From 2c70564defbb66d6c2a776719642cef2bc17a2f6 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Wed, 30 Mar 2022 14:24:54 -0400 Subject: [PATCH] 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 Change-Id: I1483642b0b8f6bc28d5b68be170a04fb419fd9b3 --- src/lttng-bytecode-interpreter.c | 2 ++ 1 file changed, 2 insertions(+) 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: -- 2.34.1