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

Peter Bergner via Glibc-cvs <[email protected]>
Newsgroups gmane.comp.lib.glibc.cvs
Message-ID <[email protected]> 
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9b5e9799b6af76e91b29334310ecd32096b274c2

commit 9b5e9799b6af76e91b29334310ecd32096b274c2
Author: Yao Zihong <[email protected]>
Date:   Wed Feb 18 15:12:09 2026 -0600

    riscv: Add RVV strcat for both multiarch and non-multiarch builds
    
    This patch adds an RVV-optimized implementation of strcat 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 (__strcat_vector) is added
    alongside the generic fallback (__strcat_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 strcat().
    
    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/strcat-generic.c           | 26 ++++++++
 sysdeps/riscv/multiarch/strcat-vector.S            | 24 +++++++
 sysdeps/riscv/rvv/strcat.S                         | 75 ++++++++++++++++++++++
 sysdeps/unix/sysv/linux/riscv/multiarch/Makefile   |  3 +
 .../sysv/linux/riscv/multiarch/ifunc-impl-list.c   |  5 ++
 sysdeps/unix/sysv/linux/riscv/multiarch/strcat.c   | 56 ++++++++++++++++
 6 files changed, 189 insertions(+)

diff --git a/sysdeps/riscv/multiarch/strcat-generic.c b/sysdeps/riscv/multiarch/strcat-generic.c
new file mode 100644
index 0000000000..e28f8f012c
--- /dev/null
+++ b/sysdeps/riscv/multiarch/strcat-generic.c
@@ -0,0 +1,26 @@
+/* Re-include the default strcat 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 STRCAT __strcat_generic
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(x)
+# include <string/strcat.c>
+#endif
diff --git a/sysdeps/riscv/multiarch/strcat-vector.S b/sysdeps/riscv/multiarch/strcat-vector.S
new file mode 100644
index 0000000000..581f075fef
--- /dev/null
+++ b/sysdeps/riscv/multiarch/strcat-vector.S
@@ -0,0 +1,24 @@
+/* Re-include the RISC-V RVV based strcat 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 STRCAT __strcat_vector
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(name)
+# include <sysdeps/riscv/rvv/strcat.S>
+#endif
diff --git a/sysdeps/riscv/rvv/strcat.S b/sysdeps/riscv/rvv/strcat.S
new file mode 100644
index 0000000000..af08ee561f
--- /dev/null
+++ b/sysdeps/riscv/rvv/strcat.S
@@ -0,0 +1,75 @@
+/* RISC-V RVV based strcat.
+   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 STRCAT
+# define STRCAT strcat
+#endif
+
+#define dst a0
+#define src a1
+#define dst_ptr a2
+
+#define ivl a3
+#define cur_vl a4
+#define active_elem_pos a5
+
+#define ELEM_LMUL_SETTING m1
+#define vmask1 v0
+#define vmask2 v1
+#define vstr1 v8
+#define vstr2 v16
+
+ENTRY (STRCAT)
+.option push
+.option arch, +v
+    mv dst_ptr, dst
+    /* Perform `strlen(dst)`.  */
+L(strlen_loop):
+    vsetvli ivl, zero, e8, ELEM_LMUL_SETTING, ta, ma
+
+    vle8ff.v vstr1, (dst_ptr)
+    vmseq.vx vmask1, vstr1, zero
+    csrr cur_vl, vl
+    vfirst.m active_elem_pos, vmask1
+    add dst_ptr, dst_ptr, cur_vl
+    bltz active_elem_pos, L(strlen_loop)
+
+    sub dst_ptr, dst_ptr, cur_vl
+    add dst_ptr, dst_ptr, active_elem_pos
+
+    /* Perform `strcpy(dst, src)`.  */
+L(strcpy_loop):
+    vsetvli ivl, zero, 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
+    vse8.v vstr1, (dst_ptr), vmask1.t
+    add dst_ptr, dst_ptr, cur_vl
+    bltz active_elem_pos, L(strcpy_loop)
+
+    ret
+.option pop
+END (STRCAT)
+libc_hidden_builtin_def (strcat)
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
index a033ea9569..41ba27793d 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
@@ -6,6 +6,9 @@ sysdep_routines += \
   memset \
   memset-generic \
   memset-vector \
+  strcat \
+  strcat-generic \
+  strcat-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 a3b5731411..af64c04249 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
@@ -53,5 +53,10 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __memset_vector)
 	      IFUNC_IMPL_ADD (array, i, memset, 1, __memset_generic))
 
+  IFUNC_IMPL (i, name, strcat,
+	      IFUNC_IMPL_ADD (array, i, strcat, rvv_enabled,
+			      __strcat_vector)
+	      IFUNC_IMPL_ADD (array, i, strcat, 1, __strcat_generic))
+
   return 0;
 }
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/strcat.c b/sysdeps/unix/sysv/linux/riscv/multiarch/strcat.c
new file mode 100644
index 0000000000..781b0d4cb1
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/strcat.c
@@ -0,0 +1,56 @@
+/* Multiple versions of strcat.
+   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 strcat so that the compiler won't complain about the type
+   mismatch with the IFUNC selector in strong_alias, below.  */
+# undef strcat
+# define strcat __redirect_strcat
+# include <stdint.h>
+# include <string.h>
+# include <ifunc-init.h>
+# include <riscv-ifunc.h>
+# include <sys/hwprobe.h>
+
+extern __typeof (__redirect_strcat) __libc_strcat;
+
+extern __typeof (__redirect_strcat) __strcat_generic attribute_hidden;
+extern __typeof (__redirect_strcat) __strcat_vector attribute_hidden;
+
+static inline __typeof (__redirect_strcat) *
+select_strcat_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 __strcat_vector;
+  return __strcat_generic;
+}
+
+riscv_libc_ifunc (__libc_strcat, select_strcat_ifunc);
+
+# undef strcat
+strong_alias (__libc_strcat, strcat);
+# ifdef SHARED
+__hidden_ver1 (strcat, __GI_strcat, __redirect_strcat)
+  __attribute__ ((visibility ("hidden"))) __attribute_copy__ (strcat);
+# endif
+#else
+# include <string/strcat.c>
+#endif
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