linux-kernel - [PATCH] amdgpu: fix gcc -Wrestrict warning

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Date:   Tue, 23 Mar 2021 14:04:20 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Arnd Bergmann <arnd@...db.de>, Huang Rui <ray.huang@....com>,
        Jinzhou Su <Jinzhou.Su@....com>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH] amdgpu: fix gcc -Wrestrict warning

From: Arnd Bergmann <arnd@...db.de>

gcc warns about an sprintf() that uses the same buffer as source
and destination, which is undefined behavior in C99:

drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c: In function 'amdgpu_securedisplay_debugfs_write':
drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c:141:6: error: 'sprintf' argument 3 overlaps destination object 'i2c_output' [-Werror=restrict]
  141 |      sprintf(i2c_output, "%s 0x%X", i2c_output,
      |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  142 |       securedisplay_cmd->securedisplay_out_message.send_roi_crc.i2c_buf[i]);
      |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c:97:7: note: destination object referenced by 'restrict'-qualified argument 1 was declared here
   97 |  char i2c_output[256];
      |       ^~~~~~~~~~

Rewrite it to remember the current offset into the buffer instead.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
index 834440ab9ff7..69d7f6bff5d4 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
@@ -136,9 +136,10 @@ static ssize_t amdgpu_securedisplay_debugfs_write(struct file *f, const char __u
 		ret = psp_securedisplay_invoke(psp, TA_SECUREDISPLAY_COMMAND__SEND_ROI_CRC);
 		if (!ret) {
 			if (securedisplay_cmd->status == TA_SECUREDISPLAY_STATUS__SUCCESS) {
+				int pos = 0;
 				memset(i2c_output,  0, sizeof(i2c_output));
 				for (i = 0; i < TA_SECUREDISPLAY_I2C_BUFFER_SIZE; i++)
-					sprintf(i2c_output, "%s 0x%X", i2c_output,
+					pos += sprintf(i2c_output + pos, " 0x%X",
 						securedisplay_cmd->securedisplay_out_message.send_roi_crc.i2c_buf[i]);
 				dev_info(adev->dev, "SECUREDISPLAY: I2C buffer out put is :%s\n", i2c_output);
 			} else {
-- 
2.29.2