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From: "Miller, Tim" <theosib@amazon.com>
To: "libc-help@sourceware.org" <libc-help@sourceware.org>
Subject: Build glibc for aarch64 with C-only versions of memcpy?
Date: Wed, 15 Dec 2021 20:31:55 +0000	[thread overview]
Message-ID: <52DC392C-C51F-41DF-9120-574221C873A8@amazon.com> (raw)

Hi,

I am doing some software profiling on an aarch64 system, and I’m using the Linux perf tool. The problem I’m running into is that “__GI___memcpy_simd” keeps showing up as the function with the most CPU usage.

Unfortunately, no matter what I do, this function keeps showing up as orphaned. That is, I cannot get a stack trace for it so I can find out who is calling it. I’ve rebuilt all of glibc with -no-omit-frame-pointer, but since this function is written in assembly, it doesn’t preserve the frame pointer. (I have tried using dwarf to get stack traces instead of the frame pointer, but that usually gets overloaded, and I still don’t get a stack trace for memcpy.)

I’ve spent about a day now, trying to hack it so that the C version in string/memcpy.c gets called instead, but everything I do leads to compile errors of some sort, either undefined symbols or doubly defined symbols. Basically, I can’t figure out how to untangle all the abstraction going on that seems to be involved in picking one memcpy implementation or another.

What is the proper way that one would go about disabling all assembly versions of memcpy for a custom built glibc?

Thanks.


             reply	other threads:[~2021-12-15 20:31 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-15 20:31 Miller, Tim [this message]
2021-12-15 20:40 ` Florian Weimer
2021-12-15 21:13   ` Miller, Tim
2021-12-15 21:28   ` Miller, Tim
2021-12-15 21:33     ` Florian Weimer
2021-12-15 21:37       ` Miller, Tim

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