[DTrace-devel] [PATCH] cg: fix return value of copyin()

[Kris Van Hees]

The copyin() function was returning the resolved alloca pointer rather
than the offset into scratchmem (as it should have).  Now that the
function is correctly marked as returning an alloca-pointer, it needs
to return the native representation of an alloca-pointer, i.e. as an
offset into scratchmem.

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 libdtrace/dt_cg.c                             | 12 ++++---
 .../funcs/copyin/tst.copyin-retval-ok.d       | 31 +++++++++++++++++++
 2 files changed, 39 insertions(+), 4 deletions(-)
 create mode 100644 test/unittest/funcs/copyin/tst.copyin-retval-ok.d

diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
index 0b8cc80a..cc6ca05c 100644
--- a/libdtrace/dt_cg.c
+++ b/libdtrace/dt_cg.c
@@ -4492,6 +4492,9 @@ dt_cg_subr_copyin(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
 
 	/* Allocate scratch space. */
 	dt_cg_subr_alloca_impl(dnp, size, dlp, drp);
+	/* Push the native alloca value to be used as return value. */
+	dt_cg_push_stack(dnp->dn_reg, dlp, drp);
+	/* Turn it into a proper alloca pointer. */
 	dt_cg_alloca_ptr(dlp, drp, dnp->dn_reg, dnp->dn_reg);
 
 	dt_cg_node(src, dlp, drp);
@@ -4506,16 +4509,17 @@ dt_cg_subr_copyin(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
 	emit(dlp, BPF_CALL_HELPER(dtp->dt_bpfhelper[BPF_FUNC_probe_read_user]));
 	dt_regset_free_args(drp);
 	emit(dlp,  BPF_BRANCH_IMM(BPF_JEQ, BPF_REG_0, 0, lbl_ok));
+	dt_regset_free(drp, BPF_REG_0);
 	dt_cg_probe_error(yypcb, DTRACEFLT_BADADDR, DT_ISREG, src->dn_reg);
+	dt_regset_free(drp, src->dn_reg);
 	emitl(dlp, lbl_badsize,
 		   BPF_NOP());
 	dt_cg_probe_error(yypcb, DTRACEFLT_BADSIZE, DT_ISREG, size->dn_reg);
+	dt_regset_free(drp, size->dn_reg);
 	emitl(dlp, lbl_ok,
 		   BPF_NOP());
-	dt_regset_free(drp, BPF_REG_0);
-
-	dt_regset_free(drp, src->dn_reg);
-	dt_regset_free(drp, size->dn_reg);
+	/* Pop the native alloca value as our value. */
+	dt_cg_pop_stack(dnp->dn_reg, dlp, drp);
 
 	TRACE_REGSET("    subr-copyin:End  ");
 }
diff --git a/test/unittest/funcs/copyin/tst.copyin-retval-ok.d b/test/unittest/funcs/copyin/tst.copyin-retval-ok.d
new file mode 100644
index 00000000..b84e7e16
--- /dev/null
+++ b/test/unittest/funcs/copyin/tst.copyin-retval-ok.d
@@ -0,0 +1,31 @@
+/*
+ * Oracle Linux DTrace.
+ * Copyright (c) 2022, 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.
+ */
+
+/*
+ * ASSERTION: Ensure the alloca()'d pointer return value of copyin() is valid.
+ *
+ * SECTION: Actions and Subroutines/copyin()
+ */
+
+#pragma D option quiet
+#pragma D option destructive
+
+BEGIN
+{
+	system("echo dtrace-copyin-test");
+}
+
+syscall::write:entry
+{
+	((uint8_t *)copyin(arg1, 32))[0];
+	exit(0);
+}
+
+ERROR
+{
+	exit(1);
+}
-- 
2.39.1