dtracing static symbols

[Daniel O'Connor]

On 11 Mar 2014, at 15:34, Prashanth Kumar <pra_udupi at yahoo.co.in> wrote:
> If the binary being traced has static symbols in its symbol table, DTrace should
> be able to trace the function. Can you describe the example where you found this
> difference in FreeBSD and OSX?

Unfortunately the static symbols don't show up in the symbol table (as shown by nm).

Is there a compile or link flag which will change that?

Here is an example..
[ur 15:43] ~ >cat static.c
#include <stdio.h>

static void
foo(void) {
	printf("Foo\n");
}

void
bar(void) {
	printf("Boo\n");
}

int
main(int argc, char **argv) {
	foo();
	bar();
	return 0;
}

[ur 15:43] ~ >cc static.c -o static
[ur 15:43] ~ >sudo dtrace -Ppid\$target -l -c ./static|less

On OSX you see..
...
956613   pid46749            static                               foo return
956614   pid46749            static                               foo entry
956615   pid46749            static                               foo 0
956616   pid46749            static                               foo 1
956617   pid46749            static                               foo 4
956618   pid46749            static                               foo 8
956619   pid46749            static                               foo f
956620   pid46749            static                               foo 11
956621   pid46749            static                               foo 16
956622   pid46749            static                               foo 19
956623   pid46749            static                               foo 1d
956624   pid46749            static                               foo 1e
..

(I'm not sure what the various numbers mean)

However on FreeBSD you don't see any thing for the binary itself, only the libraries.
This is true even if you build with..
[mdtest 5:22] ~ >cc static.o -o static
[mdtest 5:22] ~ >ctfconvert -g -L labelenv static.o
[mdtest 5:22] ~ >cc -g static.c -o static.o -c

Curiously you also can't run it with -c, I had to put a usleep() at the start and then use -p. Trying to use -c fails with..
[mdtest 5:25] ~ >sudo dtrace -Ppid\$target -l -c ./static
Foo
Bar
dtrace: failed to control pid 52006: process exited with status 0

FWIW nm on the binary shows both symbols (foo and bar)
[mdtest 5:33] ~ >nm static|egrep '(foo|bar)'
0000000000400700 T bar
00000000004006f0 t foo

Finally, while -c doesn't work on FreeBSD but actually runs the binary, -c on OSX works (but the binary isn't executed - or at least you don't see its output)

--
Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
  -- Andrew Tanenbaum
GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C






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