[PATCH 08/12] fs: exfat: Fix conversion overflow errors

[Marek Vasut]

On 3/10/25 12:17 PM, Quentin Schulz wrote:
> Hi Marek,

Hi,

> On 3/8/25 9:12 PM, Marek Vasut wrote:
>> Fix the following conversion overflow errors. The input field is already
>> limited to 3/2/1 bits using the bitwise and, move the parenthesis around
>> to avoid the bogus warning:
>>
>> "
>> fs/exfat/utf.c: In function ‘utf8_to_wchar’:
>> fs/exfat/utf.c:165:23: warning: overflow in conversion from ‘int’ to 
>> ‘wchar_t’ {aka ‘short unsigned int’} changes value from ‘(int)(short 
>> unsigned int)*input << 18 & 1835008’ to ‘0’ [-Woverflow]
>>    165 |                 *wc = ((wchar_t) input[0] & 0x07) << 18;
>>        |                       ^
>> fs/exfat/utf.c:170:23: warning: overflow in conversion from ‘int’ to 
>> ‘wchar_t’ {aka ‘short unsigned int’} changes value from ‘(int)(short 
>> unsigned int)*input << 24 & 50331648’ to ‘0’ [-Woverflow]
>>    170 |                 *wc = ((wchar_t) input[0] & 0x03) << 24;
>>        |                       ^
>> fs/exfat/utf.c:175:23: warning: overflow in conversion from ‘int’ to 
>> ‘wchar_t’ {aka ‘short unsigned int’} changes value from ‘(int)(short 
>> unsigned int)*input << 30 & 1073741824’ to ‘0’ [-Woverflow]
>>    175 |                 *wc = ((wchar_t) input[0] & 0x01) << 30;
>>        |                       ^
>> "
>>
> 
> Since this doesn't seem to be U-Boot-specific, any chance to open a Pull 
> Request on the project so we may be able to not carry this patch when 
> upgrading (yes, the last commit in the branch was two years ago, but it 
> seems the maintainer is still active on issues).
> 
> Considering that wchar_t is an unsigned short int and that USHRT_MAX is 
> 0xffff (so 2B or 16b)...
In fact, this error does not even appear in upstream , because upstream 
does not use -fshort-wchar compiler flag . U-Boot does use this compiler 
flags since 4a85663ec7ed ("kbuild: Enable -fshort-wchar") .

So I wonder if this might be the right fix here instead:

diff --git a/fs/exfat/Makefile b/fs/exfat/Makefile
index 550c0683d65..8ca112cf0e9 100644
--- a/fs/exfat/Makefile
+++ b/fs/exfat/Makefile
@@ -1,6 +1,9 @@
  # SPDX-License-Identifier: GPL-2.0+
  #

+# The utf.o does really need 32bit wchar_t
+CFLAGS_REMOVE_utf.o := -fshort-wchar
+
  obj-$(CONFIG_FS_EXFAT) += \
  	cluster.o \
  	io.o \