On Wed, 2021-03-03 at 10:41 +0100, Rasmus Villemoes wrote:
On 02/03/2021 18.42, Joe Perches wrote:
Here is a possible opportunity to reduce data usage in the kernel.
$ git grep -P -n '^static\s+(?!const|struct)(?:\w+\s+){1,3}\w+\s*\[\s*\]' drivers/ | \ grep -v __initdata | \ wc -l 3250
Meaning there are ~3000 declarations of arrays with what appears to be file static const content that are not marked const.
So there are many static arrays that could be marked const to move the compiled object code from data to text minimizing the total amount of exposed r/w data.
You can add const if you like, but it will rarely change the generated code. gcc is already smart enough to take a static array whose contents are provably never modified within the TU and put it in .rodata:
At least some or perhaps even most of the time, true, but the gcc compiler from v5 through at least v10 seems inconsistent about when it does the appropriate conversion. See the example I posted: https://lore.kernel.org/lkml/6b8b250a06a98ce42120a14824531a8641f5e8aa.camel@... It was a randomly chosen source file conversion btw, I had no prior knowledge of whether the text/data use would change. I'm unsure about clang consistently moving static but provably const arrays from data to text. I rarely use clang. At least for v11 it seems to be better though. I didn't try 10.1.