From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Mon, 1 Dec 2014 23:18:13 +0000 (-0500)
Subject: Fix: context alignment not properly handled
X-Git-Tag: v2.7.0-rc1~68
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=b2cc986adb1aa11116ace6129dc2ec7e5c9737b1;p=lttng-ust.git

Fix: context alignment not properly handled

This issue affects only architectures without efficient unaligned
accesses, only when a context field with larger alignment follows a
context field with smaller alignment. It generates unreadable traces
when such context fields are enabled in this configuration.

Fixes #867

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

diff --git a/include/lttng/ust-events.h b/include/lttng/ust-events.h
index 01f611b2..9a46e678 100644
--- a/include/lttng/ust-events.h
+++ b/include/lttng/ust-events.h
@@ -258,11 +258,12 @@ struct lttng_ctx_field {
 	void (*destroy)(struct lttng_ctx_field *field);
 };
 
-#define LTTNG_UST_CTX_PADDING	24
+#define LTTNG_UST_CTX_PADDING	20
 struct lttng_ctx {
 	struct lttng_ctx_field *fields;
 	unsigned int nr_fields;
 	unsigned int allocated_fields;
+	unsigned int largest_align;
 	char padding[LTTNG_UST_CTX_PADDING];
 };
 
@@ -590,6 +591,7 @@ void lttng_probes_exit(void);
 int lttng_find_context(struct lttng_ctx *ctx, const char *name);
 int lttng_get_context_index(struct lttng_ctx *ctx, const char *name);
 struct lttng_ctx_field *lttng_append_context(struct lttng_ctx **ctx_p);
+void lttng_context_update(struct lttng_ctx *ctx);
 void lttng_remove_context_field(struct lttng_ctx **ctx_p,
 				struct lttng_ctx_field *field);
 void lttng_destroy_context(struct lttng_ctx *ctx);
diff --git a/liblttng-ust/lttng-context-ip.c b/liblttng-ust/lttng-context-ip.c
index 6f3edf83..31283f17 100644
--- a/liblttng-ust/lttng-context-ip.c
+++ b/liblttng-ust/lttng-context-ip.c
@@ -69,5 +69,6 @@ int lttng_add_ip_to_ctx(struct lttng_ctx **ctx)
 	field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
 	field->get_size = ip_get_size;
 	field->record = ip_record;
+	lttng_context_update(*ctx);
 	return 0;
 }
diff --git a/liblttng-ust/lttng-context-perf-counters.c b/liblttng-ust/lttng-context-perf-counters.c
index 99691c06..83b371c5 100644
--- a/liblttng-ust/lttng-context-perf-counters.c
+++ b/liblttng-ust/lttng-context-perf-counters.c
@@ -402,6 +402,7 @@ int lttng_add_perf_counter_to_ctx(uint32_t type,
 	 * the field here.
 	 */
 
+	lttng_context_update(*ctx);
 	return 0;
 
 setup_error:
diff --git a/liblttng-ust/lttng-context-procname.c b/liblttng-ust/lttng-context-procname.c
index c76d8ba3..4d41593e 100644
--- a/liblttng-ust/lttng-context-procname.c
+++ b/liblttng-ust/lttng-context-procname.c
@@ -108,6 +108,7 @@ int lttng_add_procname_to_ctx(struct lttng_ctx **ctx)
 	field->get_size = procname_get_size;
 	field->record = procname_record;
 	field->get_value = procname_get_value;
+	lttng_context_update(*ctx);
 	return 0;
 }
 
diff --git a/liblttng-ust/lttng-context-pthread-id.c b/liblttng-ust/lttng-context-pthread-id.c
index bf20c695..2b90e7bc 100644
--- a/liblttng-ust/lttng-context-pthread-id.c
+++ b/liblttng-ust/lttng-context-pthread-id.c
@@ -79,5 +79,6 @@ int lttng_add_pthread_id_to_ctx(struct lttng_ctx **ctx)
 	field->get_size = pthread_id_get_size;
 	field->record = pthread_id_record;
 	field->get_value = pthread_id_get_value;
+	lttng_context_update(*ctx);
 	return 0;
 }
diff --git a/liblttng-ust/lttng-context-vpid.c b/liblttng-ust/lttng-context-vpid.c
index 949529c6..b54ada1d 100644
--- a/liblttng-ust/lttng-context-vpid.c
+++ b/liblttng-ust/lttng-context-vpid.c
@@ -115,5 +115,6 @@ int lttng_add_vpid_to_ctx(struct lttng_ctx **ctx)
 	field->get_size = vpid_get_size;
 	field->record = vpid_record;
 	field->get_value = vpid_get_value;
+	lttng_context_update(*ctx);
 	return 0;
 }
diff --git a/liblttng-ust/lttng-context-vtid.c b/liblttng-ust/lttng-context-vtid.c
index 7d83b87c..f9abadbb 100644
--- a/liblttng-ust/lttng-context-vtid.c
+++ b/liblttng-ust/lttng-context-vtid.c
@@ -98,6 +98,7 @@ int lttng_add_vtid_to_ctx(struct lttng_ctx **ctx)
 	field->get_size = vtid_get_size;
 	field->record = vtid_record;
 	field->get_value = vtid_get_value;
+	lttng_context_update(*ctx);
 	return 0;
 }
 
diff --git a/liblttng-ust/lttng-context.c b/liblttng-ust/lttng-context.c
index ecee2344..6cab7dc1 100644
--- a/liblttng-ust/lttng-context.c
+++ b/liblttng-ust/lttng-context.c
@@ -80,6 +80,7 @@ struct lttng_ctx_field *lttng_append_context(struct lttng_ctx **ctx_p)
 		*ctx_p = zmalloc(sizeof(struct lttng_ctx));
 		if (!*ctx_p)
 			return NULL;
+		(*ctx_p)->largest_align = 1;
 	}
 	ctx = *ctx_p;
 	if (ctx->nr_fields + 1 > ctx->allocated_fields) {
@@ -99,6 +100,94 @@ struct lttng_ctx_field *lttng_append_context(struct lttng_ctx **ctx_p)
 	return field;
 }
 
+/*
+ * lttng_context_update() should be called at least once between context
+ * modification and trace start.
+ */
+void lttng_context_update(struct lttng_ctx *ctx)
+{
+	int i;
+	size_t largest_align = 8;	/* in bits */
+
+	for (i = 0; i < ctx->nr_fields; i++) {
+		struct lttng_type *type;
+		size_t field_align = 8;
+
+		type = &ctx->fields[i].event_field.type;
+		switch (type->atype) {
+		case atype_integer:
+			field_align = type->u.basic.integer.alignment;
+			break;
+		case atype_array:
+		{
+			struct lttng_basic_type *btype;
+
+			btype = &type->u.array.elem_type;
+			switch (btype->atype) {
+			case atype_integer:
+				field_align = btype->u.basic.integer.alignment;
+				break;
+			case atype_string:
+				break;
+
+			case atype_array:
+			case atype_sequence:
+			default:
+				WARN_ON_ONCE(1);
+				break;
+			}
+			break;
+		}
+		case atype_sequence:
+		{
+			struct lttng_basic_type *btype;
+
+			btype = &type->u.sequence.length_type;
+			switch (btype->atype) {
+			case atype_integer:
+				field_align = btype->u.basic.integer.alignment;
+				break;
+
+			case atype_string:
+			case atype_array:
+			case atype_sequence:
+			default:
+				WARN_ON_ONCE(1);
+				break;
+			}
+
+			btype = &type->u.sequence.elem_type;
+			switch (btype->atype) {
+			case atype_integer:
+				field_align = max_t(size_t,
+					field_align,
+					btype->u.basic.integer.alignment);
+				break;
+
+			case atype_string:
+				break;
+
+			case atype_array:
+			case atype_sequence:
+			default:
+				WARN_ON_ONCE(1);
+				break;
+			}
+			break;
+		}
+		case atype_string:
+			break;
+
+		case atype_enum:
+		default:
+			WARN_ON_ONCE(1);
+			break;
+		}
+		largest_align = max_t(size_t, largest_align, field_align);
+	}
+	ctx->largest_align = largest_align >> 3;	/* bits to bytes */
+}
+
 /*
  * Remove last context field.
  */
diff --git a/liblttng-ust/lttng-ring-buffer-client.h b/liblttng-ust/lttng-ring-buffer-client.h
index e734632f..96aeb1e5 100644
--- a/liblttng-ust/lttng-ring-buffer-client.h
+++ b/liblttng-ust/lttng-ring-buffer-client.h
@@ -76,6 +76,7 @@ size_t ctx_get_size(size_t offset, struct lttng_ctx *ctx)
 
 	if (caa_likely(!ctx))
 		return 0;
+	offset += lib_ring_buffer_align(offset, ctx->largest_align);
 	for (i = 0; i < ctx->nr_fields; i++)
 		offset += ctx->fields[i].get_size(offset);
 	return offset - orig_offset;
@@ -90,6 +91,7 @@ void ctx_record(struct lttng_ust_lib_ring_buffer_ctx *bufctx,
 
 	if (caa_likely(!ctx))
 		return;
+	lib_ring_buffer_align_ctx(bufctx, ctx->largest_align);
 	for (i = 0; i < ctx->nr_fields; i++)
 		ctx->fields[i].record(&ctx->fields[i], bufctx, chan);
 }