linux-kernel - [PATCH] arm: lib: implement aeabi_uldivmod via div64_u64

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Message-Id: <20220716001616.4052225-1-ndesaulniers@google.com>
Date:   Fri, 15 Jul 2022 17:16:07 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     llvm@...ts.linux.dev, Arnd Bergmann <arnd@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Ard Biesheuval <ardb@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Gary Guo <gary@...yguo.net>,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] arm: lib: implement aeabi_uldivmod via div64_u64_rem

Compilers frequently need to defer 64b division to a libcall with this
symbol name. It essentially is div64_u64_rem, just with a different
signature. Kernel developers know to call div64_u64_rem, but compilers
don't.

Link: https://lore.kernel.org/lkml/20220524004156.0000790e@garyguo.net/
Suggested-by: Gary Guo <gary@...yguo.net>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 arch/arm/lib/Makefile         |  1 +
 arch/arm/lib/aeabi_uldivmod.c | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 arch/arm/lib/aeabi_uldivmod.c

diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 6d2ba454f25b..3fa273219312 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -29,6 +29,7 @@ endif
 obj-$(CONFIG_UACCESS_WITH_MEMCPY) += uaccess_with_memcpy.o
 
 lib-$(CONFIG_MMU) += $(mmu-y)
+lib-$(CONFIG_AEABI) += aeabi_uldivmod.o
 
 ifeq ($(CONFIG_CPU_32v3),y)
   lib-y	+= io-readsw-armv3.o io-writesw-armv3.o
diff --git a/arch/arm/lib/aeabi_uldivmod.c b/arch/arm/lib/aeabi_uldivmod.c
new file mode 100644
index 000000000000..310427893195
--- /dev/null
+++ b/arch/arm/lib/aeabi_uldivmod.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Unsigned 64b division with remainder, as is typically provided by libgcc or
+ * compiler-rt.
+ *
+ * Copyright (C) 2023 Google, LLC.
+ *
+ * Author: Nick Desaulniers <ndesaulniers@...gle.com>
+ */
+
+#include <linux/math64.h>
+
+struct result {
+	u64 quot, rem;
+};
+
+struct result __aeabi_uldivmod(u64 numerator, u64 denominator)
+{
+	struct result res;
+
+	res.quot = div64_u64_rem(numerator, denominator, &res.rem);
+	return res;
+}
-- 
2.37.0.170.g444d1eabd0-goog