Linux: Fix USE_UCONTEXT detection

On Linux, afs/param.h determines whether to use the ucontext()
function based on the glibc version. However, the glibc version
macros aren't available until a C library header has been included.

There have been a couple of attempts to fix this. The first included
afs_sysnames.h before the C library check, but this wasn't sufficient
to pull in a header for all builds. The second included stdio.h before
including afs/param.h in process.c.

Whilst the second approach works, it has the drawback that it breaks
our convention that afsconfig.h and afs/param.h must always be the first
includes in a file. More seriously, it means that the behaviour of
afs/param.h is different depending on where it appears in the include
order - which is especially dangerous for 3rd party user.

So, this patch tries to resolve all of this by explicitly including
features.h before doing the glibc version checks. The only danger I
can see here is that Linux platforms without glibc may lack a
features.h, but I suspect we have trouble building on such platforms
in any case.

Change-Id: Ief96d32b10372225335e2d2fbb7205da4bf5fc0a
Reviewed-on: http://gerrit.openafs.org/4389
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>

diff --git a/src/config/param.linux24.h b/src/config/param.linux24.h
index 3c2afa5..802a7cf 100644 (file)
--- a/src/config/param.linux24.h
+++ b/src/config/param.linux24.h
@@ -113,8 +113,9 @@
 
 #endif /* !defined(UKERNEL) */
 
-/* needed so glibc version will be defined */
-#include <afs/afs_sysnames.h>
+#if defined(UKERNEL) || !defined(KERNEL)
+#include <features.h>
+#endif
 
 #ifdef __GLIBC__
 #if (__GLIBC__ > 2) || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 3)
@@ -122,4 +123,6 @@
 #endif
 #endif
 
+#include <afs/afs_sysnames.h>
+
 #endif /* AFS_PARAM_COMMON_H */

diff --git a/src/config/param.linux26.h b/src/config/param.linux26.h
index 73836ec..ad2536b 100644 (file)
--- a/src/config/param.linux26.h
+++ b/src/config/param.linux26.h
@@ -96,8 +96,9 @@
 
 #endif /* !defined(UKERNEL) */
 
-/* needed so glibc version will be defined */
-#include <afs/afs_sysnames.h>
+#if defined(UKERNEL) || !defined(KERNEL)
+#include <features.h>
+#endif
 
 #ifdef __GLIBC__
 #if (__GLIBC__ > 2) || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 3)
@@ -105,4 +106,6 @@
 #endif
 #endif
 
+#include <afs/afs_sysnames.h>
+
 #endif /* AFS_PARAM_COMMON_H */

diff --git a/src/lwp/process.c b/src/lwp/process.c
index 06efcfb..bd18de6 100644 (file)
--- a/src/lwp/process.c
+++ b/src/lwp/process.c
@@ -10,19 +10,14 @@
 /* process.c - manage lwp context switches be means of setjmp/longjmp. */
 
 #include <afsconfig.h>
+#include <afs/param.h>
 
-/*
- * We must include at least one system header on Linux prior to including
- * afs/param.h, or the __GLIBC__ and __GLIBC_MINOR__ macros will not yet be
- * defined and we won't know whether we're using ucontext.
- */
 #include <stdio.h>
 #include <assert.h>
 #ifdef HAVE_STDLIB_H
 # include <stdlib.h>
 #endif
 
-#include <afs/param.h>
 
 #include "lwp.h"