tests: Simplify backtrace-native tests. Drop raise jmp patching for x86_64.

The backtrace-native[-biarch] testcase was a little too clever in places
making it unreliable.

On x86_64 we tried to make an interesting backtrace by catching the
first signal and then replacing the pc with the address of the first
instruction of a function. Then we would raise a new signal, through
ptrace, to create a backtrace that went from a signal frame into a
frame at the start of a function. That way we could check that we were
trying to fetch the correct CFI for the (jmp) function even at the
first instruction (normally we would substract one from the return
address to get at the call address).

This works as long as the CFI for the jmp() function is identical to
the CFI for the raise() function that we "patched away". Unfortunately
on Fedora rawhide glibc has a rewritten raise() implementation that has
different CFI, in particular the CFA is calculated differently. Making
the testcase fail because we cannot properly unwind from jmp().
So this special x86_64 case has been disabled (the code is still there
in case we find another way to test this in a more reliable way).

On Ubuntu there have been spurious testcase failures because
see_exec_module found two Dwfl_Modules with the same path. This would
trigger an assert. Although this might indicate some issue (maybe we
are not parsing the proc/pid/map correctly?) it isn't clear that it
really is a bug. Since the assert is not very helpful finding any
actual bug and for the testcase it is only necessary that the first
Dwfl_Module that represents the executable is found we just pick that
Dwfl_Module and don't iterate through any of the others.

Signed-off-by: Mark Wielaard <mjw@redhat.com>

3 files changed, 51 insertions, 22 deletions

diff --git a/tests/ChangeLog b/tests/ChangeLog
index 1d8c5b0b..2e9aa0d0 100644
--- a/tests/ChangeLog
+++ b/tests/ChangeLog
@@ -1,3 +1,19 @@
+2016-08-25  Mark Wielaard  <mjw@redhat.com>
+
+	* backtrace-child.c: Disable and add documentation about why we disable
+	RAISE_JMP_PATCHING even on x86_64.
+	* backtrace.c (is_x86_64_native): Rename to...
+	(use_raise_jmp_patching): ... this.
+	(callback_verify): Use use_raise_jmp_patching instead of
+	is_x86_64_native.
+	(see_exec_module): Return DWARF_CB_ABORT after finding the correct exe
+	path.
+	(prepare_thread): Use RAISE_JMP_PATCHING instead of __x86_64__
+	conditional.
+	(exec_dump): Only assert on data.mod != NULL. Drop ptrdiff. Use
+	RAISE_JMP_PATCHING instead of __x86_64__ conditional. Use
+	use_raise_jmp_patching instead of is_x86_64_native.
+
 2016-08-24  Mark Wielaard  <mjw@redhat.com>
 
 	* Makefile.am (EXTRA_DIST): Add testfilesparc64attrs.o.bz2.
diff --git a/tests/backtrace-child.c b/tests/backtrace-child.c
index 40e7b32d..cf4547ca 100644
--- a/tests/backtrace-child.c
+++ b/tests/backtrace-child.c
@@ -1,5 +1,5 @@
 /* Test child for parent backtrace test.
-   Copyright (C) 2013 Red Hat, Inc.
+   Copyright (C) 2013, 2016 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -19,7 +19,8 @@
    --ptraceme will call ptrace (PTRACE_TRACEME) in the two threads.
    --gencore will call abort () at its end.
    Main thread will signal SIGUSR2.  Other thread will signal SIGUSR1.
-   On x86_64 only:
+   There used to be a difference between x86_64 and other architectures.
+   To test getting a signal at the very first instruction of a function:
      PC will get changed to function 'jmp' by backtrace.c function
      prepare_thread.  Then SIGUSR2 will be signalled to backtrace-child
      which will invoke function sigusr2.
@@ -66,8 +67,17 @@
    # 5 0xf77c1a48 - 1      start
    # 6 0xf77699da - 1      start_thread
    # 7 0xf769bbfe - 1      __clone
+
+   But the raise jmp patching was unreliable. It depends on the CFI for the raise()
+   function in glibc to be the same as for the jmp() function. This is not always
+   the case. Some newer glibc versions rewrote raise() and now the CFA is calculated
+   differently. So we disable raise jmp patching everywhere.
    */
 
+#ifdef __x86_64__
+/* #define RAISE_JMP_PATCHING 1 */
+#endif
+
 #include <config.h>
 #include <assert.h>
 #include <stdlib.h>
@@ -130,7 +140,7 @@ dummy1 (void)
   asm volatile ("");
 }
 
-#ifdef __x86_64__
+#ifdef RAISE_JMP_PATCHING
 static NOINLINE_NOCLONE USED void
 jmp (void)
 {
@@ -157,7 +167,7 @@ stdarg (int f UNUSED, ...)
       assert (errno == 0);
       assert (l == 0);
     }
-#ifdef __x86_64__
+#ifdef RAISE_JMP_PATCHING
   if (! gencore)
     {
       /* Execution will get PC patched into function jmp.  */
diff --git a/tests/backtrace.c b/tests/backtrace.c
index 12476430..2440ab34 100644
--- a/tests/backtrace.c
+++ b/tests/backtrace.c
@@ -1,5 +1,5 @@
 /* Test program for unwinding of frames.
-   Copyright (C) 2013, 2014 Red Hat, Inc.
+   Copyright (C) 2013, 2014, 2016 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -64,7 +64,7 @@ dump_modules (Dwfl_Module *mod, void **userdata __attribute__ ((unused)),
   return DWARF_CB_OK;
 }
 
-static bool is_x86_64_native;
+static bool use_raise_jmp_patching;
 static pid_t check_tid;
 
 static void
@@ -93,7 +93,7 @@ callback_verify (pid_t tid, unsigned frameno, Dwarf_Addr pc,
   static bool reduce_frameno = false;
   if (reduce_frameno)
     frameno--;
-  if (! is_x86_64_native && frameno >= 2)
+  if (! use_raise_jmp_patching && frameno >= 2)
     frameno += 2;
   const char *symname2 = NULL;
   switch (frameno)
@@ -112,8 +112,8 @@ callback_verify (pid_t tid, unsigned frameno, Dwarf_Addr pc,
     case 2: // x86_64 only
       /* __restore_rt - glibc maybe does not have to have this symbol.  */
       break;
-    case 3: // x86_64 only
-      if (is_x86_64_native)
+    case 3: // use_raise_jmp_patching
+      if (use_raise_jmp_patching)
 	{
 	  /* Verify we trapped on the very first instruction of jmp.  */
 	  assert (symname != NULL && strcmp (symname, "jmp") == 0);
@@ -138,7 +138,7 @@ callback_verify (pid_t tid, unsigned frameno, Dwarf_Addr pc,
       // there is no guarantee that the compiler doesn't reorder the
       // instructions or even inserts some padding instructions at the end
       // (which apparently happens on ppc64).
-      if (is_x86_64_native)
+      if (use_raise_jmp_patching)
         assert (symname2 == NULL || strcmp (symname2, "backtracegen") != 0);
       break;
   }
@@ -243,10 +243,10 @@ see_exec_module (Dwfl_Module *mod, void **userdata __attribute__ ((unused)),
     return DWARF_CB_OK;
   assert (data->mod == NULL);
   data->mod = mod;
-  return DWARF_CB_OK;
+  return DWARF_CB_ABORT;
 }
 
-/* On x86_64 only:
+/* We used to do this on x86_64 only (see backtrace-child why we now don't):
      PC will get changed to function 'jmp' by backtrace.c function
      prepare_thread.  Then SIGUSR2 will be signalled to backtrace-child
      which will invoke function sigusr2.
@@ -254,13 +254,17 @@ see_exec_module (Dwfl_Module *mod, void **userdata __attribute__ ((unused)),
      instruction of a function.  Properly handled unwind should not slip into
      the previous unrelated function.  */
 
+#ifdef __x86_64__
+/* #define RAISE_JMP_PATCHING 1 */
+#endif
+
 static void
 prepare_thread (pid_t pid2 __attribute__ ((unused)),
 		void (*jmp) (void) __attribute__ ((unused)))
 {
-#ifndef __x86_64__
+#ifndef RAISE_JMP_PATCHING
   abort ();
-#else /* x86_64 */
+#else /* RAISE_JMP_PATCHING */
   long l;
   struct user_regs_struct user_regs;
   errno = 0;
@@ -278,7 +282,7 @@ prepare_thread (pid_t pid2 __attribute__ ((unused)),
   assert (got == pid2);
   assert (WIFSTOPPED (status));
   assert (WSTOPSIG (status) == SIGUSR1);
-#endif /* __x86_64__ */
+#endif /* RAISE_JMP_PATCHING */
 }
 
 #include <asm/unistd.h>
@@ -370,21 +374,20 @@ exec_dump (const char *exec)
   assert (ssize > 0 && ssize < (ssize_t) sizeof (data.selfpath));
   data.selfpath[ssize] = '\0';
   data.mod = NULL;
-  ptrdiff_t ptrdiff = dwfl_getmodules (dwfl, see_exec_module, &data, 0);
-  assert (ptrdiff == 0);
+  dwfl_getmodules (dwfl, see_exec_module, &data, 0);
   assert (data.mod != NULL);
   GElf_Addr loadbase;
   Elf *elf = dwfl_module_getelf (data.mod, &loadbase);
   GElf_Ehdr ehdr_mem, *ehdr = gelf_getehdr (elf, &ehdr_mem);
   assert (ehdr != NULL);
   /* It is false also on x86_64 with i386 inferior.  */
-#ifndef __x86_64__
-  is_x86_64_native = false;
-#else /* __x86_64__ */
-  is_x86_64_native = ehdr->e_machine == EM_X86_64;
+#ifndef RAISE_JMP_PATCHING
+  use_raise_jmp_patching = false;
+#else /* RAISE_JMP_PATCHING_ */
+  use_raise_jmp_patching = ehdr->e_machine == EM_X86_64;
 #endif /* __x86_64__ */
   void (*jmp) (void) = 0;
-  if (is_x86_64_native)
+  if (use_raise_jmp_patching)
     {
       // Find inferior symbol named "jmp".
       int nsym = dwfl_module_getsymtab (data.mod);