dtrace showed matched probes but nothing in output on FreeBSD 9.1-RELEASE

[Mark Johnston]

On Sat, Nov 02, 2013 at 11:56:49AM +0800, John Luk wrote:
> Hi all,
> I'm a newbie in dtrace, and I following this tutorial from Oracle:
> http://docs.oracle.com/cd/E19205-01/820-4221/ to learn dtrace. In the
> example of test.c and ufunc.d, I expected output like this:
> 
>  % dtrace -s ufunc.d -c ./a.out a.out
> 
>     dtrace: script 'ufunc.d' matched 5 probes
>     dtrace: pid 27210 has exited
> 
>     inet_makeaddr            1
>     foo1                     1
>     foo                      1
>     main                     1
>     __fsr                    1
> 
> 
> But I got this instead:
> 
> # dtrace -s ufunc.d  -c ./a.out a.out
> dtrace: script 'ufunc.d' matched 5 probes
> dtrace: pid 86498 has exited
> 
> #
> 
> My system info:
> root at home:/home/spin6lock/test # dtrace -V
> dtrace: Sun D 1.7
> root at home:/home/spin6lock/test # uname -a
> FreeBSD 9.1-RELEASE FreeBSD 9.1-RELEASE #1: Mon Oct 28 20:52:03 CST
> 2013     root at xiangling:/usr/obj/usr/src/sys/DTRACE  amd64
> 
> Any clues? Thanks in advanced.

This seems to be the result of a bug in libproc. I've included a patch
below; could you apply it and verify that it fixes the problem? Once
you've applied the patch, libproc can be rebuilt with

# cd $SRCBASE/lib/libproc
# make && make install

Thanks,
-Mark

diff --git a/lib/libproc/proc_sym.c b/lib/libproc/proc_sym.c
index 87ac471..73e9742 100644
--- a/lib/libproc/proc_sym.c
+++ b/lib/libproc/proc_sym.c
@@ -465,7 +465,9 @@ proc_name2sym(struct proc_handle *p, const char *object, const char *symbol,
 			s = elf_strptr(e, dynsymstridx, sym.st_name);
 			if (s && strcmp(s, symbol) == 0) {
 				memcpy(symcopy, &sym, sizeof(sym));
-				symcopy->st_value = map->pr_vaddr + sym.st_value;
+				if (ehdr.e_type != ET_EXEC)
+					symcopy->st_value = map->pr_vaddr +
+					    sym.st_value;
 				error = 0;
 				goto out;
 			}
@@ -509,6 +511,7 @@ proc_iter_symbyaddr(struct proc_handle *p, const char *object, int which,
 	prmap_t *map;
 	Elf_Scn *scn, *foundscn = NULL;
 	Elf_Data *data;
+	GElf_Ehdr ehdr;
 	GElf_Shdr shdr;
 	GElf_Sym sym;
 	unsigned long stridx = -1;
@@ -525,6 +528,10 @@ proc_iter_symbyaddr(struct proc_handle *p, const char *object, int which,
 		DPRINTFX("ERROR: elf_begin() failed: %s", elf_errmsg(-1));
 		goto err1;
 	}
+	if (gelf_getehdr(e, &ehdr) == NULL) {
+		DPRINTFX("ERROR: gelf_getehdr() failed: %s", elf_errmsg(-1));
+		goto err2;
+	}
 	/*
 	 * Find the section we are looking for.
 	 */
@@ -575,7 +582,8 @@ proc_iter_symbyaddr(struct proc_handle *p, const char *object, int which,
 		    (mask & TYPE_FILE) == 0)
 			continue;
 		s = elf_strptr(e, stridx, sym.st_name);
-		sym.st_value += map->pr_vaddr;
+		if (ehdr.e_type != ET_EXEC)
+			sym.st_value += map->pr_vaddr;
 		(*func)(cd, &sym, s);
 	}
 	error = 0;