From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 30 Mar 2022 16:10:53 +0000 (-0400)
Subject: Fix: bytecode interpreter context_get_index() leaves byte order uninitialized
X-Git-Url: https://git.lttng.org/?p=lttng-ust.git;a=commitdiff_plain;h=3ef88eda2c8de4df57a70b10457602d84a057007

Fix: bytecode interpreter context_get_index() leaves byte order uninitialized

Observed Issue
==============

When using the event notification capture feature to capture a context
field, e.g. '$ctx.cpu_id', the captured value is often observed in
reverse byte order.

Cause
=====

Within the bytecode interpreter, context_get_index() leaves the "rev_bo"
field uninitialized in the top of stack.

This only affects the event notification capture bytecode because the
BYTECODE_OP_GET_SYMBOL bytecode instruction (as of lttng-tools 2.13)
is only generated for capture bytecode in lttng-tools. Therefore, only
capture bytecode targeting contexts are affected by this issue. The
reason why lttng-tools uses the "legacy" bytecode instruction to get
context (BYTECODE_OP_GET_CONTEXT_REF) for the filter bytecode is to
preserve backward compatibility of filtering when interacting with
applications linked against LTTng-UST 2.12.

Solution
========

Initialize the rev_bo field based on the context field type
reserve_byte_order field.

Known drawbacks
===============

None.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I74996d501cee3c269658d98dfc0d0050b74c5ddb
---

diff --git a/src/lib/lttng-ust/lttng-bytecode-interpreter.c b/src/lib/lttng-ust/lttng-bytecode-interpreter.c
index d677fb99..7f19e981 100644
--- a/src/lib/lttng-ust/lttng-bytecode-interpreter.c
+++ b/src/lib/lttng-ust/lttng-bytecode-interpreter.c
@@ -242,6 +242,7 @@ static int context_get_index(struct lttng_ust_ctx *ctx,
 			ptr->u.u64 = v.u.s64;	/* Cast. */
 			ptr->ptr = &ptr->u.u64;
 		}
+		ptr->rev_bo = lttng_ust_get_type_integer(field->type)->reverse_byte_order;
 		break;
 	case lttng_ust_type_enum:
 	{
@@ -258,6 +259,7 @@ static int context_get_index(struct lttng_ust_ctx *ctx,
 			ptr->u.u64 = v.u.s64;	/* Cast. */
 			ptr->ptr = &ptr->u.u64;
 		}
+		ptr->rev_bo = itype->reverse_byte_order;
 		break;
 	}
 	case lttng_ust_type_array:
@@ -296,6 +298,7 @@ static int context_get_index(struct lttng_ust_ctx *ctx,
 		ctx_field->get_value(ctx_field->priv, probe_ctx, &v);
 		ptr->u.d = v.u.d;
 		ptr->ptr = &ptr->u.d;
+		ptr->rev_bo = lttng_ust_get_type_float(field->type)->reverse_byte_order;
 		break;
 	case lttng_ust_type_dynamic:
 		ctx_field->get_value(ctx_field->priv, probe_ctx, &v);
@@ -309,6 +312,11 @@ static int context_get_index(struct lttng_ust_ctx *ctx,
 			ptr->object_type = OBJECT_TYPE_U64;
 			ptr->u.u64 = v.u.u64;
 			ptr->ptr = &ptr->u.u64;
+			/*
+			 * struct lttng_ust_ctx_value does not currently
+			 * feature a byte order field.
+			 */
+			ptr->rev_bo = false;
 			dbg_printf("context get index dynamic u64 %" PRIi64 "\n", ptr->u.u64);
 			break;
 		case LTTNG_UST_DYNAMIC_TYPE_S8:
@@ -318,6 +326,11 @@ static int context_get_index(struct lttng_ust_ctx *ctx,
 			ptr->object_type = OBJECT_TYPE_S64;
 			ptr->u.s64 = v.u.s64;
 			ptr->ptr = &ptr->u.s64;
+			/*
+			 * struct lttng_ust_ctx_value does not currently
+			 * feature a byte order field.
+			 */
+			ptr->rev_bo = false;
 			dbg_printf("context get index dynamic s64 %" PRIi64 "\n", ptr->u.s64);
 			break;
 		case LTTNG_UST_DYNAMIC_TYPE_FLOAT:
@@ -325,6 +338,11 @@ static int context_get_index(struct lttng_ust_ctx *ctx,
 			ptr->object_type = OBJECT_TYPE_DOUBLE;
 			ptr->u.d = v.u.d;
 			ptr->ptr = &ptr->u.d;
+			/*
+			 * struct lttng_ust_ctx_value does not currently
+			 * feature a byte order field.
+			 */
+			ptr->rev_bo = false;
 			dbg_printf("context get index dynamic double %g\n", ptr->u.d);
 			break;
 		case LTTNG_UST_DYNAMIC_TYPE_STRING: