add facility to apply patches to all branches. (#136)

* add facility to apply patches to all branches.

This probably wont get used too often, as patches probably wont apply
cleanly across all these different branches, but makes it simple to
apply patches to many trees.

Also, add patch for
ClangBuiltLinux/linux#416

* add comment and explicit return code

* prefer if/else to capture git apply return code

Author: nickdesaulniers

driver.sh

@@ -216,6 +216,15 @@ mako_reactor() {
   make -j"${jobs:-$(nproc)}" CC="${CC}" HOSTCC="${CC}" LD="${LD}" HOSTLD="${HOSTLD:-ld}" AR="${AR}" "${@}"
 }
 
+apply_patches() {
+  patches_folder=$1
+  if [[ -d ${patches_folder} ]]; then
+    git apply -v -3 "${patches_folder}"/*.patch
+  else
+    return 0
+  fi
+}
+
 build_linux() {
   # Wrap CC in ccache if it is available (it's not strictly required)
   CC="$(command -v ccache) ${CC}"
@@ -232,8 +241,8 @@ build_linux() {
 
   git show -s | cat
 
-  patches_folder=../patches/${REPO}/${ARCH}
-  [[ -d ${patches_folder} ]] && git apply -v -3 "${patches_folder}"/*.patch
+  apply_patches "../patches/all"
+  apply_patches "../patches/${REPO}/${ARCH}"
 
   # Only clean up old artifacts if requested, the Linux build system
   # is good about figuring out what needs to be rebuilt

patches/all/v4-0001-lib-string.c-implement-a-basic-bcmp.patch

@@ -0,0 +1,101 @@
+From 2852bab291d87a6d9ff1af089c879b9f155c7be1 Mon Sep 17 00:00:00 2001
+From: Nick Desaulniers <[email protected]>
+Date: Wed, 13 Mar 2019 10:34:50 -0700
+Subject: [PATCH v4] lib/string.c: implement a basic bcmp
+
+A recent optimization in Clang (r355672) lowers comparisons of the
+return value of memcmp against zero to comparisons of the return value
+of bcmp against zero.  This helps some platforms that implement bcmp
+more efficiently than memcmp. glibc simply aliases bcmp to memcmp, but
+an optimized implementation is in the works.
+
+This results in linkage failures for all targets with Clang due to the
+undefined symbol.  For now, just implement bcmp as a tailcail to memcmp
+to unbreak the build.  This routine can be further optimized in the
+future.
+
+Other ideas discussed:
+* A weak alias was discussed, but breaks for architectures that define
+their own implementations of memcmp since aliases to declarations are
+not permitted (only definitions).  Arch-specific memcmp implementations
+typically declare memcmp in C headers, but implement them in assembly.
+* -ffreestanding also is used sporadically throughout the kernel.
+* -fno-builtin-bcmp doesn't work when doing LTO.
+
+Link: https://bugs.llvm.org/show_bug.cgi?id=41035
+Link: https://code.woboq.org/userspace/glibc/string/memcmp.c.html#bcmp
+Link: https://github.com/llvm/llvm-project/commit/8e16d73346f8091461319a7dfc4ddd18eedcff13
+Link: https://github.com/ClangBuiltLinux/linux/issues/416
+Cc: [email protected]
+Reported-by: Nathan Chancellor <[email protected]>
+Reported-by: Adhemerval Zanella <[email protected]>
+Suggested-by: Arnd Bergmann <[email protected]>
+Suggested-by: James Y Knight <[email protected]>
+Suggested-by: Masahiro Yamada <[email protected]>
+Suggested-by: Nathan Chancellor <[email protected]>
+Suggested-by: Rasmus Villemoes <[email protected]>
+Signed-off-by: Nick Desaulniers <[email protected]>
+Acked-by: Steven Rostedt (VMware) <[email protected]>
+---
+Changes V3 -> V4:
+* Include the entirety of Rasmus' sugguestion, as per Steven.
+* Change formal parameter identifiers to match the comment.
+Changes V2 -> V3:
+* Adjust comment as per Steven to Rasmus' sugguestion.
+* Pick up Steven's Ack.
+Changes V1 -> V2:
+* Add declaration to include/linux/string.h.
+* Reword comment above bcmp.
+
+ include/linux/string.h |  3 +++
+ lib/string.c           | 20 ++++++++++++++++++++
+ 2 files changed, 23 insertions(+)
+
+diff --git a/include/linux/string.h b/include/linux/string.h
+index 7927b875f80c..6ab0a6fa512e 100644
+--- a/include/linux/string.h
++++ b/include/linux/string.h
+@@ -150,6 +150,9 @@ extern void * memscan(void *,int,__kernel_size_t);
+ #ifndef __HAVE_ARCH_MEMCMP
+ extern int memcmp(const void *,const void *,__kernel_size_t);
+ #endif
++#ifndef __HAVE_ARCH_BCMP
++extern int bcmp(const void *,const void *,__kernel_size_t);
++#endif
+ #ifndef __HAVE_ARCH_MEMCHR
+ extern void * memchr(const void *,int,__kernel_size_t);
+ #endif
+diff --git a/lib/string.c b/lib/string.c
+index 38e4ca08e757..3ab861c1a857 100644
+--- a/lib/string.c
++++ b/lib/string.c
+@@ -866,6 +866,26 @@ __visible int memcmp(const void *cs, const void *ct, size_t count)
+ EXPORT_SYMBOL(memcmp);
+ #endif
+ 
++#ifndef __HAVE_ARCH_BCMP
++/**
++ * bcmp - returns 0 if and only if the buffers have identical contents.
++ * @a: pointer to first buffer.
++ * @b: pointer to second buffer.
++ * @len: size of buffers.
++ *
++ * The sign or magnitude of a non-zero return value has no particular
++ * meaning, and architectures may implement their own more efficient bcmp(). So
++ * while this particular implementation is a simple (tail) call to memcmp, do
++ * not rely on anything but whether the return value is zero or non-zero.
++ */
++#undef bcmp
++int bcmp(const void *a, const void *b, size_t len)
++{
++	return memcmp(a, b, len);
++}
++EXPORT_SYMBOL(bcmp);
++#endif
++
+ #ifndef __HAVE_ARCH_MEMSCAN
+ /**
+  * memscan - Find a character in an area of memory.
+-- 
+2.21.0.360.g471c308f928-goog
+