On Wed, Aug 28, 2024 at 12:24:12PM +0000, Arnd Bergmann wrote:
On Wed, Aug 28, 2024, at 11:18, Jason A. Donenfeld wrote:
On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
Is there a compiler flag that could be used to disable the generation of calls to memset?
-fno-tree-loop-distribute-patterns . But, as always, read up on it, see what it actually does (and how it avoids your problem, and mostly: learn what the actual problem *was*!)
This might help with various loops, but it doesn't help with the matter that this patch fixes, which is struct initialization. I just tried it with the arm64 patch to no avail.
Maybe -ffreestanding can help here? That should cause the vdso to be built with the assumption that there is no libc, so it would neither add nor remove standard library calls. Not sure if that causes other problems, e.g. if the calling conventions are different.
"GCC requires the freestanding environment provide 'memcpy', 'memmove', 'memset' and 'memcmp'."
This is precisely to implement things like struct initialisation. Maybe we should have a "-ffreeerstanding" or "-ffreefloating" or think of something funnier still environment as well, this problem has been there since the -ffreestanding flag has existed, but the problem is as old as the night.
-fno-builtin might help a bit more, but just attack the problem at its root, like I suggested?
(This isn't a new problem, originally it showed up as "GCC replaces (part of) my memcpy() implementation by a (recursive) call to memcpy()" and, well, that doesn't quite work!)
Segher