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

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=d62f110fd1d158ca912f944072fe5750b6f09155

commit d62f110fd1d158ca912f944072fe5750b6f09155
Author: Yao Zihong <[email protected]>
Date:   Tue May 5 16:12:37 2026 -0500

    riscv: Add RVV strcmp for both multiarch and non-multiarch builds
    
    This patch adds an RVV-optimized implementation of strcmp 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 (__strcmp_vector) is added
    alongside the generic fallback (__strcmp_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 strcmp().
    
    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/strcmp-generic.c           | 24 ++++++
 sysdeps/riscv/multiarch/strcmp-vector.S            | 24 ++++++
 sysdeps/riscv/rvv/strcmp.S                         | 93 ++++++++++++++++++++++
 sysdeps/unix/sysv/linux/riscv/multiarch/Makefile   |  3 +
 .../sysv/linux/riscv/multiarch/ifunc-impl-list.c   |  5 ++
 sysdeps/unix/sysv/linux/riscv/multiarch/strcmp.c   | 56 +++++++++++++
 6 files changed, 205 insertions(+)

diff --git a/sysdeps/riscv/multiarch/strcmp-generic.c b/sysdeps/riscv/multiarch/strcmp-generic.c
new file mode 100644
index 0000000000..8ef46a44b9
--- /dev/null
+++ b/sysdeps/riscv/multiarch/strcmp-generic.c
@@ -0,0 +1,24 @@
+/* Re-include the default strcmp 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 STRCMP __strcmp_generic
+# include <string/strcmp.c>
+#endif
diff --git a/sysdeps/riscv/multiarch/strcmp-vector.S b/sysdeps/riscv/multiarch/strcmp-vector.S
new file mode 100644
index 0000000000..b9d9074b24
--- /dev/null
+++ b/sysdeps/riscv/multiarch/strcmp-vector.S
@@ -0,0 +1,24 @@
+/* Re-include the RISC-V RVV based strcmp 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 STRCMP __strcmp_vector
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(name)
+# include <sysdeps/riscv/rvv/strcmp.S>
+#endif
diff --git a/sysdeps/riscv/rvv/strcmp.S b/sysdeps/riscv/rvv/strcmp.S
new file mode 100644
index 0000000000..a2f6865581
--- /dev/null
+++ b/sysdeps/riscv/rvv/strcmp.S
@@ -0,0 +1,93 @@
+/* RISC-V RVV based strcmp.
+   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 STRCMP
+# define STRCMP strcmp
+#endif
+
+#define result a0
+
+#define str1 a0
+#define str2 a1
+
+#define ivl a2
+#define temp1 a3
+#define temp2 a4
+
+#define vstr1 v0
+#define vstr2 v8
+#define vmask1 v16
+#define vmask2 v17
+
+ENTRY (STRCMP)
+.option push
+.option arch, +v
+    /* lmul=1 */
+L(Loop):
+    vsetvli ivl, zero, e8, m1, ta, ma
+    vle8ff.v vstr1, (str1)
+    /* Check if vstr1[i] == 0 */
+    vmseq.vx vmask1, vstr1, zero
+
+    vle8ff.v vstr2, (str2)
+    /* Check if vstr1[i] != vstr2[i] */
+    vmsne.vv vmask2, vstr1, vstr2
+
+    /* Find the index x for vstr1[x] == 0 */
+    vfirst.m temp1, vmask1
+    /* Find the index x for vstr1[x] != vstr2[x] */
+    vfirst.m temp2, vmask2
+
+    bgez temp1, L(check1)
+    bgez temp2, L(check2)
+
+    /* Get the current vl updated by vle8ff. */
+    csrr ivl, vl
+    add str1, str1, ivl
+    add str2, str2, ivl
+    j L(Loop)
+
+    /* temp1 >= 0 */
+L(check1):
+    bltz temp2, L(return_at_nul)
+    blt temp2, temp1, L(check2)
+L(return_at_nul):
+    /* temp2 < 0 */
+    /* temp2 >= 0 && temp1 < temp2 */
+    add str1, str1, temp1
+    add str2, str2, temp1
+    lbu temp1, 0(str1)
+    lbu temp2, 0(str2)
+    sub result, temp1, temp2
+    ret
+
+    /* temp1 < 0 */
+    /* temp2 >= 0 */
+L(check2):
+    add str1, str1, temp2
+    add str2, str2, temp2
+    lbu temp1, 0(str1)
+    lbu temp2, 0(str2)
+    sub result, temp1, temp2
+    ret
+.option pop
+END (STRCMP)
+libc_hidden_builtin_def (strcmp)
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
index 2a2b90960f..3da0306c5c 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
@@ -10,6 +10,9 @@ sysdep_routines += \
   strcat \
   strcat-generic \
   strcat-vector \
+  strcmp \
+  strcmp-generic \
+  strcmp-vector \
   strcpy \
   strcpy-generic \
   strcpy-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 2501546665..76f68c1650 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
@@ -70,5 +70,10 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __strlen_vector)
 	      IFUNC_IMPL_ADD (array, i, strlen, 1, __strlen_generic))
 
+  IFUNC_IMPL (i, name, strcmp,
+	      IFUNC_IMPL_ADD (array, i, strcmp, rvv_enabled,
+			      __strcmp_vector)
+	      IFUNC_IMPL_ADD (array, i, strcmp, 1, __strcmp_generic))
+
   return 0;
 }
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/strcmp.c b/sysdeps/unix/sysv/linux/riscv/multiarch/strcmp.c
new file mode 100644
index 0000000000..9398ad4024
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/strcmp.c
@@ -0,0 +1,56 @@
+/* Multiple versions of strcmp.
+   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 strcmp so that the compiler won't complain about the type
+   mismatch with the IFUNC selector in strong_alias, below.  */
+# undef strcmp
+# define strcmp __redirect_strcmp
+# include <stdint.h>
+# include <string.h>
+# include <ifunc-init.h>
+# include <riscv-ifunc.h>
+# include <sys/hwprobe.h>
+
+extern __typeof (__redirect_strcmp) __libc_strcmp;
+
+extern __typeof (__redirect_strcmp) __strcmp_generic attribute_hidden;
+extern __typeof (__redirect_strcmp) __strcmp_vector attribute_hidden;
+
+static inline __typeof (__redirect_strcmp) *
+select_strcmp_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 __strcmp_vector;
+  return __strcmp_generic;
+}
+
+riscv_libc_ifunc (__libc_strcmp, select_strcmp_ifunc);
+
+# undef strcmp
+strong_alias (__libc_strcmp, strcmp);
+# ifdef SHARED
+__hidden_ver1 (strcmp, __GI_strcmp, __redirect_strcmp)
+  __attribute__ ((visibility ("hidden"))) __attribute_copy__ (strcmp);
+# endif
+#else
+# include <string/strcmp.c>
+#endif