Re: [PATCH] drm/radeon/dpm: Replace one-element array and use struct_size() helper

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Am 22.05.20 um 03:25 schrieb Gustavo A. R. Silva:
The current codebase makes use of one-element arrays in the following
form:

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
_manually_.

[1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fonlinedocs%2Fgcc%2FZero-Length.html&data=02%7C01%7Cchristian.koenig%40amd.com%7C7dd54e944eff4d17178008d7fdee62d7%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637257072615411745&sdata=fQHnbXZpsgiMjHOr%2By0Uq12jpCYEYbdX5K26iNkwyeM%3D&reserved=0
[2] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FKSPP%2Flinux%2Fissues%2F21&data=02%7C01%7Cchristian.koenig%40amd.com%7C7dd54e944eff4d17178008d7fdee62d7%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637257072615411745&sdata=gg20YupmqsaW%2Bg3VyJL%2BkjE3kFwnWF1RD1D2QP04OLk%3D&reserved=0
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
---
  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;
-    NISLANDS_SMC_HW_PERFORMANCE_LEVEL   levels[1];
+    NISLANDS_SMC_HW_PERFORMANCE_LEVEL   levels[];
  };
typedef struct NISLANDS_SMC_SWSTATE NISLANDS_SMC_SWSTATE;
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) +
-		((NISLANDS_MAX_SMC_PERFORMANCE_LEVELS_PER_SWSTATE - 1) * sizeof(NISLANDS_SMC_HW_PERFORMANCE_LEVEL));
+	NISLANDS_SMC_SWSTATE *smc_state;
+	u16 state_size = struct_size(smc_state, levels,
+			NISLANDS_MAX_SMC_PERFORMANCE_LEVELS_PER_SWSTATE);

Probably better to use size_t instead of u16 here. With that fixed feel free to stick my rb on the patch.

Regards,
Christian.

  	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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