[PATCH v5 1/1] riscv: Add RVV memset for both multiarch and non-multiarch builds
Yao Zihong
zihong.plct@isrc.iscas.ac.cn
Thu Dec 11 15:33:42 GMT 2025
This patch adds an RVV-optimized implementation of memset 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 (__memset_vector) is added
alongside the generic fallback (__memset_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 memset().
Tested on MUSE-Pi (SpacemiT M1). No regressions were observed compared
with glibc master when the RVV extension was not disabled via prctl().
Co-authored-by: Jerry Shih <jerry.shih@sifive.com>
Co-authored-by: Jeff Law <jeffreyalaw@gmail.com>
Signed-off-by: Yao Zihong <zihong.plct@isrc.iscas.ac.cn>
---
.../riscv/multiarch/dl-symbol-redir-ifunc.h | 26 +++++++++
sysdeps/riscv/multiarch/memset-generic.c | 26 +++++++++
sysdeps/riscv/multiarch/memset-vector.S | 25 ++++++++
sysdeps/riscv/preconfigure | 1 +
sysdeps/riscv/preconfigure.ac | 1 +
sysdeps/riscv/rv32/rvv/Implies | 2 +
sysdeps/riscv/rv64/rvv/Implies | 2 +
sysdeps/riscv/rvv/memset.S | 53 +++++++++++++++++
.../unix/sysv/linux/riscv/multiarch/Makefile | 3 +
.../linux/riscv/multiarch/ifunc-impl-list.c | 22 +++++--
.../unix/sysv/linux/riscv/multiarch/memset.c | 58 +++++++++++++++++++
11 files changed, 215 insertions(+), 4 deletions(-)
create mode 100644 sysdeps/riscv/multiarch/dl-symbol-redir-ifunc.h
create mode 100644 sysdeps/riscv/multiarch/memset-generic.c
create mode 100644 sysdeps/riscv/multiarch/memset-vector.S
create mode 100644 sysdeps/riscv/rv32/rvv/Implies
create mode 100644 sysdeps/riscv/rv64/rvv/Implies
create mode 100644 sysdeps/riscv/rvv/memset.S
create mode 100644 sysdeps/unix/sysv/linux/riscv/multiarch/memset.c
diff --git a/sysdeps/riscv/multiarch/dl-symbol-redir-ifunc.h b/sysdeps/riscv/multiarch/dl-symbol-redir-ifunc.h
new file mode 100644
index 0000000000..2ff7369678
--- /dev/null
+++ b/sysdeps/riscv/multiarch/dl-symbol-redir-ifunc.h
@@ -0,0 +1,26 @@
+/* Symbol redirection for loader/static initialization code.
+ Copyright (C) 2025 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/>. */
+
+#ifndef _DL_IFUNC_GENERIC_H
+#define _DL_IFUNC_GENERIC_H
+
+#ifndef SHARED
+asm ("memset = __memset_generic");
+#endif
+
+#endif
diff --git a/sysdeps/riscv/multiarch/memset-generic.c b/sysdeps/riscv/multiarch/memset-generic.c
new file mode 100644
index 0000000000..c93bb43c8f
--- /dev/null
+++ b/sysdeps/riscv/multiarch/memset-generic.c
@@ -0,0 +1,26 @@
+/* Re-include the default memset implementation.
+ Copyright (C) 2025 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 MEMSET __memset_generic
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(x)
+#endif
+#include <string/memset.c>
diff --git a/sysdeps/riscv/multiarch/memset-vector.S b/sysdeps/riscv/multiarch/memset-vector.S
new file mode 100644
index 0000000000..15d262b0c7
--- /dev/null
+++ b/sysdeps/riscv/multiarch/memset-vector.S
@@ -0,0 +1,25 @@
+
+/* RVV versions memset. RISC-V version.
+ Copyright (C) 2025 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
+ <http://www.gnu.org/licenses/>. */
+
+#if IS_IN(libc)
+# define MEMSET __memset_vector
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(name)
+#include <sysdeps/riscv/rvv/memset.S>
+#endif
diff --git a/sysdeps/riscv/preconfigure b/sysdeps/riscv/preconfigure
index a96cd0d7f8..92ffa1ac02 100644
--- a/sysdeps/riscv/preconfigure
+++ b/sysdeps/riscv/preconfigure
@@ -60,6 +60,7 @@ riscv*)
version=`$CC $CFLAGS $CPPFLAGS -E -dM -xc /dev/null | sed -n 's/^#define __GNUC__ \(.*\)/\1/p'`
test $version -lt 15 && as_fn_error 1 "glibc requires GCC 15 or later for the V extension" "$LINENO" 5
test $vector -lt "1000000" && as_fn_error 1 "glibc requires at least RVV 1.0 for the V extension" "$LINENO" 5
+ float_machine=rvv
fi
base_machine=riscv
diff --git a/sysdeps/riscv/preconfigure.ac b/sysdeps/riscv/preconfigure.ac
index f95ffe83fb..99fbb0c9c9 100644
--- a/sysdeps/riscv/preconfigure.ac
+++ b/sysdeps/riscv/preconfigure.ac
@@ -60,6 +60,7 @@ riscv*)
version=`$CC $CFLAGS $CPPFLAGS -E -dM -xc /dev/null | sed -n 's/^#define __GNUC__ \(.*\)/\1/p'`
test $version -lt 15 && AC_MSG_ERROR([glibc requires GCC 15 or later for the V extension], [1])
test $vector -lt "1000000" && AC_MSG_ERROR([glibc requires at least RVV 1.0 for the V extension], [1])
+ float_machine=rvv
fi
base_machine=riscv
diff --git a/sysdeps/riscv/rv32/rvv/Implies b/sysdeps/riscv/rv32/rvv/Implies
new file mode 100644
index 0000000000..25ce1df222
--- /dev/null
+++ b/sysdeps/riscv/rv32/rvv/Implies
@@ -0,0 +1,2 @@
+riscv/rv32/rvd
+riscv/rvv
diff --git a/sysdeps/riscv/rv64/rvv/Implies b/sysdeps/riscv/rv64/rvv/Implies
new file mode 100644
index 0000000000..9993bb30e3
--- /dev/null
+++ b/sysdeps/riscv/rv64/rvv/Implies
@@ -0,0 +1,2 @@
+riscv/rv64/rvd
+riscv/rvv
diff --git a/sysdeps/riscv/rvv/memset.S b/sysdeps/riscv/rvv/memset.S
new file mode 100644
index 0000000000..2b81a937f5
--- /dev/null
+++ b/sysdeps/riscv/rvv/memset.S
@@ -0,0 +1,53 @@
+/* RISC-V RVV based memset.
+ Copyright (C) 2025 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
+ <http://www.gnu.org/licenses/>. */
+
+#include <sysdep.h>
+#include <sys/asm.h>
+
+#ifndef MEMSET
+# define MEMSET memset
+#endif
+
+#define dst a0
+#define value a1
+#define num a2
+
+#define ivl a3
+#define dst_ptr a5
+
+#define ELEM_LMUL_SETTING m8
+#define vdata v0
+
+ENTRY (MEMSET)
+.option push
+.option arch, +v
+ mv dst_ptr, dst
+
+ vsetvli ivl, num, e8, ELEM_LMUL_SETTING, ta, ma
+ vmv.v.x vdata, value
+L(loop):
+ vse8.v vdata, (dst_ptr)
+ sub num, num, ivl
+ add dst_ptr, dst_ptr, ivl
+ vsetvli ivl, num, e8, ELEM_LMUL_SETTING, ta, ma
+ bnez num, L(loop)
+
+ ret
+.option pop
+END (MEMSET)
+libc_hidden_builtin_def (memset)
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
index fcef5659d4..1d26966ded 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
@@ -3,6 +3,9 @@ sysdep_routines += \
memcpy \
memcpy-generic \
memcpy_noalignment \
+ memset \
+ memset-generic \
+ memset-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 1c1deca8f6..87456f3370 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
@@ -27,17 +27,31 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
size_t i = max;
bool fast_unaligned = false;
+ bool rvv_enabled = false;
- struct riscv_hwprobe pair = { .key = RISCV_HWPROBE_KEY_CPUPERF_0 };
- if (__riscv_hwprobe (&pair, 1, 0, NULL, 0) == 0
- && (pair.value & RISCV_HWPROBE_MISALIGNED_MASK)
+ struct riscv_hwprobe pairs[2] = {
+ {.key = RISCV_HWPROBE_KEY_CPUPERF_0},
+ {.key = RISCV_HWPROBE_KEY_IMA_EXT_0}
+ };
+
+ if (__riscv_hwprobe (pairs, 2, 0, NULL, 0) == 0) {
+ if ((pairs[0].value & RISCV_HWPROBE_MISALIGNED_MASK)
== RISCV_HWPROBE_MISALIGNED_FAST)
- fast_unaligned = true;
+ fast_unaligned = true;
+
+ if (pairs[1].value & RISCV_HWPROBE_IMA_V)
+ rvv_enabled = true;
+ }
IFUNC_IMPL (i, name, memcpy,
IFUNC_IMPL_ADD (array, i, memcpy, fast_unaligned,
__memcpy_noalignment)
IFUNC_IMPL_ADD (array, i, memcpy, 1, __memcpy_generic))
+ IFUNC_IMPL (i, name, memset,
+ IFUNC_IMPL_ADD (array, i, memset, rvv_enabled,
+ __memset_vector)
+ IFUNC_IMPL_ADD (array, i, memset, 1, __memset_generic))
+
return 0;
}
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/memset.c b/sysdeps/unix/sysv/linux/riscv/multiarch/memset.c
new file mode 100644
index 0000000000..166427bff8
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/memset.c
@@ -0,0 +1,58 @@
+/* Multiple versions of memset.
+ All versions must be listed in ifunc-impl-list.c.
+ Copyright (C) 2025 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 memset so that the compiler won't complain about the type
+ mismatch with the IFUNC selector in strong_alias, below. */
+# undef memset
+# define memset __redirect_memset
+# include <stdint.h>
+# include <string.h>
+# include <ifunc-init.h>
+# include <riscv-ifunc.h>
+# include <sys/hwprobe.h>
+
+extern __typeof (__redirect_memset) __libc_memset;
+
+extern __typeof (__redirect_memset) __memset_generic attribute_hidden;
+extern __typeof (__redirect_memset) __memset_vector attribute_hidden;
+
+static inline __typeof (__redirect_memset) *
+select_memset_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 __memset_vector;
+
+ return __memset_generic;
+}
+
+riscv_libc_ifunc (__libc_memset, select_memset_ifunc);
+
+# undef memset
+strong_alias (__libc_memset, memset);
+# ifdef SHARED
+__hidden_ver1 (memset, __GI_memset, __redirect_memset)
+ __attribute__ ((visibility ("hidden"))) __attribute_copy__ (memset);
+# endif
+#else
+# include <string/memset.c>
+#endif
--
2.47.2
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