[DTrace-devel] [PATCH v5 07/10] cg: support casts of pointers to integers

[Nick Alcock]

When we cast a pointer to an integer, we want to scalarize it,
i.e. ensure that it is no longer a map_value, so that the user can
compare it freely to other integers.

Add a new DMST_SCALARIZER field to the machine state that anyone
can stuff map_values into and pull them right back out of to
scalarize them.

Signed-off-by: Nick Alcock <nick.alcock at oracle.com>
Reviewed-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 libdtrace/dt_cg.c   | 20 +++++++++++++++++++-
 libdtrace/dt_dctx.h |  2 ++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
index 87dc836e9033..e3588a939e0b 100644
--- a/libdtrace/dt_cg.c
+++ b/libdtrace/dt_cg.c
@@ -2468,6 +2468,8 @@ dt_cg_store(dt_node_t *src, dt_irlist_t *dlp, dt_regset_t *drp, dt_node_t *dst)
  * a scalar type is being narrowed or changing signed-ness.  We first shift the
  * desired bits high (losing excess bits if narrowing) and then shift them down
  * using logical shift (unsigned result) or arithmetic shift (signed result).
+ *
+ * We also need to scalarize pointers if we are casting them to an integral type.
  */
 static void
 dt_cg_typecast(const dt_node_t *src, const dt_node_t *dst,
@@ -2489,11 +2491,27 @@ dt_cg_typecast(const dt_node_t *src, const dt_node_t *dst,
 	else
 		n = sizeof(uint64_t) * NBBY - srcsize * NBBY;
 
-	if (dt_node_is_scalar(dst) && n != 0 && (dstsize < srcsize ||
+	if (!dt_node_is_scalar(dst))
+		return;
+
+	if (n != 0 && (dstsize < srcsize ||
 	    (src->dn_flags & DT_NF_SIGNED) ^ (dst->dn_flags & DT_NF_SIGNED))) {
 		emit(dlp, BPF_MOV_REG(dst->dn_reg, src->dn_reg));
 		emit(dlp, BPF_ALU64_IMM(BPF_LSH, dst->dn_reg, n));
 		emit(dlp, BPF_ALU64_IMM((dst->dn_flags & DT_NF_SIGNED) ? BPF_ARSH : BPF_RSH, dst->dn_reg, n));
+	} else if (dt_node_is_arith(dst) && dt_node_is_pointer(src) &&
+		   (src->dn_flags & DT_NF_ALLOCA)) {
+		int mst;
+
+		if ((mst = dt_regset_alloc(drp)) == -1)
+			longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
+
+		emit(dlp,  BPF_LOAD(BPF_DW, mst, BPF_REG_FP, DT_STK_DCTX));
+		emit(dlp,  BPF_LOAD(BPF_DW, mst, mst, DCTX_MST));
+		emit(dlp,  BPF_STORE(BPF_DW, mst, DMST_SCALARIZER, src->dn_reg));
+		emit(dlp,  BPF_LOAD(BPF_DW, dst->dn_reg, mst, DMST_SCALARIZER));
+
+		dt_regset_free(drp, mst);
 	}
 }
 
diff --git a/libdtrace/dt_dctx.h b/libdtrace/dt_dctx.h
index 1ce7fc9100ea..e41f36036612 100644
--- a/libdtrace/dt_dctx.h
+++ b/libdtrace/dt_dctx.h
@@ -24,6 +24,7 @@ typedef struct dt_mstate {
 	uint32_t	tag;		/* Tag (for future use) */
 	uint32_t	scratch_top;	/* Current top of scratch space */
 	int32_t		syscall_errno;	/* syscall errno */
+	uint64_t	scalarizer;	/* used to scalarize pointers */
 	uint64_t	fault;		/* DTrace fault flags */
 	uint64_t	tstamp;		/* cached timestamp value */
 	dt_pt_regs	regs;		/* CPU registers */
@@ -36,6 +37,7 @@ typedef struct dt_mstate {
 #define DMST_TAG		offsetof(dt_mstate_t, tag)
 #define DMST_SCRATCH_TOP	offsetof(dt_mstate_t, scratch_top)
 #define DMST_ERRNO		offsetof(dt_mstate_t, syscall_errno)
+#define DMST_SCALARIZER		offsetof(dt_mstate_t, scalarizer)
 #define DMST_FAULT		offsetof(dt_mstate_t, fault)
 #define DMST_TSTAMP		offsetof(dt_mstate_t, tstamp)
 #define DMST_REGS		offsetof(dt_mstate_t, regs)
-- 
2.35.1