32 #include "lint.h"
33 #include <stdarg.h>
34 #include <ucontext.h>
35 #include <sys/stack.h>
36
37 /*
38 * The ucontext_t that the user passes in must have been primed with a
39 * call to getcontext(2), have the uc_stack member set to reflect the
40 * stack which this context will use, and have the uc_link member set
41 * to the context which should be resumed when this context returns.
42 * When makecontext() returns, the ucontext_t will be set to run the
43 * given function with the given parameters on the stack specified by
44 * uc_stack, and which will return to the ucontext_t specified by uc_link.
45 */
46
47 /*
48 * The original i386 ABI said that the stack pointer need be only 4-byte
49 * aligned before a function call (STACK_ALIGN == 4). The ABI supplement
50 * version 1.0 changed the required alignment to 16-byte for the benefit of
51 * floating point code compiled using sse2. The compiler assumes this
52 * alignment and maintains it for calls made from that function. If the
53 * stack is initially properly aligned, it will continue to be so aligned.
54 * If it is not initially so aligned, it will never become so aligned.
55 *
56 * One slightly confusing detail to keep in mind is that the 16-byte
57 * alignment (%esp & 0xf == 0) is true just *before* the call instruction.
58 * The call instruction will then push a return value, decrementing %esp by
59 * 4. Therefore, if one dumps %esp at the at the very first instruction in
60 * a function, it will end with a 0xc. The compiler expects this and
61 * compensates for it properly.
62 *
63 * Note: If you change this value, you need to change it in the following
64 * files as well:
65 *
66 * - lib/libc/i386/threads/machdep.c
67 * - lib/common/i386/crti.s
68 * - lib/common/i386/crt1.s
69 */
70 #undef STACK_ALIGN
71 #define STACK_ALIGN 16
72
73 static void resumecontext(void);
74
75 void
76 makecontext(ucontext_t *ucp, void (*func)(), int argc, ...)
77 {
78 long *sp;
79 long *tsp;
80 va_list ap;
81 size_t size;
82
83 ucp->uc_mcontext.gregs[EIP] = (greg_t)func;
84
85 size = sizeof (long) * (argc + 1);
86
87 tsp = (long *)(((uintptr_t)ucp->uc_stack.ss_sp +
88 ucp->uc_stack.ss_size - size) & ~(STACK_ALIGN - 1));
89
90 sp = tsp - 1;
91
92 va_start(ap, argc);
93
94 while (argc-- > 0) {
95 *tsp++ = va_arg(ap, long);
96 }
97
98 va_end(ap);
99
100 *sp = (long)resumecontext; /* return address */
101
102 ucp->uc_mcontext.gregs[UESP] = (greg_t)sp;
103 }
104
105
106 static void
107 resumecontext(void)
108 {
109 ucontext_t uc;
110
111 (void) getcontext(&uc);
112 (void) setcontext(uc.uc_link);
113 }
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32 #include "lint.h"
33 #include <stdarg.h>
34 #include <ucontext.h>
35 #include <sys/stack.h>
36
37 /*
38 * The ucontext_t that the user passes in must have been primed with a
39 * call to getcontext(2), have the uc_stack member set to reflect the
40 * stack which this context will use, and have the uc_link member set
41 * to the context which should be resumed when this context returns.
42 * When makecontext() returns, the ucontext_t will be set to run the
43 * given function with the given parameters on the stack specified by
44 * uc_stack, and which will return to the ucontext_t specified by uc_link.
45 */
46
47 /*
48 * The original i386 ABI said that the stack pointer need be only 4-byte
49 * aligned before a function call (STACK_ALIGN == 4). The ABI supplement
50 * version 1.0 changed the required alignment to 16-byte for the benefit of
51 * floating point code compiled using sse2. The compiler assumes this
52 * alignment and maintains it for calls it generates. If the stack is
53 * initially properly aligned, it will continue to be so aligned. If it is
54 * not initially so aligned, it will never become so aligned.
55 *
56 * One slightly confusing detail to keep in mind is that the 16-byte
57 * alignment (%esp & 0xf == 0) is true just *before* the call instruction.
58 * The call instruction will then push a return value, decrementing %esp by
59 * 4. Therefore, if one dumps %esp at the at the very first instruction in
60 * a function, it will end with a 0xc. The compiler expects this and
61 * compensates for it properly.
62 *
63 * Note: If you change this value, you need to change it in the following
64 * files as well:
65 *
66 * - lib/libc/i386/threads/machdep.c
67 * - lib/common/i386/crti.s
68 * - lib/common/i386/crt1.s
69 */
70 #undef STACK_ALIGN
71 #define STACK_ALIGN 16
72
73 static void resumecontext(void);
74
75 void
76 makecontext(ucontext_t *ucp, void (*func)(), int argc, ...)
77 {
78 long *sp;
79 long *tsp;
80 va_list ap;
81 size_t size;
82
83 ucp->uc_mcontext.gregs[EIP] = (greg_t)func;
84
85 size = sizeof (long) * (argc + 1);
86
87 tsp = (long *)(((uintptr_t)ucp->uc_stack.ss_sp +
88 ucp->uc_stack.ss_size - size) & ~(STACK_ALIGN - 1));
89
90 /*
91 * Since we're emulating the call instruction, we must push the
92 * return address (which involves adjusting the stack pointer to
93 * have the proper 4-byte bias).
94 */
95 sp = tsp - 1;
96
97 *sp = (long)resumecontext; /* return address */
98
99 ucp->uc_mcontext.gregs[UESP] = (greg_t)sp;
100
101 /*
102 * "push" all the arguments
103 */
104 va_start(ap, argc);
105 while (argc-- > 0)
106 *tsp++ = va_arg(ap, long);
107 va_end(ap);
108 }
109
110
111 static void
112 resumecontext(void)
113 {
114 ucontext_t uc;
115
116 (void) getcontext(&uc);
117 (void) setcontext(uc.uc_link);
118 }
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