[RFC PATCH 07/19] riscv: hart-features: Add fast_unaligned property

[Christoph Muellner]

From: Christoph Müllner <christoph.muellner@vrull.eu>

Having fast unaligned accesses opens the door for a performance
optimizations. Let's add this property to the hart-features
so that this property can be queried using the environment
variable RISCV_RT_FAST_UNALIGNED (e.g. by setting it to "1").

Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
---
 sysdeps/unix/sysv/linux/riscv/hart-features.c | 19 +++++++++++++++++++
 sysdeps/unix/sysv/linux/riscv/hart-features.h |  5 +++++
 2 files changed, 24 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/riscv/hart-features.c b/sysdeps/unix/sysv/linux/riscv/hart-features.c
index 6de41a26cc..b3b7955534 100644
--- a/sysdeps/unix/sysv/linux/riscv/hart-features.c
+++ b/sysdeps/unix/sysv/linux/riscv/hart-features.c
@@ -326,6 +326,22 @@ parse_rt_cboz_blocksize (struct hart_features *hart_features)
   hart_features->cboz_blocksize = v;
 }
 
+/* Parse RISCV_RT_FAST_UNALIGNED and store value.  */
+static inline void
+parse_rt_fast_unaligned (struct hart_features *hart_features)
+{
+  hart_features->rt_fast_unaligned = NULL;
+  hart_features->fast_unaligned = 0;
+
+  const char *s = simple_getenv ("RISCV_RT_FAST_UNALIGNED");
+  if (s == NULL)
+    return;
+
+  uint64_t v = _dl_strtoul (s, NULL);
+  hart_features->rt_fast_unaligned = s;
+  hart_features->fast_unaligned = v;
+}
+
 /* Discover hart features and store them.  */
 static inline void
 init_hart_features (struct hart_features *hart_features)
@@ -334,4 +350,7 @@ init_hart_features (struct hart_features *hart_features)
   parse_rt_march (hart_features);
   parse_rt_cbom_blocksize (hart_features);
   parse_rt_cboz_blocksize (hart_features);
+
+  /* Parse tuning properties.  */
+  parse_rt_fast_unaligned (hart_features);
 }
diff --git a/sysdeps/unix/sysv/linux/riscv/hart-features.h b/sysdeps/unix/sysv/linux/riscv/hart-features.h
index dd94685676..b2cefd5748 100644
--- a/sysdeps/unix/sysv/linux/riscv/hart-features.h
+++ b/sysdeps/unix/sysv/linux/riscv/hart-features.h
@@ -34,6 +34,9 @@
 #define HAVE_CBOZ_BLOCKSIZE(n)	\
 	(GLRO (dl_riscv_hart_features).cboz_blocksize == n)
 
+#define HAVE_FAST_UNALIGNED() \
+	(GLRO (dl_riscv_hart_features).fast_unaligned != 0)
+
 struct hart_features
 {
   const char* rt_march;
@@ -48,6 +51,8 @@ struct hart_features
   unsigned cbom_blocksize;
   const char* rt_cboz_blocksize;
   unsigned cboz_blocksize;
+  const char* rt_fast_unaligned;
+  unsigned fast_unaligned;
 };
 
 #endif /* _CPU_FEATURES_RISCV_H  */
-- 
2.39.1