1 /* Thread-local storage handling in the ELF dynamic linker. x86_64 version.
2 Copyright (C) 2004-2018 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
25 /* This function is used to compute the TP offset for symbols in
26 Static TLS, i.e., whose TP offset is the same for all
29 The incoming %rax points to the TLS descriptor, such that
30 0(%rax) points to _dl_tlsdesc_return itself, and 8(%rax) holds
31 the TP offset of the symbol corresponding to the object
32 denoted by the argument. */
34 .hidden _dl_tlsdesc_return
35 .global _dl_tlsdesc_return
36 .type _dl_tlsdesc_return,@function
43 .size _dl_tlsdesc_return, .-_dl_tlsdesc_return
45 /* This function is used for undefined weak TLS symbols, for
46 which the base address (i.e., disregarding any addend) should
49 %rax points to the TLS descriptor, such that 0(%rax) points to
50 _dl_tlsdesc_undefweak itself, and 8(%rax) holds the addend.
51 We return the addend minus the TP, such that, when the caller
52 adds TP, it gets the addend back. If that's zero, as usual,
53 that's most likely a NULL pointer. */
55 .hidden _dl_tlsdesc_undefweak
56 .global _dl_tlsdesc_undefweak
57 .type _dl_tlsdesc_undefweak,@function
60 _dl_tlsdesc_undefweak:
65 .size _dl_tlsdesc_undefweak, .-_dl_tlsdesc_undefweak
68 .hidden _dl_tlsdesc_dynamic
69 .global _dl_tlsdesc_dynamic
70 .type _dl_tlsdesc_dynamic,@function
72 /* %rax points to the TLS descriptor, such that 0(%rax) points to
73 _dl_tlsdesc_dynamic itself, and 8(%rax) points to a struct
74 tlsdesc_dynamic_arg object. It must return in %rax the offset
75 between the thread pointer and the object denoted by the
76 argument, without clobbering any registers.
78 The assembly code that follows is a rendition of the following
79 C code, hand-optimized a little bit.
82 _dl_tlsdesc_dynamic (register struct tlsdesc *tdp asm ("%rax"))
84 struct tlsdesc_dynamic_arg *td = tdp->arg;
85 dtv_t *dtv = *(dtv_t **)((char *)__thread_pointer + DTV_OFFSET);
86 if (__builtin_expect (td->gen_count <= dtv[0].counter
87 && (dtv[td->tlsinfo.ti_module].pointer.val
88 != TLS_DTV_UNALLOCATED),
90 return dtv[td->tlsinfo.ti_module].pointer.val + td->tlsinfo.ti_offset
93 return __tls_get_addr_internal (&td->tlsinfo) - __thread_pointer;
99 /* Preserve call-clobbered registers that we modify.
100 We need two scratch regs anyway. */
102 movq %fs:DTV_OFFSET, %rsi
104 movq TLSDESC_ARG(%rax), %rdi
106 cmpq %rax, TLSDESC_GEN_COUNT(%rdi)
108 movq TLSDESC_MODID(%rdi), %rax
110 movq (%rax,%rsi), %rax
113 addq TLSDESC_MODOFF(%rdi), %rax
120 /* Besides rdi and rsi, saved above, save rdx, rcx, r8, r9,
121 r10 and r11. Also, align the stack, that's off by 8 bytes. */
123 cfi_adjust_cfa_offset (72)
130 /* %rdi already points to the tlsinfo data structure. */
131 #ifdef NO_RTLD_HIDDEN
132 call JUMPTARGET (__tls_get_addr)
134 call HIDDEN_JUMPTARGET (__tls_get_addr)
143 cfi_adjust_cfa_offset (-72)
146 .size _dl_tlsdesc_dynamic, .-_dl_tlsdesc_dynamic
149 /* This function is a wrapper for a lazy resolver for TLS_DESC
150 RELA relocations. The incoming 0(%rsp) points to the caller's
151 link map, pushed by the dynamic object's internal lazy TLS
152 resolver front-end before tail-calling us. We need to pop it
153 ourselves. %rax points to a TLS descriptor, such that 0(%rax)
154 holds the address of the internal resolver front-end (unless
155 some other thread beat us to resolving it) and 8(%rax) holds a
156 pointer to the relocation.
158 When the actual resolver returns, it will have adjusted the
159 TLS descriptor such that we can tail-call it for it to return
160 the TP offset of the symbol. */
162 .hidden _dl_tlsdesc_resolve_rela
163 .global _dl_tlsdesc_resolve_rela
164 .type _dl_tlsdesc_resolve_rela,@function
167 /* The PLT entry will have pushed the link_map pointer. */
168 _dl_tlsdesc_resolve_rela:
169 cfi_adjust_cfa_offset (8)
170 /* Save all call-clobbered registers. Add 8 bytes for push in
171 the PLT entry to align the stack. */
173 cfi_adjust_cfa_offset (80)
176 movq %rax, %rdi /* Pass tlsdesc* in %rdi. */
178 movq 80(%rsp), %rsi /* Pass link_map* in %rsi. */
185 call _dl_tlsdesc_resolve_rela_fixup
196 cfi_adjust_cfa_offset (-88)
199 .size _dl_tlsdesc_resolve_rela, .-_dl_tlsdesc_resolve_rela
201 /* This function is a placeholder for lazy resolving of TLS
202 relocations. Once some thread starts resolving a TLS
203 relocation, it sets up the TLS descriptor to use this
204 resolver, such that other threads that would attempt to
205 resolve it concurrently may skip the call to the original lazy
206 resolver and go straight to a condition wait.
208 When the actual resolver returns, it will have adjusted the
209 TLS descriptor such that we can tail-call it for it to return
210 the TP offset of the symbol. */
212 .hidden _dl_tlsdesc_resolve_hold
213 .global _dl_tlsdesc_resolve_hold
214 .type _dl_tlsdesc_resolve_hold,@function
217 _dl_tlsdesc_resolve_hold:
219 /* Save all call-clobbered registers. */
221 cfi_adjust_cfa_offset (72)
224 movq %rax, %rdi /* Pass tlsdesc* in %rdi. */
226 /* Pass _dl_tlsdesc_resolve_hold's address in %rsi. */
227 leaq . - _dl_tlsdesc_resolve_hold(%rip), %rsi
234 call _dl_tlsdesc_resolve_hold_fixup
246 cfi_adjust_cfa_offset (-72)
249 .size _dl_tlsdesc_resolve_hold, .-_dl_tlsdesc_resolve_hold