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1c8e166fb5
Add the HAVE_INIJMP symbol to be set by architectures that support initjmp(), a non-standard extension to setjmp()/longjmp() allowing to initialize a jump buffer with a function pointer and a stack pointer. This will be useful to later introduce threads. With this new function it becomes possible to longjmp() to a particular function pointer (rather than to a point previously reached during program execution as is the case with setjmp()), and with a custom stack. Both things are needed to spin off a new thread. Then the usual setjmp()/longjmp() pair is enough to save and restore a context, i.e., switch thread. Add the initjmp() prototype to <include/setjmp.h> since it is common to all architectures. Add an entry to the API documentation: doc/api/setjmp.rst. Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org> Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
73 lines
2.2 KiB
C
73 lines
2.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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#ifndef _SETJMP_H_
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#define _SETJMP_H_ 1
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/**
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* DOC: Overview
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*
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* The long jump API allows to perform nonlocal gotos, that is jump from one
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* function to another typically further down in the stack, while properly
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* restoring the stack's state (unwinding). The two functions needed to do this
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* are setjmp() and longjmp().
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*
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* In addition to these two standard POSIX.1-2001/C89 functions, a third one is
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* present in U-Boot: initjmp(). It is an extension which allows to implement
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* user-mode threads.
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*/
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#ifdef CONFIG_HAVE_SETJMP
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#include <asm/setjmp.h>
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#else
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struct jmp_buf_data {
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};
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#endif
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#include <linux/compiler_attributes.h>
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#include <stddef.h>
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/**
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* typedef jmp_buf - information needed to restore a calling environment
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*/
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typedef struct jmp_buf_data jmp_buf[1];
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/**
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* setjmp() - prepare for a long jump
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*
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* Registers, the stack pointer, and the return address are saved in the
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* jump bufffer. The function returns zero afterwards. When longjmp() is
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* executed the function returns a second time with a non-zero value.
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*
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* @env: jump buffer used to store register values
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* Return: 0 after setting up jump buffer, non-zero after longjmp()
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*/
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int setjmp(jmp_buf env);
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/**
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* longjmp() - long jump
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*
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* Jump back to the address and the register state saved by setjmp().
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*
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* @env: jump buffer
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* @val: value to be returned by setjmp(), 0 is replaced by 1
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*/
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void longjmp(jmp_buf env, int val);
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/**
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* initjmp() - prepare for a long jump to a given function with a given stack
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*
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* This function sets up a jump buffer for later use with longjmp(). It allows
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* to branch to a specific function with a specific stack. Please note that
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* @func MUST NOT return. It shall typically restore the main stack and resume
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* execution by doing a long jump to a jump buffer initialized by setjmp()
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* before the long jump. initjmp() allows to implement multithreading.
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*
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* @env: jump buffer
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* @func: function to be called on longjmp(), MUST NOT RETURN
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* @stack_base: the stack to be used by @func (lower address)
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* @stack_sz: the stack size in bytes
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*/
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int initjmp(jmp_buf env, void __noreturn (*func)(void), void *stack_base,
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size_t stack_sz);
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#endif /* _SETJMP_H_ */
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