Remove drti.o's dependency on libelf. This makes it possible to add DTrace

probes to userland programs and libraries without also needing to link
libelf.

dtrace -G places the __SUNW_dof symbol at the beginning of the DOF (DTrace
probe and provider metdata) section in the generated object file; drti.o
now just uses this symbol to locate the section. A complication occurs
when multiple dtrace-generated object files are linked together, since the
__SUNW_dof symbol defined in each file is global. This is handled by
using objcopy(1) to convert __SUNW_dof to a local symbol once drti.o has
been linked with the generated object file. Upstream, this is done using a
linker feature not present in GNU ld.

Differential Revision:	https://reviews.freebsd.org/D1757
Reviewed by:	rpaulo
MFC after:	1 month
Relnotes:	yes

1 files changed, 10 insertions, 0 deletions

diff --git a/cddl/contrib/opensolaris/lib/libdtrace/common/dt_open.c b/cddl/contrib/opensolaris/lib/libdtrace/common/dt_open.c
index b8b1467..c952243 100644
--- a/cddl/contrib/opensolaris/lib/libdtrace/common/dt_open.c
+++ b/cddl/contrib/opensolaris/lib/libdtrace/common/dt_open.c
@@ -785,6 +785,7 @@ const char *_dtrace_defld = "/usr/ccs/bin/ld";   /* default ld(1) to invoke */
 #else
 const char *_dtrace_defcpp = "cpp"; /* default cpp(1) to invoke */
 const char *_dtrace_defld = "ld";   /* default ld(1) to invoke */
+const char *_dtrace_defobjcopy = "objcopy"; /* default objcopy(1) to invoke */
 #endif
 
 const char *_dtrace_libdir = "/usr/lib/dtrace"; /* default library directory */
@@ -1185,6 +1186,9 @@ alloc:
 	dtp->dt_cpp_argc = 1;
 	dtp->dt_cpp_args = 1;
 	dtp->dt_ld_path = strdup(_dtrace_defld);
+#ifdef __FreeBSD__
+	dtp->dt_objcopy_path = strdup(_dtrace_defobjcopy);
+#endif
 	dtp->dt_provmod = provmod;
 	dtp->dt_vector = vector;
 	dtp->dt_varg = arg;
@@ -1193,6 +1197,9 @@ alloc:
 
 	if (dtp->dt_mods == NULL || dtp->dt_provs == NULL ||
 	    dtp->dt_procs == NULL || dtp->dt_ld_path == NULL ||
+#ifdef __FreeBSD__
+	    dtp->dt_objcopy_path == NULL ||
+#endif
 	    dtp->dt_cpp_path == NULL || dtp->dt_cpp_argv == NULL)
 		return (set_open_errno(dtp, errp, EDT_NOMEM));
 
@@ -1673,6 +1680,9 @@ dtrace_close(dtrace_hdl_t *dtp)
 	free(dtp->dt_cpp_argv);
 	free(dtp->dt_cpp_path);
 	free(dtp->dt_ld_path);
+#ifdef __FreeBSD__
+	free(dtp->dt_objcopy_path);
+#endif
 
 	free(dtp->dt_mods);
 	free(dtp->dt_provs);