gdb: fix vfork with multiple threads

[deliverable/binutils-gdb.git] / gdbsupport / common-defs.h

diff --git a/gdbsupport/common-defs.h b/gdbsupport/common-defs.h
index a5c57de2f27f83ed0bb812a1ea97adb00bc905d6..5678076575664633628da4efb85fb74925294006 100644 (file)
--- a/gdbsupport/common-defs.h
+++ b/gdbsupport/common-defs.h
@@ -1,6 +1,6 @@
 /* Common definitions.
 
-   Copyright (C) 1986-2020 Free Software Foundation, Inc.
+   Copyright (C) 1986-2021 Free Software Foundation, Inc.
 
    This file is part of GDB.
 
@@ -20,20 +20,6 @@
 #ifndef COMMON_COMMON_DEFS_H
 #define COMMON_COMMON_DEFS_H
 
-#ifdef GDBSERVER
-
-#include <gnulib/config.h>
-
-#undef PACKAGE_NAME
-#undef PACKAGE
-#undef PACKAGE_VERSION
-#undef PACKAGE_STRING
-#undef PACKAGE_TARNAME
-
-#include <config.h>
-
-#else  /* GDBSERVER */
-
 #include <gdbsupport/config.h>
 
 #undef PACKAGE_NAME
@@ -44,8 +30,6 @@
 
 #include "gnulib/config.h"
 
-#endif /* GDBSERVER */
-
 /* From:
     https://www.gnu.org/software/gnulib/manual/html_node/stdint_002eh.html
 
@@ -100,7 +84,12 @@
 
 #include <stdarg.h>
 #include <stdio.h>
+
+/* Include both cstdlib and stdlib.h to ensure we have standard functions
+   defined both in the std:: namespace and in the global namespace.  */
+#include <cstdlib>
 #include <stdlib.h>
+
 #include <stddef.h>
 #include <stdint.h>
 #include <string.h>
@@ -108,16 +97,93 @@
 #include <strings.h>   /* for strcasecmp and strncasecmp */
 #endif
 #include <errno.h>
+#if HAVE_ALLOCA_H
 #include <alloca.h>
+#endif
 
 #include "ansidecl.h"
 /* This is defined by ansidecl.h, but we prefer gnulib's version.  On
    MinGW, gnulib might enable __USE_MINGW_ANSI_STDIO, which may or not
    require use of attribute gnu_printf instead of printf.  gnulib
-   checks that at configure time.  Since _GL_ATTRIBUTE_FORMAT_PRINTF
+   checks that at configure time.  Since _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD
    is compatible with ATTRIBUTE_PRINTF, simply use it.  */
 #undef ATTRIBUTE_PRINTF
-#define ATTRIBUTE_PRINTF _GL_ATTRIBUTE_FORMAT_PRINTF
+#define ATTRIBUTE_PRINTF _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD
+
+/* This is defined by ansidecl.h, but we disable the attribute.
+
+   Say a developer starts out with:
+   ...
+   extern void foo (void *ptr) __atttribute__((nonnull (1)));
+   void foo (void *ptr) {}
+   ...
+   with the idea in mind to catch:
+   ...
+   foo (nullptr);
+   ...
+   at compile time with -Werror=nonnull, and then adds:
+   ...
+    void foo (void *ptr) {
+   +  gdb_assert (ptr != nullptr);
+    }
+   ...
+   to catch:
+   ...
+   foo (variable_with_nullptr_value);
+   ...
+   at runtime as well.
+
+   Said developer then verifies that the assert works (using -O0), and commits
+   the code.
+
+   Some other developer then checks out the code and accidentally writes some
+   variant of:
+   ...
+   foo (variable_with_nullptr_value);
+   ...
+   and builds with -O2, and ... the assert doesn't trigger, because it's
+   optimized away by gcc.
+
+   There's no suppported recipe to prevent the assertion from being optimized
+   away (other than: build with -O0, or remove the nonnull attribute).  Note
+   that -fno-delete-null-pointer-checks does not help.  A patch was submitted
+   to improve gcc documentation to point this out more clearly (
+   https://gcc.gnu.org/pipermail/gcc-patches/2021-July/576218.html ).  The
+   patch also mentions a possible workaround that obfuscates the pointer
+   using:
+   ...
+    void foo (void *ptr) {
+   +  asm ("" : "+r"(ptr));
+      gdb_assert (ptr != nullptr);
+    }
+   ...
+   but that still requires the developer to manually add this in all cases
+   where that's necessary.
+
+   A warning was added to detect the situation: -Wnonnull-compare, which does
+   help in detecting those cases, but each new gcc release may indicate a new
+   batch of locations that needs fixing, which means we've added a maintenance
+   burden.
+
+   We could try to deal with the problem more proactively by introducing a
+   gdb_assert variant like:
+   ...
+   void gdb_assert_non_null (void *ptr) {
+      asm ("" : "+r"(ptr));
+      gdb_assert (ptr != nullptr);
+    }
+    void foo (void *ptr) {
+      gdb_assert_nonnull (ptr);
+    }
+   ...
+   and make it a coding style to use it everywhere, but again, maintenance
+   burden.
+
+   With all these things considered, for now we go with the solution with the
+   least maintenance burden: disable the attribute, such that we reliably deal
+   with it everywhere.  */
+#undef ATTRIBUTE_NONNULL
+#define ATTRIBUTE_NONNULL(m)
 
 #if GCC_VERSION >= 3004
 #define ATTRIBUTE_UNUSED_RESULT __attribute__ ((__warn_unused_result__))