From: Mathieu Desnoyers Date: Mon, 14 Apr 2014 14:58:52 +0000 (-0400) Subject: Fix: pad strings that are modified concurrently with tracing X-Git-Tag: v2.4.2~14 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=0b5389bbeb5da342a12a195d34ea8c6d0db55a04;p=lttng-ust.git Fix: pad strings that are modified concurrently with tracing Fixes #734 Signed-off-by: Mathieu Desnoyers --- diff --git a/include/lttng/ust-events.h b/include/lttng/ust-events.h index ac412624..3d473407 100644 --- a/include/lttng/ust-events.h +++ b/include/lttng/ust-events.h @@ -433,7 +433,10 @@ struct lttng_channel_ops { unsigned char *uuid, uint32_t chan_id); void (*channel_destroy)(struct lttng_channel *chan); - void *_deprecated1; + union { + void *_deprecated1; + unsigned long has_strcpy:1; /* ABI has strcpy */ + } u; void *_deprecated2; int (*event_reserve)(struct lttng_ust_lib_ring_buffer_ctx *ctx, uint32_t event_id); @@ -452,6 +455,8 @@ struct lttng_channel_ops { int (*is_finalized)(struct channel *chan); int (*is_disabled)(struct channel *chan); int (*flush_buffer)(struct channel *chan, struct lttng_ust_shm_handle *handle); + void (*event_strcpy)(struct lttng_ust_lib_ring_buffer_ctx *ctx, + const char *src, size_t len); }; /* diff --git a/include/lttng/ust-tracepoint-event.h b/include/lttng/ust-tracepoint-event.h index 8140b9df..d12e8bb7 100644 --- a/include/lttng/ust-tracepoint-event.h +++ b/include/lttng/ust-tracepoint-event.h @@ -520,10 +520,24 @@ size_t __event_get_align__##_provider##___##_name(_TP_ARGS_PROTO(_args)) \ __chan->ops->event_write(&__ctx, _src, \ sizeof(_type) * __get_dynamic_len(dest)); +/* + * __chan->ops->u.has_strcpy is a flag letting us know if the LTTng-UST + * tracepoint provider ABI implements event_strcpy. This dynamic check + * can be removed when the tracepoint provider ABI moves to 2. + */ +#if (LTTNG_UST_PROVIDER_MAJOR > 1) +#error "Tracepoint probe provider major version has changed. Please remove dynamic check for has_strcpy." +#endif + #undef _ctf_string #define _ctf_string(_item, _src, _nowrite) \ lib_ring_buffer_align_ctx(&__ctx, lttng_alignof(*(_src))); \ - __chan->ops->event_write(&__ctx, _src, __get_dynamic_len(dest)); + if (__chan->ops->u.has_strcpy) \ + __chan->ops->event_strcpy(&__ctx, _src, \ + __get_dynamic_len(dest)); \ + else \ + __chan->ops->event_write(&__ctx, _src, \ + __get_dynamic_len(dest)); /* Beware: this get len actually consumes the len value */ #undef __get_dynamic_len diff --git a/liblttng-ust/lttng-ring-buffer-client.h b/liblttng-ust/lttng-ring-buffer-client.h index 87d1a8cd..e734632f 100644 --- a/liblttng-ust/lttng-ring-buffer-client.h +++ b/liblttng-ust/lttng-ring-buffer-client.h @@ -601,6 +601,13 @@ void lttng_event_write(struct lttng_ust_lib_ring_buffer_ctx *ctx, const void *sr lib_ring_buffer_write(&client_config, ctx, src, len); } +static +void lttng_event_strcpy(struct lttng_ust_lib_ring_buffer_ctx *ctx, const char *src, + size_t len) +{ + lib_ring_buffer_strcpy(&client_config, ctx, src, len, '#'); +} + #if 0 static wait_queue_head_t *lttng_get_reader_wait_queue(struct channel *chan) @@ -651,6 +658,7 @@ static struct lttng_transport lttng_relay_transport = { .ops = { .channel_create = _channel_create, .channel_destroy = lttng_channel_destroy, + .u.has_strcpy = 1, .event_reserve = lttng_event_reserve, .event_commit = lttng_event_commit, .event_write = lttng_event_write, @@ -660,6 +668,7 @@ static struct lttng_transport lttng_relay_transport = { .is_finalized = lttng_is_finalized, .is_disabled = lttng_is_disabled, .flush_buffer = lttng_flush_buffer, + .event_strcpy = lttng_event_strcpy, }, .client_config = &client_config, }; diff --git a/libringbuffer/backend.h b/libringbuffer/backend.h index feefc7a3..53a97140 100644 --- a/libringbuffer/backend.h +++ b/libringbuffer/backend.h @@ -105,6 +105,96 @@ void lib_ring_buffer_write(const struct lttng_ust_lib_ring_buffer_config *config ctx->buf_offset += len; } +/* + * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL + * terminating character is found in @src. Returns the number of bytes + * copied. Does *not* terminate @dest with NULL terminating character. + */ +static inline +size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config, + char *dest, const char *src, size_t len) +{ + size_t count; + + for (count = 0; count < len; count++) { + char c; + + /* + * Only read source character once, in case it is + * modified concurrently. + */ + c = CMM_LOAD_SHARED(src[count]); + if (!c) + break; + lib_ring_buffer_do_copy(config, &dest[count], &c, 1); + } + return count; +} + +/** + * lib_ring_buffer_strcpy - write string data to a buffer backend + * @config : ring buffer instance configuration + * @ctx: ring buffer context. (input arguments only) + * @src : source pointer to copy from + * @len : length of data to copy + * @pad : character to use for padding + * + * This function copies @len - 1 bytes of string data from a source + * pointer to a buffer backend, followed by a terminating '\0' + * character, at the current context offset. This is more or less a + * buffer backend-specific strncpy() operation. If a terminating '\0' + * character is found in @src before @len - 1 characters are copied, pad + * the buffer with @pad characters (e.g. '#'). + */ +static inline +void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config, + struct lttng_ust_lib_ring_buffer_ctx *ctx, + const char *src, size_t len, int pad) +{ + struct lttng_ust_lib_ring_buffer_backend *bufb = &ctx->buf->backend; + struct channel_backend *chanb = &ctx->chan->backend; + struct lttng_ust_shm_handle *handle = ctx->handle; + size_t sbidx, count; + size_t offset = ctx->buf_offset; + struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages; + unsigned long sb_bindex, id; + + if (caa_unlikely(!len)) + return; + offset &= chanb->buf_size - 1; + sbidx = offset >> chanb->subbuf_size_order; + id = shmp_index(handle, bufb->buf_wsb, sbidx)->id; + sb_bindex = subbuffer_id_get_index(config, id); + rpages = shmp_index(handle, bufb->array, sb_bindex); + CHAN_WARN_ON(ctx->chan, + config->mode == RING_BUFFER_OVERWRITE + && subbuffer_id_is_noref(config, id)); + /* + * Underlying layer should never ask for writes across + * subbuffers. + */ + CHAN_WARN_ON(chanb, offset >= chanb->buf_size); + count = lib_ring_buffer_do_strcpy(config, + shmp_index(handle, shmp(handle, rpages->shmp)->p, + offset & (chanb->subbuf_size - 1)), + src, len - 1); + offset += count; + /* Padding */ + if (caa_unlikely(count < len - 1)) { + size_t pad_len = len - 1 - count; + + lib_ring_buffer_do_memset(shmp_index(handle, shmp(handle, rpages->shmp)->p, + offset & (chanb->subbuf_size - 1)), + pad, pad_len); + offset += pad_len; + } + /* Final '\0' */ + lib_ring_buffer_do_memset(shmp_index(handle, shmp(handle, rpages->shmp)->p, + offset & (chanb->subbuf_size - 1)), + '\0', 1); + ctx->buf_offset += len; +} + /* * This accessor counts the number of unread records in a buffer. * It only provides a consistent value if no reads not writes are performed diff --git a/libringbuffer/backend_internal.h b/libringbuffer/backend_internal.h index 3ab60a7f..1045a60c 100644 --- a/libringbuffer/backend_internal.h +++ b/libringbuffer/backend_internal.h @@ -447,6 +447,18 @@ do { \ inline_memcpy(dest, src, __len); \ } while (0) +/* + * write len bytes to dest with c + */ +static inline +void lib_ring_buffer_do_memset(char *dest, int c, unsigned long len) +{ + unsigned long i; + + for (i = 0; i < len; i++) + dest[i] = c; +} + /* arch-agnostic implementation */ static inline int lttng_ust_fls(unsigned int x)