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Message-ID: <864c7dd5-0deb-4adb-a1cf-c8a809514d7e@embeddedor.com>
Date: Tue, 11 Mar 2025 18:40:56 +1030
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
Kenneth Feng <kenneth.feng@....com>, Alex Deucher
<alexander.deucher@....com>, Christian König
<christian.koenig@....com>, Xinhui Pan <Xinhui.Pan@....com>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] drm/amd/pm: Avoid multiple
-Wflex-array-member-not-at-end warnings
Hi all,
Friendly ping: who can take this, please? :)
Thanks!
--
Gustavo
On 14/02/25 18:48, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
>
> So, in order to avoid ending up with a flexible-array member in the
> middle of other structs, we use the `struct_group_tagged()` helper
> to create a new tagged `struct NISLANDS_SMC_SWSTATE_HDR` (and `struct
> SISLANDS_SMC_SWSTATE_HDR`). This structures group together all the
> members of the flexible `struct NISLANDS_SMC_SWSTATE` (and `struct
> SISLANDS_SMC_SWSTATE`) except the flexible array.
>
> As a result, the array is effectively separated from the rest of the
> members without modifying the memory layout of the flexible structure.
> We then change the type of the middle struct members currently causing
> trouble from `struct NISLANDS_SMC_SWSTATE` to `struct
> NISLANDS_SMC_SWSTATE_HDR` (and from `struct SISLANDS_SMC_SWSTATE` to
> `struct SISLANDS_SMC_SWSTATE_HDR`).
>
> We also want to ensure that when new members need to be added to the
> flexible structure, they are always included within the newly created
> tagged struct. For this, we use `static_assert()`. This ensures that
> the memory layout for both the flexible structure and the new tagged
> struct is the same after any changes.
>
> This approach avoids having to implement `struct NISLANDS_SMC_SWSTATE_HDR`
> (and `struct SISLANDS_SMC_SWSTATE_HDR`) as a completely separate structure,
> thus preventing having to maintain two independent but basically identical
> structures, closing the door to potential bugs in the future.
>
> We also use `container_of()` whenever we need to retrieve a pointer to
> the flexible structure, through which we can access the flexible-array
> member, if necessary.
>
> So, with this changes, fix the following warnings:
>
> drivers/gpu/drm/amd/amdgpu/../pm/legacy-dpm/sislands_smc.h:218:49: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/gpu/drm/amd/amdgpu/../pm/legacy-dpm/si_dpm.h:819:41: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/gpu/drm/amd/amdgpu/../pm/legacy-dpm/si_dpm.h:818:41: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/gpu/drm/amd/amdgpu/../pm/legacy-dpm/si_dpm.h:817:41: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/gpu/drm/amd/amdgpu/../pm/legacy-dpm/si_dpm.h:816:41: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
> drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.c | 7 ++++--
> drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.h | 23 +++++++++++--------
> .../gpu/drm/amd/pm/legacy-dpm/sislands_smc.h | 15 ++++++++----
> 3 files changed, 29 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.c b/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.c
> index a87dcf0974bc..2c9d473d122f 100644
> --- a/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.c
> +++ b/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.c
> @@ -5234,7 +5234,8 @@ static int si_init_smc_table(struct amdgpu_device *adev)
>
> table->driverState.flags = table->initialState.flags;
> table->driverState.levelCount = table->initialState.levelCount;
> - table->driverState.levels[0] = table->initialState.level;
> + container_of(&table->driverState, SISLANDS_SMC_SWSTATE, __hdr)->levels[0] =
> + table->initialState.level;
>
> ret = si_do_program_memory_timing_parameters(adev, amdgpu_boot_state,
> SISLANDS_INITIAL_STATE_ARB_INDEX);
> @@ -5755,7 +5756,9 @@ static int si_upload_sw_state(struct amdgpu_device *adev,
> int ret;
> u32 address = si_pi->state_table_start +
> offsetof(SISLANDS_SMC_STATETABLE, driverState);
> - SISLANDS_SMC_SWSTATE *smc_state = &si_pi->smc_statetable.driverState;
> + SISLANDS_SMC_SWSTATE *smc_state =
> + container_of(&si_pi->smc_statetable.driverState,
> + SISLANDS_SMC_SWSTATE, __hdr);
> size_t state_size = struct_size(smc_state, levels,
> new_state->performance_level_count);
> memset(smc_state, 0, state_size);
> diff --git a/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.h b/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.h
> index 11cb7874a6bb..62530f89ebdf 100644
> --- a/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.h
> +++ b/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.h
> @@ -784,12 +784,17 @@ typedef struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL NISLANDS_SMC_HW_PERFORMANCE_LEV
>
> struct NISLANDS_SMC_SWSTATE
> {
> - uint8_t flags;
> - uint8_t levelCount;
> - uint8_t padding2;
> - uint8_t padding3;
> - NISLANDS_SMC_HW_PERFORMANCE_LEVEL levels[];
> + /* New members MUST be added within the struct_group() macro below. */
> + struct_group_tagged(NISLANDS_SMC_SWSTATE_HDR, __hdr,
> + uint8_t flags;
> + uint8_t levelCount;
> + uint8_t padding2;
> + uint8_t padding3;
> + );
> + NISLANDS_SMC_HW_PERFORMANCE_LEVEL levels[];
> };
> +static_assert(offsetof(struct NISLANDS_SMC_SWSTATE, levels) == sizeof(struct NISLANDS_SMC_SWSTATE_HDR),
> + "struct member likely outside of struct_group_tagged()");
>
> typedef struct NISLANDS_SMC_SWSTATE NISLANDS_SMC_SWSTATE;
>
> @@ -813,10 +818,10 @@ struct NISLANDS_SMC_STATETABLE
> uint32_t lowSMIO[NISLANDS_MAX_NO_VREG_STEPS];
> NISLANDS_SMC_VOLTAGEMASKTABLE voltageMaskTable;
> PP_NIslands_DPM2Parameters dpm2Params;
> - NISLANDS_SMC_SWSTATE initialState;
> - NISLANDS_SMC_SWSTATE ACPIState;
> - NISLANDS_SMC_SWSTATE ULVState;
> - NISLANDS_SMC_SWSTATE driverState;
> + struct NISLANDS_SMC_SWSTATE_HDR initialState;
> + struct NISLANDS_SMC_SWSTATE_HDR ACPIState;
> + struct NISLANDS_SMC_SWSTATE_HDR ULVState;
> + struct NISLANDS_SMC_SWSTATE_HDR driverState;
> NISLANDS_SMC_HW_PERFORMANCE_LEVEL dpmLevels[NISLANDS_MAX_SMC_PERFORMANCE_LEVELS_PER_SWSTATE - 1];
> };
>
> diff --git a/drivers/gpu/drm/amd/pm/legacy-dpm/sislands_smc.h b/drivers/gpu/drm/amd/pm/legacy-dpm/sislands_smc.h
> index 90ec411c5029..1711e3e35e80 100644
> --- a/drivers/gpu/drm/amd/pm/legacy-dpm/sislands_smc.h
> +++ b/drivers/gpu/drm/amd/pm/legacy-dpm/sislands_smc.h
> @@ -172,12 +172,17 @@ struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL {
> typedef struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL SISLANDS_SMC_HW_PERFORMANCE_LEVEL;
>
> struct SISLANDS_SMC_SWSTATE {
> - uint8_t flags;
> - uint8_t levelCount;
> - uint8_t padding2;
> - uint8_t padding3;
> + /* New members MUST be added within the struct_group() macro below. */
> + struct_group_tagged(SISLANDS_SMC_SWSTATE_HDR, __hdr,
> + uint8_t flags;
> + uint8_t levelCount;
> + uint8_t padding2;
> + uint8_t padding3;
> + );
> SISLANDS_SMC_HW_PERFORMANCE_LEVEL levels[];
> };
> +static_assert(offsetof(struct SISLANDS_SMC_SWSTATE, levels) == sizeof(struct SISLANDS_SMC_SWSTATE_HDR),
> + "struct member likely outside of struct_group_tagged()");
>
> typedef struct SISLANDS_SMC_SWSTATE SISLANDS_SMC_SWSTATE;
>
> @@ -215,7 +220,7 @@ struct SISLANDS_SMC_STATETABLE {
> struct SISLANDS_SMC_SWSTATE_SINGLE initialState;
> struct SISLANDS_SMC_SWSTATE_SINGLE ACPIState;
> struct SISLANDS_SMC_SWSTATE_SINGLE ULVState;
> - SISLANDS_SMC_SWSTATE driverState;
> + struct SISLANDS_SMC_SWSTATE_HDR driverState;
> SISLANDS_SMC_HW_PERFORMANCE_LEVEL dpmLevels[SISLANDS_MAX_SMC_PERFORMANCE_LEVELS_PER_SWSTATE];
> };
>
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