From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Sat, 20 Aug 2011 13:20:40 +0000 (-0400)
Subject: shm: introduce shmp_index
X-Git-Tag: v1.9.1~296
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=4746ae29409b78e96543a3b207c91a3c510c6476;p=lttng-ust.git

shm: introduce shmp_index

Add array offsets before checking the target pointer range.

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

diff --git a/libringbuffer/backend.h b/libringbuffer/backend.h
index e26045af..d93f6d1f 100644
--- a/libringbuffer/backend.h
+++ b/libringbuffer/backend.h
@@ -76,9 +76,9 @@ void lib_ring_buffer_write(const struct lib_ring_buffer_config *config,
 
 	offset &= chanb->buf_size - 1;
 	sbidx = offset >> chanb->subbuf_size_order;
-	id = shmp(handle, bufb->buf_wsb)[sbidx].id;
+	id = shmp_index(handle, bufb->buf_wsb, sbidx)->id;
 	sb_bindex = subbuffer_id_get_index(config, id);
-	rpages = &shmp(handle, bufb->array)[sb_bindex];
+	rpages = shmp_index(handle, bufb->array, sb_bindex);
 	CHAN_WARN_ON(ctx->chan,
 		     config->mode == RING_BUFFER_OVERWRITE
 		     && subbuffer_id_is_noref(config, id));
@@ -88,7 +88,7 @@ void lib_ring_buffer_write(const struct lib_ring_buffer_config *config,
 	 */
 	CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
 	lib_ring_buffer_do_copy(config,
-				shmp(handle, shmp(handle, rpages->shmp)->p) + (offset & ~(chanb->subbuf_size - 1)),
+				shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & ~(chanb->subbuf_size - 1)),
 				src, len);
 	ctx->buf_offset += len;
 }
@@ -110,15 +110,15 @@ unsigned long lib_ring_buffer_get_records_unread(
 	unsigned int i;
 
 	for (i = 0; i < shmp(handle, bufb->chan)->backend.num_subbuf; i++) {
-		id = shmp(handle, bufb->buf_wsb)[i].id;
+		id = shmp_index(handle, bufb->buf_wsb, i)->id;
 		sb_bindex = subbuffer_id_get_index(config, id);
-		pages = &shmp(handle, bufb->array)[sb_bindex];
+		pages = shmp_index(handle, bufb->array, sb_bindex);
 		records_unread += v_read(config, &shmp(handle, pages->shmp)->records_unread);
 	}
 	if (config->mode == RING_BUFFER_OVERWRITE) {
 		id = bufb->buf_rsb.id;
 		sb_bindex = subbuffer_id_get_index(config, id);
-		pages = &shmp(handle, bufb->array)[sb_bindex];
+		pages = shmp_index(handle, bufb->array, sb_bindex);
 		records_unread += v_read(config, &shmp(handle, pages->shmp)->records_unread);
 	}
 	return records_unread;
diff --git a/libringbuffer/backend_internal.h b/libringbuffer/backend_internal.h
index 30e32098..ba0497f9 100644
--- a/libringbuffer/backend_internal.h
+++ b/libringbuffer/backend_internal.h
@@ -190,8 +190,8 @@ void subbuffer_count_record(const struct lib_ring_buffer_config *config,
 {
 	unsigned long sb_bindex;
 
-	sb_bindex = subbuffer_id_get_index(config, shmp(handle, bufb->buf_wsb)[idx].id);
-	v_inc(config, &shmp(handle, (shmp(handle, bufb->array)[sb_bindex]).shmp)->records_commit);
+	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
+	v_inc(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_commit);
 }
 
 /*
@@ -207,9 +207,9 @@ void subbuffer_consume_record(const struct lib_ring_buffer_config *config,
 
 	sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 	CHAN_WARN_ON(shmp(handle, bufb->chan),
-		     !v_read(config, &shmp(handle, (shmp(handle, bufb->array)[sb_bindex]).shmp)->records_unread));
+		     !v_read(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_unread));
 	/* Non-atomic decrement protected by exclusive subbuffer access */
-	_v_dec(config, &shmp(handle, (shmp(handle, bufb->array)[sb_bindex]).shmp)->records_unread);
+	_v_dec(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_unread);
 	v_inc(config, &bufb->records_read);
 }
 
@@ -222,8 +222,8 @@ unsigned long subbuffer_get_records_count(
 {
 	unsigned long sb_bindex;
 
-	sb_bindex = subbuffer_id_get_index(config, shmp(handle, bufb->buf_wsb)[idx].id);
-	return v_read(config, &shmp(handle, (shmp(handle, bufb->array)[sb_bindex]).shmp)->records_commit);
+	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
+	return v_read(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_commit);
 }
 
 /*
@@ -242,8 +242,8 @@ unsigned long subbuffer_count_records_overrun(
 	struct lib_ring_buffer_backend_pages_shmp *pages;
 	unsigned long overruns, sb_bindex;
 
-	sb_bindex = subbuffer_id_get_index(config, shmp(handle, bufb->buf_wsb)[idx].id);
-	pages = &shmp(handle, bufb->array)[sb_bindex];
+	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
+	pages = shmp_index(handle, bufb->array, sb_bindex);
 	overruns = v_read(config, &shmp(handle, pages->shmp)->records_unread);
 	v_set(config, &shmp(handle, pages->shmp)->records_unread,
 	      v_read(config, &shmp(handle, pages->shmp)->records_commit));
@@ -262,8 +262,8 @@ void subbuffer_set_data_size(const struct lib_ring_buffer_config *config,
 	struct lib_ring_buffer_backend_pages_shmp *pages;
 	unsigned long sb_bindex;
 
-	sb_bindex = subbuffer_id_get_index(config, shmp(handle, bufb->buf_wsb)[idx].id);
-	pages = &shmp(handle, bufb->array)[sb_bindex];
+	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
+	pages = shmp_index(handle, bufb->array, sb_bindex);
 	shmp(handle, pages->shmp)->data_size = data_size;
 }
 
@@ -277,7 +277,7 @@ unsigned long subbuffer_get_read_data_size(
 	unsigned long sb_bindex;
 
 	sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
-	pages = &shmp(handle, bufb->array)[sb_bindex];
+	pages = shmp_index(handle, bufb->array, sb_bindex);
 	return shmp(handle, pages->shmp)->data_size;
 }
 
@@ -291,8 +291,8 @@ unsigned long subbuffer_get_data_size(
 	struct lib_ring_buffer_backend_pages_shmp *pages;
 	unsigned long sb_bindex;
 
-	sb_bindex = subbuffer_id_get_index(config, shmp(handle, bufb->buf_wsb)[idx].id);
-	pages = &shmp(handle, bufb->array)[sb_bindex];
+	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
+	pages = shmp_index(handle, bufb->array, sb_bindex);
 	return shmp(handle, pages->shmp)->data_size;
 }
 
@@ -315,7 +315,7 @@ void lib_ring_buffer_clear_noref(const struct lib_ring_buffer_config *config,
 	 * Performing a volatile access to read the sb_pages, because we want to
 	 * read a coherent version of the pointer and the associated noref flag.
 	 */
-	id = CMM_ACCESS_ONCE(shmp(handle, bufb->buf_wsb)[idx].id);
+	id = CMM_ACCESS_ONCE(shmp_index(handle, bufb->buf_wsb, idx)->id);
 	for (;;) {
 		/* This check is called on the fast path for each record. */
 		if (likely(!subbuffer_id_is_noref(config, id))) {
@@ -329,7 +329,7 @@ void lib_ring_buffer_clear_noref(const struct lib_ring_buffer_config *config,
 		}
 		new_id = id;
 		subbuffer_id_clear_noref(config, &new_id);
-		new_id = uatomic_cmpxchg(&shmp(handle, bufb->buf_wsb)[idx].id, id, new_id);
+		new_id = uatomic_cmpxchg(&shmp_index(handle, bufb->buf_wsb, idx)->id, id, new_id);
 		if (likely(new_id == id))
 			break;
 		id = new_id;
@@ -361,13 +361,13 @@ void lib_ring_buffer_set_noref_offset(const struct lib_ring_buffer_config *confi
 	 * readers of the noref flag.
 	 */
 	CHAN_WARN_ON(shmp(handle, bufb->chan),
-		     subbuffer_id_is_noref(config, shmp(handle, bufb->buf_wsb)[idx].id));
+		     subbuffer_id_is_noref(config, shmp_index(handle, bufb->buf_wsb, idx)->id));
 	/*
 	 * Memory barrier that ensures counter stores are ordered before set
 	 * noref and offset.
 	 */
 	cmm_smp_mb();
-	subbuffer_id_set_noref_offset(config, &shmp(handle, bufb->buf_wsb)[idx].id, offset);
+	subbuffer_id_set_noref_offset(config, &shmp_index(handle, bufb->buf_wsb, idx)->id, offset);
 }
 
 /**
@@ -390,7 +390,7 @@ int update_read_sb_index(const struct lib_ring_buffer_config *config,
 		 * old_wpage, because the value read will be confirmed by the
 		 * following cmpxchg().
 		 */
-		old_id = shmp(handle, bufb->buf_wsb)[consumed_idx].id;
+		old_id = shmp_index(handle, bufb->buf_wsb, consumed_idx)->id;
 		if (unlikely(!subbuffer_id_is_noref(config, old_id)))
 			return -EAGAIN;
 		/*
@@ -404,14 +404,14 @@ int update_read_sb_index(const struct lib_ring_buffer_config *config,
 			     !subbuffer_id_is_noref(config, bufb->buf_rsb.id));
 		subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id,
 					      consumed_count);
-		new_id = uatomic_cmpxchg(&shmp(handle, bufb->buf_wsb)[consumed_idx].id, old_id,
+		new_id = uatomic_cmpxchg(&shmp_index(handle, bufb->buf_wsb, consumed_idx)->id, old_id,
 				 bufb->buf_rsb.id);
 		if (unlikely(old_id != new_id))
 			return -EAGAIN;
 		bufb->buf_rsb.id = new_id;
 	} else {
 		/* No page exchange, use the writer page directly */
-		bufb->buf_rsb.id = shmp(handle, bufb->buf_wsb)[consumed_idx].id;
+		bufb->buf_rsb.id = shmp_index(handle, bufb->buf_wsb, consumed_idx)->id;
 	}
 	return 0;
 }
diff --git a/libringbuffer/frontend_api.h b/libringbuffer/frontend_api.h
index 1d8e2949..f570cc16 100644
--- a/libringbuffer/frontend_api.h
+++ b/libringbuffer/frontend_api.h
@@ -253,7 +253,7 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
 	 */
 	cmm_smp_wmb();
 
-	v_add(config, ctx->slot_size, &shmp(handle, buf->commit_hot)[endidx].cc);
+	v_add(config, ctx->slot_size, &shmp_index(handle, buf->commit_hot, endidx)->cc);
 
 	/*
 	 * commit count read can race with concurrent OOO commit count updates.
@@ -273,7 +273,7 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
 	 *   count reaches back the reserve offset for a specific sub-buffer,
 	 *   which is completely independent of the order.
 	 */
-	commit_count = v_read(config, &shmp(handle, buf->commit_hot)[endidx].cc);
+	commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, endidx)->cc);
 
 	lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1,
 				      commit_count, endidx, handle);
diff --git a/libringbuffer/frontend_internal.h b/libringbuffer/frontend_internal.h
index c60affe0..02cb4d4a 100644
--- a/libringbuffer/frontend_internal.h
+++ b/libringbuffer/frontend_internal.h
@@ -185,7 +185,7 @@ void lib_ring_buffer_vmcore_check_deliver(const struct lib_ring_buffer_config *c
 					  struct shm_handle *handle)
 {
 	if (config->oops == RING_BUFFER_OOPS_CONSISTENCY)
-		v_set(config, &shmp(handle, buf->commit_hot)[idx].seq, commit_count);
+		v_set(config, &shmp_index(handle, buf->commit_hot, idx)->seq, commit_count);
 }
 
 static inline
@@ -198,7 +198,7 @@ int lib_ring_buffer_poll_deliver(const struct lib_ring_buffer_config *config,
 
 	consumed_old = uatomic_read(&buf->consumed);
 	consumed_idx = subbuf_index(consumed_old, chan);
-	commit_count = v_read(config, &shmp(handle, buf->commit_cold)[consumed_idx].cc_sb);
+	commit_count = v_read(config, &shmp_index(handle, buf->commit_cold, consumed_idx)->cc_sb);
 	/*
 	 * No memory barrier here, since we are only interested
 	 * in a statistically correct polling result. The next poll will
@@ -275,7 +275,7 @@ int lib_ring_buffer_reserve_committed(const struct lib_ring_buffer_config *confi
 	do {
 		offset = v_read(config, &buf->offset);
 		idx = subbuf_index(offset, chan);
-		commit_count = v_read(config, &shmp(handle, buf->commit_hot)[idx].cc);
+		commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, idx)->cc);
 	} while (offset != v_read(config, &buf->offset));
 
 	return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
@@ -324,7 +324,7 @@ void lib_ring_buffer_check_deliver(const struct lib_ring_buffer_config *config,
 		 * The subbuffer size is least 2 bytes (minimum size: 1 page).
 		 * This guarantees that old_commit_count + 1 != commit_count.
 		 */
-		if (likely(v_cmpxchg(config, &shmp(handle, buf->commit_cold)[idx].cc_sb,
+		if (likely(v_cmpxchg(config, &shmp_index(handle, buf->commit_cold, idx)->cc_sb,
 					 old_commit_count, old_commit_count + 1)
 			   == old_commit_count)) {
 			/*
@@ -367,7 +367,7 @@ void lib_ring_buffer_check_deliver(const struct lib_ring_buffer_config *config,
 			 */
 			cmm_smp_mb();
 			/* End of exclusive subbuffer access */
-			v_set(config, &shmp(handle, buf->commit_cold)[idx].cc_sb,
+			v_set(config, &shmp_index(handle, buf->commit_cold, idx)->cc_sb,
 			      commit_count);
 			lib_ring_buffer_vmcore_check_deliver(config, buf,
 						 commit_count, idx, handle);
@@ -431,9 +431,9 @@ void lib_ring_buffer_write_commit_counter(const struct lib_ring_buffer_config *c
 	if (unlikely(subbuf_offset(offset - commit_count, chan)))
 		return;
 
-	commit_seq_old = v_read(config, &shmp(handle, buf->commit_hot)[idx].seq);
+	commit_seq_old = v_read(config, &shmp_index(handle, buf->commit_hot, idx)->seq);
 	while ((long) (commit_seq_old - commit_count) < 0)
-		commit_seq_old = v_cmpxchg(config, &shmp(handle, buf->commit_hot)[idx].seq,
+		commit_seq_old = v_cmpxchg(config, &shmp_index(handle, buf->commit_hot, idx)->seq,
 					   commit_seq_old, commit_count);
 }
 
diff --git a/libringbuffer/ring_buffer_backend.c b/libringbuffer/ring_buffer_backend.c
index 18dd1b01..816c99cb 100644
--- a/libringbuffer/ring_buffer_backend.c
+++ b/libringbuffer/ring_buffer_backend.c
@@ -65,7 +65,7 @@ int lib_ring_buffer_backend_allocate(const struct lib_ring_buffer_config *config
 		set_shmp(shmp(handle, bufb->array)[i].shmp,
 			zalloc_shm(shmobj,
 				sizeof(struct lib_ring_buffer_backend_pages)));
-		if (!shmp(handle, shmp(handle, bufb->array)[i].shmp))
+		if (!shmp(handle, shmp_index(handle, bufb->array, i)->shmp))
 			goto free_array;
 	}
 
@@ -78,7 +78,7 @@ int lib_ring_buffer_backend_allocate(const struct lib_ring_buffer_config *config
 		goto free_array;
 
 	for (i = 0; i < num_subbuf; i++)
-		shmp(handle, bufb->buf_wsb)[i].id = subbuffer_id(config, 0, 1, i);
+		shmp_index(handle, bufb->buf_wsb, i)->id = subbuffer_id(config, 0, 1, i);
 
 	/* Assign read-side subbuffer table */
 	if (extra_reader_sb)
@@ -95,10 +95,10 @@ int lib_ring_buffer_backend_allocate(const struct lib_ring_buffer_config *config
 		ref.offset = bufb->memory_map._ref.offset;
 		ref.offset += i * subbuf_size;
 
-		set_shmp(shmp(handle, shmp(handle, bufb->array)[i].shmp)->p,
+		set_shmp(shmp(handle, shmp_index(handle, bufb->array, i)->shmp)->p,
 			 ref);
 		if (config->output == RING_BUFFER_MMAP) {
-			shmp(handle, shmp(handle, bufb->array)[i].shmp)->mmap_offset = mmap_offset;
+			shmp(handle, shmp_index(handle, bufb->array, i)->shmp)->mmap_offset = mmap_offset;
 			mmap_offset += subbuf_size;
 		}
 	}
@@ -150,7 +150,7 @@ void lib_ring_buffer_backend_reset(struct lib_ring_buffer_backend *bufb,
 		num_subbuf_alloc++;
 
 	for (i = 0; i < chanb->num_subbuf; i++)
-		shmp(handle, bufb->buf_wsb)[i].id = subbuffer_id(config, 0, 1, i);
+		shmp_index(handle, bufb->buf_wsb, i)->id = subbuffer_id(config, 0, 1, i);
 	if (chanb->extra_reader_sb)
 		bufb->buf_rsb.id = subbuffer_id(config, 0, 1,
 						num_subbuf_alloc - 1);
@@ -159,9 +159,9 @@ void lib_ring_buffer_backend_reset(struct lib_ring_buffer_backend *bufb,
 
 	for (i = 0; i < num_subbuf_alloc; i++) {
 		/* Don't reset mmap_offset */
-		v_set(config, &shmp(handle, shmp(handle, bufb->array)[i].shmp)->records_commit, 0);
-		v_set(config, &shmp(handle, shmp(handle, bufb->array)[i].shmp)->records_unread, 0);
-		shmp(handle, shmp(handle, bufb->array)[i].shmp)->data_size = 0;
+		v_set(config, &shmp(handle, shmp_index(handle, bufb->array, i)->shmp)->records_commit, 0);
+		v_set(config, &shmp(handle, shmp_index(handle, bufb->array, i)->shmp)->records_unread, 0);
+		shmp(handle, shmp_index(handle, bufb->array, i)->shmp)->data_size = 0;
 		/* Don't reset backend page and virt addresses */
 	}
 	/* Don't reset num_pages_per_subbuf, cpu, allocated */
@@ -378,7 +378,7 @@ size_t lib_ring_buffer_read(struct lib_ring_buffer_backend *bufb, size_t offset,
 		return 0;
 	id = bufb->buf_rsb.id;
 	sb_bindex = subbuffer_id_get_index(config, id);
-	rpages = &shmp(handle, bufb->array)[sb_bindex];
+	rpages = shmp_index(handle, bufb->array, sb_bindex);
 	/*
 	 * Underlying layer should never ask for reads across
 	 * subbuffers.
@@ -386,7 +386,7 @@ size_t lib_ring_buffer_read(struct lib_ring_buffer_backend *bufb, size_t offset,
 	CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
 	CHAN_WARN_ON(chanb, config->mode == RING_BUFFER_OVERWRITE
 		     && subbuffer_id_is_noref(config, id));
-	memcpy(dest, shmp(handle, shmp(handle, rpages->shmp)->p) + (offset & ~(chanb->subbuf_size - 1)), len);
+	memcpy(dest, shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & ~(chanb->subbuf_size - 1)), len);
 	return orig_len;
 }
 
@@ -414,7 +414,7 @@ int lib_ring_buffer_read_cstr(struct lib_ring_buffer_backend *bufb, size_t offse
 	orig_offset = offset;
 	id = bufb->buf_rsb.id;
 	sb_bindex = subbuffer_id_get_index(config, id);
-	rpages = &shmp(handle, bufb->array)[sb_bindex];
+	rpages = shmp_index(handle, bufb->array, sb_bindex);
 	/*
 	 * Underlying layer should never ask for reads across
 	 * subbuffers.
@@ -422,7 +422,7 @@ int lib_ring_buffer_read_cstr(struct lib_ring_buffer_backend *bufb, size_t offse
 	CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
 	CHAN_WARN_ON(chanb, config->mode == RING_BUFFER_OVERWRITE
 		     && subbuffer_id_is_noref(config, id));
-	str = (char *)shmp(handle, shmp(handle, rpages->shmp)->p) + (offset & ~(chanb->subbuf_size - 1));
+	str = shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & ~(chanb->subbuf_size - 1));
 	string_len = strnlen(str, len);
 	if (dest && len) {
 		memcpy(dest, str, string_len);
@@ -453,10 +453,10 @@ void *lib_ring_buffer_read_offset_address(struct lib_ring_buffer_backend *bufb,
 	offset &= chanb->buf_size - 1;
 	id = bufb->buf_rsb.id;
 	sb_bindex = subbuffer_id_get_index(config, id);
-	rpages = &shmp(handle, bufb->array)[sb_bindex];
+	rpages = shmp_index(handle, bufb->array, sb_bindex);
 	CHAN_WARN_ON(chanb, config->mode == RING_BUFFER_OVERWRITE
 		     && subbuffer_id_is_noref(config, id));
-	return shmp(handle, shmp(handle, rpages->shmp)->p) + (offset & ~(chanb->subbuf_size - 1));
+	return shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & ~(chanb->subbuf_size - 1));
 }
 
 /**
@@ -481,10 +481,10 @@ void *lib_ring_buffer_offset_address(struct lib_ring_buffer_backend *bufb,
 
 	offset &= chanb->buf_size - 1;
 	sbidx = offset >> chanb->subbuf_size_order;
-	id = shmp(handle, bufb->buf_wsb)[sbidx].id;
+	id = shmp_index(handle, bufb->buf_wsb, sbidx)->id;
 	sb_bindex = subbuffer_id_get_index(config, id);
-	rpages = &shmp(handle, bufb->array)[sb_bindex];
+	rpages = shmp_index(handle, bufb->array, sb_bindex);
 	CHAN_WARN_ON(chanb, config->mode == RING_BUFFER_OVERWRITE
 		     && subbuffer_id_is_noref(config, id));
-	return shmp(handle, shmp(handle, rpages->shmp)->p) + (offset & ~(chanb->subbuf_size - 1));
+	return shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & ~(chanb->subbuf_size - 1));
 }
diff --git a/libringbuffer/ring_buffer_frontend.c b/libringbuffer/ring_buffer_frontend.c
index 6cd869c3..ee205e86 100644
--- a/libringbuffer/ring_buffer_frontend.c
+++ b/libringbuffer/ring_buffer_frontend.c
@@ -125,9 +125,9 @@ void lib_ring_buffer_reset(struct lib_ring_buffer *buf,
 	 */
 	v_set(config, &buf->offset, 0);
 	for (i = 0; i < chan->backend.num_subbuf; i++) {
-		v_set(config, &shmp(handle, buf->commit_hot)[i].cc, 0);
-		v_set(config, &shmp(handle, buf->commit_hot)[i].seq, 0);
-		v_set(config, &shmp(handle, buf->commit_cold)[i].cc_sb, 0);
+		v_set(config, &shmp_index(handle, buf->commit_hot, i)->cc, 0);
+		v_set(config, &shmp_index(handle, buf->commit_hot, i)->seq, 0);
+		v_set(config, &shmp_index(handle, buf->commit_cold, i)->cc_sb, 0);
 	}
 	uatomic_set(&buf->consumed, 0);
 	uatomic_set(&buf->record_disabled, 0);
@@ -216,10 +216,10 @@ int lib_ring_buffer_create(struct lib_ring_buffer *buf,
 	 */
 	subbuf_header_size = config->cb.subbuffer_header_size();
 	v_set(config, &buf->offset, subbuf_header_size);
-	subbuffer_id_clear_noref(config, &shmp(handle, buf->backend.buf_wsb)[0].id);
+	subbuffer_id_clear_noref(config, &shmp_index(handle, buf->backend.buf_wsb, 0)->id);
 	tsc = config->cb.ring_buffer_clock_read(shmp(handle, buf->backend.chan));
 	config->cb.buffer_begin(buf, tsc, 0, handle);
-	v_add(config, subbuf_header_size, &shmp(handle, buf->commit_hot)[0].cc);
+	v_add(config, subbuf_header_size, &shmp_index(handle, buf->commit_hot, 0)->cc);
 
 	if (config->cb.buffer_create) {
 		ret = config->cb.buffer_create(buf, priv, cpu, chanb->name, handle);
@@ -715,7 +715,7 @@ retry:
 	cmm_smp_rmb();
 	consumed_cur = uatomic_read(&buf->consumed);
 	consumed_idx = subbuf_index(consumed, chan);
-	commit_count = v_read(config, &shmp(handle, buf->commit_cold)[consumed_idx].cc_sb);
+	commit_count = v_read(config, &shmp_index(handle, buf->commit_cold, consumed_idx)->cc_sb);
 	/*
 	 * Make sure we read the commit count before reading the buffer
 	 * data and the write offset. Correct consumed offset ordering
@@ -820,9 +820,9 @@ void lib_ring_buffer_put_subbuf(struct lib_ring_buffer *buf,
 	 */
 	read_sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 	v_add(config, v_read(config,
-			     &shmp(handle, shmp(handle, bufb->array)[read_sb_bindex].shmp)->records_unread),
+			     &shmp(handle, shmp_index(handle, bufb->array, read_sb_bindex)->shmp)->records_unread),
 	      &bufb->records_read);
-	v_set(config, &shmp(handle, shmp(handle, bufb->array)[read_sb_bindex].shmp)->records_unread, 0);
+	v_set(config, &shmp(handle, shmp_index(handle, bufb->array, read_sb_bindex)->shmp)->records_unread, 0);
 	CHAN_WARN_ON(chan, config->mode == RING_BUFFER_OVERWRITE
 		     && subbuffer_id_is_noref(config, bufb->buf_rsb.id));
 	subbuffer_id_set_noref(config, &bufb->buf_rsb.id);
@@ -860,8 +860,8 @@ void lib_ring_buffer_print_subbuffer_errors(struct lib_ring_buffer *buf,
 	unsigned long cons_idx, commit_count, commit_count_sb;
 
 	cons_idx = subbuf_index(cons_offset, chan);
-	commit_count = v_read(config, &shmp(handle, buf->commit_hot)[cons_idx].cc);
-	commit_count_sb = v_read(config, &shmp(handle, buf->commit_cold)[cons_idx].cc_sb);
+	commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, cons_idx)->cc);
+	commit_count_sb = v_read(config, &shmp_index(handle, buf->commit_cold, cons_idx)->cc_sb);
 
 	if (subbuf_offset(commit_count, chan) != 0)
 		ERRMSG("ring buffer %s, cpu %d: "
@@ -965,8 +965,8 @@ void lib_ring_buffer_switch_old_start(struct lib_ring_buffer *buf,
 	 */
 	cmm_smp_wmb();
 	v_add(config, config->cb.subbuffer_header_size(),
-	      &shmp(handle, buf->commit_hot)[oldidx].cc);
-	commit_count = v_read(config, &shmp(handle, buf->commit_hot)[oldidx].cc);
+	      &shmp_index(handle, buf->commit_hot, oldidx)->cc);
+	commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, oldidx)->cc);
 	/* Check if the written buffer has to be delivered */
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->old,
 				      commit_count, oldidx, handle);
@@ -1005,8 +1005,8 @@ void lib_ring_buffer_switch_old_end(struct lib_ring_buffer *buf,
 	 * determine that the subbuffer is full.
 	 */
 	cmm_smp_wmb();
-	v_add(config, padding_size, &shmp(handle, buf->commit_hot)[oldidx].cc);
-	commit_count = v_read(config, &shmp(handle, buf->commit_hot)[oldidx].cc);
+	v_add(config, padding_size, &shmp_index(handle, buf->commit_hot, oldidx)->cc);
+	commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, oldidx)->cc);
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->old - 1,
 				      commit_count, oldidx, handle);
 	lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx,
@@ -1040,8 +1040,8 @@ void lib_ring_buffer_switch_new_start(struct lib_ring_buffer *buf,
 	 */
 	cmm_smp_wmb();
 	v_add(config, config->cb.subbuffer_header_size(),
-	      &shmp(handle, buf->commit_hot)[beginidx].cc);
-	commit_count = v_read(config, &shmp(handle, buf->commit_hot)[beginidx].cc);
+	      &shmp_index(handle, buf->commit_hot, beginidx)->cc);
+	commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, beginidx)->cc);
 	/* Check if the written buffer has to be delivered */
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->begin,
 				      commit_count, beginidx, handle);
@@ -1078,8 +1078,8 @@ void lib_ring_buffer_switch_new_end(struct lib_ring_buffer *buf,
 	 * determine that the subbuffer is full.
 	 */
 	cmm_smp_wmb();
-	v_add(config, padding_size, &shmp(handle, buf->commit_hot)[endidx].cc);
-	commit_count = v_read(config, &shmp(handle, buf->commit_hot)[endidx].cc);
+	v_add(config, padding_size, &shmp_index(handle, buf->commit_hot, endidx)->cc);
+	commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, endidx)->cc);
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->end - 1,
 				  commit_count, endidx, handle);
 	lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
@@ -1270,7 +1270,7 @@ int lib_ring_buffer_try_reserve_slow(struct lib_ring_buffer *buf,
 		  (buf_trunc(offsets->begin, chan)
 		   >> chan->backend.num_subbuf_order)
 		  - ((unsigned long) v_read(config,
-					    &shmp(handle, buf->commit_cold)[sb_index].cc_sb)
+					    &shmp_index(handle, buf->commit_cold, sb_index)->cc_sb)
 		     & chan->commit_count_mask);
 		if (likely(reserve_commit_diff == 0)) {
 			/* Next subbuffer not being written to. */
diff --git a/libringbuffer/shm.h b/libringbuffer/shm.h
index da466df7..f5cc8e69 100644
--- a/libringbuffer/shm.h
+++ b/libringbuffer/shm.h
@@ -19,28 +19,32 @@
  * both the index and offset with known boundaries.
  */
 static inline
-char *_shmp(struct shm_object_table *table, struct shm_ref *ref)
+char *_shmp_offset(struct shm_object_table *table, struct shm_ref *ref,
+		   size_t offset)
 {
 	struct shm_object *obj;
-	size_t index, offset;
+	size_t index, ref_offset;
 
 	index = (size_t) ref->index;
 	if (unlikely(index >= table->allocated_len))
 		return NULL;
 	obj = &table->objects[index];
-	offset = (size_t) ref->offset;
-	if (unlikely(offset >= obj->memory_map_size))
+	ref_offset = (size_t) ref->offset;
+	ref_offset += offset;
+	if (unlikely(ref_offset >= obj->memory_map_size))
 		return NULL;
-	return &obj->memory_map[offset];
+	return &obj->memory_map[ref_offset];
 }
 
-#define shmp(handle, ref)						\
+#define shmp_index(handle, ref, offset)					\
 	({								\
 		__typeof__((ref)._type) ____ptr_ret;			\
-		____ptr_ret = (__typeof__(____ptr_ret)) _shmp((handle)->table, &(ref)._ref);	\
+		____ptr_ret = (__typeof__(____ptr_ret)) _shmp_offset((handle)->table, &(ref)._ref, ((offset) * sizeof(*____ptr_ret)));	\
 		____ptr_ret;						\
 	})
 
+#define shmp(handle, ref)	shmp_index(handle, ref, 0)
+
 static inline
 void _set_shmp(struct shm_ref *ref, struct shm_ref src)
 {