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VDSO time functions do not call any other function, so they don't need to save/restore LR. However, retrieving the address of VDSO data page requires using LR hence saving then restoring it, which can be heavy on some CPUs. On the other hand, VDSO functions on powerpc are not standard functions and require a wrapper function to call C VDSO functions. And that wrapper has to save and restore LR in order to call the C VDSO function, so retrieving VDSO data page address in that wrapper doesn't require additional save/restore of LR. For random VDSO functions it is a bit different. Because the function calls __arch_chacha20_blocks_nostack(), it saves and restores LR. Retrieving VDSO data page address can then be done there without additional save/restore of LR. So lets implement __arch_get_vdso_rng_data() and simplify the wrapper. It starts paving the way for the day powerpc will implement a more standard ABI for VDSO functions. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://patch.msgid.link/a1a9bd0df508f1b5c04684b7366940577dfc6262.1727858295.git.christophe.leroy@csgroup.eu
15 lines
432 B
C
15 lines
432 B
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Powerpc userspace implementation of getrandom()
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*
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* Copyright (C) 2024 Christophe Leroy <christophe.leroy@csgroup.eu>, CS GROUP France
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*/
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#include <linux/time.h>
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#include <linux/types.h>
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ssize_t __c_kernel_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state,
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size_t opaque_len)
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{
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return __cvdso_getrandom(buffer, len, flags, opaque_state, opaque_len);
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}
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