commit 7cdd140cbccc8eb62a20d12a03bed83765cbc066

Author: Stefan Liebler <stli@linux.vnet.ibm.com>

Date:   Fri Jul 31 13:42:52 2015 +0200

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

        On s390/s390x backtrace(buffer, size) returns the series of called functions until

        "makecontext_ret" and additional entries (up to "size") with "makecontext_ret".

        GDB-backtrace is also warning:

        "Backtrace stopped: previous frame identical to this frame (corrupt stack?)"

        To reproduce this scenario you have to setup a new context with makecontext()

        and activate it with setcontext(). See e.g. cf() function in testcase stdlib/tst-makecontext.c.

        Or see bug in libgo "Bug 66303 - runtime.Caller() returns infinitely deep stack frames

        on s390x " (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66303).

        This patch omits the cfi_startproc/cfi_endproc directives in ENTRY/END macro of

        __makecontext_ret. Thus no frame information is generated in .eh_frame and backtrace

        stops after __makecontext_ret. There is also no .eh_frame info for _start or

        thread_start functions.

        ChangeLog:

        	[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.

diff --git a/stdlib/Makefile b/stdlib/Makefile

index 8f22c8d..c1e80d7 100644

--- a/stdlib/Makefile

+++ b/stdlib/Makefile

@@ -154,3 +154,4 @@ $(objpfx)bug-getcontext: $(link-libm)

 $(objpfx)tst-strtod-round: $(link-libm)

 $(objpfx)tst-tininess: $(link-libm)

 $(objpfx)tst-strtod-underflow: $(link-libm)

+$(objpfx)tst-makecontext: $(libdl)

diff --git a/stdlib/tst-makecontext.c b/stdlib/tst-makecontext.c

index eb6e89b..1420857 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 ab172bb..365c2b0 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 so that __makecontext_ret stops 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 cbd88e1..c4a43bd 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 so that __makecontext_ret stops 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.  */