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

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=df0669d41d753269312374e2eb6bd107bbec9c7b

commit df0669d41d753269312374e2eb6bd107bbec9c7b
Author: Yao Zihong <[email protected]>
Date:   Thu Jul 2 03:45:24 2026 +0000

    riscv: Add RVV stpncpy for both multiarch and non-multiarch builds
    
    This patch adds an RVV-optimized implementation of stpncpy 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 (__stpncpy_vector) is added
    alongside the generic fallback (__stpncpy_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 stpncpy().
    
    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/stpncpy-generic.c          | 28 +++++++
 sysdeps/riscv/multiarch/stpncpy-vector.S           | 28 +++++++
 sysdeps/riscv/rvv/stpncpy.S                        | 97 ++++++++++++++++++++++
 sysdeps/unix/sysv/linux/riscv/multiarch/Makefile   |  3 +
 .../sysv/linux/riscv/multiarch/ifunc-impl-list.c   |  5 ++
 sysdeps/unix/sysv/linux/riscv/multiarch/stpncpy.c  | 62 ++++++++++++++
 6 files changed, 223 insertions(+)

diff --git a/sysdeps/riscv/multiarch/stpncpy-generic.c b/sysdeps/riscv/multiarch/stpncpy-generic.c
new file mode 100644
index 0000000000..4be8080d88
--- /dev/null
+++ b/sysdeps/riscv/multiarch/stpncpy-generic.c
@@ -0,0 +1,28 @@
+/* Re-include the default stpncpy 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 STPNCPY __stpncpy_generic
+# undef libc_hidden_def
+# define libc_hidden_def(name)
+# undef weak_alias
+# define weak_alias(x, x2)
+# include <string/stpncpy.c>
+#endif
diff --git a/sysdeps/riscv/multiarch/stpncpy-vector.S b/sysdeps/riscv/multiarch/stpncpy-vector.S
new file mode 100644
index 0000000000..e84d28a1e4
--- /dev/null
+++ b/sysdeps/riscv/multiarch/stpncpy-vector.S
@@ -0,0 +1,28 @@
+/* Re-include the RISC-V RVV based stpncpy 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 STPNCPY __stpncpy_vector
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(name)
+# undef libc_hidden_def
+# define libc_hidden_def(name)
+# undef weak_alias
+# define weak_alias(name, alias)
+# include <sysdeps/riscv/rvv/stpncpy.S>
+#endif
diff --git a/sysdeps/riscv/rvv/stpncpy.S b/sysdeps/riscv/rvv/stpncpy.S
new file mode 100644
index 0000000000..7cfc2f76cc
--- /dev/null
+++ b/sysdeps/riscv/rvv/stpncpy.S
@@ -0,0 +1,97 @@
+/* RISC-V RVV based stpncpy.
+   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 STPNCPY
+# ifdef weak_alias
+#  define STPNCPY __stpncpy
+weak_alias (__stpncpy, stpncpy)
+# else
+#  define STPNCPY stpncpy
+# endif
+#endif
+
+#define dst a0
+#define src a1
+#define length a2
+#define dst_ptr a3
+#define active_elem_pos a4
+#define cur_vl a5
+#define ivl a6
+#define temp a1
+
+#define ELEM_LMUL_SETTING m1
+#define vmask1 v0
+#define vmask2 v1
+#define ZERO_FILL_ELEM_LMUL_SETTING m8
+#define vstr1 v8
+#define vstr2 v16
+
+ENTRY (STPNCPY)
+.option push
+.option arch, +v
+    mv dst_ptr, dst
+    /* Copy src to dst_ptr.  */
+L(stpcpy_loop):
+    vsetvli zero, length, e8, ELEM_LMUL_SETTING, ta, ma
+    vle8ff.v vstr1, (src)
+    vmseq.vx vmask2, vstr1, zero
+    csrr cur_vl, vl
+    vfirst.m active_elem_pos, vmask2
+    vmsif.m vmask1, vmask2
+    add src, src, cur_vl
+    sub length, length, cur_vl
+    vse8.v vstr1, (dst_ptr), vmask1.t
+    add dst_ptr, dst_ptr, cur_vl
+    bgez active_elem_pos, L(fill_zero)
+    bnez length, L(stpcpy_loop)
+    mv dst, dst_ptr
+    ret
+
+    /* Fill the tail zero.  */
+L(fill_zero):
+    /* We already copied the `\0` to dst, but we use `vfirst.m` to
+       get the `index` of the `\0` position. We need to adjust by `-1`
+       to get the correct remaining length for zero filling.  */
+    sub temp, cur_vl, active_elem_pos
+    addi temp, temp, -1
+    sub dst, dst_ptr, cur_vl
+    add dst, dst, active_elem_pos
+    add length, length, temp
+    /* Return early for the `strlen(src) + 1 == count` case.  */
+    bnez length, L(do_fill_zero)
+    ret
+
+L(do_fill_zero):
+    sub dst_ptr, dst_ptr, temp
+    vsetvli zero, length, e8, ZERO_FILL_ELEM_LMUL_SETTING, ta, ma
+    vmv.v.x vstr2, zero
+L(fill_zero_loop):
+    vsetvli ivl, length, e8, ZERO_FILL_ELEM_LMUL_SETTING, ta, ma
+    vse8.v vstr2, (dst_ptr)
+    sub length, length, ivl
+    add dst_ptr, dst_ptr, ivl
+    bnez length, L(fill_zero_loop)
+    ret
+.option pop
+END (STPNCPY)
+#ifdef weak_alias
+libc_hidden_def (__stpncpy)
+#endif
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
index 929df14a6f..25d8216d2e 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
@@ -19,6 +19,9 @@ sysdep_routines += \
   memset \
   memset-generic \
   memset-vector \
+  stpncpy \
+  stpncpy-generic \
+  stpncpy-vector \
   strcat \
   strcat-generic \
   strcat-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 4c28e22606..755ba9d637 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
@@ -110,5 +110,10 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __memmove_vector)
 	      IFUNC_IMPL_ADD (array, i, memmove, 1, __memmove_generic))
 
+  IFUNC_IMPL (i, name, stpncpy,
+	      IFUNC_IMPL_ADD (array, i, stpncpy, rvv_enabled,
+			      __stpncpy_vector)
+	      IFUNC_IMPL_ADD (array, i, stpncpy, 1, __stpncpy_generic))
+
   return 0;
 }
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/stpncpy.c b/sysdeps/unix/sysv/linux/riscv/multiarch/stpncpy.c
new file mode 100644
index 0000000000..989003f081
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/stpncpy.c
@@ -0,0 +1,62 @@
+/* Multiple versions of stpncpy.
+   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 stpncpy
+# include <ifunc-init.h>
+
+/* Redefine stpncpy so that the compiler won't complain about the type
+   mismatch with the IFUNC selector in weak_alias, below.  */
+# undef stpncpy
+# undef __stpncpy
+# define stpncpy REDIRECT_NAME
+# define __stpncpy __redirect___stpncpy
+# include <string.h>
+# undef stpncpy
+# undef __stpncpy
+
+# include <stdint.h>
+# include <riscv-ifunc.h>
+# include <sys/hwprobe.h>
+
+extern __typeof (REDIRECT_NAME) __stpncpy;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (generic) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (vector) attribute_hidden;
+
+static inline __typeof (REDIRECT_NAME) *
+select_stpncpy_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 (__stpncpy, select_stpncpy_ifunc);
+
+weak_alias (__stpncpy, stpncpy);
+
+# ifdef SHARED
+__hidden_ver1 (__stpncpy, __GI___stpncpy, __redirect___stpncpy)
+  __attribute__ ((visibility ("hidden")));
+# endif
+#else
+# include <string/stpncpy.c>
+#endif