aarch64: Move and update the definition of MTE_ENABLED

The hwcap value is now in linux 5.10 and in glibc bits/hwcap.h, so use
that definition.

Move the definition to init-arch.h so all ifunc selectors can use it
and expose an "mte" shorthand for mte enabled runtime.

For now we allow user code to enable tag checks and use PROT_MTE
mappings without libc involvment, this is not guaranteed ABI, but
can be useful for testing and debugging with MTE.

diff --git a/sysdeps/aarch64/multiarch/init-arch.h b/sysdeps/aarch64/multiarch/init-arch.h
index bf8264b5617d2526ecb98230128c16d75cb23140..fce260d16868668a26b8fa44cbd4742d81786733 100644 (file)
--- a/sysdeps/aarch64/multiarch/init-arch.h
+++ b/sysdeps/aarch64/multiarch/init-arch.h
@@ -17,9 +17,18 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <ldsodefs.h>
+#include <sys/auxv.h>
+
+/* Make glibc MTE-safe on a system that supports MTE in case user code
+   enables tag checks independently of the mte_status of glibc.  There
+   is currently no ABI contract for enabling tag checks in user code,
+   but this can be useful for debugging with MTE.  */
+#define MTE_ENABLED() (GLRO(dl_hwcap2) & HWCAP2_MTE)
 
 #define INIT_ARCH()                                                          \
   uint64_t __attribute__((unused)) midr =                                    \
     GLRO(dl_aarch64_cpu_features).midr_el1;                                  \
   unsigned __attribute__((unused)) zva_size =                                \
-    GLRO(dl_aarch64_cpu_features).zva_size;
+    GLRO(dl_aarch64_cpu_features).zva_size;                                  \
+  bool __attribute__((unused)) mte =                                         \
+    MTE_ENABLED ();

diff --git a/sysdeps/aarch64/multiarch/strlen.c b/sysdeps/aarch64/multiarch/strlen.c
index f3c018aab451e1b96140d48591615c401be549b5..8f38de69b5168761be8a09e5f3350f0c17b46b62 100644 (file)
--- a/sysdeps/aarch64/multiarch/strlen.c
+++ b/sysdeps/aarch64/multiarch/strlen.c
@@ -26,21 +26,12 @@
 # include <string.h>
 # include <init-arch.h>
 
-/* This should check HWCAP2_MTE when it is available: current
-   linux kernel does not expose it, but its value is reserved.
-   This is needed to make glibc MTE-safe on future systems in
-   case user code enables MTE. The ABI contract for enabling
-   MTE is not yet specified, but it can be useful for at least
-   debugging which does not need a contract.  */
-#define FUTURE_HWCAP2_MTE (1 << 18)
-#define MTE_ENABLED() (GLRO(dl_hwcap2) & FUTURE_HWCAP2_MTE)
-
 extern __typeof (__redirect_strlen) __strlen;
 
 extern __typeof (__redirect_strlen) __strlen_mte attribute_hidden;
 extern __typeof (__redirect_strlen) __strlen_asimd attribute_hidden;
 
-libc_ifunc (__strlen, (MTE_ENABLED () ? __strlen_mte : __strlen_asimd));
+libc_ifunc (__strlen, (mte ? __strlen_mte : __strlen_asimd));
 
 # undef strlen
 strong_alias (__strlen, strlen);