Exporting Graphs

Joern is used in academic research as a source for intermediate graph representations of code, particularly in machine learning and vulnerability discovery applications [e.g., 1,2,3,4,5]. To support this use-case, Joern provides both plotting capabilities in the interactive console as well as the joern-export command line utility.

In summary, Joern can create the following graph representations for C/C++ code:

  • Abstract Syntax Trees (AST)
  • Control Flow Graphs (CFG)
  • Control Dependence Graphs (CDG)
  • Data Dependence Graphs (DDG)
  • Program Dependence graphs (PDG)
  • Code Property Graphs (CPG14)

The command line tool joern-export#

All of these representations can be plotted and exported into the graphviz dot format to enable processing with third party tools or via external scripts.

To parse the code in /src/directory and dump Program Dependence Graphs for all methods into the directory outdir, you can run the following commands on the system shell:

joern-parse /src/directory
joern-export --repr pdg --out outdir

For a complete overview of options, run joern-export --help.

Plotting and Exporting on the Joern Console#

If you would like to explore graph representations interactively, you can do so on the Joern shell. To this end, we define the following steps on method nodes to dump representations in dot format.

cpg.method($name).dotAst.l // output AST in dot format
cpg.method($name).dotCfg.l // output CFG in dot format
...
cpg.method($name).dotCpg14.l // output CPG'14 in dot format

You can also plot and view representations using the following queries:

cpg.method($name).plotDotAst // plot AST
cpg.method($name).ploDotCfg // plot CFG
...
cpg.method($name).plotDotCpg14 // plot CPG'14

Note that the ossdataflow layer needs to have been calculated for the source CPG via run.ossdataflow.

Example#

Generate the CPG along with the data flow layer for a sample function named myfunc.

joern> importCode.c.fromString( """
int myfunc(int b) {
int a = 42;
if (b > 10) {
foo(a)
}
bar(a);
}
"""
)
joern> run.ossdataflow

You can now plot the AST as follows:

joern> cpg.method("myfunc").plotDotAst

You can obtain the dot representation of the AST as well:

joern> cpg.method("myfunc").dotAst.l
res4: List[String] = List(
"""digraph myfunc {
"1000102" [label = "(METHOD,myfunc)" ]
"1000103" [label = "(PARAM,int b)" ]
"1000104" [label = "(BLOCK,,)" ]
"1000105" [label = "(LOCAL,a: int)" ]
"1000106" [label = "(<operator>.assignment,a = 42)" ]
"1000107" [label = "(IDENTIFIER,a,a = 42)" ]
"1000108" [label = "(LITERAL,42,a = 42)" ]
"1000109" [label = "(CONTROL_STRUCTURE,if (b > 10),if (b > 10))" ]
"1000110" [label = "(<operator>.greaterThan,b > 10)" ]
"1000111" [label = "(IDENTIFIER,b,b > 10)" ]
"1000112" [label = "(LITERAL,10,b > 10)" ]
"1000113" [label = "(BLOCK,,)" ]
"1000114" [label = "(bar,bar(a))" ]
"1000115" [label = "(IDENTIFIER,a,bar(a))" ]
"1000116" [label = "(METHOD_RETURN,int)" ]
"1000102" -> "1000103"
"1000102" -> "1000104"
"1000102" -> "1000116"
"1000104" -> "1000105"
"1000104" -> "1000106"
"1000104" -> "1000109"
"1000104" -> "1000114"
"1000106" -> "1000107"
"1000106" -> "1000108"
"1000109" -> "1000110"
"1000109" -> "1000113"
"1000110" -> "1000111"
"1000110" -> "1000112"
"1000114" -> "1000115"
}
"""
)

Dumping representations for all functions from the shell#

You can also dump all representations into the directory out using

run.dumpast
run.dumpcfg
...
run.dumpcpg14

References#

Research that employs Joern as an extraction tool for intermediate representations of code:

(1) Devign: Effective Vulnerability Identification by Learning Comprehensive Program Semantics via Graph Neural Networks, Zhou et al., NIPS'19

(2) Source Code Authorship Attribution using LongShort-Term Memory Based Networks, Alsulami et al., ESORICS'17

(3)VulPecker: an automated vulnerability detection system based on code similarity analysis, Li et al., ACSAC'16

(4) Git blame who?: Stylistic authorship attribution of small, incomplete source code fragments, Dauber et al., PETS-19/3

(5) SPIDER: Enabling Fast Patch Propagation In Related Software Repositories, Machiry et al., S&P'20

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