[glibc] riscv: Add RVV strlen for both multiarch and non-multiarch builds

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=07122a9d8d4597321e77d97f9ba18c11a42d8b5b

commit 07122a9d8d4597321e77d97f9ba18c11a42d8b5b
Author: Yao Zihong <[email protected]>
Date:   Thu Apr 30 15:15:36 2026 -0500

    riscv: Add RVV strlen for both multiarch and non-multiarch builds
    
    This patch adds an RVV-optimized implementation of strlen for RISC-V and
    enables it for both multiarch (IFUNC) and non-multiarch builds.
    
    The implementation integrates Hau Hsu's 2023 RVV work under a unified
    ifunc-based framework. A vectorized version (__strlen_vector) is added
    alongside the generic fallback (__strlen_generic). The runtime resolver
    selects the RVV variant when RISCV_HWPROBE_KEY_IMA_EXT_0 reports vector
    support (RVV).
    
    Currently, the resolver still selects the RVV variant even when the RVV
    extension is disabled via prctl(). As a consequence, any process that
    has RVV disabled via prctl() will receive SIGILL when calling strlen().
    
    Co-authored-by: Hau Hsu <[email protected]>
    Co-authored-by: Jerry Shih <[email protected]>
    Signed-off-by: Yao Zihong <[email protected]>
    Reviewed-by: Peter Bergner <[email protected]>

Diff:
---
 sysdeps/riscv/multiarch/strlen-generic.c           | 24 +++++++++
 sysdeps/riscv/multiarch/strlen-vector.S            | 26 ++++++++++
 sysdeps/riscv/rvv/strlen.S                         | 58 ++++++++++++++++++++++
 sysdeps/unix/sysv/linux/riscv/multiarch/Makefile   |  3 ++
 .../sysv/linux/riscv/multiarch/ifunc-impl-list.c   |  5 ++
 sysdeps/unix/sysv/linux/riscv/multiarch/strlen.c   | 56 +++++++++++++++++++++
 6 files changed, 172 insertions(+)

diff --git a/sysdeps/riscv/multiarch/strlen-generic.c b/sysdeps/riscv/multiarch/strlen-generic.c
new file mode 100644
index 0000000000..6317b1cb44
--- /dev/null
+++ b/sysdeps/riscv/multiarch/strlen-generic.c
@@ -0,0 +1,24 @@
+/* Re-include the default strlen implementation.
+   Copyright (C) 2026 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 <string.h>
+
+#if IS_IN(libc)
+# define STRLEN __strlen_generic
+# include <string/strlen.c>
+#endif
diff --git a/sysdeps/riscv/multiarch/strlen-vector.S b/sysdeps/riscv/multiarch/strlen-vector.S
new file mode 100644
index 0000000000..b7841ed295
--- /dev/null
+++ b/sysdeps/riscv/multiarch/strlen-vector.S
@@ -0,0 +1,26 @@
+/* Re-include the RISC-V RVV based strlen implementation.
+   Copyright (C) 2026 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/>.  */
+
+#if IS_IN(libc)
+# define STRLEN __strlen_vector
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(name)
+# undef weak_alias
+# define weak_alias(name, alias)
+# include <sysdeps/riscv/rvv/strlen.S>
+#endif
diff --git a/sysdeps/riscv/rvv/strlen.S b/sysdeps/riscv/rvv/strlen.S
new file mode 100644
index 0000000000..0a3b18eb0c
--- /dev/null
+++ b/sysdeps/riscv/rvv/strlen.S
@@ -0,0 +1,58 @@
+/* RISC-V RVV based strlen.
+   Copyright (C) 2026 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 <sysdep.h>
+#include <sys/asm.h>
+
+#ifndef STRLEN
+# define STRLEN __strlen
+#endif
+
+#define result a0
+#define str a0
+#define copy_str a1
+#define ivl a2
+#define cur_vl a2
+#define end_offset a3
+
+#define ELEM_LMUL_SETTING m2
+#define vstr v0
+#define vmask_end v2
+
+ENTRY (STRLEN)
+.option push
+.option arch, +v
+    mv copy_str, str
+L(loop):
+    vsetvli ivl, zero, e8, ELEM_LMUL_SETTING, ta, ma
+    vle8ff.v vstr, (copy_str)
+    csrr cur_vl, vl
+    vmseq.vi vmask_end, vstr, 0
+    vfirst.m end_offset, vmask_end
+    add copy_str, copy_str, cur_vl
+    bltz end_offset, L(loop)
+
+    add str, str, cur_vl
+    add copy_str, copy_str, end_offset
+    sub result, copy_str, result
+
+    ret
+.option pop
+END (STRLEN)
+weak_alias (STRLEN, strlen)
+libc_hidden_builtin_def (strlen)
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
index 32be517d21..2a2b90960f 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
@@ -13,6 +13,9 @@ sysdep_routines += \
   strcpy \
   strcpy-generic \
   strcpy-vector \
+  strlen \
+  strlen-generic \
+  strlen-vector \
   # sysdep_routines
 
 CFLAGS-memcpy_noalignment.c += -mno-strict-align
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
index 0eb55a5ad8..2501546665 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
@@ -65,5 +65,10 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __strcpy_vector)
 	      IFUNC_IMPL_ADD (array, i, strcpy, 1, __strcpy_generic))
 
+  IFUNC_IMPL (i, name, strlen,
+	      IFUNC_IMPL_ADD (array, i, strlen, rvv_enabled,
+			      __strlen_vector)
+	      IFUNC_IMPL_ADD (array, i, strlen, 1, __strlen_generic))
+
   return 0;
 }
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/strlen.c b/sysdeps/unix/sysv/linux/riscv/multiarch/strlen.c
new file mode 100644
index 0000000000..9975286b85
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/strlen.c
@@ -0,0 +1,56 @@
+/* Multiple versions of strlen.
+   All versions must be listed in ifunc-impl-list.c.
+   Copyright (C) 2026 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/>.  */
+
+#if IS_IN (libc)
+/* Redefine strlen so that the compiler won't complain about the type
+   mismatch with the IFUNC selector in strong_alias, below.  */
+# undef strlen
+# define strlen __redirect_strlen
+# include <stdint.h>
+# include <string.h>
+# include <ifunc-init.h>
+# include <riscv-ifunc.h>
+# include <sys/hwprobe.h>
+
+extern __typeof (__redirect_strlen) __libc_strlen;
+
+extern __typeof (__redirect_strlen) __strlen_generic attribute_hidden;
+extern __typeof (__redirect_strlen) __strlen_vector attribute_hidden;
+
+static inline __typeof (__redirect_strlen) *
+select_strlen_ifunc (uint64_t dl_hwcap, __riscv_hwprobe_t hwprobe_func)
+{
+  unsigned long long int v;
+  if (__riscv_hwprobe_one (hwprobe_func, RISCV_HWPROBE_KEY_IMA_EXT_0, &v) == 0
+      && (v & RISCV_HWPROBE_IMA_V) == RISCV_HWPROBE_IMA_V)
+    return __strlen_vector;
+  return __strlen_generic;
+}
+
+riscv_libc_ifunc (__libc_strlen, select_strlen_ifunc);
+
+# undef strlen
+strong_alias (__libc_strlen, strlen);
+# ifdef SHARED
+__hidden_ver1 (strlen, __GI_strlen, __redirect_strlen)
+  __attribute__ ((visibility ("hidden"))) __attribute_copy__ (strlen);
+# endif
+#else
+# include <string/strlen.c>
+#endif