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Re: [PATCH 3/3] aarch64: Save and restore SVE registers in ld.so

From: Szabolcs Nagy <szabolcs dot nagy at arm dot com>
To: Richard Henderson <richard dot henderson at linaro dot org>, Florian Weimer <fweimer at redhat dot com>, rth at twiddle dot net, libc-alpha at sourceware dot org
Cc: nd at arm dot com, marcus dot shawcroft at linaro dot org
Date: Thu, 2 Aug 2018 14:32:57 +0100
Subject: Re: [PATCH 3/3] aarch64: Save and restore SVE registers in ld.so
References: <20180801222347.18903-1-rth@twiddle.net> <20180801222347.18903-4-rth@twiddle.net> <4f5e94bb-aef5-f545-5b1c-ea77221c73cc@redhat.com> <221a9df1-dee4-6830-51e0-b16d27addea8@linaro.org>

On 02/08/18 14:05, Richard Henderson wrote:

On 08/02/2018 03:29 AM, Florian Weimer wrote:

On 08/02/2018 12:23 AM, rth@twiddle.net wrote:

+/*
+ * For functions conforming to the procedure call standard as
+ * amended for SVE support (ARM_100986_0000_00_en (SVEpcs 00bet1)),
+ * we must save the entire contents of Z0-Z7 as well as P0-P3.
+ */


What's the worst-case additional stack usage due to this change?


The current architectural maximum vector size is 256 bytes,
so 2176 bytes total.


that limit can increase in the future and saving 8 z regs is not enough,
you need to save all 32 if the resolver code may touch the 32 fp regs.
(so with 256byte regs it's 8k + 128bytes for 4 pregs)

Follow-Ups:
- Re: [PATCH 3/3] aarch64: Save and restore SVE registers in ld.so
  - From: Carlos O'Donell

References:
- [PATCH 0/3] aarch64: Update ld.so for vector abi
  - From: rth
- [PATCH 3/3] aarch64: Save and restore SVE registers in ld.so
  - From: rth
- Re: [PATCH 3/3] aarch64: Save and restore SVE registers in ld.so
  - From: Florian Weimer
- Re: [PATCH 3/3] aarch64: Save and restore SVE registers in ld.so
  - From: Richard Henderson

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