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< title > Information on using the Static Analyzer ("LLVM Checker")< / title >
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< h1 > Information on using the Static Analyzer ("LLVM Checker")< / h1 >
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< p > This documents provides some notes on using the LLVM/clang static analyzer to
find bugs in C and Objective-C programs.< / p >
< p > Please note that this tool is < b > very early< / b > in development, and there are
< b > many planned enhancements< / b > to improve both the precision and scope of its
analysis algorithms as well as the kinds bugs it will find.< / p >
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< p > This document is arranged into the following sections:< / p >
< ul >
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< li > < a href = "#Contents" > Obtaining the Analyzer< / a > < / li >
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< li > < a href = "#BasicUsage" > Basic Usage< / a > < / li >
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< li > < a href = "#Output" > Output of the Analyzer< / a > < / li >
< li > < a href = "#RecommendedUsageGuidelines" > Recommended Usage Guidelines< / a > < / li >
< li > < a href = "#Debugging" > Debugging the Analyzer< / a >
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< / ul >
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< h2 id = "ReleaseContents" > Obtaining the Analyzer< / h2 >
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< p > Using the analyzer involves executing < tt > scan-build< / tt > (see < a
href="#BasicUsage">Basic Usage< / a > ). < tt > scan-build< / tt > will first look for a
< tt > clang< / tt > executable in the same directory as < tt > scan-build< / tt > , and then
search your path.< / p >
< p > If one is using the analyzer directly from the Clang sources, it suffices to
just directly execute < tt > scan-build< / tt > in the < tt > utils< / tt > directory. No
other special installation is needed.< / p >
< h3 > Packaged Builds (currently Mac-Only)< / h3 >
< p > Semi-regular builds of the analyzer on Mac OS X (10.5) are available < a
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href="http://keeda.stanford.edu/~kremenek/checker">here< / a > . Packaged builds for
other platforms may eventually be provided, but as the tool is in its early
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stages we are not actively promoting releases yet. If you wish to help
contribute regular builds of the analyzer on other platforms, please email the
< a href = "http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev" > Clang Developers'
mailing list< / a > .< / p >
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< p > Packaged builds of the analyzer expand to the following files:< / p >
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< table id = "package" >
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< thead > < tr > < td > File< / td > < td > Purpose< / td > < / tr > < / thead >
< tr > < td > < tt > < b > scan-build< / b > < / tt > < / td > < td > Script for running the analyzer over a project build. < b > This is the only file you care about.< / b > < / td > < / tr >
< tr > < td > < tt > ccc-analyzer< / tt > < / td > < td > GCC interceptor (called by scan-build)< / td > < / tr >
< tr > < td > < tt > clang< / tt > < / td > < td > Static Analyzer (called by ccc-analyzer)< / td > < tr >
< tr > < td > < tt > sorttable.js< / tt > < / td > < td > JavaScript used for displaying error reports< / td > < / tr >
< / table >
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< h3 > Other Platforms (Building the Analyzer from Source)< / h3 >
< p > Packaged builds simply consist of a few files from the Clang source tree,
meaning that < b > anyone< / b > who can build Clang can use the static analyzer.
Please see the < a href = "get_started.html" > Getting Started< / a > page for more
details on downloading and compiling Clang.< / p >
< p > All files used by the analyzer (and included in packaged builds; < a
href="#package">see above< / a > ) other than a compiled < tt > clang< / tt > executable
are found in the < tt > utils< / tt > subdirectory in the Clang tree.< / p >
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< h2 id = "BasicUsage" > Basic Usage< / h2 >
< p > The analyzer is executed from the command-line. To run the analyzer, you will
use < tt > scan-build< / tt > to analyze the source files compiled by < tt > gcc< / tt >
during a project build.< / p >
< p > For example, to analyze the files compiled under a build:< / p >
< pre >
$ < b > scan-build< / b > make
$ < b > scan-build< / b > xcodebuild
< / pre >
< p > In the first case < tt > scan-build< / tt > analyzes the code of a project built
with < tt > make< / tt > , andin the second case < tt > scan-build< / tt > analyzes a project
built using < tt > xcodebuild< / tt > . In general, the format is: < / p >
< pre >
$ < b > scan-build< / b > < i > [scan-build options]< / i > < b > < command> < / b > < i > [command options]< / i >
< / pre >
< p > Operationally, < tt > scan-build< / tt > literally runs < command > with all of the
subsequent options passed to it. For example< / p >
< pre >
$ scan-build make < b > -j4< / b >
< / pre >
< p > In this example, < tt > scan-build< / tt > makes no effort to interpret the options
after the build command (in this case, < tt > make< / tt > ); it just passes them
through. In general, < tt > scan-build< / tt > should support parallel builds, but
< b > not distributed builds< / b > . Similarly, you can use < tt > scan-build< / tt > to
analyze specific files:
< pre >
$ scan-build gcc -c < b > t1.c t2.c< / b >
< / pre >
< p >
This example causes the files < tt > t1.c< / tt > and < tt > t2.c< / tt > to be analyzed.
< / p >
< h3 > Other Options< / h3 >
< p >
As mentioned above, extra options can be passed to < tt > scan-build< / tt > . These
options prefix the build command. For example:< / p >
< pre >
$ scan-build < b > -k -V< / b > make
$ scan-build < b > -k -V< / b > xcodebuild
< / pre >
< p > Here are a complete list of options:< / p >
< table >
< thead > < tr > < td > Option< / td > < td > Description< / td > < / tr > < / thead >
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< tr > < td > < b > -a< / b > < / td >
< td > The analysis to run. The default analysis is < i > checker-cfref< / i > . Valid options are: < i > checker-cfref< / i > , < i > fsyntax-only< / i > .
These translate into options passed down to the < tt > clang< / tt > executable, and currently this option is mainly used for debugging.< / td > < / tr >
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< tr > < td > < b > -o< / b > < / td > < td > Target directory for HTML report files. Subdirectories will be
created as needed to represent separate "runs" of the analyzer. If this option
is not specified, a directory is created in < tt > /tmp< / tt > to store the
reports.< / td > < tr >
< tr > < td > < b > -h< / b > < br > < i > < nobr > (or no arguments)< / nobr > < / i > < / td > < td > Display < tt > scan-build< / tt > options.< / td > < / tr >
< tr > < td > < b > -k< / b > < br > < nobr > < b > --keep-going< / b > < / nobr > < / td > < td > Add a "keep on going" option to the
specified build command. < p > This option currently supports < tt > make< / tt > and
< tt > xcodebuild< / tt > .< / p > < p > This is a convenience option; one can specify this
behavior directly using build options.< / p > < / td > < / tr >
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< tr > < td > < b > -v< b > < / td > < td > Verbose output from scan-build and the analyzer. < b > A second and third
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"-v" increases verbosity< / b > , and is useful for filing bug reports against the analyzer.< / td > < / tr >
< tr > < td > < b > -V< / b > < / td > < td > View analysis results in a web browser when the build command completes.< / td > < / tr >
< / table >
< p > These options can also be viewed by running < tt > scan-build< / tt > with no
arguments:< / p >
< pre >
$ < b > scan-build< / b >
USAGE: scan-build [options] < build command> [build options]
OPTIONS:
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-a - The analysis to run. The default is 'checker-cfref'.
Valid options are: 'checker-cfref', 'fsyntax-only'
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-o - Target directory for HTML report files. Subdirectories
will be created as needed to represent separate "runs" of
the analyzer. If this option is not specified, a directory
is created in /tmp to store the reports.
< b > ...< / b >
< / pre >
< h2 id = "Output" > Output of the Analyzer< / h2 >
< p >
The output of the analyzer is a set of HTML files, each one which represents a
separate bug report. A single < tt > index.html< / tt > file is generated for
surveying all of the bugs. You can then just open < tt > index.html< / tt > in a web
browser to view the bug reports.
< / p >
< p >
Where the HTML files are generated is specified with a < b > -o< / b > option to
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< tt > scan-build< / tt > . If < b > -o< / b > isn't specified, a directory in < tt > /tmp< / tt >
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is created to store the files (< tt > scan-build< / tt > will print a message telling
you where they are). If you want to view the reports immediately after the build
completes, pass < b > -V< / b > to < tt > scan-build< / tt > .
< / p >
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< h2 id = "RecommendedUsageGuidelines" > Recommended Usage Guidelines< / h2 >
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Here are a few recommendations with running the analyzer:
< h3 > Always Analyze a Project in its "Debug" Configuration< / h3 >
Most projects can be built in a "debug" mode that enables assertions. Assertions
are picked up by the static analyzer to prune infeasible paths, which in some
cases can greatly reduce the number of false positives (bogus error reports)
emitted by the tool.
< h3 > Pass -k to < tt > scan-build< / tt > < / h3 >
< p > While < tt > ccc-analyzer< / tt > invokes < tt > gcc< / tt > to compile code, any
problems in correctly forwarding arguments to < tt > gcc< / tt > may result in a build
failure. Passing < b > -k< / b > to < tt > scan-build< / tt > potentially allows you to
analyze other code in a project for which this problem doesn't occur.< / p >
< p > Also, it is useful to analyze a project even if not all of the source files
are compilable. This is great when using < tt > scan-build< / tt > as part of your
compile-debug cycle.< / p >
< h3 > Use Verbose Output when Debugging < tt > scan-build< / tt > < / h3 >
< tt > scan-build< / tt > takes a < b > -v< / b > option to emit verbose output about what
it's doing; two < b > -v< / b > options emit more information. Redirecting the output
of < tt > scan-build< / tt > to a text file (make sure to redirect standard error) is
useful for filing bug reports against < tt > scan-build< / tt > or the analyzer, as we
can see the exact options (and files) passed to the analyzer. For more
comprehendible logs, don't perform a parallel build.
< h2 id = "Debugging" > Debugging the Analyzer< / h2 >
This section provides information on debugging the analyzer, and troubleshooting
it when you have problems analyzing a particular project.
< h3 > How it Works< / h3 >
To analyze a project, < tt > scan-build< / tt > simply sets the environment variable
< tt > CC< / tt > to the full path to < tt > ccc-analyzer< / tt > . It also sets a few other
environment variables to communicate to < tt > ccc-analyzer< / tt > where to dump HTML
report files.
< p > Some Makefiles (or equivalent project files) hardcode the compiler; for such
projects simply overriding < tt > CC< / tt > won't cause < tt > ccc-analyzer< / tt > to be
called. This will cause the compiled code < b > to not be analyzed.< / b > < / p > If you
find that your code isn't being analyzed, check to see if < tt > CC< / tt > is
hardcoded. If this is the case, you can hardcode it instead to the < b > full
path< / b > to < tt > ccc-analyzer< / tt > .< / p >
< p > When applicable, you can also run < tt > ./configure< / tt > for a project through
< tt > scan-build< / tt > so that configure sets up the location of < tt > CC< / tt > based
on the environment passed in from < tt > scan-build< / tt > :
< pre >
$ scan-build < b > ./configure< / b >
< / pre >
< p > < tt > scan-build< / tt > has special knowledge about < tt > configure< / tt > , so it in
most cases will not actually analyze the configure tests run by
< tt > configure< / tt > .< / p >
< p > Under the hood, < tt > ccc-analyzer< / tt > directly invokes < tt > gcc< / tt > to
compile the actual code in addition to running the analyzer (which occurs by it
calling < tt > clang< / tt > ). < tt > ccc-analyzer< / tt > tries to correctly forward all
the arguments over to < tt > gcc< / tt > , but this may not work perfectly (please
report bugs of this kind).
< h3 > Filing Bugs< / h3 >
We encourage users to file bug reports for any problems that they encounter.
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< p > < b > Outside Apple< / b > : Please < a
href="http://llvm.org/bugs/enter_bug.cgi?product=clang">file bugs< / a > (against
Clang) in LLVM's Bugzilla database.< / p >
< p > < b > Apple-internal< / b > : Please file bugs in Radar against the < b > llvm - clang< / b >
component.< / p >
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