all: remove Linux 2.4 vs 2.6 detection

Linux 2.4 is dead.
(The libthread code hasn't worked for Linux 2.4 for a long time.)

INSTALL

@@ -66,23 +66,6 @@ DragonFly|*BSD)
 esac
 
 (
-if [ `uname` = Linux ]; then
-	# On Linux, we use the kernel version to decide whether
-	# to use pthreads or not.  On 2.6 versions that aren't
-	# linking with NPTL by default, pretend to be an older kernel.
-	echo "* Running on Linux: checking for NPTL..."
-	gcc lib/linux-isnptl.c -lpthread
-	if ./a.out >/dev/null
-	then	
-		echo "	NPTL found."
-		echo "SYSVERSION=2.6.x" >>$PLAN9/config
-	else
-		echo "	NPTL not found."
-		echo "SYSVERSION=2.4.x" >>$PLAN9/config
-	fi
-	rm -f ./a.out
-fi
-
 if [ `uname` = SunOS ]; then
 	# On Solaris x86, uname -p cannot be trusted.
 	echo "* Running on Solaris: checking architecture..."

bin/9c

@@ -103,14 +103,6 @@ case "$tag" in
 			cflags="-c -g"
 			;;
 		esac
-		case "${SYSVERSION:-`uname -r`}" in
-		2.4.*)
-			cflags="$cflags -D__Linux24__"
-			;;
-		2.6.*)
-			cflags="$cflags -D__Linux26__"
-			;;
-		esac
 		;;
 *OSF1*)		cc=${CC9:-cc}; cflags="-g -O -c" ;;
 *SunOS*-cc)	cc=cc;

bin/9l

@@ -25,12 +25,7 @@ case "$tag" in
 *Linux*)
 	ld=${CC9:-gcc}
 	userpath=true
-	extralibs="$extralibs -lutil -lresolv"
-	case "${SYSVERSION:-`uname -r`}" in
-	2.6.* | [3-9].* | [1-9][0-9].*)
-		extralibs="$extralibs -lpthread"
-		;;
-	esac
+	extralibs="$extralibs -lutil -lresolv -lpthread"
 	;;
 *Darwin*x86_64*)
 	ld="${CC9:-gcc} -m64"

include/u.h

@@ -66,10 +66,8 @@ typedef long p9jmp_buf[sizeof(sigjmp_buf)/sizeof(long)];
 
 #if defined(__linux__)
 #	include <sys/types.h>
-#	if defined(__Linux26__)
 #	include <pthread.h>
 #	define PLAN9PORT_USING_PTHREADS 1
-#	endif
 #	if defined(__USE_MISC)
 #		undef _NEEDUSHORT
 #		undef _NEEDUINT

lib/linux-isnptl.c

@@ -1,16 +0,0 @@
-#include <pthread.h>
-#include <unistd.h>
-#include <stdlib.h>
-#include <stdio.h>
-
-int
-main(void)
-{
-	ulong x;
-
-	x = (ulong)pthread_self();
-	printf("%lx\n", x);
-	if(x < 1024*1024)
-		exit(1);	/* NOT NPTL */
-	exit(0);
-}

man/man1/9c.1

@@ -79,9 +79,7 @@ to the include path.
 .I 9c
 also defines
 .B __sun__
-on SunOS systems and
-.B __Linux26__
-on Linux systems with 2.6-series kernels.
+on SunOS systems.
 .PP
 .I 9a
 assembles the named files into object files for the current system.

man/man1/install.1

@@ -76,20 +76,9 @@ prints suggested settings for the environment variables
 and
 .BR $PATH .
 .PP
-Plan 9 from User Space uses different threading implementations on Linux 2.6 and
-later kernels than on 2.4 and earlier;
-and on FreeBSD 5 and later kernels than on FreeBSD 4 and earlier.
-Running binaries from one class on another will not work.
-.PP
-Some Linux 2.6 systems (e.g., Gentoo) do not use the new NPTL pthread library
-even though the kernel supports them.  On these systems, plan9port must 
-fall back on the threading code intended for Linux 2.4.  To accomplish this,
 .I INSTALL
-checks whether the running system uses NPTL and sets
-.B SYSVERSION
-in
-.B \*9/config
-accordingly.
+writes various autodetected settings to
+.BR \*9/config .
 The file
 .B \*9/LOCAL.config
 is appended to

src/libthread/README.Linux

@@ -1,40 +0,0 @@
-Thread support on Linux is confused by the recent thread local storage (TLS)
-support that has been put into the ELF tool chain.  The TLS libraries are 
-installed in /lib/tls on most Linux systems.
-
-We provide two different implementations of the os-dependent parts
-of libthread for Linux.  The first is intended for use on Linux 2.4 and earlier
-kernels, which do not support TLS.  It is in Linux.c and Linuxasm.c and
-does not use the pthread interface.  The second is intended for Linux 2.6
-and later kernels, which do support TLS.  It is in pthread.c and uses the
-standard pthread interface.  It expects to be linked against the TLS-aware
-thread library aka NPTL.
-
-If you use Linux.c and Linuxasm.c with TLS libraries, they do not
-set up the TLS properly so you will get incorrect programs.
-For example, there will only be one errno among all the procs
-in your program instead of one per proc.  The pthread NPTL
-implementation is needed to use the TLS libraries properly.
-
-If you use pthread.c without TLS libraries (i.e., with the old Linux
-pthread library known as LinuxThreads), then you will also get
-incorrect programs, although more obviously so.  The LinuxThreads
-library assumes it can look at the stack pointer to distinguish between
-threads, but libthread does its own stack management, breaking this
-assumption.  If you run a pthread-compiled program with the 
-LinuxThreads library, LinuxThreads itself will cause a segmentation
-fault in __pthread_getspecific() the first time it is called from a
-non-standard stack.
-
-So, it is important that you compile binaries that match your
-system's choice of TLS vs. not-TLS libraries.  The hard part is figuring
-out which your system has chosen.  Plan9port looks at the kernel
-version you are running and assumes that on kernels that support
-TLS (2.6+) you will be using TLS.
-
-Apparently Gentoo and maybe other distributions do not follow this rule.
-They use non-TLS libraries even on kernels that can support TLS.
-To accomodate them, you can add a line SYSVERSION=2.4 to $PLAN9/config
-to force the build to think you are running an old kernel.
-The INSTALL script sets up this file automatically on Linux systems.
-

src/libthread/sysofiles.sh

@@ -2,12 +2,11 @@
 
 test -f $PLAN9/config && . $PLAN9/config
 
-tag="$OBJTYPE-$SYSNAME-${SYSVERSION:-`uname -r`}-${CC9:-cc}"
-case "$tag" in
-*-NetBSD-*)
+case "$SYSNAME" in
+NetBSD)
 	echo ${SYSNAME}-${OBJTYPE}-asm.o $SYSNAME.o pthread.o stkmalloc.o
 	;;
-*-OpenBSD-*)
+OpenBSD)
 	echo ${SYSNAME}-${OBJTYPE}-asm.o ${SYSNAME}-${OBJTYPE}.o pthread.o stkmmap.o
 	;;
 *)