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452cddbff7
Extend the static_call infrastructure to optimize the following common
pattern:
if (func_ptr)
func_ptr(args...)
For the trampoline (which is in effect a tail-call), we patch the
JMP.d32 into a RET, which then directly consumes the trampoline call.
For the in-line sites we replace the CALL with a NOP5.
NOTE: this is 'obviously' limited to functions with a 'void' return type.
NOTE: DEFINE_STATIC_COND_CALL() only requires a typename, as opposed
to a full function.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20200818135805.042977182@infradead.org
41 lines
1.6 KiB
C
41 lines
1.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_STATIC_CALL_H
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#define _ASM_STATIC_CALL_H
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#include <asm/text-patching.h>
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/*
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* For CONFIG_HAVE_STATIC_CALL_INLINE, this is a temporary trampoline which
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* uses the current value of the key->func pointer to do an indirect jump to
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* the function. This trampoline is only used during boot, before the call
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* sites get patched by static_call_update(). The name of this trampoline has
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* a magical aspect: objtool uses it to find static call sites so it can create
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* the .static_call_sites section.
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*
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* For CONFIG_HAVE_STATIC_CALL, this is a permanent trampoline which
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* does a direct jump to the function. The direct jump gets patched by
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* static_call_update().
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*
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* Having the trampoline in a special section forces GCC to emit a JMP.d32 when
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* it does tail-call optimization on the call; since you cannot compute the
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* relative displacement across sections.
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*/
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#define __ARCH_DEFINE_STATIC_CALL_TRAMP(name, insns) \
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asm(".pushsection .static_call.text, \"ax\" \n" \
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".align 4 \n" \
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".globl " STATIC_CALL_TRAMP_STR(name) " \n" \
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STATIC_CALL_TRAMP_STR(name) ": \n" \
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insns " \n" \
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".type " STATIC_CALL_TRAMP_STR(name) ", @function \n" \
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".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \
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".popsection \n")
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#define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func) \
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__ARCH_DEFINE_STATIC_CALL_TRAMP(name, ".byte 0xe9; .long " #func " - (. + 4)")
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#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) \
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__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; nop; nop; nop; nop")
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#endif /* _ASM_STATIC_CALL_H */
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