ar: Correct -N COUNT off-by-one

When using instance [COUNT], the instance check is wrong.
instance-- == 0 should be --instance == 0.

Add a testcase run-ar-N.sh that uses -N COUNT with extract and delete
operations checking the right instance was extracted and deleted.

https://sourceware.org/bugzilla/show_bug.cgi?id=28725

Reported-by: panxiaohe <panxh_ran@163.com>
Signed-off-by: Mark Wielaard <mark@klomp.org>

5 files changed, 81 insertions, 2 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 88db4051..9348c562 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2022-08-28  Mark Wielaard  <mark@klomp.org>
+
+	* ar.c (do_oper_extract): Predecrement instance before compare
+	to zero.
+	(do_oper_delete): Likewise.
+
 2022-08-10  Andreas Schwab  <schwab@suse.de>
 
 	* readelf.c (print_attributes): Also handle SHT_RISCV_ATTRIBUTES.
diff --git a/src/ar.c b/src/ar.c
index 9e8df120..04456c18 100644
--- a/src/ar.c
+++ b/src/ar.c
@@ -518,7 +518,7 @@ do_oper_extract (int oper, const char *arfname, char **argv, int argc,
 	  ENTRY entry;
 	  entry.key = arhdr->ar_name;
 	  ENTRY *res = hsearch (entry, FIND);
-	  if (res != NULL && (instance < 0 || instance-- == 0)
+	  if (res != NULL && (instance < 0 || --instance == 0)
 	      && !found[(char **) res->data - argv])
 	    found[(char **) res->data - argv] = do_extract = true;
 	}
@@ -952,7 +952,7 @@ do_oper_delete (const char *arfname, char **argv, int argc,
 	  ENTRY entry;
 	  entry.key = arhdr->ar_name;
 	  ENTRY *res = hsearch (entry, FIND);
-	  if (res != NULL && (instance < 0 || instance-- == 0)
+	  if (res != NULL && (instance < 0 || --instance == 0)
 	      && !found[(char **) res->data - argv])
 	    found[(char **) res->data - argv] = do_delete = true;
 	}
diff --git a/tests/ChangeLog b/tests/ChangeLog
index 8d87f05d..f2cc7875 100644
--- a/tests/ChangeLog
+++ b/tests/ChangeLog
@@ -1,3 +1,9 @@
+2022-08-26  Mark Wielaard  <mark@klomp.org>
+
+	* run-ar-N.sh: New test.
+	* Makefile.am (TESTS): Add run-ar-N.sh.
+	(EXTRA_DIST): Likewise.
+
 2022-09-02  Frank Ch. Eigler  <fche@redhat.com>
 
 	* run-debuginfod-response-headers.sh: Use case-insensitive
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 87988fb9..85514898 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -100,6 +100,7 @@ test-nlist$(EXEEXT): test-nlist.c
 	  $(test_nlist_CFLAGS) $(GCOV_FLAGS) -o $@ $< $(test_nlist_LDADD)
 
 TESTS = run-arextract.sh run-arsymtest.sh run-ar.sh newfile test-nlist \
+	run-ar-N.sh \
 	update1 update2 update3 update4 \
 	run-show-die-info.sh run-get-files.sh run-get-lines.sh \
 	run-next-files.sh run-next-lines.sh \
@@ -254,6 +255,7 @@ endif
 endif
 
 EXTRA_DIST = run-arextract.sh run-arsymtest.sh run-ar.sh \
+	     run-ar-N.sh \
 	     run-show-die-info.sh run-get-files.sh run-get-lines.sh \
 	     run-next-files.sh run-next-lines.sh testfile-only-debug-line.bz2 \
 	     run-get-pubnames.sh run-get-aranges.sh \
diff --git a/tests/run-ar-N.sh b/tests/run-ar-N.sh
new file mode 100755
index 00000000..de8f62b3
--- /dev/null
+++ b/tests/run-ar-N.sh
@@ -0,0 +1,65 @@
+#! /usr/bin/env bash
+# Copyright (C) 2022 Mark J. Wielaard <mark@klomp.org>
+# This file is part of elfutils.
+#
+# This file is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# elfutils is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. $srcdir/test-subr.sh
+
+tempfiles testfile test.ar
+
+echo create test.ar with 3 testfile
+echo 1 > testfile
+testrun ${abs_top_builddir}/src/ar -vr test.ar testfile
+echo 2 > testfile
+testrun ${abs_top_builddir}/src/ar -vq test.ar testfile
+testrun ${abs_top_builddir}/src/ar -t test.ar
+echo 3 > testfile
+testrun ${abs_top_builddir}/src/ar -vq test.ar testfile
+testrun_compare ${abs_top_builddir}/src/ar -t test.ar << EOF
+testfile
+testfile
+testfile
+EOF
+
+echo list content of testfile 1 2 3
+testrun ${abs_top_builddir}/src/ar -vx -N 1 test.ar testfile
+diff -u testfile - << EOF
+1
+EOF
+testrun ${abs_top_builddir}/src/ar -vx -N 2 test.ar testfile
+diff -u testfile - << EOF
+2
+EOF
+testrun ${abs_top_builddir}/src/ar -vx -N 3 test.ar testfile
+diff -u testfile - << EOF
+3
+EOF
+
+echo delete testfile 2
+testrun ${abs_top_builddir}/src/ar -vd -N 2 test.ar testfile
+testrun_compare ${abs_top_builddir}/src/ar -t test.ar << EOF
+testfile
+testfile
+EOF
+testrun ${abs_top_builddir}/src/ar -vx -N 1 test.ar testfile
+diff -u testfile - << EOF
+1
+EOF
+testrun ${abs_top_builddir}/src/ar -vx -N 2 test.ar testfile
+diff -u testfile - << EOF
+3
+EOF
+
+exit 0