Differential D22787

[PowerPC] Define powerpc IFUNC kernel/userspace ABI.
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Authored by bdragon on Dec 12 2019, 11:18 PM.

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jhibbits

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rS356061: [PowerPC] Define powerpc IFUNC kernel/userspace ABI.

Summary

This is a prerequisite for anything IFUNC in the ELFv2 / clang switch.

Since probing cpu info on powerpc is a privileged operation, define that we pass AT_HWCAP / AT_HWCAP2 through as cpu_features and cpu_features2 to ifunc resolvers. (This is particularly important when dealing with non-PLT GNU IFUNC, which is not allowed to PLT call from resolvers and therefore can't access global variables.)

This naming convention matches how we expose these two variables in machine/cpu.h. It is a FreeBSD/powerpc specific convention.

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rS FreeBSD src repository - subversion

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bdragon created this revision.Dec 12 2019, 11:18 PM

Herald added subscribers: alfredo, luporl, imp. · View Herald TranscriptDec 12 2019, 11:18 PM

bdragon added inline comments.Dec 12 2019, 11:21 PM

sys/powerpc/include/ifunc.h
3	I'm not sure what to do about the license header. Is it okay to leave it as is?
47	Specifically defining as register_t on purpose here. We only use the low order 32 bits of the variables so it should be okay on any powerpc variant.

bdragon mentioned this in D22789: [PowerPC] powerpc64 rtld IFUNC handling code.Dec 12 2019, 11:50 PM

luporl added a child revision: D15368: strcpy optimization for PowerPC64.Dec 13 2019, 2:03 PM

luporl added a child revision: D15118: memcpy optimization for powerpc64.

luporl added a child revision: D15369: strncpy optimization for PowerPC64.Dec 13 2019, 2:09 PM

kib added a subscriber: kib.Dec 13 2019, 3:41 PM

kib added inline comments.

sys/powerpc/include/ifunc.h
3	I think you should add your copyright assert there.
6	Part of this software. If you want to keep this line.
54	Does PPC allows to pass up to 10 args in registers ?

jhibbits added inline comments.Dec 13 2019, 3:58 PM

sys/powerpc/include/ifunc.h
47	Why not use int, in that case? Are you expecting sys/types.h be included in all resolver files?

bdragon added inline comments.Dec 13 2019, 6:57 PM

sys/powerpc/include/ifunc.h
47	I am, yes. This file defines a contract between software (especially libc) and the runtime linker (in DEFINE_UIFUNC) and between the kernel and the kernel linker (in DEFINE_IFUNC). This is a machine dependent interface, and I'd rather be precise about it.
54	Register passing is r3-r10, so 8 args total.

bdragon added inline comments.Dec 13 2019, 7:05 PM

sys/powerpc/include/ifunc.h
47	Additionally, if non PLT gnu ifunc is in use, there are severe restrictions on how a resolver works -- it can not make PLT calls of any sort, and it may be called at any point, so must be self-contained.

jhibbits added inline comments.Dec 23 2019, 3:28 PM

sys/powerpc/include/ifunc.h
3	Not a copyright expert by any means, but I think kib's saying the triviality of the file means the FreeBSD Foundation copyright is unnecessary, as is his below. You effectively have copyright over more than half the non-license portion of the file, relative to the x86 ifunc.h.
47	Why not include sys/types.h in this file, then? It's not without precedent (machine/cpufunc.h does already).