PLEASE READ! - I am currently refactoring Weaver to use libbpf instead of bcc which would include various other major improvements. If you're currently using weaver please be aware that features/bug fixes are being held off until the major refactor occurs. This will be tracked in the branch "refactor"

Weaver is a CLI tool that allows you to trace Go programs in order to inspect what values are passed to specified functions. It leverages eBPF attached to uprobes.

There are two modes of operation, one that uses a 'functions file', and one that extracts a symbol table from a passed binary and filters by Go packages. More information on functionality in docs.

Take the following example program:

test_prog.go

package main

//go:noinline
func test_function(int, [2]int) {}

//go:noinline
func other_test_function(rune, int64) {}

func main() {
	test_function(3, [2]int{1, 2})
	other_test_function('a', 33)
}

Let's say we want to know what values are passed to test_function and other_test_function whenever the program is run. Once the program is compiled (make) we just have to create a file which specifies each function to trace:

functions_to_trace.txt

main.test_function(int, [2]int)
main.other_test_function(rune, int64)

Notice that we have to specify the parameter data types. (You can use weaver --types to see what data types are supported.)

Now we can call weaver like so:

sudo weaver -f /path/to/functions_to_trace.txt /path/to/test-prog-binary

Weaver will then sit idle without any output until test-prog is run and the test_function and other_test_function functions are called. This will also work on an already running Go Program.

{"functionName":"main.other_test_function","args":[{"type":"RUNE","value":"a"},{"type":"INT64","value":"33"}],"procInfo":{"pid":43300,"ppid":42754,"comm":"test-prog-binar"}}
{"functionName":"main.test_function","args":[{"type":"INT","value":"3"},{"type":"INT_ARRAY","value":"1, 2"}],"procInfo":{"pid":43300,"ppid":42754,"comm":"test-prog-binar"}}

For the same example Go program as above, you can choose to not specify a functions file. The command would like like this:

sudo weaver /path/to/test-prog-binary

This will default to only tracing functions in the main package, however you can use the --packages flag to specify a comma seperated list of packages (typially of the form github.com/x/y)

Output does include argument vlaues in this mode.

{"functionName":"main.main","procInfo":{"pid":44411,"ppid":42754,"comm":"test-prog-binar"}}
{"functionName":"main.test_function","procInfo":{"pid":44411,"ppid":42754,"comm":"test-prog-binar"}}

Currently weaver supports basic data types but getting support for user defined types is a high priority. Getting following types defined are a work in progress:

• user/stdlib defined structs
• user/stdlib defined interfaces

• bcc / bcc-devel
• linux kernel version > 4.14 (please make bug reports if your kernel version doesn't work)

make will compile the weaver binary to bin/weaver (It also creates the smoke test binary and print-stack utility)

Can't build? Please make an issue!

Check issues for tasks currently being tracked. Please open bug reports, i'm sure there are plenty :-)

Short term goals include:

• Testing
• Output options
• Inspecting binaries for parameter data types instead of specifying them with a functions file
• CI/CD infrastructre

image modified version of art by Ashley McNamara (license) based on art by Renee French.