[gdb/testsuite] Add check-readmore

Consider the gdb output:
...
27        return SYSCALL_CANCEL (nanosleep, requested_time, remaining);^M
(gdb) ^M
Thread 2 "run-attach-whil" stopped.^M
...

When trying to match the gdb prompt using gdb_test which uses '$gdb_prompt $',
it may pass or fail.

This sort of thing needs to be fixed (see commit b0e2f96b56b), but there's
currently no way to reliably find this type of FAILs.

We have check-read1, but that one actually make the test pass reliably.

We need something like the opposite of check-read1: something that makes
expect read a bit slower, or more exhaustively.

Add a new test target check-readmore that implements this.

There are two methods of implementing this in read1.c:
- the first method waits a bit before doing a read
- the second method does a read and then decides whether to
  return or to wait a bit and do another read, and so on.

The second method is potentially faster, has less risc of timeout and could
potentially detect more problems.  The first method has a simpler
implementation.

The second method is enabled by default.  The default waiting period is 10
miliseconds.

The first method can be enabled using:
...
$ export READMORE_METHOD=1
...
and the waiting period can be specified in miliseconds using:
...
$ export READMORE_SLEEP=9
...

Also a log file can be specified using:
...
$ export READMORE_LOG=$(pwd -P)/LOG
...

Tested on x86_64-linux.

Testing with check-readmore showed these regressions:
...
FAIL: gdb.base/bp-cmds-continue-ctrl-c.exp: run: stop with control-c (continue)
FAIL: gdb.base/bp-cmds-continue-ctrl-c.exp: attach: stop with control-c (continue)
...

I have not been able to find a problem in the test-case, and I think it's the
nature of both the test-case and readmore that makes it run longer.  Make
these pass by increasing the alarm timeout from 60 to 120 seconds.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27957

1 files changed, 30 insertions, 13 deletions

diff --git a/gdb/testsuite/Makefile.in b/gdb/testsuite/Makefile.in
index 20cb3da..6b4c758 100644
--- a/gdb/testsuite/Makefile.in
+++ b/gdb/testsuite/Makefile.in
@@ -39,6 +39,8 @@ CC=@CC@
 
 EXPECT = `if [ "$${READ1}" != "" ] ; then \
             echo $${rootme}/expect-read1; \
+          elif [ "$${READMORE}" != "" ] ; then \
+            echo $${rootme}/expect-readmore; \
           elif [ -f $${rootme}/../../expect/expect ] ; then \
             echo $${rootme}/../../expect/expect ; \
           else \
@@ -161,6 +163,9 @@ check: all $(abs_builddir)/site.exp
 check-read1: read1.so expect-read1
 	$(MAKE) READ1="1" check
 
+check-readmore: readmore.so expect-readmore
+	$(MAKE) READMORE="1" check
+
 # Check whether we need to print the timestamp for each line of
 # status.
 TIMESTAMP = $(if $(TS),| $(srcdir)/print-ts.py $(if $(TS_FORMAT),$(TS_FORMAT),),)
@@ -344,7 +349,7 @@ clean mostlyclean:
 	-rm -f *.dwo *.dwp
 	-rm -rf outputs temp cache
 	-rm -rf gdb.perf/workers gdb.perf/outputs gdb.perf/temp gdb.perf/cache
-	-rm -f read1.so expect-read1
+	-rm -f read1.so expect-read1 readmore.so expect-readmore
 
 distclean maintainer-clean realclean: clean
 	-rm -f *~ core
@@ -367,18 +372,22 @@ TAGS: force
 		-
 
 # Build the expect wrapper script that preloads the read1.so library.
-expect-read1:
+expect-read1 expect-readmore:
 	$(ECHO_GEN) \
-	rm -f expect-read1-tmp; \
-	touch expect-read1-tmp; \
-	echo "# THIS FILE IS GENERATED -*- buffer-read-only: t -*- \n" >>expect-read1-tmp; \
-	echo "# vi:set ro: */\n\n" >>expect-read1-tmp; \
-	echo "# To regenerate this file, run:\n" >>expect-read1-tmp; \
-	echo "#      make clean; make/\n" >>expect-read1-tmp; \
-	echo "export LD_PRELOAD=`pwd`/read1.so" >>expect-read1-tmp; \
-	echo 'exec expect "$$@"' >>expect-read1-tmp; \
-	chmod +x expect-read1-tmp; \
-	mv expect-read1-tmp expect-read1
+	rm -f $@-tmp; \
+	touch $@-tmp; \
+	echo "# THIS FILE IS GENERATED -*- buffer-read-only: t -*- \n" >>$@-tmp; \
+	echo "# vi:set ro: */\n\n" >>$@-tmp; \
+	echo "# To regenerate this file, run:\n" >>$@-tmp; \
+	echo "#      make clean; make/\n" >>$@-tmp; \
+	if [ $@ = expect-read1 ]; then \
+	  echo "export LD_PRELOAD=`pwd`/read1.so" >>$@-tmp; \
+	else \
+	  echo "export LD_PRELOAD=`pwd`/readmore.so" >>$@-tmp; \
+	fi; \
+	echo 'exec expect "$$@"' >>$@-tmp; \
+	chmod +x $@-tmp; \
+	mv $@-tmp $@
 
 # Build the read1.so preload library.  This overrides the `read'
 # function, making it read one byte at a time.  Running the testsuite
@@ -386,9 +395,17 @@ expect-read1:
 read1.so: lib/read1.c
 	$(ECHO_CC) $(CC) -o $@ ${srcdir}/lib/read1.c -Wall -g -shared -fPIC $(CFLAGS)
 
+# Build the readmore.so preload library.  This overrides the `read'
+# function, making it try harder to read more at a time.  Running the
+# testsuite with this catches racy tests.
+readmore.so: lib/read1.c
+	$(ECHO_CC) $(CC) -o $@ ${srcdir}/lib/read1.c -Wall -g -shared -fPIC \
+	  $(CFLAGS) -DREADMORE
+
 # Build the read1 machinery.
-.PHONY: read1
+.PHONY: read1 readmore
 read1: read1.so expect-read1
+readmore: readmore.so expect-readmore
 
 # Disable implicit make rules.
 include $(srcdir)/../disable-implicit-rules.mk