elf: Add glibc-hwcaps support for LD_LIBRARY_PATH

This hacks non-power-set processing into _dl_important_hwcaps.
Once the legacy hwcaps handling goes away, the subdirectory
handling needs to be reworked, but it is premature to do this
while both approaches are still supported.

ld.so supports two new arguments, --glibc-hwcaps-prepend and
--glibc-hwcaps-mask.  Each accepts a colon-separated list of
glibc-hwcaps subdirectory names.  The prepend option adds additional
subdirectories that are searched first, in the specified order.  The
mask option restricts the automatically selected subdirectories to
those listed in the option argument.  For example, on systems where
/usr/lib64 is on the library search path,
--glibc-hwcaps-prepend=valgrind:debug causes the dynamic loader to
search the directories /usr/lib64/glibc-hwcaps/valgrind and
/usr/lib64/glibc-hwcaps/debug just before /usr/lib64 is searched.

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

1 files changed, 10 insertions, 1 deletions

diff --git a/elf/dl-main.h b/elf/dl-main.h
index b51256d..566713a 100644
--- a/elf/dl-main.h
+++ b/elf/dl-main.h
@@ -84,6 +84,14 @@ struct dl_main_state
   /* The preload list passed as a command argument.  */
   const char *preloadarg;
 
+  /* Additional glibc-hwcaps subdirectories to search first.
+     Colon-separated list.  */
+  const char *glibc_hwcaps_prepend;
+
+  /* Mask for the internal glibc-hwcaps subdirectories.
+     Colon-separated list.  */
+  const char *glibc_hwcaps_mask;
+
   enum rtld_mode mode;
 
   /* True if any of the debugging options is enabled.  */
@@ -98,7 +106,8 @@ struct dl_main_state
 static inline void
 call_init_paths (const struct dl_main_state *state)
 {
-  _dl_init_paths (state->library_path, state->library_path_source);
+  _dl_init_paths (state->library_path, state->library_path_source,
+                  state->glibc_hwcaps_prepend, state->glibc_hwcaps_mask);
 }
 
 /* Print ld.so usage information and exit.  */