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Introduce a utility for reading boot images #2095

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1 change: 1 addition & 0 deletions base/cvd/cuttlefish/host/commands/assemble_cvd/BUILD.bazel
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Original file line number Diff line number Diff line change
Expand Up @@ -109,6 +109,7 @@ cf_cc_library(
"//cuttlefish/common/libs/utils:files",
"//cuttlefish/common/libs/utils:subprocess",
"//cuttlefish/common/libs/utils:subprocess_managed_stdio",
"//cuttlefish/host/commands/assemble_cvd/boot_image",
"//cuttlefish/host/commands/assemble_cvd/disk:generate_persistent_bootconfig",
"//cuttlefish/host/libs/avb",
"//cuttlefish/host/libs/config:config_utils",
Expand Down
17 changes: 17 additions & 0 deletions base/cvd/cuttlefish/host/commands/assemble_cvd/boot_image/BUILD.bazel
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@@ -0,0 +1,17 @@
load("//cuttlefish/bazel:rules.bzl", "cf_cc_library")

package(
default_visibility = ["//:android_cuttlefish"],
)

cf_cc_library(
name = "boot_image",
srcs = ["boot_image.cc"],
hdrs = ["boot_image.h"],
deps = [
"//cuttlefish/common/libs/fs",
"//cuttlefish/result",
"@abseil-cpp//absl/strings",
"@mkbootimg//:bootimg_header",
],
)
99 changes: 99 additions & 0 deletions base/cvd/cuttlefish/host/commands/assemble_cvd/boot_image/boot_image.cc
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@@ -0,0 +1,99 @@
//
// Copyright (C) 2026 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "cuttlefish/host/commands/assemble_cvd/boot_image/boot_image.h"

#include <stdint.h>

#include <string>
#include <string_view>
#include <variant>

#include "absl/strings/str_cat.h"
#include "bootimg.h"

#include "cuttlefish/common/libs/fs/shared_buf.h"
#include "cuttlefish/common/libs/fs/shared_fd.h"
#include "cuttlefish/result/result.h"

namespace cuttlefish {

// https://source.android.com/docs/core/architecture/bootloader/boot-image-header

Result<BootImage> BootImage::Read(std::string_view path) {
const SharedFD fd = SharedFD::Open(std::string(path), O_RDONLY);
CF_EXPECTF(fd->IsOpen(), "Failed to open '{}': '{}'", path, fd->StrError());

std::string magic(BOOT_MAGIC_SIZE, ' ');
CF_EXPECT_EQ(ReadExact(fd, &magic), BOOT_MAGIC_SIZE, fd->StrError());
CF_EXPECT_EQ(magic, BOOT_MAGIC);

const off_t version_off = BOOT_MAGIC_SIZE + (sizeof(uint32_t) * 8);
CF_EXPECT_EQ(fd->LSeek(version_off, SEEK_SET), version_off, fd->StrError());
uint32_t version;
CF_EXPECT_EQ(ReadExactBinary(fd, &version), sizeof(version), fd->StrError());

CF_EXPECT_EQ(fd->LSeek(SEEK_SET, 0), 0, fd->StrError());

switch (version) {
case 0: {
boot_img_hdr_v0 v0;
CF_EXPECT_EQ(ReadExactBinary(fd, &v0), sizeof(v0), fd->StrError());
return BootImage(fd, v0);
}
case 1: {
boot_img_hdr_v1 v1;
CF_EXPECT_EQ(ReadExactBinary(fd, &v1), sizeof(v1), fd->StrError());
return BootImage(fd, v1);
}
case 2: {
boot_img_hdr_v2 v2;
CF_EXPECT_EQ(ReadExactBinary(fd, &v2), sizeof(v2), fd->StrError());
return BootImage(fd, v2);
}
case 3: {
boot_img_hdr_v3 v3;
CF_EXPECT_EQ(ReadExactBinary(fd, &v3), sizeof(v3), fd->StrError());
return BootImage(fd, v3);
}
case 4: {
boot_img_hdr_v4 v4;
CF_EXPECT_EQ(ReadExactBinary(fd, &v4), sizeof(v4), fd->StrError());
return BootImage(fd, v4);
}
default:
return CF_ERRF("Unknown header version {}", version);
}
}

BootImage::BootImage(SharedFD fd, HeaderVariant header)
: fd_(fd), header_(header) {}

static std::string KernelCommandLineImpl(const boot_img_hdr_v0& v0) {
const char* cmdline = reinterpret_cast<const char*>(v0.cmdline);
const char* extra_cmdline(reinterpret_cast<const char*>(v0.extra_cmdline));
return absl::StrCat(cmdline, extra_cmdline);
}

static std::string KernelCommandLineImpl(const boot_img_hdr_v3& v3) {
return std::string(reinterpret_cast<const char*>(v3.cmdline));
}

std::string BootImage::KernelCommandLine() const {
auto visitor = [](const auto& hdr) { return KernelCommandLineImpl(hdr); };
return std::visit(visitor, header_);
}

} // namespace cuttlefish
45 changes: 45 additions & 0 deletions base/cvd/cuttlefish/host/commands/assemble_cvd/boot_image/boot_image.h
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@@ -0,0 +1,45 @@
//
// Copyright (C) 2026 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#pragma once

#include <string_view>
#include <variant>

#include "bootimg.h"

#include "cuttlefish/common/libs/fs/shared_fd.h"
#include "cuttlefish/result/result.h"

namespace cuttlefish {

class BootImage {
public:
static Result<BootImage> Read(std::string_view path);

std::string KernelCommandLine() const;

private:
using HeaderVariant =
std::variant<boot_img_hdr_v0, boot_img_hdr_v1, boot_img_hdr_v2,
boot_img_hdr_v3, boot_img_hdr_v4>;

BootImage(SharedFD, HeaderVariant);

SharedFD fd_;
HeaderVariant header_;
};

} // namespace cuttlefish
7 changes: 4 additions & 3 deletions base/cvd/cuttlefish/host/commands/assemble_cvd/boot_image_utils.cc
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Expand Up @@ -33,6 +33,7 @@
#include "cuttlefish/common/libs/utils/files.h"
#include "cuttlefish/common/libs/utils/subprocess.h"
#include "cuttlefish/common/libs/utils/subprocess_managed_stdio.h"
#include "cuttlefish/host/commands/assemble_cvd/boot_image/boot_image.h"
#include "cuttlefish/host/libs/avb/avb.h"
#include "cuttlefish/host/libs/config/config_utils.h"
#include "cuttlefish/host/libs/config/known_paths.h"
Expand Down Expand Up @@ -275,10 +276,10 @@ Result<void> RepackBootImage(const Avb& avb,
const std::string& boot_image_path,
const std::string& new_boot_image_path,
const std::string& build_dir) {
std::string boot_params =
CF_EXPECT(UnpackBootImage(boot_image_path, build_dir));
CF_EXPECT(UnpackBootImage(boot_image_path, build_dir));

auto kernel_cmdline = ExtractValue(boot_params, "command line args: ");
BootImage boot_image = CF_EXPECT(BootImage::Read(boot_image_path));
std::string kernel_cmdline = boot_image.KernelCommandLine();
VLOG(0) << "Cmdline from boot image is " << kernel_cmdline;

auto tmp_boot_image_path = new_boot_image_path + TMP_EXTENSION;
Expand Down
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