[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 b0e2f96b56), 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

gdb/Makefile.in

@@ -1681,12 +1681,12 @@ check-perf: force
 	  $(MAKE) $(TARGET_FLAGS_TO_PASS) check-perf; \
 	else true; fi
 
-check-read1: force
+check-read1 check-readmore: force
 	@if [ -f testsuite/Makefile ]; then \
 	  rootme=`pwd`; export rootme; \
 	  rootsrc=`cd $(srcdir); pwd`; export rootsrc; \
 	  cd testsuite; \
-	  $(MAKE) $(TARGET_FLAGS_TO_PASS) check-read1; \
+	  $(MAKE) $(TARGET_FLAGS_TO_PASS) $@; \
 	else true; fi
 
 check-parallel: force

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

gdb/testsuite/README

@@ -361,7 +361,7 @@ fail, it can also have the effect of making otherwise failing tests pass.
 This happens f.i. if the test is trying to match a gdb prompt using an end of
 input marker "${gdb_prompt} $" and there is output after the gdb prompt.  This
 may either pass or fail in normal operation, but using check-read1 will ensure
-that it passes.
+that it passes.  Use check-readmore to detect this type of failure.
 
 Testsuite Configuration
 ***********************

gdb/testsuite/gdb.base/bp-cmds-continue-ctrl-c.c

@@ -26,7 +26,7 @@ foo (void)
 int
 main ()
 {
-  alarm (60);
+  alarm (120);
 
   while (1)
     foo ();

gdb/testsuite/lib/read1.c

@@ -21,14 +21,62 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <stdio.h>
 
-/* Wrap 'read', forcing it to return only one byte at a time, if
-   reading from the terminal.  */
+/* Default READMORE method.  */
+#define READMORE_METHOD_DEFAULT 2
+
+/* Default READMORE sleep time in miliseconds.  */
+#define READMORE_SLEEP_DEFAULT 10
+
+/* Helper function.  Intialize *METHOD according to environment variable
+   READMORE_METHOD, and *SLEEP according to environment variable
+   READMORE_SLEEP.  */
+
+static void
+init_readmore (int *method, unsigned int *sleep, FILE **log)
+{
+  char *env = getenv ("READMORE_METHOD");
+  if (env == NULL)
+    *method = READMORE_METHOD_DEFAULT;
+  else if (strcmp (env, "1") == 0)
+    *method = 1;
+  else if (strcmp (env, "2") == 0)
+    *method = 2;
+  else
+    /* Default.  */
+    *method = READMORE_METHOD_DEFAULT;
+
+  env = getenv ("READMORE_SLEEP");
+  if (env == NULL)
+    *sleep = READMORE_SLEEP_DEFAULT;
+  else
+    *sleep = atoi (env);
+
+  env = getenv ("READMORE_LOG");
+  if (env == NULL)
+    *log = NULL;
+  else
+    *log = fopen (env, "w");
+}
+
+/* Wrap 'read', and modify it's behaviour using READ1 or READMORE style.  */
 
 ssize_t
 read (int fd, void *buf, size_t count)
 {
   static ssize_t (*read2) (int fd, void *buf, size_t count) = NULL;
+  static FILE *log;
+  int readmore;
+#ifdef READMORE
+  readmore = 1;
+#else
+  readmore = 0;
+#endif
+  static int readmore_method;
+  static unsigned int readmore_sleep;
   if (read2 == NULL)
     {
       /* Use setenv (v, "", 1) rather than unsetenv (v) to work around
@@ -37,8 +85,88 @@ read (int fd, void *buf, size_t count)
 	 for existence from another interp".  */
       setenv ("LD_PRELOAD", "", 1);
       read2 = dlsym (RTLD_NEXT, "read");
+      if (readmore)
+	init_readmore (&readmore_method, &readmore_sleep, &log);
     }
-  if (count > 1 && isatty (fd) >= 1)
-    count = 1;
+
+  /* Only modify 'read' behaviour when reading from the terminal.  */
+  if (isatty (fd) == 0)
+    goto fallback;
+
+  if (!readmore)
+    {
+      /* READ1.  Force read to return only one byte at a time.  */
+      return read2 (fd, buf, 1);
+    }
+
+  if (readmore_method == 1)
+    {
+      /* READMORE, method 1.  Wait a little before doing a read.  */
+      usleep (readmore_sleep * 1000);
+      return read2 (fd, buf, count);
+    }
+
+  if (readmore_method == 2)
+    {
+      /* READMORE, method 2.  After doing a read, either return or wait
+	 a little and do another read, and so on.  */
+      ssize_t res, total;
+      int iteration;
+      int max_iterations = -1;
+
+      total = 0;
+      for (iteration = 1; ; iteration++)
+	{
+	  res = read2 (fd, (char *)buf + total, count - total);
+	  if (log != NULL)
+	    fprintf (log,
+		     "READ (%d): fd: %d, COUNT: %zd, RES: %zd, ERRNO: %s\n",
+		     iteration, fd, count - total, res,
+		     res == -1 ? strerror (errno) : "none");
+	  if (res == -1)
+	    {
+	      if (iteration == 1)
+		{
+		  /* Error on first read, report.  */
+		  total = -1;
+		  break;
+		}
+
+	      if (total > 0
+		  && (errno == EAGAIN || errno == EWOULDBLOCK || errno == EIO))
+		{
+		  /* Ignore error, but don't try anymore reading.  */
+		  errno = 0;
+		  break;
+		}
+
+	      /* Other error, report back.  */
+	      total = -1;
+	      break;
+	    }
+
+	  total += res;
+	  if (total == count)
+	    /* Buf full, no need to do any more reading.  */
+	    break;
+
+	  /* Handle end-of-file.  */
+	  if (res == 0)
+	    break;
+
+	  if (iteration == max_iterations)
+	    break;
+
+	  usleep (readmore_sleep * 1000);
+	}
+
+      if (log)
+	fprintf (log, "READ returning: RES: %zd, ERRNO: %s\n",
+		 total, total == -1 ? strerror (errno) : "none");
+      return total;
+    }
+
+ fallback:
+  /* Fallback, regular read.  */
   return read2 (fd, buf, count);
 }