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

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9b8ff36d0c881bfa08dfece10df89b1c199b23ee

commit 9b8ff36d0c881bfa08dfece10df89b1c199b23ee
Author: Yao Zihong <[email protected]>
Date:   Tue May 5 16:22:29 2026 -0500

    riscv: Add RVV strncmp for both multiarch and non-multiarch builds
    
    This patch adds an RVV-optimized implementation of strncmp 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 (__strncmp_vector) is added
    alongside the generic fallback (__strncmp_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 strncmp().
    
    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/strncmp-generic.c          | 26 +++++++
 sysdeps/riscv/multiarch/strncmp-vector.S           | 24 ++++++
 sysdeps/riscv/rvv/strncmp.S                        | 88 ++++++++++++++++++++++
 sysdeps/unix/sysv/linux/riscv/multiarch/Makefile   |  3 +
 .../sysv/linux/riscv/multiarch/ifunc-impl-list.c   |  5 ++
 sysdeps/unix/sysv/linux/riscv/multiarch/strncmp.c  | 56 ++++++++++++++
 6 files changed, 202 insertions(+)

diff --git a/sysdeps/riscv/multiarch/strncmp-generic.c b/sysdeps/riscv/multiarch/strncmp-generic.c
new file mode 100644
index 0000000000..3d61dce1be
--- /dev/null
+++ b/sysdeps/riscv/multiarch/strncmp-generic.c
@@ -0,0 +1,26 @@
+/* Re-include the default strncmp 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 STRNCMP __strncmp_generic
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(x)
+# include <string/strncmp.c>
+#endif
diff --git a/sysdeps/riscv/multiarch/strncmp-vector.S b/sysdeps/riscv/multiarch/strncmp-vector.S
new file mode 100644
index 0000000000..91e25ea826
--- /dev/null
+++ b/sysdeps/riscv/multiarch/strncmp-vector.S
@@ -0,0 +1,24 @@
+/* Re-include the RISC-V RVV based strncmp 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 STRNCMP __strncmp_vector
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(name)
+# include <sysdeps/riscv/rvv/strncmp.S>
+#endif
diff --git a/sysdeps/riscv/rvv/strncmp.S b/sysdeps/riscv/rvv/strncmp.S
new file mode 100644
index 0000000000..79c85f530c
--- /dev/null
+++ b/sysdeps/riscv/rvv/strncmp.S
@@ -0,0 +1,88 @@
+/* RISC-V RVV based strncmp.
+   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 STRNCMP
+# define STRNCMP strncmp
+#endif
+
+#define result a0
+
+#define str1 a0
+#define str2 a1
+#define length a2
+
+#define ivl a3
+#define temp1 a4
+#define temp2 a5
+
+#define ELEM_LMUL_SETTING m1
+#define vstr1 v0
+#define vstr2 v4
+#define vmask1 v8
+#define vmask2 v9
+
+ENTRY (STRNCMP)
+.option push
+.option arch, +v
+    beqz length, L(zero_length)
+L(loop):
+    vsetvli zero, length, e8, ELEM_LMUL_SETTING, ta, ma
+
+    vle8ff.v vstr1, (str1)
+    /* vstr1[i] == 0.  */
+    vmseq.vx vmask1, vstr1, zero
+
+    vle8ff.v vstr2, (str2)
+    /* vstr1[i] != vstr2[i].  */
+    vmsne.vv vmask2, vstr1, vstr2
+
+    csrr ivl, vl
+
+    /* r = mask1 | mask2
+    We can use vfirst.m to get the first zero char or the
+    first different char between str1 and str2. */
+    vmor.mm vmask1, vmask1, vmask2
+
+    sub length, length, ivl
+
+    vfirst.m temp1, vmask1
+
+    bgez temp1, L(end_loop)
+
+    add str1, str1, ivl
+    add str2, str2, ivl
+    bnez length, L(loop)
+
+L(end_loop):
+    add str1, str1, temp1
+    add str2, str2, temp1
+    lbu temp1, 0(str1)
+    lbu temp2, 0(str2)
+
+    sub result, temp1, temp2
+    ret
+
+L(zero_length):
+    li result, 0
+    ret
+.option pop
+END (STRNCMP)
+libc_hidden_builtin_def (strncmp)
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
index 3da0306c5c..2fdd4af3eb 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
@@ -19,6 +19,9 @@ sysdep_routines += \
   strlen \
   strlen-generic \
   strlen-vector \
+  strncmp \
+  strncmp-generic \
+  strncmp-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 76f68c1650..a6765e5978 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
@@ -75,5 +75,10 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __strcmp_vector)
 	      IFUNC_IMPL_ADD (array, i, strcmp, 1, __strcmp_generic))
 
+  IFUNC_IMPL (i, name, strncmp,
+	      IFUNC_IMPL_ADD (array, i, strncmp, rvv_enabled,
+			      __strncmp_vector)
+	      IFUNC_IMPL_ADD (array, i, strncmp, 1, __strncmp_generic))
+
   return 0;
 }
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/strncmp.c b/sysdeps/unix/sysv/linux/riscv/multiarch/strncmp.c
new file mode 100644
index 0000000000..781e562629
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/strncmp.c
@@ -0,0 +1,56 @@
+/* Multiple versions of strncmp.
+   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 strncmp so that the compiler won't complain about the type
+   mismatch with the IFUNC selector in strong_alias, below.  */
+# undef strncmp
+# define strncmp __redirect_strncmp
+# include <stdint.h>
+# include <string.h>
+# include <ifunc-init.h>
+# include <riscv-ifunc.h>
+# include <sys/hwprobe.h>
+
+extern __typeof (__redirect_strncmp) __libc_strncmp;
+
+extern __typeof (__redirect_strncmp) __strncmp_generic attribute_hidden;
+extern __typeof (__redirect_strncmp) __strncmp_vector attribute_hidden;
+
+static inline __typeof (__redirect_strncmp) *
+select_strncmp_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 __strncmp_vector;
+  return __strncmp_generic;
+}
+
+riscv_libc_ifunc (__libc_strncmp, select_strncmp_ifunc);
+
+# undef strncmp
+strong_alias (__libc_strncmp, strncmp);
+# ifdef SHARED
+__hidden_ver1 (strncmp, __GI_strncmp, __redirect_strncmp)
+  __attribute__ ((visibility ("hidden"))) __attribute_copy__ (strncmp);
+# endif
+#else
+# include <string/strncmp.c>
+#endif