This document is the reference manual for the LLVM testing infrastructure. It documents the structure of the LLVM testing infrastructure, the tools needed to use it, and how to add and run tests.
In order to use the LLVM testing infrastructure, you will need all of the software required to build LLVM, as well as Python 2.4 or later.
The LLVM testing infrastructure contains two major categories of tests: regression tests and whole programs. The regression tests are contained inside the LLVM repository itself under llvm/test and are expected to always pass -- they should be run before every commit. The whole programs tests are referred to as the "LLVM test suite" and are in the test-suite module in subversion.
The regression tests are small pieces of code that test a specific feature of LLVM or trigger a specific bug in LLVM. They are usually written in LLVM assembly language, but can be written in other languages if the test targets a particular language front end (and the appropriate --with-llvmgcc options were used at configure time of the llvm module). These tests are driven by the 'lit' testing tool, which is part of LLVM.
These code fragments are not complete programs. The code generated from them is never executed to determine correct behavior.
These code fragment tests are located in the llvm/test directory.
Typically when a bug is found in LLVM, a regression test containing just enough code to reproduce the problem should be written and placed somewhere underneath this directory. In most cases, this will be a small piece of LLVM assembly language code, often distilled from an actual application or benchmark.
The test suite contains whole programs, which are pieces of code which can be compiled and linked into a stand-alone program that can be executed. These programs are generally written in high level languages such as C or C++, but sometimes they are written straight in LLVM assembly.
These programs are compiled and then executed using several different methods (native compiler, LLVM C backend, LLVM JIT, LLVM native code generation, etc). The output of these programs is compared to ensure that LLVM is compiling the program correctly.
In addition to compiling and executing programs, whole program tests serve as a way of benchmarking LLVM performance, both in terms of the efficiency of the programs generated as well as the speed with which LLVM compiles, optimizes, and generates code.
The test-suite is located in the test-suite Subversion module.
The test suite contains tests to check quality of debugging information. The test are written in C based languages or in LLVM assembly language.
These tests are compiled and run under a debugger. The debugger output is checked to validate of debugging information. See README.txt in the test suite for more information . This test suite is located in the debuginfo-tests Subversion module.
The tests are located in two separate Subversion modules. The regressions tests are in the main "llvm" module under the directory llvm/test (so you get these tests for free with the main llvm tree). The more comprehensive test suite that includes whole programs in C and C++ is in the test-suite module. This module should be checked out to the llvm/projects directory (don't use another name than the default "test-suite", for then the test suite will be run every time you run make in the main llvm directory). When you configure the llvm module, the test-suite directory will be automatically configured. Alternatively, you can configure the test-suite module manually.
To run all of the LLVM regression tests, use master Makefile in the llvm/test directory:
% gmake -C llvm/test
or
% gmake check
If you have Clang checked out and built, you can run the LLVM and Clang tests simultaneously using:
or
% gmake check-all
To run the tests with Valgrind (Memcheck by default), just append VG=1 to the commands above, e.g.:
% gmake check VG=1
To run individual tests or subsets of tests, you can use the 'llvm-lit' script which is built as part of LLVM. For example, to run the 'Integer/BitCast.ll' test by itself you can run:
% llvm-lit ~/llvm/test/Integer/BitCast.ll
or to run all of the ARM CodeGen tests:
% llvm-lit ~/llvm/test/CodeGen/ARM
For more information on using the 'lit' tool, see 'llvm-lit --help' or the 'lit' man page.
To run the comprehensive test suite (tests that compile and execute whole programs), first checkout and setup the test-suite module:
% cd llvm/projects % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite % cd .. % ./configure --with-llvmgccdir=$LLVM_GCC_DIR
where $LLVM_GCC_DIR is the directory where you installed llvm-gcc, not its src or obj dir. The --with-llvmgccdir option assumes that the llvm-gcc-4.2 module was configured with --program-prefix=llvm-, and therefore that the C and C++ compiler drivers are called llvm-gcc and llvm-g++ respectively. If this is not the case, use --with-llvmgcc/--with-llvmgxx to specify each executable's location.
Then, run the entire test suite by running make in the test-suite directory:
% cd projects/test-suite % gmake
Usually, running the "nightly" set of tests is a good idea, and you can also let it generate a report by running:
% cd projects/test-suite % gmake TEST=nightly report report.html
Any of the above commands can also be run in a subdirectory of projects/test-suite to run the specified test only on the programs in that subdirectory.
To run debugging information tests simply checkout the tests inside clang/test directory.
%cd clang/test % svn co http://llvm.org/svn/llvm-project/debuginfo-tests/trunk debuginfo-tests
These tests are already set up to run as part of clang regression tests.
The LLVM regression tests are driven by 'lit' and are located in the llvm/test directory.
This directory contains a large array of small tests that exercise various features of LLVM and to ensure that regressions do not occur. The directory is broken into several sub-directories, each focused on a particular area of LLVM. A few of the important ones are:
The regression test structure is very simple, but does require some information to be set. This information is gathered via configure and is written to a file, lit.site.cfg in llvm/test. The llvm/test Makefile does this work for you.
In order for the regression tests to work, each directory of tests must have a dg.exp file. Lit looks for this file to determine how to run the tests. This file is just a Tcl script and it can do anything you want, but we've standardized it for the LLVM regression tests. If you're adding a directory of tests, just copy dg.exp from another directory to get running. The standard dg.exp simply loads a Tcl library (test/lib/llvm.exp) and calls the llvm_runtests function defined in that library with a list of file names to run. The names are obtained by using Tcl's glob command. Any directory that contains only directories does not need the dg.exp file.
The llvm-runtests function lookas at each file that is passed to it and gathers any lines together that match "RUN:". This are the "RUN" lines that specify how the test is to be run. So, each test script must contain RUN lines if it is to do anything. If there are no RUN lines, the llvm-runtests function will issue an error and the test will fail.
RUN lines are specified in the comments of the test program using the keyword RUN followed by a colon, and lastly the command (pipeline) to execute. Together, these lines form the "script" that llvm-runtests executes to run the test case. The syntax of the RUN lines is similar to a shell's syntax for pipelines including I/O redirection and variable substitution. However, even though these lines may look like a shell script, they are not. RUN lines are interpreted directly by the Tcl exec command. They are never executed by a shell. Consequently the syntax differs from normal shell script syntax in a few ways. You can specify as many RUN lines as needed.
lit performs substitution on each RUN line to replace LLVM tool names with the full paths to the executable built for each tool (in $(LLVM_OBJ_ROOT)/$(BuildMode)/bin). This ensures that lit does not invoke any stray LLVM tools in the user's path during testing.
Each RUN line is executed on its own, distinct from other lines unless its last character is \. This continuation character causes the RUN line to be concatenated with the next one. In this way you can build up long pipelines of commands without making huge line lengths. The lines ending in \ are concatenated until a RUN line that doesn't end in \ is found. This concatenated set of RUN lines then constitutes one execution. Tcl will substitute variables and arrange for the pipeline to be executed. If any process in the pipeline fails, the entire line (and test case) fails too.
Below is an example of legal RUN lines in a .ll file:
; RUN: llvm-as < %s | llvm-dis > %t1 ; RUN: llvm-dis < %s.bc-13 > %t2 ; RUN: diff %t1 %t2
As with a Unix shell, the RUN: lines permit pipelines and I/O redirection to be used. However, the usage is slightly different than for Bash. To check what's legal, see the documentation for the Tcl exec command and the tutorial. The major differences are:
There are some quoting rules that you must pay attention to when writing your RUN lines. In general nothing needs to be quoted. Tcl won't strip off any quote characters so they will get passed to the invoked program. For example:
... | grep 'find this string'
This will fail because the ' characters are passed to grep. This would instruction grep to look for 'find in the files this and string'. To avoid this use curly braces to tell Tcl that it should treat everything enclosed as one value. So our example would become:
... | grep {find this string}
Additionally, the characters [ and ] are treated specially by Tcl. They tell Tcl to interpret the content as a command to execute. Since these characters are often used in regular expressions this can have disastrous results and cause the entire test run in a directory to fail. For example, a common idiom is to look for some basicblock number:
... | grep bb[2-8]
This, however, will cause Tcl to fail because its going to try to execute a program named "2-8". Instead, what you want is this:
... | grep {bb\[2-8\]}
Finally, if you need to pass the \ character down to a program, then it must be doubled. This is another Tcl special character. So, suppose you had:
... | grep 'i32\*'
This will fail to match what you want (a pointer to i32). First, the ' do not get stripped off. Second, the \ gets stripped off by Tcl so what grep sees is: 'i32*'. That's not likely to match anything. To resolve this you must use \\ and the {}, like this:
... | grep {i32\\*}
If your system includes GNU grep, make sure that GREP_OPTIONS is not set in your environment. Otherwise, you may get invalid results (both false positives and false negatives).
A powerful feature of the RUN: lines is that it allows any arbitrary commands to be executed as part of the test harness. While standard (portable) unix tools like 'grep' work fine on run lines, as you see above, there are a lot of caveats due to interaction with Tcl syntax, and we want to make sure the run lines are portable to a wide range of systems. Another major problem is that grep is not very good at checking to verify that the output of a tools contains a series of different output in a specific order. The FileCheck tool was designed to help with these problems.
FileCheck (whose basic command line arguments are described in the FileCheck man page is designed to read a file to check from standard input, and the set of things to verify from a file specified as a command line argument. A simple example of using FileCheck from a RUN line looks like this:
; RUN: llvm-as < %s | llc -march=x86-64 | FileCheck %s
This syntax says to pipe the current file ("%s") into llvm-as, pipe that into llc, then pipe the output of llc into FileCheck. This means that FileCheck will be verifying its standard input (the llc output) against the filename argument specified (the original .ll file specified by "%s"). To see how this works, lets look at the rest of the .ll file (after the RUN line):
define void @sub1(i32* %p, i32 %v) {
entry:
; CHECK: sub1:
; CHECK: subl
%0 = tail call i32 @llvm.atomic.load.sub.i32.p0i32(i32* %p, i32 %v)
ret void
}
define void @inc4(i64* %p) {
entry:
; CHECK: inc4:
; CHECK: incq
%0 = tail call i64 @llvm.atomic.load.add.i64.p0i64(i64* %p, i64 1)
ret void
}
Here you can see some "CHECK:" lines specified in comments. Now you can see how the file is piped into llvm-as, then llc, and the machine code output is what we are verifying. FileCheck checks the machine code output to verify that it matches what the "CHECK:" lines specify.
The syntax of the CHECK: lines is very simple: they are fixed strings that must occur in order. FileCheck defaults to ignoring horizontal whitespace differences (e.g. a space is allowed to match a tab) but otherwise, the contents of the CHECK: line is required to match some thing in the test file exactly.
One nice thing about FileCheck (compared to grep) is that it allows merging test cases together into logical groups. For example, because the test above is checking for the "sub1:" and "inc4:" labels, it will not match unless there is a "subl" in between those labels. If it existed somewhere else in the file, that would not count: "grep subl" matches if subl exists anywhere in the file.
The FileCheck -check-prefix option allows multiple test configurations to be driven from one .ll file. This is useful in many circumstances, for example, testing different architectural variants with llc. Here's a simple example:
; RUN: llvm-as < %s | llc -mtriple=i686-apple-darwin9 -mattr=sse41 \
; RUN: | FileCheck %s -check-prefix=X32
; RUN: llvm-as < %s | llc -mtriple=x86_64-apple-darwin9 -mattr=sse41 \
; RUN: | FileCheck %s -check-prefix=X64
define <4 x i32> @pinsrd_1(i32 %s, <4 x i32> %tmp) nounwind {
%tmp1 = insertelement <4 x i32> %tmp, i32 %s, i32 1
ret <4 x i32> %tmp1
; X32: pinsrd_1:
; X32: pinsrd $1, 4(%esp), %xmm0
; X64: pinsrd_1:
; X64: pinsrd $1, %edi, %xmm0
}
In this case, we're testing that we get the expected code generation with both 32-bit and 64-bit code generation.
Sometimes you want to match lines and would like to verify that matches happen on exactly consequtive lines with no other lines in between them. In this case, you can use CHECK: and CHECK-NEXT: directives to specify this. If you specified a custom check prefix, just use "<PREFIX>-NEXT:". For example, something like this works as you'd expect:
define void @t2(<2 x double>* %r, <2 x double>* %A, double %B) {
%tmp3 = load <2 x double>* %A, align 16
%tmp7 = insertelement <2 x double> undef, double %B, i32 0
%tmp9 = shufflevector <2 x double> %tmp3,
<2 x double> %tmp7,
<2 x i32> < i32 0, i32 2 >
store <2 x double> %tmp9, <2 x double>* %r, align 16
ret void
; CHECK: t2:
; CHECK: movl 8(%esp), %eax
; CHECK-NEXT: movapd (%eax), %xmm0
; CHECK-NEXT: movhpd 12(%esp), %xmm0
; CHECK-NEXT: movl 4(%esp), %eax
; CHECK-NEXT: movapd %xmm0, (%eax)
; CHECK-NEXT: ret
}
CHECK-NEXT: directives reject the input unless there is exactly one newline between it an the previous directive. A CHECK-NEXT cannot be the first directive in a file.
The CHECK-NOT: directive is used to verify that a string doesn't occur between two matches (or the first match and the beginning of the file). For example, to verify that a load is removed by a transformation, a test like this can be used:
define i8 @coerce_offset0(i32 %V, i32* %P) {
store i32 %V, i32* %P
%P2 = bitcast i32* %P to i8*
%P3 = getelementptr i8* %P2, i32 2
%A = load i8* %P3
ret i8 %A
; CHECK: @coerce_offset0
; CHECK-NOT: load
; CHECK: ret i8
}
The CHECK: and CHECK-NOT: directives both take a pattern to match. For most uses of FileCheck, fixed string matching is perfectly sufficient. For some things, a more flexible form of matching is desired. To support this, FileCheck allows you to specify regular expressions in matching strings, surrounded by double braces: {{yourregex}}. Because we want to use fixed string matching for a majority of what we do, FileCheck has been designed to support mixing and matching fixed string matching with regular expressions. This allows you to write things like this:
; CHECK: movhpd {{[0-9]+}}(%esp), {{%xmm[0-7]}}
In this case, any offset from the ESP register will be allowed, and any xmm register will be allowed.
Because regular expressions are enclosed with double braces, they are visually distinct, and you don't need to use escape characters within the double braces like you would in C. In the rare case that you want to match double braces explicitly from the input, you can use something ugly like {{[{][{]}} as your pattern.
It is often useful to match a pattern and then verify that it occurs again later in the file. For codegen tests, this can be useful to allow any register, but verify that that register is used consistently later. To do this, FileCheck allows named variables to be defined and substituted into patterns. Here is a simple example:
; CHECK: test5:
; CHECK: notw [[REGISTER:%[a-z]+]]
; CHECK: andw {{.*}}[[REGISTER]]
The first check line matches a regex (%[a-z]+) and captures it into the variables "REGISTER". The second line verifies that whatever is in REGISTER occurs later in the file after an "andw". FileCheck variable references are always contained in [[ ]] pairs, are named, and their names can be formed with the regex "[a-zA-Z][a-zA-Z0-9]*". If a colon follows the name, then it is a definition of the variable, if not, it is a use.
FileCheck variables can be defined multiple times, and uses always get the latest value. Note that variables are all read at the start of a "CHECK" line and are all defined at the end. This means that if you have something like "CHECK: [[XYZ:.*]]x[[XYZ]]" that the check line will read the previous value of the XYZ variable and define a new one after the match is performed. If you need to do something like this you can probably take advantage of the fact that FileCheck is not actually line-oriented when it matches, this allows you to define two separate CHECK lines that match on the same line.
With a RUN line there are a number of substitutions that are permitted. In general, any Tcl variable that is available in the substitute function (in test/lib/llvm.exp) can be substituted into a RUN line. To make a substitution just write the variable's name preceded by a $. Additionally, for compatibility reasons with previous versions of the test library, certain names can be accessed with an alternate syntax: a % prefix. These alternates are deprecated and may go away in a future version.
Here are the available variable names. The alternate syntax is listed in parentheses.
To add more variables, two things need to be changed. First, add a line in the test/Makefile that creates the site.exp file. This will "set" the variable as a global in the site.exp file. Second, in the test/lib/llvm.exp file, in the substitute proc, add the variable name to the list of "global" declarations at the beginning of the proc. That's it, the variable can then be used in test scripts.
To make RUN line writing easier, there are several shell scripts located in the llvm/test/Scripts directory. This directory is in the PATH when running tests, so you can just call these scripts using their name. For example:
Sometimes it is necessary to mark a test case as "expected fail" or XFAIL. You can easily mark a test as XFAIL just by including XFAIL: on a line near the top of the file. This signals that the test case should succeed if the test fails. Such test cases are counted separately by the testing tool. To specify an expected fail, use the XFAIL keyword in the comments of the test program followed by a colon and one or more regular expressions (separated by a comma). The regular expressions allow you to XFAIL the test conditionally by host platform. The regular expressions following the : are matched against the target triplet for the host machine. If there is a match, the test is expected to fail. If not, the test is expected to succeed. To XFAIL everywhere just specify XFAIL: *. Here is an example of an XFAIL line:
; XFAIL: darwin,sun
To make the output more useful, the llvm_runtest function wil scan the lines of the test case for ones that contain a pattern that matches PR[0-9]+. This is the syntax for specifying a PR (Problem Report) number that is related to the test case. The number after "PR" specifies the LLVM bugzilla number. When a PR number is specified, it will be used in the pass/fail reporting. This is useful to quickly get some context when a test fails.
Finally, any line that contains "END." will cause the special interpretation of lines to terminate. This is generally done right after the last RUN: line. This has two side effects: (a) it prevents special interpretation of lines that are part of the test program, not the instructions to the test case, and (b) it speeds things up for really big test cases by avoiding interpretation of the remainder of the file.
The test-suite module contains a number of programs that can be compiled with LLVM and executed. These programs are compiled using the native compiler and various LLVM backends. The output from the program compiled with the native compiler is assumed correct; the results from the other programs are compared to the native program output and pass if they match.
When executing tests, it is usually a good idea to start out with a subset of the available tests or programs. This makes test run times smaller at first and later on this is useful to investigate individual test failures. To run some test only on a subset of programs, simply change directory to the programs you want tested and run gmake there. Alternatively, you can run a different test using the TEST variable to change what tests or run on the selected programs (see below for more info).
In addition for testing correctness, the test-suite directory also performs timing tests of various LLVM optimizations. It also records compilation times for the compilers and the JIT. This information can be used to compare the effectiveness of LLVM's optimizations and code generation.
test-suite tests are divided into three types of tests: MultiSource, SingleSource, and External.
The SingleSource directory contains test programs that are only a single source file in size. These are usually small benchmark programs or small programs that calculate a particular value. Several such programs are grouped together in each directory.
The MultiSource directory contains subdirectories which contain entire programs with multiple source files. Large benchmarks and whole applications go here.
The External directory contains Makefiles for building code that is external to (i.e., not distributed with) LLVM. The most prominent members of this directory are the SPEC 95 and SPEC 2000 benchmark suites. The External directory does not contain these actual tests, but only the Makefiles that know how to properly compile these programs from somewhere else. The presence and location of these external programs is configured by the test-suite configure script.
Each tree is then subdivided into several categories, including applications, benchmarks, regression tests, code that is strange grammatically, etc. These organizations should be relatively self explanatory.
Some tests are known to fail. Some are bugs that we have not fixed yet; others are features that we haven't added yet (or may never add). In the regression tests, the result for such tests will be XFAIL (eXpected FAILure). In this way, you can tell the difference between an expected and unexpected failure.
The tests in the test suite have no such feature at this time. If the test passes, only warnings and other miscellaneous output will be generated. If a test fails, a large <program> FAILED message will be displayed. This will help you separate benign warnings from actual test failures.
First, all tests are executed within the LLVM object directory tree. They are not executed inside of the LLVM source tree. This is because the test suite creates temporary files during execution.
To run the test suite, you need to use the following steps:
Check out the test-suite module with:
% svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
This will get the test suite into llvm/projects/test-suite.
Configure and build llvm.
Configure and build llvm-gcc.
Install llvm-gcc somewhere.
Re-configure llvm from the top level of each build tree (LLVM object directory tree) in which you want to run the test suite, just as you do before building LLVM.
During the re-configuration, you must either: (1) have llvm-gcc you just built in your path, or (2) specify the directory where your just-built llvm-gcc is installed using --with-llvmgccdir=$LLVM_GCC_DIR.
You must also tell the configure machinery that the test suite is available so it can be configured for your build tree:
% cd $LLVM_OBJ_ROOT ; $LLVM_SRC_ROOT/configure [--with-llvmgccdir=$LLVM_GCC_DIR]
[Remember that $LLVM_GCC_DIR is the directory where you installed llvm-gcc, not its src or obj directory.]
You can now run the test suite from your build tree as follows:
% cd $LLVM_OBJ_ROOT/projects/test-suite % make
Note that the second and third steps only need to be done once. After you have the suite checked out and configured, you don't need to do it again (unless the test code or configure script changes).
In order to run the External tests in the test-suite module, you must specify --with-externals. This must be done during the re-configuration step (see above), and the llvm re-configuration must recognize the previously-built llvm-gcc. If any of these is missing or neglected, the External tests won't work.
In addition to the regular "whole program" tests, the test-suite module also provides a mechanism for compiling the programs in different ways. If the variable TEST is defined on the gmake command line, the test system will include a Makefile named TEST.<value of TEST variable>.Makefile. This Makefile can modify build rules to yield different results.
For example, the LLVM nightly tester uses TEST.nightly.Makefile to create the nightly test reports. To run the nightly tests, run gmake TEST=nightly.
There are several TEST Makefiles available in the tree. Some of them are designed for internal LLVM research and will not work outside of the LLVM research group. They may still be valuable, however, as a guide to writing your own TEST Makefile for any optimization or analysis passes that you develop with LLVM.
There are a number of ways to run the tests and generate output. The most simple one is simply running gmake with no arguments. This will compile and run all programs in the tree using a number of different methods and compare results. Any failures are reported in the output, but are likely drowned in the other output. Passes are not reported explicitely.
Somewhat better is running gmake TEST=sometest test, which runs the specified test and usually adds per-program summaries to the output (depending on which sometest you use). For example, the nightly test explicitely outputs TEST-PASS or TEST-FAIL for every test after each program. Though these lines are still drowned in the output, it's easy to grep the output logs in the Output directories.
Even better are the report and report.format targets (where format is one of html, csv, text or graphs). The exact contents of the report are dependent on which TEST you are running, but the text results are always shown at the end of the run and the results are always stored in the report.<type>.format file (when running with TEST=<type>). The report also generate a file called report.<type>.raw.out containing the output of the entire test run.
Assuming you can run the test suite, (e.g. "gmake TEST=nightly report" should work), it is really easy to run optimizations or code generator components against every program in the tree, collecting statistics or running custom checks for correctness. At base, this is how the nightly tester works, it's just one example of a general framework.
Lets say that you have an LLVM optimization pass, and you want to see how many times it triggers. First thing you should do is add an LLVM statistic to your pass, which will tally counts of things you care about.
Following this, you can set up a test and a report that collects these and formats them for easy viewing. This consists of two files, a "test-suite/TEST.XXX.Makefile" fragment (where XXX is the name of your test) and a "test-suite/TEST.XXX.report" file that indicates how to format the output into a table. There are many example reports of various levels of sophistication included with the test suite, and the framework is very general.
If you are interested in testing an optimization pass, check out the "libcalls" test as an example. It can be run like this:
% cd llvm/projects/test-suite/MultiSource/Benchmarks # or some other level % make TEST=libcalls report
This will do a bunch of stuff, then eventually print a table like this:
Name | total | #exit | ... FreeBench/analyzer/analyzer | 51 | 6 | FreeBench/fourinarow/fourinarow | 1 | 1 | FreeBench/neural/neural | 19 | 9 | FreeBench/pifft/pifft | 5 | 3 | MallocBench/cfrac/cfrac | 1 | * | MallocBench/espresso/espresso | 52 | 12 | MallocBench/gs/gs | 4 | * | Prolangs-C/TimberWolfMC/timberwolfmc | 302 | * | Prolangs-C/agrep/agrep | 33 | 12 | Prolangs-C/allroots/allroots | * | * | Prolangs-C/assembler/assembler | 47 | * | Prolangs-C/bison/mybison | 74 | * | ...
This basically is grepping the -stats output and displaying it in a table. You can also use the "TEST=libcalls report.html" target to get the table in HTML form, similarly for report.csv and report.tex.
The source for this is in test-suite/TEST.libcalls.*. The format is pretty simple: the Makefile indicates how to run the test (in this case, "opt -simplify-libcalls -stats"), and the report contains one line for each column of the output. The first value is the header for the column and the second is the regex to grep the output of the command for. There are lots of example reports that can do fancy stuff.