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Re: Avoid backtrace tests matching filenames when searching forfunction names


On Wed, 23 Jan 2013, Roland McGrath wrote:

> > +  if (p)
> > +    return strstr (p, name) != NULL;
> > +  else
> > +    return false;
> 
>   return p != NULL && strstr (p, name) != NULL;

OK, this version uses that approach.  Tested x86_64.

> > > What's the reason for putting NO_INLINE on do_test?
> > 
> > Generally trying to control what the sequence of functions should look 
> > like as much as possible, even though in fact it's not possible to get a 
> > name for do_test in the backtrace, so the testing stops before there.
> 
> There is no point in attempting to ensure there is a frame for do_test and
> then not testing that there is one.  

There's the test of the total number of functions in the backtrace.  But 
the basic reason is general prudence, trying to make it as clear as 
possible to the reader what the expected backtrace should be, and as 
unlikely as possible that the sequence of frames actually does depend on 
what the compiler does, since the tests are about glibc and not GCC.

(I don't think those NO_INLINEs are at all related to this patch 
refactoring the tests and improving the robustness of the matching of 
function names, anyway.)

2013-01-23  Joseph Myers  <joseph@codesourcery.com>

	* debug/tst-backtrace.h: New file.
	* debug/tst-backtrace2.c: Include tst-backtrace.h.
	(ret): Remove variable.
	(x): Likewise.
	(FAIL): Remove macro.
	(NO_INLINE): Likewise.
	(fn1): Use match function instead of strstr.
	* debug/tst-backtrace3.c: Include tst-backtrace.h.
	(ret): Remove variable.
	(x): Likewise.
	(FAIL): Remove macro.
	(NO_INLINE): Likewise.
	(fn): Use match function instead of strstr.
	* debug/tst-backtrace4.c: Include tst-backtrace.h.
	(ret): Remove variable.
	(x): Likewise.
	(FAIL): Remove macro.
	(NO_INLINE): Likewise.
	(handle_signal): Use match function instead of strstr.
	* debug/tst-backtrace5.c: Include tst-backtrace.h.
	(ret): Remove variable.
	(x): Likewise.
	(FAIL): Remove macro.
	(NO_INLINE): Likewise.
	(handle_signal): Use match function instead of strstr.

diff --git a/debug/tst-backtrace.h b/debug/tst-backtrace.h
new file mode 100644
index 0000000..0a89488
--- /dev/null
+++ b/debug/tst-backtrace.h
@@ -0,0 +1,48 @@
+/* Test backtrace and backtrace_symbols: common code for examining
+   backtraces.
+   Copyright (C) 2013 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+
+/* Set to a non-zero value if the test fails.  */
+volatile int ret;
+
+/* Accesses to X are used to prevent optimization.  */
+volatile int x;
+
+/* Called if the test fails.  */
+#define FAIL() \
+  do { printf ("Failure on line %d\n", __LINE__); ret = 1; } while (0)
+
+/* Use this attribute to prevent inlining, so that all expected frames
+   are present.  */
+#define NO_INLINE __attribute__ ((noinline))
+
+/* Look for a match in SYM from backtrace_symbols to NAME, a fragment
+   of a function name.  Ignore the filename before '(', but presume
+   that the function names are chosen so they cannot accidentally
+   match the hex offset before the closing ')'. */
+
+static inline bool
+match (const char *sym, const char *name)
+{
+  char *p = strchr (sym, '(');
+  return p != NULL && strstr (p, name) != NULL;
+}
diff --git a/debug/tst-backtrace2.c b/debug/tst-backtrace2.c
index e1d4572..1bdef0d 100644
--- a/debug/tst-backtrace2.c
+++ b/debug/tst-backtrace2.c
@@ -22,27 +22,15 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "tst-backtrace.h"
+
 static int do_test (void);
 #define TEST_FUNCTION do_test ()
 #include "../test-skeleton.c"
 
-/* Set to a non-zero value if the test fails.  */
-int ret;
-
-/* Accesses to X are used to prevent optimization.  */
-volatile int x;
-
-/* Called if the test fails.  */
-#define FAIL() \
-  do { printf ("Failure on line %d\n", __LINE__); ret = 1; } while (0)
-
 /* The backtrace should include at least f1, f2, f3, and do_test.  */
 #define NUM_FUNCTIONS 4
 
-/* Use this attribute to prevent inlining, so that all expected frames
-   are present.  */
-#define NO_INLINE __attribute__ ((noinline))
-
 NO_INLINE void
 fn1 (void)
 {
@@ -71,14 +59,14 @@ fn1 (void)
   for (i = 0; i < n; ++i)
     printf ("Function %d: %s\n", i, symbols[i]);
   /* Check that the function names obtained are accurate.  */
-  if (strstr (symbols[0], "fn1") == NULL)
+  if (!match (symbols[0], "fn1"))
     {
       FAIL ();
       return;
     }
   /* Symbol names are not available for static functions, so we do not
      check f2.  */
-  if (strstr (symbols[2], "fn3") == NULL)
+  if (!match (symbols[2], "fn3"))
     {
       FAIL ();
       return;
diff --git a/debug/tst-backtrace3.c b/debug/tst-backtrace3.c
index 4d3309b..182f423 100644
--- a/debug/tst-backtrace3.c
+++ b/debug/tst-backtrace3.c
@@ -22,27 +22,15 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "tst-backtrace.h"
+
 static int do_test (void);
 #define TEST_FUNCTION do_test ()
 #include "../test-skeleton.c"
 
-/* Set to a non-zero value if the test fails.  */
-int ret;
-
-/* Accesses to X are used to prevent optimization.  */
-volatile int x;
-
-/* Called if the test fails.  */
-#define FAIL() \
-  do { printf ("Failure on line %d\n", __LINE__); ret = 1; } while (0)
-
 /* The backtrace should include at least 3 * fn, and do_test.  */
 #define NUM_FUNCTIONS 4
 
-/* Use this attribute to prevent inlining, so that all expected frames
-   are present.  */
-#define NO_INLINE __attribute__ ((noinline))
-
 NO_INLINE int
 fn (int c)
 {
@@ -77,7 +65,7 @@ fn (int c)
     printf ("Function %d: %s\n", i, symbols[i]);
   /* Check that the function names obtained are accurate.  */
   for (i = 0; i < n - 1; ++i)
-    if (strstr (symbols[i], "fn") == NULL)
+    if (!match (symbols[i], "fn"))
       {
 	FAIL ();
 	return 1;
diff --git a/debug/tst-backtrace4.c b/debug/tst-backtrace4.c
index 41a3f51..9c0c2a2 100644
--- a/debug/tst-backtrace4.c
+++ b/debug/tst-backtrace4.c
@@ -25,28 +25,16 @@
 #include <signal.h>
 #include <unistd.h>
 
+#include "tst-backtrace.h"
+
 static int do_test (void);
 #define TEST_FUNCTION do_test ()
 #include "../test-skeleton.c"
 
-/* Set to a non-zero value if the test fails.  */
-volatile int ret;
-
-/* Accesses to X are used to prevent optimization.  */
-volatile int x;
-
-/* Called if the test fails.  */
-#define FAIL() \
-  do { printf ("Failure on line %d\n", __LINE__); ret = 1; } while (0)
-
 /* The backtrace should include at least handle_signal, a signal
    trampoline, 3 * fn, and do_test.  */
 #define NUM_FUNCTIONS 6
 
-/* Use this attribute to prevent inlining, so that all expected frames
-   are present.  */
-#define NO_INLINE __attribute__ ((noinline))
-
 volatile int sig_handled = 0;
 
 void
@@ -79,14 +67,14 @@ handle_signal (int signum)
   for (i = 0; i < n; ++i)
     printf ("Function %d: %s\n", i, symbols[i]);
   /* Check that the function names obtained are accurate.  */
-  if (strstr (symbols[0], "handle_signal") == NULL)
+  if (!match (symbols[0], "handle_signal"))
     {
       FAIL ();
       return;
     }
   /* Do not check name for signal trampoline.  */
   for (i = 2; i < n - 1; i++)
-    if (strstr (symbols[i], "fn") == NULL)
+    if (!match (symbols[i], "fn"))
       {
 	FAIL ();
 	return;
diff --git a/debug/tst-backtrace5.c b/debug/tst-backtrace5.c
index eb16c23..ca47437 100644
--- a/debug/tst-backtrace5.c
+++ b/debug/tst-backtrace5.c
@@ -26,28 +26,16 @@
 #include <signal.h>
 #include <unistd.h>
 
+#include "tst-backtrace.h"
+
 static int do_test (void);
 #define TEST_FUNCTION do_test ()
 #include "../test-skeleton.c"
 
-/* Set to a non-zero value if the test fails.  */
-volatile int ret;
-
-/* Accesses to X are used to prevent optimization.  */
-volatile int x;
-
-/* Called if the test fails.  */
-#define FAIL() \
-  do { printf ("Failure on line %d\n", __LINE__); ret = 1; } while (0)
-
 /* The backtrace should include at least handle_signal, a signal
    trampoline, read, 3 * fn, and do_test.  */
 #define NUM_FUNCTIONS 7
 
-/* Use this attribute to prevent inlining, so that all expected frames
-   are present.  */
-#define NO_INLINE __attribute__ ((noinline))
-
 void
 handle_signal (int signum)
 {
@@ -76,24 +64,24 @@ handle_signal (int signum)
   for (i = 0; i < n; ++i)
     printf ("Function %d: %s\n", i, symbols[i]);
   /* Check that the function names obtained are accurate.  */
-  if (strstr (symbols[0], "handle_signal") == NULL)
+  if (!match (symbols[0], "handle_signal"))
     {
       FAIL ();
       return;
     }
   /* Do not check name for signal trampoline.  */
   i = 2;
-  if (strstr (symbols[i++], "read") == NULL)
+  if (!match (symbols[i++], "read"))
     {
       /* Perhaps symbols[2] is __kernel_vsyscall?  */
-      if (strstr (symbols[i++], "read") == NULL)
+      if (!match (symbols[i++], "read"))
 	{
 	  FAIL ();
 	  return;
 	}
     }
   for (; i < n - 1; i++)
-    if (strstr (symbols[i], "fn") == NULL)
+    if (!match (symbols[i], "fn"))
       {
 	FAIL ();
 	return;

-- 
Joseph S. Myers
joseph@codesourcery.com


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