[DTrace-devel] [PATCH 2/7] types: populate intrinsics from the kernel if possible

[Nick Alcock]

The primary purpose of types in the C container, like types in DTrace in
general, is not just to write D programs and #include C headers -- it's
also to interoperate with the type system used by the kernel.

As such, we really should be getting types in this dict *from* the
kernel if at all possible.  This also means we are insulated from the
kernel suddenly changing its type system on us (being freestanding,
the kernel can break platform ABI like that fairly freely, as it
recently did with the unconditional unsignednessing of char); whatever
the types are, we just pick them up, and then any types the users (or
the D container, or the syslibs, or...) base on them will be compatible
with whatever the kernel's definition is.

A lot of types in the _dtrace_intrinsics_* arrays are now redundant, but
precisely which those *are* depends on the running kernel, so we leave
the lot so that we can always use those types in D even if the kernel
doesn't define them at all.  (But in practice all the useful ones will
always come from vmlinux from now on -- except for void, which we
define ourselves because of the IS_VOID() macro. Nobody's ever going to
check void for assignment-compatibility anyway, and the definition of
void in particular is woolly in CTF and different implementations have
defined it in rather different ways.  Let's stick to one consistent
intrinsic instead.)

Signed-off-by: Nick Alcock <nick.alcock at oracle.com>
---
 libdtrace/dt_open.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/libdtrace/dt_open.c b/libdtrace/dt_open.c
index f0dc2575377f2..f0ef053f5274d 100644
--- a/libdtrace/dt_open.c
+++ b/libdtrace/dt_open.c
@@ -939,10 +939,31 @@ dt_vopen(int version, int flags, int *errp,
 	dmp->dm_flags = DT_DM_LOADED; /* fake up loaded bit */
 
 	/*
-	 * Fill the dynamic "C" CTF container with all of the intrinsic
-	 * integer and floating-point types appropriate for this data model.
+	 * Fill the dynamic "C" CTF container with all of the intrinsic integer
+	 * and floating-point types appropriate for this data model; but first,
+	 * try to prepopulate them all from the vmlinux` container, so that our
+	 * types are compatible with the kernel's type system.  Or at least,
+	 * almost all of them: "void" has special hardwired behaviour in
+	 * dt_parser.h and nobody's likely to check it for
+	 * assignment-compatibility, so use the hardwired intrinsic for that
+	 * unconditionally.
 	 */
 	for (; dinp->din_name != NULL; dinp++) {
+		dtrace_typeinfo_t ti;
+
+		if (strcmp(dinp->din_name, "void") != 0 &&
+		    dtrace_lookup_by_type(dtp, "vmlinux", dinp->din_name,
+			&ti) == 0) {
+			if (ctf_add_type(dmp->dm_ctfp, ti.dtt_ctfp,
+				ti.dtt_type) != CTF_ERR)
+				continue;
+			else
+				dt_dprintf("Attempt to add %s from the kernel "
+				    "CTF failed: %s.  Using hardwired def.)\n",
+				    dinp->din_name,
+				    ctf_errmsg(ctf_errno(dmp->dm_ctfp)));
+		}
+
 		if (dinp->din_kind == CTF_K_INTEGER) {
 			err = ctf_add_integer(dmp->dm_ctfp, CTF_ADD_ROOT,
 			    dinp->din_name, &dinp->din_data);
-- 
2.39.1.268.g9de2f9a303