elf: Limit tst-prelink-cmp target archs

elf/tst-prelink-cmp was initially added for x86 (commit fe534fe898) to validate
the fix for Bug 19178, and later applied to all architectures that use GLOB_DAT
relocations (commit 89569c8bb6).  However, that bug only affected targets that
handle GLOB_DAT relocations as ELF_TYPE_CLASS_EXTERN_PROTECTED_DATA, so the test
should only apply to targets defining DL_EXTERN_PROTECTED_DATA, which gates the
usage of the elf type class above.  For all other targets not meeting that
criteria, the test now returns with UNSUPPORTED status.

Fixes the test on POWER10 processors, which started using R_PPC64_GLOB_DAT.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

3 files changed, 51 insertions, 8 deletions

diff --git a/elf/Makefile b/elf/Makefile
index 5e7f938e2d..5d666b1b0c 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -457,12 +457,10 @@ update-all-abi: update-all-abi-ld
 
 ifeq ($(have-glob-dat-reloc),yes)
 tests += tst-prelink
+tests-internal += tst-prelink-cmp
 # Don't compile tst-prelink.c with PIE for GLOB_DAT relocation.
 CFLAGS-tst-prelink.c += -fno-pie
 tst-prelink-no-pie = yes
-ifeq ($(run-built-tests),yes)
-tests-special += $(objpfx)tst-prelink-cmp.out
-endif
 endif
 
 # The test requires shared _and_ PIE because the executable
@@ -1605,10 +1603,7 @@ tst-prelink-ENV = LD_TRACE_PRELINKING=1
 $(objpfx)tst-prelink-conflict.out: $(objpfx)tst-prelink.out
 	grep stdout $< | grep conflict | $(AWK) '{ print $$10, $$11 }' > $@
 
-$(objpfx)tst-prelink-cmp.out: tst-prelink.exp \
-			      $(objpfx)tst-prelink-conflict.out
-	cmp $^ > $@; \
-	$(evaluate-test)
+$(objpfx)tst-prelink-cmp.out: $(objpfx)tst-prelink-conflict.out
 
 $(objpfx)tst-ldconfig-X.out : tst-ldconfig-X.sh $(objpfx)ldconfig
 	$(SHELL) $< '$(common-objpfx)' '$(test-wrapper-env)' \
diff --git a/elf/tst-prelink-cmp.c b/elf/tst-prelink-cmp.c
new file mode 100644
index 0000000000..588c21171c
--- /dev/null
+++ b/elf/tst-prelink-cmp.c
@@ -0,0 +1,49 @@
+/* Test the output from the environment variable, LD_TRACE_PRELINKING,
+   for prelink.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <ldsodefs.h>
+#include <support/check.h>
+#include <support/xstdio.h>
+#include <support/support.h>
+#include <support/test-driver.h>
+
+static int
+do_test (void)
+{
+#ifndef DL_EXTERN_PROTECTED_DATA
+  return EXIT_UNSUPPORTED;
+#else
+  char *src = xasprintf ("%s/elf/tst-prelink-conflict.out",
+                         support_objdir_root);
+  FILE *f = xfopen (src,"r");
+  size_t buffer_length = 0;
+  char *buffer = NULL;
+
+  const char *expected = "/0 stdout\n";
+
+  xgetline (&buffer, &buffer_length, f);
+  TEST_COMPARE_STRING (expected, buffer);
+
+  free (buffer);
+  xfclose (f);
+  return 0;
+#endif
+}
+
+#include <support/test-driver.c>
diff --git a/elf/tst-prelink.exp b/elf/tst-prelink.exp
deleted file mode 100644
index b35b4c9705..0000000000
--- a/elf/tst-prelink.exp
+++ /dev/null
@@ -1 +0,0 @@
-/0 stdout