d36ea2 100644
--- a/sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S
+++ b/sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S
@@ -17,6 +17,14 @@
 
 #include <sysdep.h>
 
+/* We do not want .eh_frame info for __makecontext_ret to stop unwinding
+   if backtrace() was called within a context created by makecontext.
+   (there is also no .eh_frame info for _start or thread_start)  */
+#undef cfi_startproc
+#define cfi_startproc
+#undef cfi_endproc
+#define cfi_endproc
+
 ENTRY(__makecontext_ret)
 	basr  %r14,%r7
 	ltr   %r8,%r8			/* Check whether uc_link is 0.  */
diff --git a/sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S b/sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S
index 11a3cd3..64619f1 100644
--- a/sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S
+++ b/sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S
@@ -17,6 +17,14 @@
 
 #include <sysdep.h>
 
+/* We do not want .eh_frame info for __makecontext_ret to stop unwinding
+   if backtrace() was called within a context created by makecontext.
+   (there is also no .eh_frame info for _start or thread_start)  */
+#undef cfi_startproc
+#define cfi_startproc
+#undef cfi_endproc
+#define cfi_endproc
+
 ENTRY(__makecontext_ret)
 	basr	%r14,%r7
 	ltgr	%r8,%r8			/* Check whether uc_link is 0.  */