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Date:   Thu, 21 May 2020 20:25:47 -0500
From:   "Gustavo A. R. Silva" <>
To:     Alex Deucher <>,
        Christian K├Ânig <>,
        David Airlie <>,
        Daniel Vetter <>
        "Gustavo A. R. Silva" <>
Subject: [PATCH] drm/radeon/dpm: Replace one-element array and use
 struct_size() helper

The current codebase makes use of one-element arrays in the following

struct something {
    int length;
    u8 data[1];

struct something *instance;

instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
instance->length = size;
memcpy(instance->data, source, size);

but the preferred mechanism to declare variable-length types such as
these ones is a flexible array member[1][2], introduced in C99:

struct foo {
        int stuff;
        struct boo array[];

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on. So, replace
the one-element array with a flexible-array member.

Also, make use of the new struct_size() helper to properly calculate the
size of struct NISLANDS_SMC_SWSTATE.

This issue was found with the help of Coccinelle and, audited and fixed

[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <>
 drivers/gpu/drm/amd/amdgpu/si_dpm.h | 2 +-
 drivers/gpu/drm/radeon/ni_dpm.c     | 7 ++++---
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/si_dpm.h b/drivers/gpu/drm/amd/amdgpu/si_dpm.h
index 6b7d292b919f3..bc0be6818e218 100644
--- a/drivers/gpu/drm/amd/amdgpu/si_dpm.h
+++ b/drivers/gpu/drm/amd/amdgpu/si_dpm.h
@@ -781,7 +781,7 @@ struct NISLANDS_SMC_SWSTATE
     uint8_t                             levelCount;
     uint8_t                             padding2;
     uint8_t                             padding3;
diff --git a/drivers/gpu/drm/radeon/ni_dpm.c b/drivers/gpu/drm/radeon/ni_dpm.c
index b57c37ddd164c..7d81dde509dc9 100644
--- a/drivers/gpu/drm/radeon/ni_dpm.c
+++ b/drivers/gpu/drm/radeon/ni_dpm.c
@@ -2685,11 +2685,12 @@ static int ni_upload_sw_state(struct radeon_device *rdev,
 	struct rv7xx_power_info *pi = rv770_get_pi(rdev);
 	u16 address = pi->state_table_start +
 		offsetof(NISLANDS_SMC_STATETABLE, driverState);
-	u16 state_size = sizeof(NISLANDS_SMC_SWSTATE) +
+	u16 state_size = struct_size(smc_state, levels,
 	int ret;
-	NISLANDS_SMC_SWSTATE *smc_state = kzalloc(state_size, GFP_KERNEL);
+	smc_state = kzalloc(state_size, GFP_KERNEL);
 	if (smc_state == NULL)
 		return -ENOMEM;

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