[DTrace-devel] [PATCH 2/6] Support storing variables by reference

[eugene.loh at oracle.com]

From: Eugene Loh <eugene.loh at oracle.com>

Initial support for storing variables by reference -- that is,
by copying them via the dt_memcpy() routine.  Ultimately, this
support will have to be expanded to include kernel and userspace
memory.

Note that dt_memcpy() is currently limited to 256 bytes.

Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
---
 bpf/Build                               |  3 +-
 libdtrace/dt_cg.c                       | 43 +++++++++++++++++--------
 test/unittest/struct/tst.StructInside.d |  3 +-
 3 files changed, 32 insertions(+), 17 deletions(-)

diff --git a/bpf/Build b/bpf/Build
index f8d736e7..5133a2f2 100644
--- a/bpf/Build
+++ b/bpf/Build
@@ -25,8 +25,9 @@ bpf_dlib_SOURCES = \
 	agg_lqbin.c agg_qbin.c \
 	get_bvar.c \
 	get_tvar.c set_tvar.c \
+	memcpy.c \
 	probe_error.c \
-	memcpy.c strnlen.c
+	strnlen.c
 
 bpf-check: $(objdir)/include/.dir.stamp
 	$(BPFC) $(BPFCPPFLAGS) $(bpf_dlib_CPPFLAGS) $(BPFCFLAGS) -S \
diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
index 9243f0a7..ab3fe761 100644
--- a/libdtrace/dt_cg.c
+++ b/libdtrace/dt_cg.c
@@ -656,6 +656,26 @@ dt_cg_fill_gap(dt_pcb_t *pcb, int gap)
 		emit(dlp, BPF_STORE_IMM(BPF_W, BPF_REG_9, off, 0));
 }
 
+static void
+dt_cg_memcpy(dt_irlist_t *dlp, dt_regset_t *drp, int dst, int src, size_t size)
+{
+	dt_ident_t *idp;
+
+	if (dt_regset_xalloc_args(drp) == -1)
+		longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
+
+	emit(dlp,  BPF_MOV_REG(BPF_REG_1, dst));
+	emit(dlp,  BPF_MOV_REG(BPF_REG_2, src));
+	emit(dlp,  BPF_MOV_IMM(BPF_REG_3, size));
+	idp = dt_dlib_get_func(yypcb->pcb_hdl, "dt_memcpy");
+	assert(idp != NULL);
+	dt_regset_xalloc(drp, BPF_REG_0);
+	emite(dlp, BPF_CALL_FUNC(idp->di_id), idp);
+	dt_regset_free_args(drp);
+	/* FIXME: check BPF_REG_0 for error? */
+	dt_regset_free(drp, BPF_REG_0);
+}
+
 static void
 dt_cg_spill_store(int reg)
 {
@@ -1851,19 +1871,9 @@ dt_cg_store(dt_node_t *src, dt_irlist_t *dlp, dt_regset_t *drp, dt_node_t *dst)
 	else
 		size = dt_node_type_size(src);
 
-	if (src->dn_flags & DT_NF_REF) {
-#ifdef FIXME
-		if ((reg = dt_regset_alloc(drp)) == -1)
-			longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
-		dt_cg_setx(dlp, reg, size);
-		instr = DIF_INSTR_COPYS(src->dn_reg, reg, dst->dn_reg);
-		dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
-		dt_regset_free(drp, reg);
-#else
-		xyerror(D_UNKNOWN, "internal error -- cg cannot store "
-			"values passed by ref\n");
-#endif
-	} else {
+	if (src->dn_flags & DT_NF_REF)
+		dt_cg_memcpy(dlp, drp, dst->dn_reg, src->dn_reg, size);
+	else {
 		uint8_t	sz;
 
 		if (dst->dn_flags & DT_NF_BITFIELD)
@@ -1919,7 +1929,12 @@ dt_cg_store_var(dt_node_t *src, dt_irlist_t *dlp, dt_regset_t *drp,
 			longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
 		emit(dlp, BPF_LOAD(BPF_DW, reg, BPF_REG_FP, DT_STK_DCTX));
 		emit(dlp, BPF_LOAD(BPF_DW, reg, reg, DCTX_GVARS));
-		emit(dlp, BPF_STORE(BPF_DW, reg, idp->di_offset, src->dn_reg));
+		if ((src->dn_flags & DT_NF_REF) == 0)
+			emit(dlp, BPF_STORE(BPF_DW, reg, idp->di_offset, src->dn_reg));
+		else {
+			emit(dlp, BPF_ALU64_IMM(BPF_ADD, reg, idp->di_offset));
+			dt_cg_memcpy(dlp, drp, reg, src->dn_reg, idp->di_size);
+		}
 		dt_regset_free(drp, reg);
 		return;
 	}
diff --git a/test/unittest/struct/tst.StructInside.d b/test/unittest/struct/tst.StructInside.d
index 71b2a839..2e1a8218 100644
--- a/test/unittest/struct/tst.StructInside.d
+++ b/test/unittest/struct/tst.StructInside.d
@@ -1,10 +1,9 @@
 /*
  * Oracle Linux DTrace.
- * Copyright (c) 2006, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2006, 2021, Oracle and/or its affiliates. All rights reserved.
  * Licensed under the Universal Permissive License v 1.0 as shown at
  * http://oss.oracle.com/licenses/upl.
  */
-/* @@xfail: dtv2 */
 
 /*
  * ASSERTION:
-- 
2.18.4