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39 .Nd kernel TLS (thread local storage) support
45 .Fn set_tls_area "int which" "struct tls_info *info" "size_t infosize"
47 .Fn get_tls_area "int which" "struct tls_info *info" "size_t infosize"
51 system call creates an entry for the TLS facility
53 representing thread local storage as specified by the
56 A descriptor representing the facility is returned, or -1 if an error occurred.
57 The facility may be cleared by specifying a NULL pointer and an infosize of 0.
60 system call retrieves the requested TLS facility.
61 A descriptor representing the facility is returned, or -1 if an error occurred.
62 If you simply want the
63 descriptor you may specify a NULL pointer and an infosize of 0.
65 The returned descriptor and the TLS mechanism is machine-dependent.
67 three global segment descriptors are supported (0, 1, and 2) and the %gs
68 load value is returned.
74 should first be zerod (to remain compatible with future extensions)
78 void *base; /* base address of TLS area */
79 int size; /* size of TLS area in bytes */
83 The actual implementation of the area is machine-dependent.
85 is unable to accommodate the supplied size it may create a larger area.
86 If the kernel is unable to accommodate the supplied base address an error
89 A return value of 0 is returned on success, -1 on error.
94 * Pseudo example showing how the TLS system calls work on IA32.
104 static int getdata(int offset);
107 main(int ac, char **av)
111 struct tls_info info;
114 info.size = sizeof(X);
115 if ((gs = set_tls_area(0, &info, sizeof(info))) < 0) {
119 printf("gs = %04x\en", gs);
120 __asm __volatile("mov %0,%%gs" : : "g" (gs) );
122 if (get_tls_area(0, &info, sizeof(info)) < 0) {
126 printf("%p/%d\en", info.base, info.size);
129 printf("should be 1: %d\en", getdata(0));
131 printf("should be 2: %d\en", getdata(0));
133 printf("this should fault:\en");
144 __asm __volatile("movl %%gs:(%0),%%eax; movl %%eax,%1" : "+r" (offset) : "m"
153 The specified facility index,
157 An invalid parameter has been specified.
159 (get_tls_area) The specified facility has not been initialized with
160 .Fn sys_set_tls_area .
169 function calls first appeared in