From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 30 Mar 2022 18:24:54 +0000 (-0400)
Subject: Fix: bytecode interpreter context_get_index() leaves byte order uninitialized
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=2c70564defbb66d6c2a776719642cef2bc17a2f6;p=lttng-modules.git

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: I1483642b0b8f6bc28d5b68be170a04fb419fd9b3
---

diff --git a/src/lttng-bytecode-interpreter.c b/src/lttng-bytecode-interpreter.c
index a2a932c6..4b100ab8 100644
--- a/src/lttng-bytecode-interpreter.c
+++ b/src/lttng-bytecode-interpreter.c
@@ -294,6 +294,7 @@ static int context_get_index(struct lttng_kernel_probe_ctx *lttng_probe_ctx,
 			ptr->u.u64 = v.u.s64;	/* Cast. */
 			ptr->ptr = &ptr->u.u64;
 		}
+		ptr->rev_bo = lttng_kernel_get_type_integer(field->type)->reverse_byte_order;
 		break;
 	case lttng_kernel_type_enum:
 	{
@@ -310,6 +311,7 @@ static int context_get_index(struct lttng_kernel_probe_ctx *lttng_probe_ctx,
 			ptr->u.u64 = v.u.s64;	/* Cast. */
 			ptr->ptr = &ptr->u.u64;
 		}
+		ptr->rev_bo = integer_type->reverse_byte_order;
 		break;
 	}
 	case lttng_kernel_type_array: