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));
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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/crt/i86/crti.s
68 * - lib/crt/i86/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));
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