Change in coreboot[master]: soc/nvidia/tegra210: Prevent implicit integer promotion

[Jacob Garber (Code Review)]

Jacob Garber has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/34529 )

Change subject: soc/nvidia/tegra210: Prevent implicit integer promotion
......................................................................

soc/nvidia/tegra210: Prevent implicit integer promotion

The perennial problem with u16 << 16 strikes again - the u16 is
implicitly promoted to an int before the shift, which will then have
undefined behaviour if the highest bit of the u16 was set. Cast bytes
to a u32 beforehand to prevent this.

Change-Id: Iaf0fb1040ccafafde0093e9bb192c802b86cb2ac
Signed-off-by: Jacob Garber 
Found-by: Coverity CID 1294800
---
M src/soc/nvidia/tegra210/dsi.c
1 file changed, 2 insertions(+), 2 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/29/34529/1

diff --git a/src/soc/nvidia/tegra210/dsi.c b/src/soc/nvidia/tegra210/dsi.c
index ae20d44..6b94e24 100644
--- a/src/soc/nvidia/tegra210/dsi.c
+++ b/src/soc/nvidia/tegra210/dsi.c
@@ -380,8 +380,8 @@
    	}

tegra_dsi_writel(dsi, 0, DSI_PKT_LEN_0_1);
-		tegra_dsi_writel(dsi, bytes << 16, DSI_PKT_LEN_2_3);
-		tegra_dsi_writel(dsi, bytes << 16, DSI_PKT_LEN_4_5);
+		tegra_dsi_writel(dsi, (u32)bytes << 16, DSI_PKT_LEN_2_3);
+		tegra_dsi_writel(dsi, (u32)bytes << 16, DSI_PKT_LEN_4_5);
    	tegra_dsi_writel(dsi, 0, DSI_PKT_LEN_6_7);

value = MIPI_DCS_WRITE_MEMORY_START << 8 |

[Julius Werner (Code Review)]

Julius Werner has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/34529 )

Change subject: soc/nvidia/tegra210: Prevent implicit integer promotion
......................................................................

Patch Set 1:

IIRC we had some sort of general agreement in coreboot that we don't care about -Wshift-overflow=2 and don't want to litter all our code with casts just to work around this purely theoretical non-problem? If so, wouldn't this be the same kind of issue, and shouldn't we then equally ignore it?

[Jacob Garber (Code Review)]

Jacob Garber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/34529 )

Change subject: soc/nvidia/tegra210: Prevent implicit integer promotion
......................................................................

Patch Set 1:
> Patch Set 1:
>
> IIRC we had some sort of general agreement in coreboot that we don't care about -Wshift-overflow=2 and don't want to litter all our code with casts just to work around this purely theoretical non-problem? If so, wouldn't this be the same kind of issue, and shouldn't we then equally ignore it?

Hmmmm, I didn't know about that and that's a good point. In this case though things are slightly worse, since tegra_dsi_writel() expects a 64 bit integer for that argument, and if it's negative it will be sign extended to a very large unsigned integer. In this case, tegra_dsi_writel() only needs to write a 32 bit integer, so I think I'll change the argument to a u32 instead to avoid the sign extension.

[Julius Werner (Code Review)]

Julius Werner has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/34529 )

Change subject: soc/nvidia/tegra210: Prevent implicit integer promotion
......................................................................

Patch Set 1: Code-Review+2
> Hmmmm, I didn't know about that and that's a good point. In this case though things are slightly worse, since tegra_dsi_writel() expects a 64 bit integer for that argument, and if it's negative it will be sign extended to a very large unsigned integer. In this case, tegra_dsi_writel() only needs to write a 32 bit integer, so I think I'll change the argument to a u32 instead to avoid the sign extension.

Okay, the sign extension is a valid concern. Your suggestion sounds good, or I'd also be fine with the original CL in that case.

Change in coreboot[master]: soc/nvidia/tegra210: Prevent unintended sign extension

[Jacob Garber (Code Review)]

Hello Julius Werner, David Hendricks, build bot (Jenkins), Patrick Georgi, Martin Roth,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/34529

to look at the new patch set (#2).

Change subject: soc/nvidia/tegra210: Prevent unintended sign extension
......................................................................

soc/nvidia/tegra210: Prevent unintended sign extension

The perennial problem with u16 << 16 strikes again - the u16 is
implicitly promoted to an int before the shift, which will then become
negative if the highest bit of the u16 was set. Normally this isn't much
of a problem, but in this case tegra_dsi_writel() expects a 64 bit integer
for that argument, and so it will be sign-extended to a very large
unsigned integer if it is negative. Cast bytes to a u32 beforehand to
prevent the implicit promotion and thus this problem.

Change-Id: Iaf0fb1040ccafafde0093e9bb192c802b86cb2ac
Signed-off-by: Jacob Garber 
Found-by: Coverity CID 1294800
---
M src/soc/nvidia/tegra210/dsi.c
1 file changed, 2 insertions(+), 2 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/29/34529/2

Change in coreboot[master]: soc/nvidia/tegra210: Prevent unintended sign extension

[Paul Menzel (Code Review)]

Paul Menzel has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/34529 )

Change subject: soc/nvidia/tegra210: Prevent unintended sign extension
......................................................................

Patch Set 2: Code-Review+1

Change in coreboot[master]: soc/nvidia/tegra210: Prevent unintended sign extension

[Patrick Georgi (Code Review)]

Patrick Georgi has submitted this change and it was merged. ( https://review.coreboot.org/c/coreboot/+/34529 )

Change subject: soc/nvidia/tegra210: Prevent unintended sign extension
......................................................................

soc/nvidia/tegra210: Prevent unintended sign extension

The perennial problem with u16 << 16 strikes again - the u16 is
implicitly promoted to an int before the shift, which will then become
negative if the highest bit of the u16 was set. Normally this isn't much
of a problem, but in this case tegra_dsi_writel() expects a 64 bit integer
for that argument, and so it will be sign-extended to a very large
unsigned integer if it is negative. Cast bytes to a u32 beforehand to
prevent the implicit promotion and thus this problem.

Change-Id: Iaf0fb1040ccafafde0093e9bb192c802b86cb2ac
Signed-off-by: Jacob Garber 
Found-by: Coverity CID 1294800
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34529
Reviewed-by: Paul Menzel 
Reviewed-by: Julius Werner 
Tested-by: build bot (Jenkins) 
---
M src/soc/nvidia/tegra210/dsi.c
1 file changed, 2 insertions(+), 2 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Paul Menzel: Looks good to me, but someone else must approve
  Julius Werner: Looks good to me, approved

diff --git a/src/soc/nvidia/tegra210/dsi.c b/src/soc/nvidia/tegra210/dsi.c
index a383ff2..7d54c9e 100644
--- a/src/soc/nvidia/tegra210/dsi.c
+++ b/src/soc/nvidia/tegra210/dsi.c
@@ -380,8 +380,8 @@
    	}

tegra_dsi_writel(dsi, 0, DSI_PKT_LEN_0_1);
-		tegra_dsi_writel(dsi, bytes << 16, DSI_PKT_LEN_2_3);
-		tegra_dsi_writel(dsi, bytes << 16, DSI_PKT_LEN_4_5);
+		tegra_dsi_writel(dsi, (u32)bytes << 16, DSI_PKT_LEN_2_3);
+		tegra_dsi_writel(dsi, (u32)bytes << 16, DSI_PKT_LEN_4_5);
    	tegra_dsi_writel(dsi, 0, DSI_PKT_LEN_6_7);

value = MIPI_DCS_WRITE_MEMORY_START << 8 |