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stap static function

https://www.sourceware.org/ml/systemtap/2007-q3/msg00132.html https://www.sourceware.org/ml/systemtap/2007-q3/msg00134.html

The result is that parameters to inlined functions are not properly
recorded, and inlined functions cannot have .return probes.

What this all means is that, for now, systemtap probes
desired in such functions need to be relocated to somewhere within
their callers.

find out function name of function pointer

For example:

global addr

probe kernel.function("__netif_rx_schedule") {
	addr = sprintf("%p", $dev->poll);
}

probe end {
	printf("Function address and name are:\n");
	print_stack(addr);
}

Sometimes, the address is in a different module, so the module name, instead of the function name, will be printed. In this case, do a grep into '/proc/kallsyms' should be able to find out the function name.

find functions that can be instrumented

# stap -p2 -e 'probe kernel.function("*") {}' 2>&1 | grep ^kernel.fun

generate call graph with function names

probe module("ext4").function("*").call {
	printf("%s -> %s\n", thread_indent(1), probefunc());
}

probe module("ext4").function("*").return {
	printf("%s <- %s\n", thread_indent(-1), probefunc());
}

generate call graph of functions within a file

probe kernel.function("*@net/core/ethtool.c").call {
	printf("%s -> %s\n", thread_indent(1), probefunc());
}

probe kernel.function("*@net/core/ethtool.c*").return {
	printf("%s <- %s\n", thread_indent(-1), probefunc());
}

print and count the stacktraces when a function is called

https://sourceware.org/systemtap/examples/profiling/pf4.stp https://sourceware.org/systemtap/examples/profiling/pf4.txt

# cat proxy_lookup.stp
#!/usr/bin/env stap
#
# Usage:
#    stap -d /usr/local/lib64/ganesha/libfsalpcache.so   \
#         -d /usr/local/lib64/ganesha/libfsalproxy.so \
#         -d /root/stable/fsl-nfs-ganesha/release/MainNFSD/ganesha.nfsd \
#         proxy_lookup.stp

global stacktraces;

probe
process("/usr/local/lib64/ganesha/libfsalproxy.so").function("pxy_lookup") {
	bt = sprint_ubacktrace()
	stacktraces[bt] <<< 1
}

probe end {
	foreach (bt in stacktraces-) {
		printf("count: %d\n%s\n",
			@sum(stacktraces[bt]),
			bt);
	}
}

Example output:

[root@SGDP04 systemtap]# stap \
	-d /usr/local/lib64/ganesha/libfsalpcache.so \
	-d /usr/local/lib64/ganesha/libfsalproxy.so \
	-d /root/stable/fsl-nfs-ganesha/release/MainNFSD/ganesha.nfsd \
	proxy_lookup.stp
WARNING: Missing unwind data for module, rerun with 'stap -d /usr/lib64/libpthread-2.17.so'
^Ccount: 708
pxy_lookup+0x15 [libfsalproxy.so.4.2.0]
cachefs_lookup+0x4c [libfsalpcache.so.4.2.0]
pcachefs_lookup+0x43 [libfsalpcache.so.4.2.0]
populate_dirent+0x6a [ganesha.nfsd]
pxy_do_readdir+0x29c [libfsalproxy.so.4.2.0]
pxy_readdir+0x71 [libfsalproxy.so.4.2.0]
read_dirents+0x5c [libfsalpcache.so.4.2.0]
cache_inode_readdir_populate+0x1b3 [ganesha.nfsd]
cache_inode_readdir+0x717 [ganesha.nfsd]
nfs4_op_readdir+0x445 [ganesha.nfsd]
nfs4_Compound+0x9f7 [ganesha.nfsd]
nfs_rpc_execute+0x1f70 [ganesha.nfsd]
worker_run+0x1
count: 625
pxy_lookup+0x15 [libfsalproxy.so.4.2.0]
cachefs_lookup+0x4c [libfsalpcache.so.4.2.0]
cachefs_file_unlink+0x28 [libfsalpcache.so.4.2.0]
pcachefs_unlink+0x2f [libfsalpcache.so.4.2.0]
cache_inode_remove+0x53a [ganesha.nfsd]
nfs4_op_remove+0x111 [ganesha.nfsd]
nfs4_Compound+0x9f7 [ganesha.nfsd]
nfs_rpc_execute+0x1f70 [ganesha.nfsd]
worker_run+0x1ba [ganesha.nfsd]
fridgethr_start_routine+0xd7 [ganesha.nfsd]
0x7f625859adf5 [libpthread-2.17.so+0x7df5]