On 1/29/24 03:06, Geert Uytterhoeven wrote:
[ ... ]
> parisc-gcc1[23]/parisc-{allmod,def}config
>
> + /kisskb/src/drivers/hwmon/pc87360.c: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]: => 383:51
>
The "fix" for this problem would be similar to commit 4265eb062a73 ("hwmon: (pc87360)
Bounds check data->innr usage"). The change would be something like
- for (i = 0; i < data->tempnr; i++) {
+ for (i = 0; i < min(data->tempnr, ARRAY_SIZE(data->temp_max)); i++) {
but that would be purely random because the loop accesses several arrays
indexed with i, and tempnr is never >= ARRAY_SIZE(data->temp_max).
I kind of resist making such changes to the code just because the compiler
is clueless.
Are we sprinkling the kernel code with code like this to make the compiler happy ?
Guenter
On 1/29/24 15:58, Guenter Roeck wrote:
> On 1/29/24 03:06, Geert Uytterhoeven wrote:
> [ ... ]
>> parisc-gcc1[23]/parisc-{allmod,def}config
>>
>> + /kisskb/src/drivers/hwmon/pc87360.c: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]: => 383:51
>>
>
> The "fix" for this problem would be similar to commit 4265eb062a73 ("hwmon: (pc87360)
> Bounds check data->innr usage"). The change would be something like
>
> - for (i = 0; i < data->tempnr; i++) {
> + for (i = 0; i < min(data->tempnr, ARRAY_SIZE(data->temp_max)); i++) {
>
> but that would be purely random because the loop accesses several arrays
> indexed with i, and tempnr is never >= ARRAY_SIZE(data->temp_max).
> I kind of resist making such changes to the code just because the compiler
> is clueless.
I agree with your analysis.
But I'm wondering why this warning just seem to appear on parisc.
I would expect gcc on other platforms to complain as well ?!?
Helge
> Are we sprinkling the kernel code with code like this to make the compiler happy ?
>
> Guenter
>
>
Helge Deller <[email protected]> writes:
> On 1/29/24 15:58, Guenter Roeck wrote:
>> On 1/29/24 03:06, Geert Uytterhoeven wrote:
>> [ ... ]
>>> parisc-gcc1[23]/parisc-{allmod,def}config
>>>
>>> + /kisskb/src/drivers/hwmon/pc87360.c: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]: => 383:51
>>>
>>
>> The "fix" for this problem would be similar to commit 4265eb062a73 ("hwmon: (pc87360)
>> Bounds check data->innr usage"). The change would be something like
>>
>> - for (i = 0; i < data->tempnr; i++) {
>> + for (i = 0; i < min(data->tempnr, ARRAY_SIZE(data->temp_max)); i++) {
>>
>> but that would be purely random because the loop accesses several arrays
>> indexed with i, and tempnr is never >= ARRAY_SIZE(data->temp_max).
>> I kind of resist making such changes to the code just because the compiler
>> is clueless.
>
> I agree with your analysis.
> But I'm wondering why this warning just seem to appear on parisc.
> I would expect gcc on other platforms to complain as well ?!?
-Wstringop-overflow and -Wstringop-truncation are known noisy warnings
because they're implemented in GCC's "middle-end". Whether or not they
fire depends on other optimisations.
See also https://lore.kernel.org/linux-hardening/CAHk-=wjG4jdE19-vWWhAX3ByfbNr4DJS-pwiN9oY38WkhMZ57g@mail.gmail.com/.
>
> Helge
>
>> Are we sprinkling the kernel code with code like this to make the compiler happy ?
>>
>> Guenter
>>
>>
thanks,
sam
On 1/29/24 23:49, Helge Deller wrote:
> On 1/29/24 15:58, Guenter Roeck wrote:
>> On 1/29/24 03:06, Geert Uytterhoeven wrote:
>> [ ... ]
>>> parisc-gcc1[23]/parisc-{allmod,def}config
>>>
>>> + /kisskb/src/drivers/hwmon/pc87360.c: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]: => 383:51
>>>
>>
>> The "fix" for this problem would be similar to commit 4265eb062a73 ("hwmon: (pc87360)
>> Bounds check data->innr usage"). The change would be something like
>>
>> - for (i = 0; i < data->tempnr; i++) {
>> + for (i = 0; i < min(data->tempnr, ARRAY_SIZE(data->temp_max)); i++) {
>>
>> but that would be purely random because the loop accesses several arrays
>> indexed with i, and tempnr is never >= ARRAY_SIZE(data->temp_max).
>> I kind of resist making such changes to the code just because the compiler
>> is clueless.
>
> I agree with your analysis.
> But I'm wondering why this warning just seem to appear on parisc.
> I would expect gcc on other platforms to complain as well ?!?
>
I have seen that problem before, where specifically gcc for x86 doesn't even
generate warnings for really problematic code but gcc for other architectures
does. I never found out what causes this. Don't ask me for examples, I didn't
write it down, forgot specifics, and just accepted it as "one of those things".
Guenter