| [9] | 1 | /* The <setjmp.h> header relates to the C phenomenon known as setjmp/longjmp.
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| 2 | * It is used to escape out of the current situation into a previous one.
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| 3 | * A typical example is in an editor, where hitting DEL breaks off the current
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| 4 | * command and puts the editor back in the main loop, though care has to be
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| 5 | * taken when the DEL occurs while executing a library function, since
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| 6 | * some of them are not reentrant.
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| 7 | *
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| 8 | * POSIX does not require the process signal mask to be saved and restored
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| 9 | * during setjmp/longjmp. However, the current implementation does this
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| 10 | * in order to agree with OSF/1 and other BSD derived systems.
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| 11 | *
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| 12 | * The pair of functions _setjmp/_longjmp may be used when the signal
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| 13 | * mask is not to be saved/restored. These functions are traditional
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| 14 | * in BSD systems.
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| 15 | *
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| 16 | * There are different ways of implementing setjmp/longjmp. Probably
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| 17 | * the best way is to unify it with signal handling. This is true for the
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| 18 | * following reasons: Both setjmp/longjmp and signal delivery must save
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| 19 | * a context so that it may be restored later. The jmp_buf necessarily
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| 20 | * contains signal information, namely the signal mask to restore. Both
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| 21 | * longjmp and the return of a signal handler must trap to the operating
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| 22 | * system to restore the previous signal mask. Finally, the jmp_buf
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| 23 | * and the sigcontext structure contain the registers to restore.
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| 24 | *
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| 25 | * Some compilers, namely ACK, will not enregister any variables inside a
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| 26 | * function containing a call to setjmp, even if those variables are
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| 27 | * explicitly declared as register variables. Thus for ACK, the
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| 28 | * identification of the jmp_buf with a sigcontext structure would cause
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| 29 | * unnecessary overhead: the jmp_buf has room for all the registers, but
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| 30 | * the only registers that need to be saved are the stack pointer,
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| 31 | * frame pointer, and program counter.
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| 32 | *
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| 33 | * So, for ACK a jmp_buf is much smaller than a sigcontext structure, and
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| 34 | * longjmp does not directly call sigreturn. Instead, longjmp calls a
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| 35 | * front-end function which initializes the appropriate fields of a
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| 36 | * sigcontext structure, marks this structure as containing no valid
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| 37 | * general purpose registers, and then calls sigreturn.
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| 38 | *
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| 39 | * The POSIX sigjmp_buf is identical to the jmp_buf in all cases.
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| 40 | *
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| 41 | * Different compilers have different symbols that they recognize as
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| 42 | * setjmp symbols. ACK recognizes __setjmp, the GNU C compiler
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| 43 | * recognizes setjmp and _setjmp, and BCC recognizes all three.
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| 44 | * When these symbols occur within a function, the compiler may keep
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| 45 | * all local variables on the stack, avoid certain optimizations, or
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| 46 | * pass hidden arguments to the setjmp function.
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| 47 | *
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| 48 | * Thus, setjmp implementations vary in two independent ways which may
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| 49 | * be identified through the following preprocessor tokens:
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| 50 | *
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| 51 | * _SETJMP_SYMBOL -- If 0, this means the compiler treats setjmp and _setjmp
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| 52 | * specially. If 1, this means the compiler treats __setjmp specially.
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| 53 | *
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| 54 | * _SETJMP_SAVES_REGS -- If 1, this means setjmp/longjmp must explicitly
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| 55 | * save and restore all registers. This also implies that a jmp_buf is
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| 56 | * different than a sigcontext structure. If 0, this means that the compiler
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| 57 | * will not use register variables within a function that calls one of
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| 58 | * its SETJMP_SYMBOLs.
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| 59 | *
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| 60 | * When _SETJMP_SYMBOL = 1, the implementation has a few dozen bytes of
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| 61 | * unnecessary overhead. This happens in the following manner: a program uses
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| 62 | * _setjmp/_longjmp because it is not interested in saving and restoring the
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| 63 | * signal mask. Nevertheless, because _setjmp expands to the general purpose
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| 64 | * function __setjmp, code for sigprocmask(2) is linked into the program.
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| 65 | */
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| 66 |
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| 67 | #ifndef _SETJMP_H
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| 68 | #define _SETJMP_H
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| 69 |
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| 70 | #ifndef _ANSI_H
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| 71 | #include <ansi.h>
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| 72 | #endif
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| 73 |
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| 74 | #if !defined(__ACK__) && !defined(__BCC__) && !defined(__GNUC__)
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| 75 | #define __ACK__
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| 76 | #endif
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| 77 |
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| 78 | #ifdef __ACK__
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| 79 | #define _SETJMP_SYMBOL 1
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| 80 | #define _SETJMP_SAVES_REGS 0
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| 81 | #endif
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| 82 | #ifdef __BCC__
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| 83 | #define _SETJMP_SYMBOL 0
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| 84 | #define _SETJMP_SAVES_REGS 1
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| 85 | #endif
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| 86 | #ifdef __GNUC__
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| 87 | #define _SETJMP_SYMBOL 1
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| 88 | #define _SETJMP_SAVES_REGS 1
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| 89 | #endif
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| 90 |
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| 91 | /* The jmp_buf data type. Do not change the order of these fields -- some
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| 92 | * C library code refers to these fields by name. When _SETJMP_SAVES_REGS
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| 93 | * is 1, the file <sys/jmp_buf.h> gives the usage of the sixteen registers.
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| 94 | */
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| 95 | typedef struct {
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| 96 | int __flags; /* XXX - long might give better alignment */
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| 97 | long __mask; /* must have size >= sizeof(sigset_t) */
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| 98 | #if (_SETJMP_SAVES_REGS == 0)
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| 99 | _PROTOTYPE(void (*__pc),(void)); /* program counter */
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| 100 | void *__sp; /* stack pointer */
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| 101 | void *__lb; /* local base (ACKspeak for frame pointer) */
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| 102 | #else
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| 103 | void *__regs[16]; /* size is machine dependent */
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| 104 | #endif
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| 105 | } jmp_buf[1];
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| 106 |
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| 107 | #if (_SETJMP_SYMBOL == 1)
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| 108 |
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| 109 | _PROTOTYPE( int __setjmp, (jmp_buf _env, int _savemask) );
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| 110 | _PROTOTYPE( void longjmp, (jmp_buf _env, int _val) );
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| 111 | _PROTOTYPE(int sigjmp, (jmp_buf _jb, int _retval) );
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| 112 |
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| 113 | #define setjmp(env) __setjmp((env), 1)
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| 114 |
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| 115 | #ifdef _MINIX
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| 116 | #define _setjmp(env) __setjmp((env), 0)
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| 117 | _PROTOTYPE(void _longjmp, (jmp_buf _env, int _val) );
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| 118 | #endif
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| 119 |
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| 120 | #ifdef _POSIX_SOURCE
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| 121 | typedef jmp_buf sigjmp_buf;
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| 122 | #ifdef __GNUC__
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| 123 | #define siglongjmp longjmp
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| 124 | #else
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| 125 | _PROTOTYPE( void siglongjmp, (sigjmp_buf _env, int _val) );
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| 126 | #endif
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| 127 |
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| 128 | #define sigsetjmp(env, savemask) __setjmp((env), (savemask))
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| 129 | #endif /* _POSIX_SOURCE */
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| 130 |
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| 131 | #endif /* _SETJMP_SYMBOL == 1 */
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| 132 |
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| 133 | #if (_SETJMP_SYMBOL == 0)
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| 134 |
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| 135 | _PROTOTYPE( int setjmp, (jmp_buf _env) );
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| 136 | _PROTOTYPE( void longjmp, (jmp_buf _env, int _val) );
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| 137 |
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| 138 | #ifdef _MINIX
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| 139 | _PROTOTYPE( int _setjmp, (jmp_buf _env) );
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| 140 | _PROTOTYPE( void _longjmp, (jmp_buf _env, int _val) );
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| 141 | #endif
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| 142 |
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| 143 | #ifdef _POSIX_SOURCE
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| 144 | #define sigjmp_buf jmp_buf
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| 145 | _PROTOTYPE( void siglongjmp, (sigjmp_buf _env, int _val) );
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| 146 | /* XXX - the name _setjmp is no good - that's why ACK used __setjmp. */
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| 147 | #define sigsetjmp(env, savemask) ((savemask) ? setjmp(env) : _setjmp(env))
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| 148 | #endif /* _POSIX_SOURCE */
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| 149 |
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| 150 | #endif /* _SETJMP_SYMBOL == 0 */
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| 151 |
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| 152 | #endif /* _SETJMP_H */
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