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

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=2efc7026287273b4b3a1ce1a7b27791d3d860a5c

commit 2efc7026287273b4b3a1ce1a7b27791d3d860a5c
Author: Yao Zihong <[email protected]>
Date:   Thu Jun 4 18:28:06 2026 -0500

    riscv: Add RVV memcmp for both multiarch and non-multiarch builds
    
    This patch adds an RVV-optimized implementation of memcmp 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 (__memcmp_vector) is added
    alongside the generic fallback (__memcmp_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 memcmp().
    
    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/dl-symbol-redir-ifunc.h    |  1 +
 sysdeps/riscv/multiarch/memcmp-generic.c           | 30 ++++++++
 sysdeps/riscv/multiarch/memcmp-vector.S            | 30 ++++++++
 sysdeps/riscv/rvv/memcmp.S                         | 84 ++++++++++++++++++++++
 sysdeps/unix/sysv/linux/riscv/multiarch/Makefile   |  3 +
 .../sysv/linux/riscv/multiarch/ifunc-impl-list.c   |  5 ++
 sysdeps/unix/sysv/linux/riscv/multiarch/memcmp.c   | 60 ++++++++++++++++
 7 files changed, 213 insertions(+)

diff --git a/sysdeps/riscv/multiarch/dl-symbol-redir-ifunc.h b/sysdeps/riscv/multiarch/dl-symbol-redir-ifunc.h
index c6f2aacd17..f81e5b7e6d 100644
--- a/sysdeps/riscv/multiarch/dl-symbol-redir-ifunc.h
+++ b/sysdeps/riscv/multiarch/dl-symbol-redir-ifunc.h
@@ -20,6 +20,7 @@
 #define _DL_IFUNC_GENERIC_H
 
 #ifndef SHARED
+asm ("memcmp = __memcmp_generic");
 asm ("memcpy = __memcpy_generic");
 asm ("memset = __memset_generic");
 asm ("strlen = __strlen_generic");
diff --git a/sysdeps/riscv/multiarch/memcmp-generic.c b/sysdeps/riscv/multiarch/memcmp-generic.c
new file mode 100644
index 0000000000..14f6752406
--- /dev/null
+++ b/sysdeps/riscv/multiarch/memcmp-generic.c
@@ -0,0 +1,30 @@
+/* Re-include the default memcmp 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 MEMCMP __memcmp_generic
+# undef libc_hidden_def
+# define libc_hidden_def(x)
+# undef weak_alias
+# define weak_alias(x, x2)
+# undef strong_alias
+# define strong_alias(x, x2)
+# include <string/memcmp.c>
+#endif
diff --git a/sysdeps/riscv/multiarch/memcmp-vector.S b/sysdeps/riscv/multiarch/memcmp-vector.S
new file mode 100644
index 0000000000..b447e945a8
--- /dev/null
+++ b/sysdeps/riscv/multiarch/memcmp-vector.S
@@ -0,0 +1,30 @@
+/* Re-include the RISC-V RVV based memcmp 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 MEMCMP __memcmp_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)
+# undef strong_alias
+# define strong_alias(name, alias)
+# include <sysdeps/riscv/rvv/memcmp.S>
+#endif
diff --git a/sysdeps/riscv/rvv/memcmp.S b/sysdeps/riscv/rvv/memcmp.S
new file mode 100644
index 0000000000..004bf538f0
--- /dev/null
+++ b/sysdeps/riscv/rvv/memcmp.S
@@ -0,0 +1,84 @@
+/* RISC-V RVV based memcmp.
+   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 MEMCMP
+# define MEMCMP memcmp
+#endif
+
+#define result a0
+
+#define src1 a0
+#define src2 a1
+#define num a2
+
+#define ivl a3
+#define temp a4
+
+#define ELEM_LMUL_SETTING m8
+#define vdata1 v0
+#define vdata2 v8
+#define vmask v16
+#define vtemp1 v16
+#define vtemp2 v24
+
+ENTRY (MEMCMP)
+.option push
+.option arch, +v
+L(loop):
+    vsetvli ivl, num, e8, ELEM_LMUL_SETTING, ta, ma
+
+    vle8.v vdata1, (src1)
+    vle8.v vdata2, (src2)
+
+    vmsne.vv vmask, vdata1, vdata2
+    sub num, num, ivl
+    vfirst.m temp, vmask
+
+    bgez temp, L(found)
+
+    add src1, src1, ivl
+    add src2, src2, ivl
+
+    bnez num, L(loop)
+
+    li result, 0
+    ret
+L(found):
+    vrgather.vx vtemp1, vdata1, temp
+    vrgather.vx vtemp2, vdata2, temp
+    vmv.x.s result, vtemp1
+    vmv.x.s temp, vtemp2
+    andi result, result, 0xff
+    andi temp, temp, 0xff
+    sub result, result, temp
+    ret
+.option pop
+END (MEMCMP)
+libc_hidden_builtin_def(memcmp)
+#ifdef weak_alias
+#undef bcmp
+weak_alias (MEMCMP, bcmp)
+#endif
+
+#undef __memcmpeq
+strong_alias (MEMCMP, __memcmpeq)
+libc_hidden_builtin_def (MEMCMP)
+libc_hidden_def (__memcmpeq)
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
index 2fdd4af3eb..20ff2bdca2 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
@@ -1,5 +1,8 @@
 ifeq ($(subdir),string)
 sysdep_routines += \
+  memcmp \
+  memcmp-generic \
+  memcmp-vector \
   memcpy \
   memcpy-generic \
   memcpy-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 a6765e5978..1d09cf27a3 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
@@ -80,5 +80,10 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __strncmp_vector)
 	      IFUNC_IMPL_ADD (array, i, strncmp, 1, __strncmp_generic))
 
+  IFUNC_IMPL (i, name, memcmp,
+	      IFUNC_IMPL_ADD (array, i, memcmp, rvv_enabled,
+			      __memcmp_vector)
+	      IFUNC_IMPL_ADD (array, i, memcmp, 1, __memcmp_generic))
+
   return 0;
 }
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/memcmp.c b/sysdeps/unix/sysv/linux/riscv/multiarch/memcmp.c
new file mode 100644
index 0000000000..20e7b046ab
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/memcmp.c
@@ -0,0 +1,60 @@
+/* Multiple versions of memcmp.
+   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 memcmp so that the compiler won't complain about the type
+   mismatch with the IFUNC selector in strong_alias, below.  */
+# undef memcmp
+# define memcmp __redirect_memcmp
+# include <stdint.h>
+# include <string.h>
+# include <ifunc-init.h>
+# include <riscv-ifunc.h>
+# include <sys/hwprobe.h>
+
+extern __typeof (__redirect_memcmp) __libc_memcmp;
+
+extern __typeof (__redirect_memcmp) __memcmp_generic attribute_hidden;
+extern __typeof (__redirect_memcmp) __memcmp_vector attribute_hidden;
+
+static inline __typeof (__redirect_memcmp) *
+select_memcmp_ifunc (uint64_t dl_hwcap, __riscv_hwprobe_t hwprobe_func)
+{
+  unsigned long long 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 __memcmp_vector;
+
+  return __memcmp_generic;
+}
+
+riscv_libc_ifunc (__libc_memcmp, select_memcmp_ifunc);
+
+# undef memcmp
+# undef bcmp
+strong_alias (__libc_memcmp, memcmp);
+weak_alias (memcmp, bcmp);
+# ifdef SHARED
+__hidden_ver1 (memcmp, __GI_memcmp, __redirect_memcmp)
+  __attribute__ ((visibility ("hidden"))) __attribute_copy__ (memcmp);
+# endif
+#else
+# include <string/memcmp.c>
+#endif