linux-kernel - [PATCH tip/core/rcu 8/8] rcutorture: Make use of nolibc when available

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Date:   Sun, 11 Nov 2018 12:01:43 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        Willy Tarreau <w@....eu>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 8/8] rcutorture: Make use of nolibc when available

From: Willy Tarreau <w@....eu>

This reduces the size of the init executable from ~800 kB to ~800 bytes
on x86_64. This is only implemented for x86_64, i386, arm and arm64.
Others not tested.

Signed-off-by: Willy Tarreau <w@....eu>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 .../selftests/rcutorture/bin/mkinitrd.sh       | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/rcutorture/bin/mkinitrd.sh b/tools/testing/selftests/rcutorture/bin/mkinitrd.sh
index 56a56ea06983..da298394daa2 100755
--- a/tools/testing/selftests/rcutorture/bin/mkinitrd.sh
+++ b/tools/testing/selftests/rcutorture/bin/mkinitrd.sh
@@ -82,8 +82,10 @@ cd $D
 mkdir -p initrd
 cd initrd
 cat > init.c << '___EOF___'
+#ifndef NOLIBC
 #include <unistd.h>
 #include <sys/time.h>
+#endif
 
 volatile unsigned long delaycount;
 
@@ -113,7 +115,21 @@ int main(int argc, int argv[])
 	return 0;
 }
 ___EOF___
-${CROSS_COMPILE}gcc -s -static -Os -o init init.c
+
+# build using nolibc on supported archs (smaller executable) and fall
+# back to regular glibc on other ones.
+if echo -e "#if __x86_64__||__i386__||__i486__||__i586__||__i686__" \
+           "||__ARM_EABI__||__aarch64__\nyes\n#endif" \
+   | ${CROSS_COMPILE}gcc -E -nostdlib -xc - \
+   | grep -q '^yes'; then
+	# architecture supported by nolibc
+        ${CROSS_COMPILE}gcc -fno-asynchronous-unwind-tables -fno-ident \
+		-nostdlib -include ../bin/nolibc.h -lgcc -s -static -Os \
+		-o init init.c
+else
+	${CROSS_COMPILE}gcc -s -static -Os -o init init.c
+fi
+
 rm init.c
 echo "Done creating a statically linked C-language initrd"
 
-- 
2.17.1