Re: [PATCH] Avoid attempt for runtime checks if all environments are defined

[Siddhesh Poyarekar <siddhesh at sourceware dot org>]

On Thu, Jun 23, 2016 at 03:35:50PM -0400, Mike Frysinger wrote:
> On 23 Jun 2016 23:00, Siddhesh Poyarekar wrote:
> > macros undefined, which means that no such additiona execve is needed
> 
> "additional"
> 
> > +  #define ALL_ENVIRONMENTS_DEFINED 1
> 
> don't indent the #

Thanks, pushed with those changes.

Siddhesh

>From d7e64365fea8d9223a233487de1e1d6e3d21c553 Mon Sep 17 00:00:00 2001
From: Siddhesh Poyarekar <siddhesh@sourceware.org>
Date: Fri, 24 Jun 2016 01:58:44 +0530
Subject: [PATCH] Avoid attempt for runtime checks if all environments are
 defined

getconf has the capability to do a runtime check for environment
support in cases where there is optional support for an environment
(_POSIX_V7_ILP32_OFF32 on x86_64 for example) and this is indicated by
not defining the _POSIX_V7_ILP32_OFF32 macro, which results in getconf
doing an additional execve of _POSIX_V7_ILP32_OFF32 in the
$GETCONF_DIR.

The default bits/environments.h however does not leave any environment
macros undefined, which means that no such additional execve is
needed.  gcc trunk catches this as a build failure since it finds that
the code block inside switch(specs[i].num) is not reachable.  Avoid
this error by not bothering about the additional exec (and looking in
specific environments) when all environments are defined.

Tested on aarch64.

	* posix/getconf.c: Define ALL_ENVIRONMENTS_DEFINED if all
	environment macros are defined.
	(main): Avoid execve if ALL_ENVIRONMENTS_DEFINED is defined.
---
 ChangeLog       |  6 +++++
 posix/getconf.c | 84 ++++++++++++++++++++++++++++++++++++++++-----------------
 2 files changed, 66 insertions(+), 24 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index ce5070f..66bb323 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2016-06-23  Siddhesh Poyarekar  <siddhesh@sourceware.org>
+
+	* posix/getconf.c: Define ALL_ENVIRONMENTS_DEFINED if all
+	environment macros are defined.
+	(main): Avoid execve if ALL_ENVIRONMENTS_DEFINED is defined.
+
 2016-06-23  Florian Weimer  <fweimer@redhat.com>
 
 	[BZ #20191]
diff --git a/posix/getconf.c b/posix/getconf.c
index 3e03396..5a65df8 100644
--- a/posix/getconf.c
+++ b/posix/getconf.c
@@ -29,6 +29,23 @@
 #define NEED_SPEC_ARRAY 1
 #include <posix-conf-vars.h>
 
+/* If all of the environments are defined in environments.h, then we don't need
+   to bother with doing a runtime check for a specific environment.  */
+#if (defined _SC_V6_ILP32_OFF32 \
+     && defined _SC_V7_LPBIG_OFFBIG \
+     && defined _SC_XBS5_LP64_OFF64 \
+     && defined _SC_V6_LP64_OFF64 \
+     && defined _SC_V7_ILP32_OFFBIG \
+     && defined _SC_V6_LPBIG_OFFBIG \
+     && defined _SC_V7_LP64_OFF64 \
+     && defined _SC_V7_ILP32_OFF32 \
+     && defined _SC_XBS5_LPBIG_OFFBIG \
+     && defined _SC_XBS5_ILP32_OFFBIG \
+     && defined _SC_V6_ILP32_OFFBIG \
+     && defined _SC_XBS5_ILP32_OFF32)
+# define ALL_ENVIRONMENTS_DEFINED 1
+#endif
+
 struct conf
   {
     const char *name;
@@ -488,6 +505,24 @@ environment SPEC.\n\n"));
       return 0;
     }
 
+#ifdef ALL_ENVIRONMENTS_DEFINED
+  if (argc > 1 && strncmp (argv[1], "-v", 2) == 0)
+    {
+      if (argv[1][2] == '\0')
+	{
+	  if (argc < 3)
+	    usage ();
+
+	  argv += 2;
+	  argc -= 2;
+	}
+      else
+	{
+	  argv += 1;
+	  argc += 1;
+	}
+    }
+#else
   const char *getconf_dir = getenv ("GETCONF_DIR") ?: GETCONF_DIR;
   size_t getconf_dirlen = strlen (getconf_dir);
 
@@ -538,42 +573,42 @@ environment SPEC.\n\n"));
 
       switch (specs[i].num)
 	{
-#ifndef _XBS5_ILP32_OFF32
+# ifndef _XBS5_ILP32_OFF32
 	  case _SC_XBS5_ILP32_OFF32:
-#endif
-#ifndef _XBS5_ILP32_OFFBIG
+# endif
+# ifndef _XBS5_ILP32_OFFBIG
 	  case _SC_XBS5_ILP32_OFFBIG:
-#endif
-#ifndef _XBS5_LP64_OFF64
+# endif
+# ifndef _XBS5_LP64_OFF64
 	  case _SC_XBS5_LP64_OFF64:
-#endif
-#ifndef _XBS5_LPBIG_OFFBIG
+# endif
+# ifndef _XBS5_LPBIG_OFFBIG
 	  case _SC_XBS5_LPBIG_OFFBIG:
-#endif
-#ifndef _POSIX_V6_ILP32_OFF32
+# endif
+# ifndef _POSIX_V6_ILP32_OFF32
 	  case _SC_V6_ILP32_OFF32:
-#endif
-#ifndef _POSIX_V6_ILP32_OFFBIG
+# endif
+# ifndef _POSIX_V6_ILP32_OFFBIG
 	  case _SC_V6_ILP32_OFFBIG:
-#endif
-#ifndef _POSIX_V6_LP64_OFF64
+# endif
+# ifndef _POSIX_V6_LP64_OFF64
 	  case _SC_V6_LP64_OFF64:
-#endif
-#ifndef _POSIX_V6_LPBIG_OFFBIG
+# endif
+# ifndef _POSIX_V6_LPBIG_OFFBIG
 	  case _SC_V6_LPBIG_OFFBIG:
-#endif
-#ifndef _POSIX_V7_ILP32_OFF32
+# endif
+# ifndef _POSIX_V7_ILP32_OFF32
 	  case _SC_V7_ILP32_OFF32:
-#endif
-#ifndef _POSIX_V7_ILP32_OFFBIG
+# endif
+# ifndef _POSIX_V7_ILP32_OFFBIG
 	  case _SC_V7_ILP32_OFFBIG:
-#endif
-#ifndef _POSIX_V7_LP64_OFF64
+# endif
+# ifndef _POSIX_V7_LP64_OFF64
 	  case _SC_V7_LP64_OFF64:
-#endif
-#ifndef _POSIX_V7_LPBIG_OFFBIG
+# endif
+# ifndef _POSIX_V7_LPBIG_OFFBIG
 	  case _SC_V7_LPBIG_OFFBIG:
-#endif
+# endif
 	    {
 	      const char *args[argc + 3];
 	      size_t spec_len = strlen (spec);
@@ -592,6 +627,7 @@ environment SPEC.\n\n"));
 	    break;
 	}
     }
+#endif
 
   if (argc > 1 && strcmp (argv[1], "-a") == 0)
     {
-- 
2.5.5