elf: Add glibc-hwcaps subdirectory support to ld.so cache processing

This recognizes the DL_CACHE_HWCAP_EXTENSION flag in cache entries,
and picks the supported cache entry with the highest priority.

The elf/tst-glibc-hwcaps-prepend-cache test documents a non-desired
aspect of the current cache implementation: If the cache selects a DSO
that does not exist on disk, _dl_map_object falls back to open_path,
which may or may not find an alternative implementation.  This is an
existing limitation that also applies to the legacy hwcaps processing
for ld.so.cache.

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

1 files changed, 18 insertions, 0 deletions

diff --git a/elf/Makefile b/elf/Makefile
index b28930432d..95cbf66c25 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -173,6 +173,12 @@ tests-container := \
 			  tst-ldconfig-bad-aux-cache \
 			  tst-ldconfig-ld_so_conf-update
 
+ifeq (no,$(build-hardcoded-path-in-tests))
+# This is an ld.so.cache test, and RPATH/RUNPATH in the executable
+# interferes with its test objectives.
+tests-container += tst-glibc-hwcaps-prepend-cache
+endif
+
 tests := tst-tls9 tst-leaks1 \
 	tst-array1 tst-array2 tst-array3 tst-array4 tst-array5 \
 	tst-auxv tst-stringtable
@@ -1865,6 +1871,14 @@ $(objpfx)tst-glibc-hwcaps-prepend.out: \
 	  $< > $@; \
 	$(evaluate-test)
 
+# Like tst-glibc-hwcaps-prepend, but uses a container and loads the
+# library via ld.so.cache.  Test setup is contained in the test
+# itself.
+$(objpfx)tst-glibc-hwcaps-prepend-cache: $(libdl)
+$(objpfx)tst-glibc-hwcaps-prepend-cache.out: \
+  $(objpfx)tst-glibc-hwcaps-prepend-cache $(objpfx)libmarkermod1-1.so \
+  $(objpfx)libmarkermod1-2.so $(objpfx)libmarkermod1-3.so
+
 # tst-glibc-hwcaps-mask checks that --glibc-hwcaps-mask can be used to
 # suppress all auto-detected subdirectories.
 $(objpfx)tst-glibc-hwcaps-mask: $(objpfx)libmarkermod1-1.so
@@ -1876,3 +1890,7 @@ $(objpfx)tst-glibc-hwcaps-mask.out: \
 	  --glibc-hwcaps-mask does-not-exist \
 	  $< > $@; \
 	$(evaluate-test)
+
+# Generic dependency for sysdeps implementation of
+# tst-glibc-hwcaps-cache.
+$(objpfx)tst-glibc-hwcaps-cache.out: $(objpfx)tst-glibc-hwcaps