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

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=59cb960a22fbacb8b8baaa049529bf4638dfc625

commit 59cb960a22fbacb8b8baaa049529bf4638dfc625
Author: Yao Zihong <[email protected]>
Date:   Fri Jul 3 21:59:53 2026 +0000

    riscv: Add RVV strncpy for both multiarch and non-multiarch builds
    
    This patch adds an RVV-optimized implementation of strncpy 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 (__strncpy_vector) is added
    alongside the generic fallback (__strncpy_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 strncpy().
    
    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/strncpy-generic.c          | 26 ++++++++++
 sysdeps/riscv/multiarch/strncpy-vector.S           | 24 +++++++++
 sysdeps/riscv/rvv/stpncpy.S                        | 27 ++++++++--
 sysdeps/riscv/rvv/strncpy.S                        | 20 ++++++++
 sysdeps/unix/sysv/linux/riscv/multiarch/Makefile   |  3 ++
 .../sysv/linux/riscv/multiarch/ifunc-impl-list.c   |  5 ++
 sysdeps/unix/sysv/linux/riscv/multiarch/strncpy.c  | 59 ++++++++++++++++++++++
 7 files changed, 159 insertions(+), 5 deletions(-)

diff --git a/sysdeps/riscv/multiarch/strncpy-generic.c b/sysdeps/riscv/multiarch/strncpy-generic.c
new file mode 100644
index 0000000000..726ca9ed5f
--- /dev/null
+++ b/sysdeps/riscv/multiarch/strncpy-generic.c
@@ -0,0 +1,26 @@
+/* Re-include the default strncpy 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 STRNCPY __strncpy_generic
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(x)
+# include <string/strncpy.c>
+#endif
diff --git a/sysdeps/riscv/multiarch/strncpy-vector.S b/sysdeps/riscv/multiarch/strncpy-vector.S
new file mode 100644
index 0000000000..32256f7695
--- /dev/null
+++ b/sysdeps/riscv/multiarch/strncpy-vector.S
@@ -0,0 +1,24 @@
+/* Re-include the RISC-V RVV based strncpy 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 STRNCPY __strncpy_vector
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(x)
+# include <sysdeps/riscv/rvv/strncpy.S>
+#endif
diff --git a/sysdeps/riscv/rvv/stpncpy.S b/sysdeps/riscv/rvv/stpncpy.S
index 7cfc2f76cc..71bb46b04e 100644
--- a/sysdeps/riscv/rvv/stpncpy.S
+++ b/sysdeps/riscv/rvv/stpncpy.S
@@ -19,12 +19,20 @@
 #include <sysdep.h>
 #include <sys/asm.h>
 
-#ifndef STPNCPY
-# ifdef weak_alias
-#  define STPNCPY __stpncpy
+#ifndef USE_AS_STRNCPY
+# ifndef STPNCPY
+#  ifdef weak_alias
+#   define STPNCPY __stpncpy
 weak_alias (__stpncpy, stpncpy)
+#  else
+#   define STPNCPY stpncpy
+#  endif
+# endif
+#else
+# ifndef STRNCPY
+#  define STPNCPY strncpy
 # else
-#  define STPNCPY stpncpy
+#  define STPNCPY STRNCPY
 # endif
 #endif
 
@@ -62,7 +70,9 @@ L(stpcpy_loop):
     add dst_ptr, dst_ptr, cur_vl
     bgez active_elem_pos, L(fill_zero)
     bnez length, L(stpcpy_loop)
+#ifndef USE_AS_STRNCPY
     mv dst, dst_ptr
+#endif
     ret
 
     /* Fill the tail zero.  */
@@ -72,8 +82,10 @@ L(fill_zero):
        to get the correct remaining length for zero filling.  */
     sub temp, cur_vl, active_elem_pos
     addi temp, temp, -1
+#ifndef USE_AS_STRNCPY
     sub dst, dst_ptr, cur_vl
     add dst, dst, active_elem_pos
+#endif
     add length, length, temp
     /* Return early for the `strlen(src) + 1 == count` case.  */
     bnez length, L(do_fill_zero)
@@ -92,6 +104,11 @@ L(fill_zero_loop):
     ret
 .option pop
 END (STPNCPY)
-#ifdef weak_alias
+
+#ifndef USE_AS_STRNCPY
+# ifdef weak_alias
 libc_hidden_def (__stpncpy)
+# endif
+#else
+libc_hidden_builtin_def (strncpy)
 #endif
diff --git a/sysdeps/riscv/rvv/strncpy.S b/sysdeps/riscv/rvv/strncpy.S
new file mode 100644
index 0000000000..961c16416e
--- /dev/null
+++ b/sysdeps/riscv/rvv/strncpy.S
@@ -0,0 +1,20 @@
+/* RISC-V RVV based strncpy.
+   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/>.  */
+
+#define USE_AS_STRNCPY
+#include <sysdeps/riscv/rvv/stpncpy.S>
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
index 25d8216d2e..4991466369 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
@@ -40,6 +40,9 @@ sysdep_routines += \
   strncmp \
   strncmp-generic \
   strncmp-vector \
+  strncpy \
+  strncpy-generic \
+  strncpy-vector \
   strrchr \
   strrchr-generic \
   strrchr-vector \
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 755ba9d637..ac2b25de74 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
@@ -115,5 +115,10 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __stpncpy_vector)
 	      IFUNC_IMPL_ADD (array, i, stpncpy, 1, __stpncpy_generic))
 
+  IFUNC_IMPL (i, name, strncpy,
+	      IFUNC_IMPL_ADD (array, i, strncpy, rvv_enabled,
+			      __strncpy_vector)
+	      IFUNC_IMPL_ADD (array, i, strncpy, 1, __strncpy_generic))
+
   return 0;
 }
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/strncpy.c b/sysdeps/unix/sysv/linux/riscv/multiarch/strncpy.c
new file mode 100644
index 0000000000..2ed6878bfd
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/strncpy.c
@@ -0,0 +1,59 @@
+/* Multiple versions of strncpy.
+   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)
+#define SYMBOL_NAME strncpy
+# include <ifunc-init.h>
+
+/* Redefine strncpy so that the compiler won't complain about the type
+   mismatch with the IFUNC selector in strong_alias, below.  */
+# undef strncpy
+# define strncpy REDIRECT_NAME
+# include <string.h>
+# undef strncpy
+
+# include <stdint.h>
+# include <riscv-ifunc.h>
+# include <sys/hwprobe.h>
+
+extern __typeof (REDIRECT_NAME) __strncpy;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (generic) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (vector) attribute_hidden;
+
+static inline __typeof (REDIRECT_NAME) *
+select_strncpy_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 OPTIMIZE (vector);
+  return OPTIMIZE (generic);
+}
+
+riscv_libc_ifunc (__strncpy, select_strncpy_ifunc);
+
+strong_alias (__strncpy, strncpy);
+
+# ifdef SHARED
+__hidden_ver1 (strncpy, __GI_strncpy, REDIRECT_NAME)
+  __attribute__ ((visibility ("hidden"))) __attribute_copy__ (strncpy);
+# endif
+#else
+# include <string/strncpy.c>
+#endif