Re: [U-Boot] [PATCH] x86: lib: Implement standalone __udivdi3 etc instead of libgcc ones

[Simon Glass]

On 16 November 2017 at 03:27, Stefan Roese  wrote:
> This patch removes the inclusion of the libgcc math functions and
> replaces them by functions coded in C, taken from the coreboot
> project. This makes U-Boot building more independent from the toolchain
> installed / available on the build system.
>
> The code taken from coreboot is authored from Vadim Bendebury
>  on 2014-11-28 and committed with commit
> ID e63990ef [libpayload: provide basic 64bit division implementation].
>
> I modified the code so that its checkpatch clean without any
> functional changes.
>
> Signed-off-by: Stefan Roese 
> Cc: Simon Glass 
> Cc: Bin Meng 
> ---
>  arch/x86/config.mk|   3 --
>  arch/x86/lib/Makefile |   2 +-
>  arch/x86/lib/div64.c  | 113 
> ++
>  arch/x86/lib/gcc.c|  29 -
>  4 files changed, 114 insertions(+), 33 deletions(-)
>  create mode 100644 arch/x86/lib/div64.c
>  delete mode 100644 arch/x86/lib/gcc.c

Reviewed-by: Simon Glass 
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[U-Boot] [PATCH] x86: lib: Implement standalone __udivdi3 etc instead of libgcc ones

[Stefan Roese]

This patch removes the inclusion of the libgcc math functions and
replaces them by functions coded in C, taken from the coreboot
project. This makes U-Boot building more independent from the toolchain
installed / available on the build system.

The code taken from coreboot is authored from Vadim Bendebury
 on 2014-11-28 and committed with commit
ID e63990ef [libpayload: provide basic 64bit division implementation].

I modified the code so that its checkpatch clean without any
functional changes.

Signed-off-by: Stefan Roese 
Cc: Simon Glass 
Cc: Bin Meng 
---
 arch/x86/config.mk|   3 --
 arch/x86/lib/Makefile |   2 +-
 arch/x86/lib/div64.c  | 113 ++
 arch/x86/lib/gcc.c|  29 -
 4 files changed, 114 insertions(+), 33 deletions(-)
 create mode 100644 arch/x86/lib/div64.c
 delete mode 100644 arch/x86/lib/gcc.c

diff --git a/arch/x86/config.mk b/arch/x86/config.mk
index 8835dcf36f..472ada5490 100644
--- a/arch/x86/config.mk
+++ b/arch/x86/config.mk
@@ -34,9 +34,6 @@ PLATFORM_RELFLAGS += -ffunction-sections -fvisibility=hidden
 PLATFORM_LDFLAGS += -Bsymbolic -Bsymbolic-functions
 PLATFORM_LDFLAGS += -m $(if $(IS_32BIT),elf_i386,elf_x86_64)
 
-LDFLAGS_FINAL += --wrap=__divdi3 --wrap=__udivdi3
-LDFLAGS_FINAL += --wrap=__moddi3 --wrap=__umoddi3
-
 # This is used in the top-level Makefile which does not include
 # PLATFORM_LDFLAGS
 LDFLAGS_EFI_PAYLOAD := -Bsymbolic -Bsymbolic-functions -shared --no-undefined
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index fe00d7573f..d9b23f5cc4 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -18,7 +18,7 @@ obj-$(CONFIG_SEABIOS) += coreboot_table.o
 obj-y  += early_cmos.o
 obj-$(CONFIG_EFI) += efi/
 obj-y  += e820.o
-obj-y  += gcc.o
+obj-y  += div64.o
 obj-y  += init_helpers.o
 obj-y  += interrupts.o
 obj-y  += lpc-uclass.o
diff --git a/arch/x86/lib/div64.c b/arch/x86/lib/div64.c
new file mode 100644
index 00..4efed74037
--- /dev/null
+++ b/arch/x86/lib/div64.c
@@ -0,0 +1,113 @@
+/*
+ * This file is copied from the coreboot repository as part of
+ * the libpayload project:
+ *
+ * Copyright 2014 Google Inc.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include 
+
+union overlay64 {
+   u64 longw;
+   struct {
+   u32 lower;
+   u32 higher;
+   } words;
+};
+
+u64 __ashldi3(u64 num, unsigned int shift)
+{
+   union overlay64 output;
+
+   output.longw = num;
+   if (shift >= 32) {
+   output.words.higher = output.words.lower << (shift - 32);
+   output.words.lower = 0;
+   } else {
+   if (!shift)
+   return num;
+   output.words.higher = (output.words.higher << shift) |
+   (output.words.lower >> (32 - shift));
+   output.words.lower = output.words.lower << shift;
+   }
+   return output.longw;
+}
+
+u64 __lshrdi3(u64 num, unsigned int shift)
+{
+   union overlay64 output;
+
+   output.longw = num;
+   if (shift >= 32) {
+   output.words.lower = output.words.higher >> (shift - 32);
+   output.words.higher = 0;
+   } else {
+   if (!shift)
+   return num;
+   output.words.lower = output.words.lower >> shift |
+   (output.words.higher << (32 - shift));
+   output.words.higher = output.words.higher >> shift;
+   }
+   return output.longw;
+}
+
+#define MAX_32BIT_UINT u64)1) << 32) - 1)
+
+static u64 _64bit_divide(u64 dividend, u64 divider, u64 *rem_p)
+{
+   u64 result = 0;
+
+   /*
+* If divider is zero - let the rest of the system care about the
+* exception.
+*/
+   if (!divider)
+   return 1 / (u32)divider;
+
+   /* As an optimization, let's not use 64 bit division unless we must. */
+   if (dividend <= MAX_32BIT_UINT) {
+   if (divider > MAX_32BIT_UINT) {
+   result = 0;
+   if (rem_p)
+   *rem_p = divider;
+   } else {
+   result = (u32)dividend / (u32)divider;
+   if (rem_p)
+   *rem_p = (u32)dividend % (u32)divider;
+   }
+   return result;
+   }
+
+   while (divider <= dividend) {
+   u64 locald = divider;
+   u64 limit = __lshrdi3(dividend, 1);
+   int shifts = 0;
+
+   while (locald <= limit) {
+   shifts++;
+   locald = locald + locald;
+   }
+   result |= __ashldi3(1, shifts);
+   dividend -= locald;
+   }
+
+   if (rem_p)
+   *rem_p = dividend;
+
+   return result;
+}
+
+u64 __udivdi3(u64 num, u64 den)
+{