[S] Change in coreboot[master]: vga: Fix the support of extended ASCII

[Felix Held (Code Review)]

Felix Held has submitted this change. ( https://review.coreboot.org/c/coreboot/+/73090 )

Change subject: vga: Fix the support of extended ASCII
......................................................................

vga: Fix the support of extended ASCII

VGA defineds the extended ASCII set based on CP437, but there is a bug
on printing them: in vga_write_at_offset(), we perform a bitwise or
between 'unsigned short' and 'signed char':

```
    p[i] = 0x0F00 | string[i];
```

If we want to show an extended ASCII character, string[i] will be
negative and this bitwise operation will fail due to their implicit
casting rule: convert signed char to unsigned short by adding 65536.

To fix this, we need to cast the string to unsigned char manually
somewhere. Since we still want to leverage the built-in string utilities
which only accepts const char*, we still preserve the original
prototypes before, and cast it until we write into the frame buffer.

BRANCH=brya
BUG=b:264666392
TEST=emerge-brya coreboot chromeos-bootimage
     and verify drawing characters with code > 127.

Change-Id: I9cd65fe9794e5b0d338147924f28efd27fc8a1e8
Signed-off-by: Hsuan Ting Chen 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/73090
Tested-by: build bot (Jenkins) 
Reviewed-by: Angel Pons 
Reviewed-by: Tarun Tuli 
---
M src/drivers/pc80/vga/vga.c
1 file changed, 37 insertions(+), 1 deletion(-)

Approvals:
  build bot (Jenkins): Verified
  Angel Pons: Looks good to me, approved
  Tarun Tuli: Looks good to me, approved

diff --git a/src/drivers/pc80/vga/vga.c b/src/drivers/pc80/vga/vga.c
index a52ba6d..a9befca 100644
--- a/src/drivers/pc80/vga/vga.c
+++ b/src/drivers/pc80/vga/vga.c
@@ -267,7 +267,7 @@

for (i = 0; i < (VGA_COLUMNS - offset); i++) {
    	if (i < len)
-			p[i] = 0x0F00 | string[i];
+			p[i] = 0x0F00 | (unsigned char)string[i];
    	else
    		p[i] = 0x0F00;
    }