[imm_rom_ext] Add hello world IM_EXT

* Add minimized C code, startup asm and linker script for a standalone
  IM_EXT build target.
* Add a bazel rule `imm_rom_ext_section`, which will transform binaries
  into object files and turn it to a target that can be directly used as
  deps of ROM_EXT's bazel targets.
* Add a map for all IM_EXT target that can be used and make the ROM_EXT
  targets iterate the map to generate multiple targets.
* Update the ROM_EXT to use in e2e verified boot test.

Test: String `Immutable` appears in the UART output of the test target
`verified_boot:position_romext_virtual_a_with_hello_world_imm_romext_enabled_fpga_cw340_rom_ext`:
```
OpenTitan:4001-0002-01
ROM:0a7a997f
bootstrap:1
OpenTitan:4001-0002-01
ROM:0a7a997f
Immutable
Starting ROM_EXT 0.1
```

Signed-off-by: Chia-Wei Liu <[email protected]>

sw/device/silicon_creator/imm_rom_ext/BUILD

@@ -2,10 +2,58 @@
 # Licensed under the Apache License, Version 2.0, see LICENSE for details.
 # SPDX-License-Identifier: Apache-2.0
 
+load("@lowrisc_opentitan//rules/opentitan:transform.bzl", "obj_transform")
+load("//rules/opentitan:defs.bzl", "OPENTITAN_CPU", "opentitan_binary")
+load("//rules:linker.bzl", "ld_library")
+load("//sw/device/silicon_creator/imm_rom_ext:utils.bzl", "imm_rom_ext_section")
+
 package(default_visibility = ["//visibility:public"])
 
 cc_library(
     name = "main_lib",
     srcs = ["imm_rom_ext.c"],
     hdrs = ["imm_rom_ext.h"],
 )
+
+ld_library(
+    name = "ld_hello_world",
+    script = "hello_world.ld",
+    deps = [
+        "//hw/top_earlgrey/sw/autogen:top_earlgrey_memory",
+        "//sw/device:info_sections",
+    ],
+)
+
+cc_library(
+    name = "hello_world",
+    srcs = [
+        "hello_world.c",
+        "hello_world_start.S",
+    ],
+    hdrs = ["hello_world.h"],
+    target_compatible_with = [OPENTITAN_CPU],
+    deps = [
+        "//sw/device/silicon_creator/lib/drivers:uart",
+    ],
+)
+
+opentitan_binary(
+    name = "hello_world_binaries",
+    # TODO(#22780): Integrate real keys for A1 flows.
+    # TODO(#24368): Support multiple executing environments. Currently all
+    # environments derive the same binary so only one environment is kept here,
+    # but we need to support multiple executing environments and make sure
+    # ROM_EXT targets choose the matched environment when linking IMM_ROM_EXT. 
+    exec_env = [
+        "//hw/top_earlgrey:fpga_cw340",
+    ],
+    linker_script = ":ld_hello_world",
+    deps = [
+        ":hello_world",
+    ],
+)
+
+imm_rom_ext_section(
+    name = "hello_world_section",
+    srcs = [":hello_world_binaries"],
+)

sw/device/silicon_creator/imm_rom_ext/defs.bzl

@@ -0,0 +1,9 @@
+# Copyright lowRISC contributors (OpenTitan project).
+# Licensed under the Apache License, Version 2.0, see LICENSE for details.
+# SPDX-License-Identifier: Apache-2.0
+
+# The target list should contian prebuilt artifacts and run-time build targets.
+IMM_ROM_EXT_TARGETS = {
+    "nop": "//sw/device/silicon_creator/imm_rom_ext/prebuilts:nop_imm_rom_ext",
+    "hello_world": "//sw/device/silicon_creator/imm_rom_ext:hello_world_section",
+}

sw/device/silicon_creator/imm_rom_ext/hello_world.c

@@ -0,0 +1,25 @@
+// Copyright lowRISC contributors (OpenTitan project).
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+#include "sw/device/silicon_creator/imm_rom_ext/hello_world.h"
+
+#include "sw/device/silicon_creator/lib/drivers/uart.h"
+
+void imm_rom_ext_main(void) {
+  // Print "Immutable" to the UART console.
+  //                        l b a t u m m I
+  const uint64_t kStr1 = 0x6c626174756d6d49;
+  //                        e
+  const uint32_t kStr2 = 0x65;
+  const uint32_t kNewline = 0x0a0d;
+  uart_write_imm(kStr1);
+  uart_write_imm(kStr2);
+  uart_write_imm(kNewline);
+
+  // Wait until the UART is done transmitting.
+  while (!uart_tx_idle()) {
+  }
+
+  return;
+}

sw/device/silicon_creator/imm_rom_ext/hello_world.h

@@ -0,0 +1,18 @@
+// Copyright lowRISC contributors (OpenTitan project).
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+#ifndef OPENTITAN_SW_DEVICE_SILICON_CREATOR_IMM_ROM_EXT_HELLO_WORLD_H_
+#define OPENTITAN_SW_DEVICE_SILICON_CREATOR_IMM_ROM_EXT_HELLO_WORLD_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void imm_rom_ext_main(void);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // OPENTITAN_SW_DEVICE_SILICON_CREATOR_IMM_ROM_EXT_HELLO_WORLD_H_

sw/device/silicon_creator/imm_rom_ext/hello_world.ld

@@ -0,0 +1,46 @@
+/* Copyright lowRISC contributors (OpenTitan project). */
+/* Licensed under the Apache License, Version 2.0, see LICENSE for details. */
+/* SPDX-License-Identifier: Apache-2.0 */
+
+/**
+ * TODO(#24368): Adapt the linker script for real IMM_ROM_EXT. This linker
+ * script only works for hello-world IMM_ROM_EXT.
+ */
+OUTPUT_ARCH(riscv)
+
+/**
+ * Indicate that there are no dynamic libraries, whatsoever.
+ */
+__DYNAMIC = 0;
+
+/* DV Log offset (has to be different to other boot stages). */
+_dv_log_offset = 0x10000;
+
+ENTRY(_imm_rom_ext_start_boot)
+
+SECTIONS {
+  .rom_ext_immutable : ALIGN(4) {
+    /* Ibex */
+    *(.vectors)
+    . = ALIGN(256);
+    /* CRT */
+    *(.crt)
+    . = ALIGN(4);
+    /* Text */
+    *(.text)
+    *(.text.*)
+    . = ALIGN(4);
+    /* Read-only Data */
+    *(.srodata)
+    *(.srodata.*)
+    *(.rodata)
+    *(.rodata.*)
+    . = ALIGN(4);
+    *(.data)
+    . = ALIGN(4);
+    *(.bss)
+    . = ALIGN(4);
+  }
+
+  INCLUDE sw/device/info_sections.ld
+}

sw/device/silicon_creator/imm_rom_ext/hello_world_start.S

@@ -0,0 +1,14 @@
+// Copyright lowRISC contributors (OpenTitan project).
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+// TODO(#24368): Adapt the startup assembly for real IMM_ROM_EXT. This startup
+// assembly only works for hello-world IMM_ROM_EXT.
+#include "hw/top_earlgrey/sw/autogen/top_earlgrey_memory.h"
+
+  .balign 4
+  .global _imm_rom_ext_start_boot
+  .type _imm_rom_ext_start_boot, @function
+_imm_rom_ext_start_boot:
+  tail imm_rom_ext_main
+  .size _imm_rom_ext_start_boot, .-_imm_rom_ext_start_boot

sw/device/silicon_creator/imm_rom_ext/utils.bzl

@@ -0,0 +1,55 @@
+# Copyright lowRISC contributors (OpenTitan project).
+# Licensed under the Apache License, Version 2.0, see LICENSE for details.
+# SPDX-License-Identifier: Apache-2.0
+
+load("@rules_cc//cc:find_cc_toolchain.bzl", "find_cc_toolchain")
+load("@lowrisc_opentitan//rules:rv.bzl", "rv_rule")
+
+def _bin_to_imm_rom_ext_object_impl(ctx):
+    cc_toolchain = find_cc_toolchain(ctx)
+    outputs = []
+    for src in ctx.files.srcs:
+        if src.extension != "bin":
+            continue
+        object = ctx.actions.declare_file(
+            "{}.{}".format(
+                src.basename.replace("." + src.extension, ""),
+                "o",
+            ),
+        )
+        ctx.actions.run(
+            outputs = [object],
+            inputs = [src] + cc_toolchain.all_files.to_list(),
+            arguments = [
+                "-I",
+                "binary",
+                "-O",
+                "elf32-littleriscv",
+                "--rename-section",
+                ".data=.rom_ext_immutable,alloc,load,readonly,data,contents",
+                src.path,
+                object.path,
+            ],
+            executable = cc_toolchain.objcopy_executable,
+        )
+        outputs.append(object)
+    return [DefaultInfo(files = depset(outputs), runfiles = ctx.runfiles(files = outputs))]
+
+bin_to_imm_rom_ext_object = rv_rule(
+    implementation = _bin_to_imm_rom_ext_object_impl,
+    attrs = {
+        "srcs": attr.label_list(allow_files = True),
+        "_cc_toolchain": attr.label(default = Label("@bazel_tools//tools/cpp:current_cc_toolchain")),
+    },
+    toolchains = ["@rules_cc//cc:toolchain_type"],
+)
+
+def imm_rom_ext_section(name, srcs):
+    object_target_name = name + "_object"
+    bin_to_imm_rom_ext_object(name = object_target_name, srcs = srcs)
+    native.cc_import(
+        name = name,
+        objects = [object_target_name],
+        data = [object_target_name],
+        alwayslink = 1,
+    )

sw/device/silicon_creator/rom_ext/BUILD

@@ -12,6 +12,10 @@ load(
     "//sw/device/silicon_creator/rom_ext:defs.bzl",
     "ROM_EXT_VERSION",
 )
+load(
+    "//sw/device/silicon_creator/imm_rom_ext:defs.bzl",
+    "IMM_ROM_EXT_TARGETS",
+)
 
 package(default_visibility = ["//visibility:public"])
 
@@ -327,29 +331,33 @@ opentitan_binary(
     ],
 )
 
-opentitan_binary(
-    name = "rom_ext_with_nop_imm_slot_virtual",
-    testonly = True,
-    # TODO(#22780): Integrate real keys for A1 flows.
-    ecdsa_key = {"//sw/device/silicon_creator/rom/keys/fake/ecdsa:prod_key_0_ecdsa_p256": "prod_key_0"},
-    exec_env = [
-        "//hw/top_earlgrey:fpga_cw310",
-        "//hw/top_earlgrey:fpga_cw340",
-        "//hw/top_earlgrey:sim_dv_base",
-        "//hw/top_earlgrey:sim_verilator_base",
-        "//hw/top_earlgrey:silicon_creator",
-    ],
-    linker_script = ":ld_slot_virtual",
-    manifest = ":manifest",
-    deps = [
-        ":rom_ext",
-        "//sw/device/lib/crt",
-        "//sw/device/silicon_creator/imm_rom_ext/prebuilts:nop_imm_rom_ext",
-        "//sw/device/silicon_creator/lib:manifest_def",
-        "//sw/device/silicon_creator/lib/ownership:test_owner",
-        "//sw/device/silicon_creator/lib/ownership/keys/fake",
-    ],
-)
+[
+    opentitan_binary(
+        name = "rom_ext_with_{}_imm_slot_virtual".format(name),
+        testonly = True,
+        # TODO(#22780): Integrate real keys for A1 flows.
+        ecdsa_key = {"//sw/device/silicon_creator/rom/keys/fake/ecdsa:prod_key_0_ecdsa_p256": "prod_key_0"},
+        exec_env = [
+            "//hw/top_earlgrey:fpga_cw310",
+            "//hw/top_earlgrey:fpga_cw340",
+            "//hw/top_earlgrey:sim_dv_base",
+            "//hw/top_earlgrey:sim_verilator_base",
+            "//hw/top_earlgrey:silicon_creator",
+        ],
+        linker_script = ":ld_slot_virtual",
+        manifest = ":manifest",
+        deps = [
+            ":rom_ext",
+            "//sw/device/lib/crt",
+            "//sw/device/silicon_creator/lib:manifest_def",
+            "//sw/device/silicon_creator/lib/ownership:test_owner",
+            "//sw/device/silicon_creator/lib/ownership/keys/fake",
+        ] + [
+            imm_rom_ext_target,
+        ],
+    )
+    for name, imm_rom_ext_target in IMM_ROM_EXT_TARGETS.items()
+]
 
 manifest(d = {
     "name": "manifest_bad_address_translation",