To: bug-pth@gnu.org
Subject: [PATCH] fix pth for makecontext-less glibc on Linux 3.x kernels
Cc: pth-users@gnu.org

Attempting to build pth-2.0.7 on arm-linux-gnueabi, running a 3.x
kernel, and with a glibc that doesn't yet have makecontext et al
(glibc-2.14.1 in my case) results in the following during configure:

Machine Context Implementation:
checking for ucontext.h... yes
checking for makecontext... no
checking for swapcontext... no
checking for getcontext... no
checking for setcontext... no
checking for usable SVR4/SUSv2 makecontext(2)/swapcontext(2)... no
checking for signal.h... (cached) yes
checking for sigsetjmp... no
checking for siglongjmp... yes
checking for setjmp... yes
checking for longjmp... yes
checking for _setjmp... yes
checking for _longjmp... yes
checking for sigaltstack... yes
checking for sigstack... yes
checking for signal-mask aware setjmp(3)/longjmp(3)... yes: sjljlx
checking for typedef stack_t... (cached) yes
checking for direction of stack growth... down
checking for makecontext... (cached) no
checking for stack setup via makecontext... N.A.
checking for sigaltstack... (cached) yes
checking for typedef stack_t... (cached) yes
checking for stack setup via sigaltstack... ok
checking for sigstack... (cached) yes
checking for stack setup via sigstack... guessed
decision on mctx implementation... sjlj/sjljlx/none

Note the "sjljlx", that's bogus since sjljlx is a fallback for
truly ancient systems; the correct choice is ssjlj.

Configure succeeds, but 'make' then results in:

./shtool scpp -o pth_p.h -t pth_p.h.in -Dcpp -Cintern -M '==#==' pth_compat.c pth_debug.c pth_syscall.c pth_errno.c pth_ring.c pth_mctx.c pth_uctx.c pth_clean.c pth_time.c pth_tcb.c pth_util.c pth_pqueue.c pth_event.c pth_sched.c pth_data.c pth_msg.c pth_cancel.c pth_sync.c pth_attr.c pth_lib.c pth_fork.c pth_high.c pth_ext.c pth_string.c pthread.c
./libtool --mode=compile --quiet gcc -c -I. -O2 -pipe pth_debug.c
./libtool --mode=compile --quiet gcc -c -I. -O2 -pipe pth_ring.c
./libtool --mode=compile --quiet gcc -c -I. -O2 -pipe pth_pqueue.c
./libtool --mode=compile --quiet gcc -c -I. -O2 -pipe pth_time.c
./libtool --mode=compile --quiet gcc -c -I. -O2 -pipe pth_errno.c
./libtool --mode=compile --quiet gcc -c -I. -O2 -pipe pth_mctx.c
pth_mctx.c: In function '__pth_mctx_set':
pth_mctx.c:480:2: error: #error "Unsupported Linux (g)libc version and/or platform"
make: *** [pth_mctx.lo] Error 1

This happens because there's a Linux kernel version check that
unfortunately only recognises 2.x versions, so it classifies a
3.x kernel as "braindead", which selects sjljlx and causes the
breakage.

The fix is to expand the kernel version regexp in aclocal.m4 to
also accept 3.x kernels; with that fix configure says:

checking for signal-mask aware setjmp(3)/longjmp(3)... yes: ssjlj
checking for typedef stack_t... (cached) yes
checking for direction of stack growth... down
checking for makecontext... (cached) no
checking for stack setup via makecontext... N.A.
checking for sigaltstack... (cached) yes
checking for typedef stack_t... (cached) yes
checking for stack setup via sigaltstack... ok
checking for sigstack... (cached) yes
checking for stack setup via sigstack... guessed
decision on mctx implementation... sjlj/ssjlj/sas

Both 'make' and 'make test' then succeed.

m68k-linux' glibc also lacks makecontext() et al, so it too is sensitive
to the kernel version check.  For m68k there is some specific support
in the sjljlx fallback code which appears to work, but with the fix
m68k too gets to use sjlj/ssjlj/sas (which works fine btw).

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
---
--- pth-2.0.7/aclocal.m4.~1~	2006-06-08 19:54:01.000000000 +0200
+++ pth-2.0.7/aclocal.m4	2012-05-30 18:44:42.000000000 +0200
@@ -1074,7 +1074,7 @@ case $PLATFORM in
         braindead=no
         case "x`uname -r`" in
 changequote(, )dnl
-            x2.[23456789]* ) ;;
+            x2.[23456789]* | x3.[0-9]* ) ;;
 changequote([, ])
             * ) braindead=yes ;;
         esac
--- pth-2.0.7/configure.~1~	2006-06-08 20:14:48.000000000 +0200
+++ pth-2.0.7/configure	2012-05-30 18:45:03.000000000 +0200
@@ -22512,7 +22512,7 @@ case $PLATFORM in
     *-*-linux* )
         braindead=no
         case "x`uname -r`" in
-            x2.[23456789]* ) ;;
+            x2.[23456789]* | x3.[0-9]* ) ;;
 
             * ) braindead=yes ;;
         esac