Re: USDT support (in build framework)?

On Thu, Mar 23, 2023 at 11:58:07AM +0000, Domagoj Stolfa wrote:
> Hi:
> 
> 
> I've done this for bhyve, specifically for virtio-net. I believe this is 
> the whole patch I needed:
> 
> 
> +OBJS:=bhyve_provider.o ${OBJS}
> +DTRACE_OBJS=${SRCS:C/\.c/.o/}
> +
> +beforelinking:
> +       dtrace -G -s ${BHYVE_SRCDIR}/bhyve_provider.d ${DTRACE_OBJS}
> +
> 
> 
> however, it has been a while and I don't 100% recall if anything else 
> was necessary. I had to create a helper DTRACE_OBJS because using OBJS 
> would cause linking to fail later on. I'm sure there are better ways of 
> doing it, but this seems to work for me. Let me know if it fails!

For a while it's been possible to simply add the provider definition to
SRCS.  We have rules in share/mk that handle the rest.  Below is a patch
which adds a USDT probe to cat(1) as an example, the probe just prints
the file name of each file that gets processed.

BTW, I can't seem to declare a probe argument with type const char * -
when dtrace -h generates the header, the const qualifer gets stripped
away.  That seems like a bug.

# dtrace -n 'cat$target:::foo {printf("%s", copyinstr(arg0));}' -c "cat /dev/null"
dtrace: description 'cat$target:::foo ' matched 1 probe
CPU     ID                    FUNCTION:NAME
  6  99502                    scanfiles:foo /dev/null
dtrace: pid 80789 has exited

diff --git a/bin/cat/Makefile b/bin/cat/Makefile
index 06bb071363f8..81cad980eaa3 100644
--- a/bin/cat/Makefile
+++ b/bin/cat/Makefile
@@ -5,6 +5,7 @@
 
 PACKAGE=runtime
 PROG=	cat
+SRCS=	cat.c catprov.d
 
 .ifdef BOOTSTRAPPING
 # For the bootstrap cat we disable all wide char support to allow building
diff --git a/bin/cat/cat.c b/bin/cat/cat.c
index 5a1fab0c26a0..91f31d0b4668 100644
--- a/bin/cat/cat.c
+++ b/bin/cat/cat.c
@@ -74,6 +74,8 @@ __FBSDID("$FreeBSD$");
 #include <casper/cap_fileargs.h>
 #include <casper/cap_net.h>
 
+#include "catprov.h"
+
 static int bflag, eflag, lflag, nflag, sflag, tflag, vflag;
 static int rval;
 static const char *filename;
@@ -266,6 +268,7 @@ scanfiles(char *argv[], int cooked __unused)
 				fd = udom_open(path, O_RDONLY);
 #endif
 		}
+		CAT_FOO(__DECONST(char *, filename));
 		if (fd < 0) {
 			warn("%s", path);
 			rval = 1;
diff --git a/bin/cat/catprov.d b/bin/cat/catprov.d
new file mode 100644
index 000000000000..5d9d2444cc23
--- /dev/null
+++ b/bin/cat/catprov.d
@@ -0,0 +1,3 @@
+provider cat {
+	probe foo(char *);
+};