[bazel] Switch lowRISC toolchain from CRT to local version

This removes the dependency on CRT and registers the new rules-based
toolchain instead.

Since `guards` is now enabled by default and `pedantic` is now disabled
by default, we can remove those configurations from `.bazelrc`. The
configuration to disable `guards` is still present.

Without CRT, we also don't need to manually load the following repos
into the airgapped environment:

* `@python3_toolchains`
* `@ninja_1.11.0_linux`
* `@cmake-3.23.2-linux-x86_64`

Signed-off-by: James Wainwright <james.wainwright@lowrisc.org>

Author: jwnrt

.bazelrc

@@ -14,16 +14,6 @@ build --conlyopt='-std=gnu11'
 # disassemblies when compilation mode is fastbuild.
 build --strip='never'
 
-# Override default enablement of flags from @crt//common to control C compiler
-# warnings.
-build --features=-pedantic_warnings
-build --host_features=-pedantic_warnings
-
-# Enable toolchain hardening features.
-# `guards` adds `unimp` guard instructions after unconditional jumps.
-build --features=guards
-build --host_features=guards
-
 # Use --config=disable_hardening to disable hardening to measure the
 # impact of the hardened sequences on code size.
 build:disable_hardening --features=-guards --copt=-DOT_DISABLE_HARDENING=1

MODULE.bazel

@@ -143,3 +143,5 @@ use_repo(
 )
 
 register_toolchains("//rules/opentitan:localtools")
+
+register_toolchains("//third_party/lowrisc:cc_toolchain_opentitan")

WORKSPACE.bzlmod

@@ -6,14 +6,3 @@
 # //third_party/README.md first.
 
 workspace(name = "lowrisc_opentitan")
-
-# CRT is the Compiler Repository Toolkit.  It contains the configuration for
-# the windows compiler.
-load("//third_party/crt:repos.bzl", "crt_repos")
-crt_repos()
-load("@crt//:repos.bzl", "crt_repos")
-crt_repos()
-load("@crt//:deps.bzl", "crt_deps")
-crt_deps()
-load("@crt//config:registration.bzl", "crt_register_toolchains")
-crt_register_toolchains(riscv32 = True)

rules/rv.bzl

@@ -5,7 +5,7 @@
 """Helpers for transitioning to the RISC-V target."""
 
 OPENTITAN_CPU = "@platforms//cpu:riscv32"
-OPENTITAN_PLATFORM = "@crt//platforms/riscv32:opentitan"
+OPENTITAN_PLATFORM = "//third_party/lowrisc:opentitan_platform"
 
 # This constant holds a dictionary of per-device dependencies which are used to
 # generate slightly different binaries for each hardware target, including two

util/prep-bazel-airgapped-build.sh

@@ -143,11 +143,8 @@ if [[ ${AIRGAPPED_DIR_CONTENTS} == "ALL" || \
     //... \
     @lowrisc_toolchain//... \
     @local_config_platform//... \
-    @python3_toolchains//... \
     @riscv-compliance//... \
     @rules_foreign_cc//toolchains/... \
-    @ninja_1.11.0_linux//... \
-    @cmake-3.23.2-linux-x86_64//... \
   # We don't need all bitstreams in the cache, we just need the latest one so
   # that the cache is "initialized" and "offline" mode will work correctly.
   mkdir -p ${BAZEL_AIRGAPPED_DIR}/${BAZEL_BITSTREAMS_CACHEDIR}