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 b57edacde71f4cc5d2f67f8fe4ccde224a777727..d558b6b2be26ce8feec1a941f6080b76074baec2 100644 (file)
--- 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: