Downstream patch to add bootcode for AArch64 FVPs #852 (ARM-software#564)

This patch:
   1.  Create new picolibc changes in downstream to add bootcode for AArch64 FVPs which is  authored by: **Oliver Stannard**. The AArch64 FVP (Fixed Virtual Platform) models differ from QEMU in a few ways which affect the crt0 code:
    * The memory map is different, so needs different page tables.
   * They boot up at EL3, instead of EL1, so we need to set the EL3
       versions of the system registers.
    * Add option to build crt0 bootcode for different machines
    * Build new FVP variants of crt0, instead of replacing QEMU ones
    * Split assembly parts of AArch64 crt0 into a separate file
    * Make error checking target-specific

And also this patch:
      1. Split and group the related picolibc changes into single
	patch.
     2. Do the necessary changes in the documentation to reflect these
	changes.

Author: simpal01

CMakeLists.txt

@@ -47,7 +47,7 @@
 #   git -C repos clone https://github.com/llvm/llvm-project.git
 #   git -C repos/llvm-project am -k $PWD/patches/llvm-project/*.patch
 #   git -C repos clone https://github.com/picolibc/picolibc.git
-#   git -C repos/picolibc apply $PWD/patches/picolibc.patch
+#   git -C repos/picolibc apply $PWD/patches/picolibc/*.patch
 #   mkdir build
 #   cd build
 #   cmake .. -GNinja -DFETCHCONTENT_SOURCE_DIR_LLVMPROJECT=../repos/llvm-project -DFETCHCONTENT_SOURCE_DIR_PICOLIBC=../repos/picolibc
@@ -289,6 +289,11 @@ set(LLVM_PATCH_COMMAND ${Python3_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/cmake/p
 if(APPLY_LLVM_PERFORMANCE_PATCHES)
     set(LLVM_PATCH_COMMAND ${LLVM_PATCH_COMMAND} && ${Python3_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/cmake/patch_llvm.py ${CMAKE_CURRENT_SOURCE_DIR}/patches/llvm-project-perf)
 endif()
+set(
+    picolibc_patches
+    ${CMAKE_CURRENT_SOURCE_DIR}/patches/picolibc/0001-Enable-libcxx-builds.patch
+    ${CMAKE_CURRENT_SOURCE_DIR}/patches/picolibc/0002-Add-bootcode-for-AArch64-FVPs.patch
+)
 
 FetchContent_Declare(llvmproject
     GIT_REPOSITORY https://github.com/llvm/llvm-project.git
@@ -308,7 +313,7 @@ FetchContent_Declare(picolibc
     GIT_TAG "${picolibc_TAG}"
     GIT_SHALLOW "${picolibc_SHALLOW}"
     GIT_PROGRESS TRUE
-    PATCH_COMMAND git reset --quiet --hard && git clean --quiet --force -dx && git apply ${CMAKE_CURRENT_SOURCE_DIR}/patches/picolibc.patch
+    PATCH_COMMAND git reset --quiet --hard && git clean --quiet --force -dx && git apply ${picolibc_patches}
     # We only want to download the content, not configure it at this
     # stage. picolibc will be built in many configurations using
     # ExternalProject_Add using the sources that are checked out here.

docs/building-from-source.md

@@ -89,7 +89,7 @@ mkdir repos
 git -C repos clone https://github.com/llvm/llvm-project.git
 git -C repos/llvm-project am -k "$PWD"/patches/llvm-project/*.patch
 git -C repos clone https://github.com/picolibc/picolibc.git
-git -C repos/picolibc apply "$PWD"/patches/picolibc.patch
+git -C repos/picolibc apply "$PWD"/patches/picolibc/*.patch
 mkdir build
 cd build
 cmake .. -GNinja -DFETCHCONTENT_SOURCE_DIR_LLVMPROJECT=../repos/llvm-project -DFETCHCONTENT_SOURCE_DIR_PICOLIBC=../repos/picolibc

patches/picolibc.patch renamed to patches/picolibc/0001-Enable-libcxx-builds.patch

@@ -1,8 +1,20 @@
+From 42f07bef7775a1387f9707e959f8b6782f9d6808 Mon Sep 17 00:00:00 2001
+From: Simi Pallipurath <[email protected]>
+Date: Thu, 14 Nov 2024 10:07:08 +0000
+Subject: [PATCH 1/2] [PATCH 1/2] Enable libcxx builds
+
+Modifications to build config and linker script required to enable
+libc++ builds.
+---
+ meson.build    | 12 ++++++++++++
+ picolibc.ld.in |  3 +++
+ 2 files changed, 15 insertions(+)
+
 diff --git a/meson.build b/meson.build
-index f90f5b818..2f8d63733 100644
+index 012d664bd..4161d6574 100644
 --- a/meson.build
 +++ b/meson.build
-@@ -1310,6 +1310,18 @@ if get_option('newlib-retargetable-locking') != get_option('newlib-multithread')
+@@ -1318,6 +1318,18 @@ if get_option('newlib-retargetable-locking') != get_option('newlib-multithread')
    error('newlib-retargetable-locking and newlib-multithread must be set to the same value')
  endif