Using LLVM 9.0.1 Toolset

Red Hat Developer Tools 1

Installing and using the LLVM 9.0.1 toolset

Eva-Lotte Gebhardt

Zuzana Zoubkova

Olga Tikhomirova

Supriya Takkhi

Peter Macko

Kevin Owen

Vladimir Slavik

Red Hat Developer Group Documentation Team

Abstract

LLVM is a Red Hat offering for developers on the Red Hat Enterprise Linux platform. The Using LLVM provides an overview of this product, explains how to invoke and use the LLVM versions of the tools, and links to resources with more in-depth information.

Chapter 1. LLVM

1.1. About LLVM Toolset

LLVM Toolset is a Red Hat offering for developers on the Red Hat Enterprise Linux platform. It provides the LLVM compiler infrastructure framework, the Clang compiler for the C and C++ languages, the LLDB debugger, and related tools for code analysis.

LLVM Toolset is distributed as a part of Red Hat Developer Tools for Red Hat Enterprise Linux 7 and is available as a module in Red Hat Enterprise Linux 8.

The following components are available as a part of LLVM Toolset:

Table 1.1. LLVM Components

NameVersionDescription

clang

9.0.1

An LLVM compiler front end for C and C++.

lldb

9.0.1

A C and C++ debugger using portions of LLVM.

compiler-rt

9.0.1

Runtime libraries for LLVM.

llvm

9.0.1

A collection of modular and reusable compiler and toolchain technologies.

libomp

9.0.1

A library for utilization of Open MP API specification for parallel programming.

lld

9.0.1

An LLVM linker.

python-lit

0.9.0

A software testing tool for LLVM- and Clang-based test suites.

Important

LLVM Toolset for Red Hat Enterprise Linux 7 also provides CMake as a separate package. On Red Hat Enterprise Linux 8, CMake is available in the system repository. For more information on how to install CMake, see Section 1.4, “Installing LLVM Toolset”.

1.2. Compatibility

LLVM Toolset is available for Red Hat Enterprise Linux 7 and Red Hat Enterprise Linux 8 on the following architectures:

  • The 64-bit Intel and AMD architectures
  • The 64-bit ARM architecture
  • The IBM Power Systems architecture
  • The little-endian variant of IBM Power Systems architecture
  • The IBM Z Systems architecture

1.3. Getting access to LLVM Toolset on Red Hat Enterprise Linux 7

This chapter lists the steps to perform before installing LLVM Toolset on a Red Hat Enterprise Linux 7 system. Complete the following steps to attach a subscription that provides access to the repository for Red Hat Developer Tools, and then enable the Red Hat Developer Tools and Red Hat Software Collections repositories.

Prerequisites

  • Verify that wget is installed on your system. The tool is available from the default Red Hat Enterprise Linux repositories. To install it, run the following command as root:

    # yum install wget

Procedure

  1. Get the latest subscription data from the server:

    # subscription-manager refresh
  2. Use the following command to register the system:

    # subscription-manager register

    You can also register the system by following the appropriate steps in Registering and Unregistering a System in the Red Hat Subscription Management document.

  3. Display a list of all subscriptions that are available for your system and identify the pool ID for the subscription:

    # subscription-manager list --available

    This command displays the subscription name, unique identifier, expiration date, and other details related to it. The pool ID is listed on a line beginning with Pool ID.

  4. Attach the subscription that provides access to the Red Hat Developer Tools repository. Use the pool ID you identified in the previous step.

    # subscription-manager attach --pool=<appropriate pool ID from the subscription>
  5. Verify the list of subscriptions attached to your system:

    # sudo subscription-manager list --consumed
  6. Enable the rhel-7-variant-devtools-rpms repository:

    # subscription-manager repos --enable rhel-7-variant-devtools-rpms

    Replace variant with the Red Hat Enterprise Linux system variant (server or workstation).

    Consider using Red Hat Enterprise Linux Server to access the widest range of the development tools.

  7. Enable the rhel-variant-rhscl-7-rpms repository:

    # subscription-manager repos --enable rhel-variant-rhscl-7-rpms

    Replace variant with the Red Hat Enterprise Linux system variant (server or workstation).

  8. Add the Red Hat Developer Tools GPG key to your system:

    # cd /etc/pki/rpm-gpg
    # wget -O RPM-GPG-KEY-redhat-devel https://www.redhat.com/security/data/a5787476.txt
    # rpm --import RPM-GPG-KEY-redhat-devel

Once the subscription is attached to the system and the repositories are enabled, install LLVM Toolset as described in Section 1.4, “Installing LLVM Toolset”.

Additional Resources

  • For more information on how to register your system using Red Hat Subscription Management and associate it with subscriptions, see the Red Hat Subscription Management collection of guides.

1.4. Installing LLVM Toolset

LLVM Toolset is distributed as a collection of RPM packages that can be installed, updated, uninstalled, and inspected by using the standard package management tools that are included in Red Hat Enterprise Linux.

Note that a valid subscription that provides access to the Red Hat Developer Tools content set is required in order to install LLVM Toolset on your Red Hat Enterprise Linux 7 system. For detailed instructions on how to associate your Red Hat Enterprise Linux 7 system with an appropriate subscription and get access to LLVM Toolset, see Section 1.3, “Getting access to LLVM Toolset on Red Hat Enterprise Linux 7”.

Important

Before installing LLVM Toolset, install all available Red Hat Enterprise Linux updates.

  1. Install all of the components included in LLVM Toolset for your operating system:

    • On Red Hat Enterprise Linux 7, install the llvm-toolset-9.0 collection:

      # yum install llvm-toolset-9.0
    • On Red Hat Enterprise Linux 8, install the llvm-toolset module:

      # yum module install llvm-toolset

      This installs all development and debugging tools, and other dependent packages to the system.

1.4.1. Installing CMake on Red Hat Enterprise Linux

CMake is available as a separate package. To install CMake:

On Red Hat Enterprise Linux 7, install the llvm-toolset-9.0-cmake package:

# yum install llvm-toolset-9.0-cmake llvm-toolset-9.0-cmake-doc

On Red Hat Enterprise Linux 8, install the cmake package:

# yum install cmake cmake-doc

1.4.1.1. CMake installable documentation

The cmake package contains installed documentation. On Red Hat Enterprise Linux 7, find the documentation in opt/rh/llvm-toolset-9.0/root/usr/share/doc/llvm-toolset-9.0-cmake-3.6.2/html/index.html, on Red Hat Enterprise Linux 8 in /usr/share/doc/llvm/html/index.html.

1.4.2. Installable documentation

The following section describes how to install the LLVM Toolset installable documentation.

  • On Red Hat Enterprise Linux 7, install the llvm-doc-9.0 package:
# yum install llvm-toolset-9.0-llvm-doc

The documentation is available in /opt/rh/llvm-toolset-9.0/root/usr/share/doc/llvm-toolset-9.0-llvm-9.0.1/html/index.html.

  • On Red Hat Enterprise Linux 8, install the llvm-doc package:
# yum install llvm llvm-doc

The documentation is available in /usr/share/doc/llvm/html/index.html.

The documenation for CMake is not included in the LLVM documentation package. To install the documentation for CMake, see Section 1.4.1.1, “CMake installable documentation”.

1.5. Additional Resources

A detailed description of LLVM Toolset and all its features is beyond the scope of this document. For more information, see the resources listed below.

Online documentation

Chapter 2. clang

clang is a LLVM compiler front end for C-based languages: C, C++, Objective C/C++, OpenCL, and Cuda.

LLVM Toolset is distributed with clang 9.0.1.

2.1. Using clang

Note

You can execute any command using the scl utility on Red Hat Enterprise Linux 7, causing it to be run with the LLVM binaries available. To use LLVM Toolset on Red Hat Enterprise Linux 7 without a need to use scl enable with every command, run a shell session with:

$ scl enable llvm-toolset-9.0.1 'bash'

2.1.1. Compiling a C source file to a binary file

To compile a C program to a binary file:

  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'clang -o output_file source_file'
  • For Red Hat Enterprise Linux 8:

    $ clang -o output_file source_file

This creates a binary file named output_file in the current working directory. If the -o option is omitted, the compiler creates a binary file named a.out by default.

Example 2.1. Compiling a C Program with clang

Consider a source file named hello.c with the following contents:

#include <stdio.h>

int main(int argc, char *argv[]) {
  printf("Hello, World!\n");
  return 0;
}

Compile this source code on the command line by using the clang compiler from LLVM Toolset:

  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'clang -o hello hello.c'
  • For Red Hat Enterprise Linux 8:

    $ clang -o hello hello.c

This creates a new binary file called hello in the current working directory.

2.1.2. Compiling a C source file to an object file

When you are working on a project that consists of several source files, it is common to compile an object file for each of the source files first and then link these object files together. This way, when you change a single source file, you can recompile only this file without having to compile the entire project.

To compile a C source file to an object file:

  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'clang -o object_file -c source_file'
  • For Red Hat Enterprise Linux 8:

    $ clang -o object_file -c source_file

This creates an object file named object_file. If the -o option is omitted, the compiler creates a file named after the source file with the .o file extension.

2.1.4. Using the clang Integrated Assembler

To produce an object file from an assembly language program, run the clang tool as follows:

  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'clang -o object_file source_file'
  • For Red Hat Enterprise Linux 8:

    $ clang -o object_file source_file

This creates an object file named object_file in the current working directory.

2.2. Running a C program

When clang compiles a program, it creates an executable binary file. To run this program on the command line, change to the directory with the executable file and run the program:

$ ./file_name

Example 2.2. Running a C program on the command line

Assuming that you have successfully compiled the hello binary file as shown in Example 2.1, “Compiling a C Program with clang”, you can run it by typing the following command:

$ ./hello
Hello, World!

2.3. Using clang++

Note

You can execute any command using the scl utility on Red Hat Enterprise Linux 7, causing it to be run with the LLVM binaries available. To use LLVM Toolset on Red Hat Enterprise Linux 7 without a need to use scl enable with every command, run a shell session with:

$ scl enable llvm-toolset-9.0.1 'bash'

2.3.1. Compiling a C++ Source File to a Binary File

To compile a C++ program on the command line, run the clang++ compiler as follows:

  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'clang++ -o output_file source_file ...'
  • For Red Hat Enterprise Linux 8:

    $ clang++ -o output_file source_file ...

This creates a binary file named output_file in the current working directory. If the -o option is omitted, the clang++ compiler creates a file named a.out by default.

2.3.2. Compiling a C++ source file to an object file

When you are working on a project that consists of several source files, it is common to compile an object file for each of the source files first and then link these object files together. This way, when you change a single source file, you can recompile only this file without having to compile the entire project.

To compile an object file on the command line:

  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'clang++ -o object_file -c source_file'
  • For Red Hat Enterprise Linux 8:

    $ clang++ -o object_file -c source_file

This creates an object file named object_file. If the -o option is omitted, the clang++ compiler creates a file named after the source file with the .o file extension.

2.3.3. Linking C++ object files to a binary file

To link object files together and create a binary file:

  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'clang++ -o output_file object_file ...'
  • For Red Hat Enterprise Linux 8:

    $ clang++ -o output_file object_file ...
Important

Certain more recent library features are statically linked into applications built with LLVM Toolset to support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor security risk as standard Red Hat Enterprise Linux errata do not change this code. If the need arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a security erratum.

Because of this accitional security risk, developers are strongly advised not to statically link their entire application for the same reasons.

Example 2.3. Compiling a C++ Program on the Command Line

Consider a source file named hello.cpp with the following contents:

#include <iostream>

using namespace std;

int main(int argc, char *argv[]) {
  cout << "Hello, World!" << endl;
  return 0;
}

Compile this source code on the command line by using the clang++ compiler from LLVM:

  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'clang++ -o hello hello.cpp'
  • For Red Hat Enterprise Linux 8:

    $ clang++ -o hello hello.cpp

This creates a new binary file called hello in the current working directory.

2.4. Running a C++ program

When clang++ compiles a program, it creates an executable binary file. Change to the directory with the executable file and run this program:

./file_name

Example 2.4. Running a C++ program on the command line

Assuming that you have successfully compiled the hello binary file as shown in Example 2.3, “Compiling a C++ Program on the Command Line”, you can run it by typing the following at a shell prompt:

$ ./hello
Hello, World!

2.5. Additional Resources

A detailed description of the clang compiler and its features is beyond the scope of this document. For more information, see the resources listed below.

Installed documentation

  • clang(1) — The manual page for the clang compiler provides detailed information on its usage; with few exceptions, clang++ accepts the same command line options as clang. To display the manual page for the version included in LLVM Toolset:
  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'man clang'
  • For Red Hat Enterprise Linux 8:

    $ man clang

Online documentation

  • clang — The clang compiler documentation provides detailed information about use of clang.

See Also

  • Chapter 1, LLVM — An overview of LLVM and more information on how to install it on your system.

Chapter 3. lldb

lldb is a command line tool you can use to debug programs written in C and C++. It allows you to inspect memory within the code being debugged, control the execution state of the code, detect the execution of particular sections of code, and much more.

LLVM Toolset is distributed with lldb 9.0.1.

Note

You can execute any command using the scl utility on Red Hat Enterprise Linux 7, causing it to be run with the LLVM binaries available. To use LLVM Toolset on Red Hat Enterprise Linux 7 without a need to use scl enable with every command, run a shell session with:

$ scl enable llvm-toolset-9.0.1 'bash'

3.1. Preparing a program for debugging

To compile a C or C++ program with debugging information that lldb can read, make sure the compiler you use is instructed to create debug information.

3.2. Running lldb

To run lldb on a program you want to debug:

  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'lldb program_file_name'
  • For Red Hat Enterprise Linux 8:

    $ lldb program_file_name

This command starts lldb in an interactive mode and displays the default prompt, (lldb).

To quit the debugging session and return to the shell prompt, run the following command at any time:

(lldb) quit

Example 3.1. Running the lldb Utility on the fibonacci Binary File

Consider a C source file named fibonacci.c with the following content:

#include <stdio.h>
#include <limits.h>

int main (int argc, char *argv[]) {
  unsigned long int a = 0;
  unsigned long int b = 1;
  unsigned long int sum;

  while (b < LONG_MAX) {
    printf("%ld ", b);
    sum = a + b;
    a = b;
    b = sum;
  }
  return 0;
}

Enable the debug information and compile the fibonacci.c source file with the following command:

  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'clang -g -o fibonacci fibonacci.c'
  • For Red Hat Enterprise Linux 8:

    $ clang -g -o fibonacci fibonacci.c

Refer to Section 3.1, “Preparing a program for debugging” for information about controlling debug information using GCC or clang.

Start debugging the program with lldb:

  • For Red Hat Enterprise Linux 7:

    $ scl enable llvm-toolset-9.0.1 'lldb fibonacci'
    (lldb) target create "fibonacci"
    Current executable set to 'fibonacci' (x86_64).
    (lldb)
  • For Red Hat Enterprise Linux 8:

    $ lldb fibonacci
    (lldb) target create "fibonacci"
    Current executable set to 'fibonacci' (x86_64).
    (lldb)

The output indicates that the program fibonacci is ready for debugging.

3.3. Listing the source code

To view the source code of the program you are debugging:

(lldb) list

As a result, the first ten lines of the source code are displayed.

To display the code from a particular line:

(lldb) list source_file_name:line_number

Additionally, lldb displays source code listing automatically in the following situations:

  • Before you start the execution of the program you are debugging, lldb displays the first ten lines of the source code.
  • Each time the execution of the program is stopped, lldb displays the lines that surround the line on which the execution stops.

3.4. Using breakpoints

Setting a New Breakpoint

To set a new breakpoint at a certain line:

(lldb) breakpoint source_file_name:line_number

To set a breakpoint on a certain function:

(lldb) breakpoint source_file_name:function_name

Example 3.2. Setting a new breakpoint

This example assumes that you have successfully compiled the fibonacci.c file as shown in Example 3.1, “Running the lldb Utility on the fibonacci Binary File”.

Set two breakpoints at line 10 by running the following commands:

(lldb) b 10
Breakpoint 1: where = fibonacci`main + 33 at fibonacci.c:10, address = 0x000000000040054e
(lldb)  breakpoint set -f fibonacci.c --line 10
Breakpoint 2: where = fibonacci`main + 33 at fibonacci.c:10, address = 0x000000000040054e
Note

In lldb, the command b is not an alias to breakpoint. You can use both commands to set breakpoints, but b uses a subset of the syntax supported by gdb’s break command, and breakpoint uses lldb syntax for setting breakpoints.

Listing Breakpoints

To display a list of currently set breakpoints:

(lldb) breakpoint list

Example 3.3. Listing Breakpoints

This example assumes that you have successfully followed the instructions in Example 3.2, “Setting a new breakpoint”.

Display the list of currently set breakpoints:

(lldb) breakpoint list
Current breakpoints:
1: file = 'fibonacci.c', line = 10, exact_match = 0, locations = 1
  1.1: where = fibonacci`main + 33 at fibonacci.c:10, address = fibonacci[0x000000000040054e], unresolved, hit count = 0

2: file = 'fibonacci.c', line = 10, exact_match = 0, locations = 1
  2.1: where = fibonacci`main + 33 at fibonacci.c:10, address = fibonacci[0x000000000040054e], unresolved, hit count = 0

Deleting Existing Breakpoints

To delete a breakpoint that is set at a certain line:

(lldb) breakpoint clear -f source_file_name -l line_number

Example 3.4. Deleting an Existing Breakpoint

This example assumes that you have successfully compiled the fibonacci.c file.

Set a new breakpoint at line 7:

(lldb) b 7
Breakpoint 3: where = fibonacci`main + 31 at fibonacci.c:9, address = 0x000000000040054c

Remove this breakpoint:

(lldb) breakpoint clear -l 7 -f fibonacci.c
1 breakpoints cleared:
3: file = 'fibonacci.c', line = 7, exact_match = 0, locations = 1

3.5. Starting Execution

To start an execution of the program you are debugging:

(lldb) run

If the program accepts command-line arguments, you can provide them as arguments to the run command:

(lldb) run argument

The execution stops when the first breakpoint is reached, when an error occurs, or when the program terminates.

Example 3.5. Executing the fibonacci Binary File in lldb

This example assumes that you have successfully followed the instructions in Example 3.2, “Setting a new breakpoint”.

Execute the fibonacci binary file in lldb:

(lldb) run
Process 21054 launched: 'fibonacci' (x86_64)
Process 21054 stopped
* thread #1, name = 'fibonacci', stop reason = breakpoint 1.1
    frame #0: fibonacci`main(argc=1, argv=0x00007fffffffdeb8) at fibonacci.c:10
   7      unsigned long int sum;
   8
   9      while (b < LONG_MAX) {
-> 10       printf("%ld ", b);
   11       sum = a + b;
   12       a = b;
   13       b = sum;

Execution of the program stops at the breakpoint set in Example 3.2, “Setting a new breakpoint”.

3.6. Displaying Current Program Data

The lldb tool enables you to display data relevant to the program state, including:

  • Variables of any complexity
  • Any valid expressions
  • Function call return values

The common usage is to display the value of a variable. To display the current value of a certain variable:

(lldb) print variable_name

Example 3.6. Displaying the current values of variables

This example assumes that you have successfully followed the instructions in Example 3.5, “Executing the fibonacci Binary File in lldb”. Execution of the fibonacci binary stopped after reaching the breakpoint at line 10.

Display the current values of variables a and b:

(lldb) print a
$0 = 0
(lldb) print b
$1 = 1

3.7. Continuing execution after a breakpoint

To resume the execution of the program you are debugging after it reached a breakpoint:

(lldb) continue

The execution stops again when it reaches another breakpoint.

To skip a certain number of breakpoints, typically when you are debugging a loop, run the continue command in the following form:

(lldb) continue -i number_of_breakpoints_to_skip
Note

If the breakpoint is set on a loop, in order to skip the whole loop, you will have to set the number_of_breakpoints_to_skip to match the loop iteration count.

The lldb tool enables you to execute a single line of code from the current line pointer with step:

(lldb) step

To execute a certain number of lines:

(lldb) step -c number

Example 3.7. Continuing the execution of the fibonacci binary file after a breakpoint

This example assumes that you have successfully followed the instructions in Example 3.5, “Executing the fibonacci Binary File in lldb”. The execution of the fibonacci binary stopped after reaching the breakpoint at line 10.

Resume the execution:

(lldb) continue
Process 21580 resuming
Process 21580 stopped
* thread #1, name = 'fibonacci', stop reason = breakpoint 1.1
    frame #0: fibonacci`main(argc=1, argv=0x00007fffffffdeb8) at fibonacci.c:10
   7      unsigned long int sum;
   8
   9      while (b < LONG_MAX) {
-> 10       printf("%ld ", b);
   11       sum = a + b;
   12       a = b;
   13       b = sum;

The execution stops the next time it reaches a breakpoint. In this case, it is the same breakpoint. Execute the next three lines of code:

(lldb) step -c 3
Process 21580 stopped
* thread #1, name = 'fibonacci', stop reason = step in
    frame #0: fibonacci`main(argc=1, argv=0x00007fffffffdeb8) at fibonacci.c:11
   8
   9      while (b < LONG_MAX) {
   10       printf("%ld ", b);
-> 11       sum = a + b;
   12       a = b;
   13       b = sum;
   14     }

Verify the current value of the sum variable:

(lldb) print sum
$2 = 2

3.8. Additional Resources

A detailed description of the lldb debugger and all its features is beyond the scope of this document. For more information, see the resources listed below.

Online documentation

See also

  • Chapter 1, LLVM — An overview of LLVM and more information on how to install it.

Chapter 4. Container images with LLVM Toolset

LLVM Toolset is available as container images for RHEL 7 and RHEL 8. They can be downloaded from the Red Hat Container Registry.

4.1. Image contents

The RHEL 7 and RHEL 8 container images provide content corresponding to the following packages:

ComponentVersionPackage

llvm

9.0.1

llvm-toolset-9.0.1-llvm

clang

9.0.1

llvm-toolset-9.0.1-clang

lldb

9.0.1

llvm-toolset-9.0.1-lldb

Runtime libraries

9.0.1

llvm-toolset-9.0.1-compiler-rt

OpenMP library

9.0.1

llvm-toolset-9.0.1-libomp

lld

9.0.1

llvm-toolset-9.0.1-lld

python-lit

0.9.0

llvm-toolset-9.0.1-python-lit

4.2. Accessing the images

To pull the required image, run the following command as root:

For the RHEL 7 container image:

# podman pull registry.redhat.io/devtools/llvm-toolset-rhel7

For the RHEL 8 container image:

# podman pull registry.redhat.io/rhel8/llvm-toolset

4.3. Using as builder images with Source-to-Image

LLVM Toolset container image is prepared for use as a Source-to-Image (S2I) builder image.

To be able to build and run your application:

  • Add your own assemble script to /.s2i/bin.
  • Add your own run script to /.s2i/bin.
  • Run the following command:

    $ s2i build \file://.app container-image container-image-application name.

Example 4.1. Building an LLVM application image using Source-to-Image

To build the hello-world application:

$ git clone https://github.com/sclorg/llvm-container
s2i build llvm-container/7/test/hello-world/app/ devtools/llvm-toolset-rhel7 llvm-hello-world

A locally available application image hello-world is built from the repository on GitHub using the llvm-toolset container image.

To fully leverage the LLVM as a S2I builder image, build custom images based on it, with modified S2I assemble scripts and further modifications to accomodate the particular application being built.

A detailed description of the LLVM usage with Source-to-Image is beyond the scope of this document. For more information about Source-to-Image, see:

4.4. Additional resources

Chapter 5. Changes in LLVM 9.0.1 Toolset

LLVM Toolset has been updated from version 8.0.1 to 9.0.1.

With this update, the asm goto statements are now supported. This change allows to compile the Linux kernel on the AMD64 and Intel 64 architectures.

For more information, see the upstream LLVM 9.0.0 Release Notes.

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