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-Tag: v2.12.5~5
X-Git-Url: http://git.lttng.org/?a=commitdiff_plain;h=6f0a5631039e42ef0b9665942257867e1fab4faa;p=lttng-ust.git

Fix: bytecode interpreter context_get_index() leaves byte order uninitialized

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

With lttng-ust 2.13, 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.

This issue is not visible in lttng-ust 2.12 because it does not
implement the event notification capture feature. However, it would
become observable if a lttng-tools emits a filter bytecode
BYTECODE_OP_GET_SYMBOL instruction to load the context value. For
compatibility purposes, lttng-tools only uses
BYTECODE_OP_GET_CONTEXT_REF to load the filter context fields,
but nothing prevents a future lttng-tools version from using
BYTECODE_OP_GET_SYMBOL instead.

Cause
=====

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

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/liblttng-ust/lttng-filter-interpreter.c b/liblttng-ust/lttng-filter-interpreter.c
index b57edacd..d558b6b2 100644
--- a/liblttng-ust/lttng-filter-interpreter.c
+++ b/liblttng-ust/lttng-filter-interpreter.c
@@ -246,6 +246,7 @@ static int context_get_index(struct lttng_ctx *ctx,
 			ptr->u.u64 = v.u.s64;	/* Cast. */
 			ptr->ptr = &ptr->u.u64;
 		}
+		ptr->rev_bo = field->type.u.basic.integer.reverse_byte_order;
 		break;
 	case atype_enum:
 	{
@@ -262,6 +263,7 @@ static int context_get_index(struct lttng_ctx *ctx,
 			ptr->u.u64 = v.u.s64;	/* Cast. */
 			ptr->ptr = &ptr->u.u64;
 		}
+		ptr->rev_bo = itype->reverse_byte_order;
 		break;
 	}
 	case atype_array:
@@ -300,6 +302,7 @@ static int context_get_index(struct lttng_ctx *ctx,
 		ctx_field->get_value(ctx_field, &v);
 		ptr->u.d = v.u.d;
 		ptr->ptr = &ptr->u.d;
+		ptr->rev_bo = field->type.u.basic._float.reverse_byte_order;
 		break;
 	case atype_dynamic:
 		ctx_field->get_value(ctx_field, &v);
@@ -310,12 +313,22 @@ static int context_get_index(struct lttng_ctx *ctx,
 			ptr->object_type = OBJECT_TYPE_S64;
 			ptr->u.s64 = v.u.s64;
 			ptr->ptr = &ptr->u.s64;
+			/*
+			 * struct lttng_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_DOUBLE:
 			ptr->object_type = OBJECT_TYPE_DOUBLE;
 			ptr->u.d = v.u.d;
 			ptr->ptr = &ptr->u.d;
+			/*
+			 * struct lttng_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: