salp's Introduction

Salp

Salp is a library that enables Go programs to create and fire USDT probes at runtime. Such probes allow API-stable (i.e. not dependent on function names) tracing of executables written in Go - especially important since function tracing of Go code requires some unappealing (though not unimpressive) hacks. Salp uses the libstapsdt library to create and fire these probes.

Build

Dependencies

Salp depends on libstapsdt which in turn depends on libelf and libdl. libstapsdt can be built from source or (for debian based distros) installed via an Ubuntu PPA. Full instructions are available in the docs for libstapsdt

Build and Test

If libstdapsdt is installed globally (e.g. from the PPA above or via make install), you should be able to simply go build or go test. However if you have built libstapsdt from source then you will need to tell the cgo tool how to find the headers and .so files for libstapsdt using the CGO_CFLAGS, CGO_LDFLAGS, and LD_LIBRARY_PATH environment variables.

export CGO_CFLAGS="-I/path/to/libstapsdt/src"
export CGO_LDFLAGS="-L/path/to/libstapsdt/out"
export LD_LIBRARY_PATH="/path/to/libstapsdt/out"

Demo

This repository contains a demo executable that will fire two different probes every second. The demo can be observed using the trace and tplist tools from the bcc project. Use two terminals to run the demo - one to execute the tracable salpdemo go program and one to run the bcc tools and see their output. In the first window run

go run internal/salpdemo.go

This program will print out how to monitor itself but then won't print out anything after that. In the second window run the bcc trace program on the salpdemo process, monitoring probes p1 and p2.

sudo trace -p "$(pgrep -n salpdemo)"                    \
    'u::p1 "i=%d err='%s' date='%s'", arg1, arg2, arg3' \
    'u::p2 "j=%d flag=%d", arg1, arg2'

or alternatively the same thing with bpftrace

sudo bpftrace -p "$(pgrep -n salpdemo)" /dev/stdin <<EOF
  usdt:p1 { printf("i=%d err='%s' date='%s'\n", arg0, str(arg1), str(arg2)); }
  usdt:p2 { printf("j=%d flag=%d\n", arg0, arg1); }
EOF

Either trace invocations will output the values of the three args to probe 1 and the two args to probe 2.

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salp's Issues

Stub out on OS X

I'm not interested in instrumenting on OS X but compiling would be good.

setting the env. variables CGO_* and LD_* prevent compilation

If I see the environment variables CGO_CFLAGS, CGO_LDFLAGS, and LD_LIBRARY_PATH then my program will NOT compile. I get the following error:

/usr/local/go/pkg/tool/linux_amd64/link: running gcc failed: exit status 1
/home/opc/libstapsdt/out/libstapsdt.a(libstapsdt.o): In function providerLoad': libstapsdt.c:(.text+0x63e): undefined reference to dlopen'
libstapsdt.c:(.text+0x65b): undefined reference to dlerror' libstapsdt.c:(.text+0x6ae): undefined reference to dlsym'
libstapsdt.c:(.text+0x6b7): undefined reference to dlerror' /home/opc/libstapsdt/out/libstapsdt.a(libstapsdt.o): In function providerUnload':
libstapsdt.c:(.text+0x74e): undefined reference to dlclose' libstapsdt.c:(.text+0x757): undefined reference to dlerror'
/home/opc/libstapsdt/out/libstapsdt.a(shared-lib.o): In function createElf': shared-lib.c:(.text+0x11): undefined reference to elf_version'
shared-lib.c:(.text+0x30): undefined reference to elf_begin' /home/opc/libstapsdt/out/libstapsdt.a(shared-lib.o): In function createElfHeader':
shared-lib.c:(.text+0xb8): undefined reference to elf64_newehdr' /home/opc/libstapsdt/out/libstapsdt.a(shared-lib.o): In function createElfProgramHeaders':
shared-lib.c:(.text+0x122): undefined reference to elf64_newphdr' /home/opc/libstapsdt/out/libstapsdt.a(shared-lib.o): In function dynElfSave':
shared-lib.c:(.text+0xad9): undefined reference to elf_ndxscn' shared-lib.c:(.text+0xbbe): undefined reference to elf_ndxscn'
shared-lib.c:(.text+0xf14): undefined reference to elf_ndxscn' shared-lib.c:(.text+0x10ff): undefined reference to elf_ndxscn'
shared-lib.c:(.text+0x1122): undefined reference to elf_update' shared-lib.c:(.text+0x1402): undefined reference to elf_update'
shared-lib.c:(.text+0x16ec): undefined reference to elf_ndxscn' shared-lib.c:(.text+0x1763): undefined reference to elf_ndxscn'
shared-lib.c:(.text+0x17f7): undefined reference to elf_ndxscn' shared-lib.c:(.text+0x186c): undefined reference to elf_ndxscn'
shared-lib.c:(.text+0x18e1): undefined reference to elf_ndxscn' shared-lib.c:(.text+0x198d): undefined reference to elf_flagphdr'
shared-lib.c:(.text+0x19a1): undefined reference to elf_update' /home/opc/libstapsdt/out/libstapsdt.a(shared-lib.o): In function dynElfClose':
shared-lib.c:(.text+0x1bbe): undefined reference to elf_end' /home/opc/libstapsdt/out/libstapsdt.a(section.o): In function sectionInit':
section.c:(.text+0x4d): undefined reference to elf_newscn' section.c:(.text+0x85): undefined reference to elf_newdata'
section.c:(.text+0xbf): undefined reference to elf64_getshdr' /home/opc/libstapsdt/out/libstapsdt.a(hash-table.o): In function hashTableFromSymbolTable':
hash-table.c:(.text+0xae): undefined reference to `elf_hash'
collect2: error: ld returned 1 exit status

When I remove those environment variables then my program will compile. I have to set the environment variables for the program to run. You just can't have them set when compiling the program.

mmcshane / salp Goto Github PK

salp's Introduction

Salp

Build

Dependencies

Build and Test

Demo

salp's People

Contributors

Stargazers

Watchers

Forkers

salp's Issues

Stub out on OS X

setting the env. variables CGO_* and LD_* prevent compilation

Eliminate libstapsdt dependency

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