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Merged
merged 7 commits into from
Sep 3, 2025
Merged

flex array: Replace 0 length arrays #95134

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0b41495
bt: audio: Use proper flexible array
ceolin Aug 29, 2025
4e046c1
lib: heap: Use proper flexible array
ceolin Aug 29, 2025
0ca4f46
bt: controller/util: Use proper flexible array
ceolin Aug 29, 2025
9be698b
tests: bt/tester: Use proper flexible array
ceolin Aug 29, 2025
6d3965f
bt: host/classic: Use proper flexible array
ceolin Aug 29, 2025
fe60526
bt: controller/openisa: Use proper flexible array
ceolin Aug 29, 2025
0df79cf
bt: host/classic: Use proper flexible array
ceolin Aug 29, 2025
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2 changes: 1 addition & 1 deletion lib/heap/heap.h
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Original file line number Diff line number Diff line change
Expand Up @@ -74,7 +74,7 @@ struct z_heap {
size_t allocated_bytes;
size_t max_allocated_bytes;
#endif
struct z_heap_bucket buckets[0];
struct z_heap_bucket buckets[];
};

static inline bool big_heap_chunks(chunksz_t chunks)
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10 changes: 5 additions & 5 deletions subsys/bluetooth/audio/has_internal.h
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Expand Up @@ -68,7 +68,7 @@ struct bt_has {

struct bt_has_cp_hdr {
uint8_t opcode;
uint8_t data[0];
uint8_t data[];
} __packed;

struct bt_has_cp_read_presets_req {
Expand All @@ -80,25 +80,25 @@ struct bt_has_cp_read_preset_rsp {
uint8_t is_last;
uint8_t index;
uint8_t properties;
uint8_t name[0];
uint8_t name[];
} __packed;

struct bt_has_cp_preset_changed {
uint8_t change_id;
uint8_t is_last;
uint8_t additional_params[0];
uint8_t additional_params[];
} __packed;

struct bt_has_cp_generic_update {
uint8_t prev_index;
uint8_t index;
uint8_t properties;
uint8_t name[0];
uint8_t name[];
} __packed;

struct bt_has_cp_write_preset_name {
uint8_t index;
uint8_t name[0];
uint8_t name[];
} __packed;

struct bt_has_cp_set_active_preset {
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4 changes: 2 additions & 2 deletions subsys/bluetooth/audio/pacs_internal.h
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Expand Up @@ -23,12 +23,12 @@ struct bt_pac_codec {
struct bt_pac_ltv {
uint8_t len;
uint8_t type;
uint8_t value[0];
uint8_t value[];
} __packed;

struct bt_pac_ltv_data {
uint8_t len;
struct bt_pac_ltv data[0];
struct bt_pac_ltv data[];
} __packed;

struct bt_pacs_read_rsp {
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4 changes: 2 additions & 2 deletions subsys/bluetooth/audio/tbs_internal.h
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Expand Up @@ -246,12 +246,12 @@ struct bt_tbs_call_cp_retrieve {

struct bt_tbs_call_cp_originate {
uint8_t opcode;
uint8_t uri[0];
uint8_t uri[];
} __packed;

struct bt_tbs_call_cp_join {
uint8_t opcode;
uint8_t call_indexes[0];
uint8_t call_indexes[];
} __packed;

union bt_tbs_call_cp_t {
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18 changes: 6 additions & 12 deletions subsys/bluetooth/controller/ll_sw/openisa/lll/pdu_vendor.h
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Expand Up @@ -4,33 +4,27 @@
* SPDX-License-Identifier: Apache-2.0
*/

#include <zephyr/sys/util.h>

/* Minimum vendor specific Rx payload buffer allocation */
#define LL_VND_OCTETS_RX_MIN 0

/* No vendor Data PDU struct octet3 */
struct pdu_data_vnd_octet3 {
union {
uint8_t resv[0];
} __packed;
FLEXIBLE_ARRAY_DECLARE(uint8_t, resv);
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@cvinayak cvinayak Aug 29, 2025

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I have concern (not verified) that __packed has been removed by the introduction of FLEXIBLE_ARRAY_DECLARE. Is this truly equivalent?

I see prior PRs have already change some in subsys/bluetooth/controller/ll_sw/pdu.h file.

Can we have a __packed variant of this "workaround" define, like FLEXIBLE_ARRAY_DECLARE_PACKED?

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@Thalley Thalley Aug 29, 2025

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Out of curiosity, did __packed for an array of size 0 really do anything?

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@jhedberg jhedberg Aug 29, 2025

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And even if it wasn't of size 0, since the elements are byte aligned, I don't think __packed would do anything at all.

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@cvinayak cvinayak Aug 29, 2025 •
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__packed struct or union when nested need __packed individually every time; besides themselves being packed, the parent struct or union which has __packed still need to include them without which the members are machine word aligned/sized (please run a sample on Cortex-M0 nRF51 and you will hit hardfaults based on how linking has been unlucky... i.e. increasing/decreasing buffer counts will misalign these structs).

This file is not the best example, as the union has only one zero length byte array.

But here :

zephyr/subsys/bluetooth/controller/ll_sw/nordic/lll/pdu_vendor.h

Lines 17 to 25 in e028ecf

struct pdu_data_vnd_octet3 {
union {
uint8_t resv[OCTET3_LEN]; /* nRF specific octet3 required for NRF_CCM use */
#if !defined(CONFIG_BT_CTLR_DATA_LENGTH_CLEAR)
struct pdu_cte_info cte_info; /* BT 5.1 Core spec. CTEInfo storage */
#endif /* !CONFIG_BT_CTLR_DATA_LENGTH_CLEAR */
} __packed;
} __packed;

The union needs __packed so that it take 1 byte and not 4 bytes in size.

It is best to have a FLEXIBLE_ARRAY_DECLARE_PACKED for code that had __packed for the union inside other __packed union/structs... and also where FLEXIBLE_ARRAY_DECLARE added new union/struct into __packed structs/unions. Hence to also correct the other PR that made changes to as here: 1a56b90

There is also zero length array alignment requirements for nRF51: 701d524

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@ceolin ceolin Aug 30, 2025

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I think this example is wrong. With/without packed you will get 4 bytes if CONFIG_BT_CTLR_DATA_LENGTH_CLEAR is not defined. And since this union is the only element of the structure pdu_data_vnd_octet3 that is packed you will get 1 byte size when CONFIG_BT_CTLR_DATA_LENGTH_CLEAR is defined.

If you noticed, I have just changed for this specific use case where the union.

I am wondering if I am missing something here though. Did you get any memory alignment issue ? Printing the struct sizes I get exactly the same thing and the alignment should be correct.

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@cvinayak cvinayak Aug 30, 2025

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ok... I did a quick diff of .lst file of a sample for BBC microbit board (adding CONFIG_OUTPUT_DISASSEMBLY=y), with and without 56e2b01, and I see no difference. I am ok for now.

} __packed;

/* No vendor BIS PDU struct octet3 */
struct pdu_bis_vnd_octet3 {
union {
uint8_t resv[0];
} __packed;
FLEXIBLE_ARRAY_DECLARE(uint8_t, resv);
} __packed;

/* No vendor CIS PDU struct octet3 */
struct pdu_cis_vnd_octet3 {
union {
uint8_t resv[0];
} __packed;
FLEXIBLE_ARRAY_DECLARE(uint8_t, resv);
} __packed;

/* No ISOAL helper vendor ISO PDU struct octet3 */
struct pdu_iso_vnd_octet3 {
union {
uint8_t resv[0];
} __packed;
FLEXIBLE_ARRAY_DECLARE(uint8_t, resv);
} __packed;
2 changes: 1 addition & 1 deletion subsys/bluetooth/controller/util/dbuf.h
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Expand Up @@ -18,7 +18,7 @@ struct dbuf_hdr {
/* Size in a bytes of a single element stored in double buffer. */
uint8_t elem_size;
/* Pointer for actual buffer memory. Its size should be 2 times @p elem_size. */
uint8_t data[0];
uint8_t data[];
};

/**
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4 changes: 2 additions & 2 deletions subsys/bluetooth/host/classic/avdtp_internal.h
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Expand Up @@ -189,13 +189,13 @@ struct bt_avdtp_recovery_capabilities {
struct bt_avdtp_media_codec_capabilities {
uint8_t media_type;
uint8_t media_code_type;
uint8_t media_codec_spec_info[0];
uint8_t media_codec_spec_info[];
} __packed;

struct bt_avdtp_content_protection_capabilities {
uint8_t cp_type_lsb;
uint8_t cp_type_msb;
uint8_t cp_type_spec_value[0];
uint8_t cp_type_spec_value[];
} __packed;

struct bt_avdtp_header_compression_capabilities {
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5 changes: 3 additions & 2 deletions subsys/bluetooth/host/classic/l2cap_br_internal.h
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Expand Up @@ -10,6 +10,7 @@

#include <zephyr/bluetooth/l2cap.h>
#include <zephyr/sys/iterable_sections.h>
#include <zephyr/sys/util.h>
#include "l2cap_br_interface.h"

#define BT_L2CAP_CID_BR_SIG 0x0001
Expand Down Expand Up @@ -177,12 +178,12 @@ struct bt_l2cap_disconn_rsp {

#define BT_L2CAP_ECHO_REQ 0x08
struct bt_l2cap_echo_req {
uint8_t data[0];
FLEXIBLE_ARRAY_DECLARE(uint8_t, data);
} __packed;

#define BT_L2CAP_ECHO_RSP 0x09
struct bt_l2cap_echo_rsp {
uint8_t data[0];
FLEXIBLE_ARRAY_DECLARE(uint8_t, data);
} __packed;

#define BT_L2CAP_INFO_CONNLESS_MTU 0x0001
Expand Down
11 changes: 6 additions & 5 deletions tests/bluetooth/tester/src/audio/btp/btp_bap.h
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Expand Up @@ -11,11 +11,12 @@
#include <zephyr/bluetooth/addr.h>
#include <zephyr/bluetooth/audio/audio.h>
#include <zephyr/bluetooth/iso.h>
#include <zephyr/sys/util.h>

/* BAP commands */
#define BTP_BAP_READ_SUPPORTED_COMMANDS 0x01
struct btp_bap_read_supported_commands_rp {
uint8_t data[0];
FLEXIBLE_ARRAY_DECLARE(uint8_t, data);
} __packed;

#define BTP_BAP_DISCOVER 0x02
Expand All @@ -31,7 +32,7 @@ struct btp_bap_send_cmd {
bt_addr_le_t address;
uint8_t ase_id;
uint8_t data_len;
uint8_t data[0];
uint8_t data[];
} __packed;

struct btp_bap_send_rp {
Expand Down Expand Up @@ -148,7 +149,7 @@ struct btp_bap_add_broadcast_src_cmd {
uint8_t padv_sync;
uint16_t padv_interval;
uint8_t num_subgroups;
uint8_t subgroups[0];
uint8_t subgroups[];
} __packed;

#define BTP_BAP_REMOVE_BROADCAST_SRC 0x15
Expand All @@ -164,7 +165,7 @@ struct btp_bap_modify_broadcast_src_cmd {
uint8_t padv_sync;
uint16_t padv_interval;
uint8_t num_subgroups;
uint8_t subgroups[0];
uint8_t subgroups[];
} __packed;

#define BTP_BAP_SET_BROADCAST_CODE 0x17
Expand Down Expand Up @@ -287,7 +288,7 @@ struct btp_bap_broadcast_receive_state_ev {
uint8_t pa_sync_state;
uint8_t big_encryption;
uint8_t num_subgroups;
uint8_t subgroups[0];
uint8_t subgroups[];
} __packed;

#define BTP_BAP_EV_PA_SYNC_REQ 0x8a
Expand Down
15 changes: 8 additions & 7 deletions tests/bluetooth/tester/src/audio/btp/btp_cap.h
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Expand Up @@ -11,12 +11,13 @@
#include <zephyr/bluetooth/addr.h>
#include <zephyr/bluetooth/audio/audio.h>
#include <zephyr/bluetooth/iso.h>
#include <zephyr/sys/util.h>
#include <zephyr/sys/util_macro.h>

/* CAP commands */
#define BTP_CAP_READ_SUPPORTED_COMMANDS 0x01
struct btp_cap_read_supported_commands_rp {
uint8_t data[0];
FLEXIBLE_ARRAY_DECLARE(uint8_t, data);
} __packed;

#define BTP_CAP_DISCOVER 0x02
Expand All @@ -41,7 +42,7 @@ struct btp_cap_unicast_setup_ase_cmd {
uint8_t presentation_delay[3];
uint8_t cc_ltvs_len;
uint8_t metadata_ltvs_len;
uint8_t ltvs[0];
uint8_t ltvs[];
} __packed;

#define BTP_CAP_UNICAST_AUDIO_START 0x04
Expand All @@ -55,13 +56,13 @@ struct btp_cap_unicast_audio_start_cmd {
#define BTP_CAP_UNICAST_AUDIO_UPDATE 0x05
struct btp_cap_unicast_audio_update_cmd {
uint8_t stream_count;
uint8_t update_data[0];
uint8_t update_data[];
} __packed;
struct btp_cap_unicast_audio_update_data {
bt_addr_le_t address;
uint8_t ase_id;
uint8_t metadata_ltvs_len;
uint8_t metadata_ltvs[0];
uint8_t metadata_ltvs[];
} __packed;

#define BTP_CAP_UNICAST_AUDIO_STOP 0x06
Expand All @@ -80,7 +81,7 @@ struct btp_cap_broadcast_source_setup_stream_cmd {
uint16_t cid;
uint8_t cc_ltvs_len;
uint8_t metadata_ltvs_len;
uint8_t ltvs[0];
uint8_t ltvs[];
} __packed;

#define BTP_CAP_BROADCAST_SOURCE_SETUP_SUBGROUP 0x08
Expand All @@ -92,7 +93,7 @@ struct btp_cap_broadcast_source_setup_subgroup_cmd {
uint16_t cid;
uint8_t cc_ltvs_len;
uint8_t metadata_ltvs_len;
uint8_t ltvs[0];
uint8_t ltvs[];
} __packed;

#define BTP_CAP_BROADCAST_SOURCE_SETUP 0x09
Expand Down Expand Up @@ -145,7 +146,7 @@ struct btp_cap_broadcast_source_stop_cmd {
struct btp_cap_broadcast_source_update_cmd {
uint8_t source_id;
uint8_t metadata_ltvs_len;
uint8_t metadata_ltvs[0];
uint8_t metadata_ltvs[];
} __packed;

/* CAP events */
Expand Down
3 changes: 2 additions & 1 deletion tests/bluetooth/tester/src/audio/btp/btp_mcp.h
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Expand Up @@ -11,11 +11,12 @@

#include <zephyr/bluetooth/addr.h>
#include <zephyr/bluetooth/services/ots.h>
#include <zephyr/sys/util.h>

/* MCP commands */
#define BTP_MCP_READ_SUPPORTED_COMMANDS 0x01
struct btp_mcp_read_supported_commands_rp {
uint8_t data[0];
FLEXIBLE_ARRAY_DECLARE(uint8_t, data);
} __packed;

#define BTP_MCP_DISCOVER 0x02
Expand Down
2 changes: 1 addition & 1 deletion tests/bluetooth/tester/src/audio/btp/btp_micp.h
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Expand Up @@ -13,7 +13,7 @@
/* MICP commands */
#define BTP_MICP_READ_SUPPORTED_COMMANDS 0x01
struct btp_micp_read_supported_commands_rp {
uint8_t data[0];
FLEXIBLE_ARRAY_DECLARE(uint8_t, data);
} __packed;

#define BTP_MICP_CTLR_DISCOVER 0x02
Expand Down
2 changes: 1 addition & 1 deletion tests/bluetooth/tester/src/audio/btp/btp_pacs.h
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Expand Up @@ -11,7 +11,7 @@
/* PACS commands */
#define BTP_PACS_READ_SUPPORTED_COMMANDS 0x01
struct btp_pacs_read_supported_commands_rp {
uint8_t data[0];
FLEXIBLE_ARRAY_DECLARE(uint8_t, data);
} __packed;

#define BTP_PACS_CHARACTERISTIC_SINK_PAC 0x01
Expand Down
5 changes: 3 additions & 2 deletions tests/bluetooth/tester/src/btp/btp_core.h
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Expand Up @@ -8,16 +8,17 @@
*/

#include <stdint.h>
#include <zephyr/sys/util.h>

/* Core Service */
#define BTP_CORE_READ_SUPPORTED_COMMANDS 0x01
struct btp_core_read_supported_commands_rp {
uint8_t data[0];
FLEXIBLE_ARRAY_DECLARE(uint8_t, data);
} __packed;

#define BTP_CORE_READ_SUPPORTED_SERVICES 0x02
struct btp_core_read_supported_services_rp {
uint8_t data[0];
FLEXIBLE_ARRAY_DECLARE(uint8_t, data);
} __packed;

#define BTP_CORE_REGISTER_SERVICE 0x03
Expand Down
7 changes: 4 additions & 3 deletions tests/bluetooth/tester/src/btp/btp_gap.h
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Expand Up @@ -12,12 +12,13 @@

#include <zephyr/bluetooth/addr.h>
#include <zephyr/bluetooth/iso.h>
#include <zephyr/sys/util.h>

/* GAP Service */
/* commands */
#define BTP_GAP_READ_SUPPORTED_COMMANDS 0x01
struct btp_gap_read_supported_commands_rp {
uint8_t data[0];
FLEXIBLE_ARRAY_DECLARE(uint8_t, data);
} __packed;

#define BTP_GAP_READ_CONTROLLER_INDEX_LIST 0x02
Expand Down Expand Up @@ -360,7 +361,7 @@ struct btp_gap_big_create_sync_cmd {
uint32_t mse;
uint16_t sync_timeout;
uint8_t encryption;
uint8_t broadcast_code[0];
uint8_t broadcast_code[];
} __packed;

#define BTP_GAP_CREATE_BIG_ENC_DISABLE 0x00
Expand All @@ -377,7 +378,7 @@ struct btp_gap_create_big_cmd {
uint8_t packing;
uint8_t framing;
uint8_t encryption;
uint8_t broadcast_code[0];
uint8_t broadcast_code[];
} __packed;

#define BTP_GAP_BIS_BROADCAST 0x2e
Expand Down
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