Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

From
Segher Boessenkool <hidden>
Date
2024-08-28 12:40:10
Also in
linux-arch, linux-fsdevel, linux-kselftest, linux-mm, linuxppc-dev, lkml
Reply to
Jason A. Donenfeld, 2024-08-28
On Wed, Aug 28, 2024 at 01:18:34PM +0200, Jason A. Donenfeld wrote:
On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
quoted
On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
quoted
quoted
+		for (i = 0; i < ARRAY_SIZE(params->reserved); i++)
+			params->reserved[i] = 0;
This is a loop.  With -ftree-loop-distribute-patterns, the default at
-O2, this is optimised to

    memset(params->reserved, 0, ...);

(which is perfectly fine, since memset is required to be there even
for freestanding environments, this is documented!)
quoted
-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.
It very much *does* help.  Try harder?  Maybe you typoed?


Segher
Thread (64 messages) 64 messages, 10 authors, last reply 2024-08-30
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