[RFA:] Stricter libstdc++ testsuite gate for working target file I/O

[Hans-Peter Nilsson <hans-peter dot nilsson at axis dot com>]

First but incidentally, we never did any useful target file I/O
in the the check_v3_target_fileio gate, we just tried to open
"." and seek to 0 (a nop at best; could also be construed as
invalid).  The test-suite does actual file I/O gated by that
'// { dg-require-fileio "" }' line: reading, writing, seeking,
so I think the gate function should try that, using the same
machinery as the actual tests.

Several tests require a working lseek primitive.  I think it's
easy enough to get seeking with a negative offset wrong in a
simulator(*) that it's worth testing for that.  Also, the
generic framework for the lseek syscall in the GNU simulators at
src/sim has a bug causing an invalid seek, like backwards from
position 0, to return 0 instead of properly yielding an error.
(I have patches for those simulator bugs, upcoming on
gdb-patches@, and I'll delay committing this patch until those
patches are applied.)

((*) where the API to the host uses "long" for syscall parameters
like src/sim struct cb_syscall, and the target is ILP32 like
cris-*-*, and if you handle your targets addresses as
zero-extended (as most targets except MIPS and SH/SH64, IIUC) so
you handle syscall parameters generally using unsigned 32-bit
numbers and you don't special-case the lseek position parameter
to properly get it sign-extended rather than zero-extended when
on a LP64 host...)

Here's a patch fixing the check_v3_target_fileio gate function.
I can't think of a system that this fixup would *incorrectly*
flag as not working.  It catches both the mentioned simulator
bugs (thus avoiding spurious failures leading to bogus bug
reports wasting maintainer time :) but passes for a fixed
(cris-elf) simulator and natively on a x86_64-unknown-linux-gnu
(manually testing the code).  Also, as a sanity check, ran a
complete regtest for cris-elf (fixed simulator) at r164529 with
no regressions.

While working on this I noticed that several tests miss the
// { dg-require-fileio "" }
line, which I'll add as obvious, later.

The bugs at this PR didn't stop there (with this one in the
test-suite, two simulator bugs and actually also one in
libstdc++ proper ironically found by the buggy simulator; a
patch has already been posted to add a properly "working"
testcase IIUC).  I also ran into
<http://subversion.tigris.org/issues/show_bug.cgi?id=2333> which
manifested as "svn diff -c164529" not showing
27_io/basic_filebuf/sync/wchar_t/1.cc as a deleted file, as it
dies for 27_io/basic_filebuf/sync/char/1.cc.  So be warned:
don't ultimately trust applying patches from svn diff -rOLD:NEW
as a way of patching up your tree; beware of deleted directories.
At least with subversion lower than 1.7.0 (to wit, 1.6.9).

Ok to commit?  Would it be ok to backport to open branches?

	PR libstdc++/45841
	* testsuite/lib/libstdc++.exp (check_v3_target_fileio): Rewrite to
	use an actual testsuite file and machinery, not ".".  Specifically
	check that incorrectly seeking backwards from 0 yields an error,
	and that reading, seeking backwards and reading again works.

--- libstdc++-v3/testsuite/lib/libstdc++.exp.orig	Wed Sep 15 23:27:44 2010
+++ libstdc++-v3/testsuite/lib/libstdc++.exp	Wed Oct  6 00:01:46 2010
@@ -631,6 +631,7 @@ proc check_v3_target_fileio { } {
     global et_fileio_saved
     global et_fileio_target_name
     global tool	
+    global srcdir
 
     if { ![info exists et_fileio_target_name] } {
 	set et_fileio_target_name ""
@@ -656,6 +657,8 @@ proc check_v3_target_fileio { } {
 	# the file functions
 	set src fileio[pid].cc
 	set exe fileio[pid].x
+	set testfile "cin_unget-1.txt"
+	v3-copy-files "$srcdir/data/$testfile"
 
 	set f [open $src "w"]
 	puts $f "#include <sys/types.h>"
@@ -663,20 +666,26 @@ proc check_v3_target_fileio { } {
 	puts $f "#include <fcntl.h>"
 	puts $f "#include <unistd.h>"
 	puts $f "#include <errno.h>"
+	puts $f "#include <string.h>"
 	puts $f "using namespace std;"	
 	puts $f "int main ()"
 	puts $f "{"
-	puts $f "  int fd  = open (\".\", O_RDONLY);"
+	puts $f "  int fd  = open (\"$testfile\", O_RDONLY);"
 	puts $f "  int ret = 0;"
+	puts $f "  char buf\[10\];"
 	puts $f "  if (fd == -1)"
-	puts $f "  {"
-	puts $f "    int err = errno;"
-	puts $f "    if (err == EIO || err == ENOSYS)"
-	puts $f "      ret = 1;"
-	puts $f "  }"
+	puts $f "    ret = 1;"
 	puts $f "  else"
 	puts $f "  {"
-	puts $f "    if (lseek (fd, 0, SEEK_CUR) == -1)"
+	puts $f "    if (lseek (fd, -1, SEEK_CUR) != -1 || errno != EINVAL)"
+	puts $f "      ret = 1;"
+	puts $f "    errno = 0;"
+	puts $f "    if (lseek (fd, 0, SEEK_CUR) != 0"
+	puts $f "        || read (fd, buf, 4) != 4"
+	puts $f "        || memcmp (buf, \"1234\", 4) != 0"
+	puts $f "        || lseek (fd, -2, SEEK_CUR) != 2"
+	puts $f "        || read (fd, buf, 2) != 2"
+	puts $f "        || memcmp (buf, \"34\", 2) != 0)"
 	puts $f "      ret = 1;"
 	puts $f "    close (fd);"
 	puts $f "  }"

brgds, H-P