glibc/sysdeps/i386/dl-tlsdesc.S

/* Thread-local storage handling in the ELF dynamic linker.  i386 version.
   Copyright (C) 2004-2020 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <sysdep.h>
#include <tls.h>
#include "tlsdesc.h"

	.text

     /* This function is used to compute the TP offset for symbols in
	Static TLS, i.e., whose TP offset is the same for all
	threads.

	The incoming %eax points to the TLS descriptor, such that
	0(%eax) points to _dl_tlsdesc_return itself, and 4(%eax) holds
	the TP offset of the symbol corresponding to the object
	denoted by the argument.  */

	.hidden _dl_tlsdesc_return
	.global	_dl_tlsdesc_return
	.type	_dl_tlsdesc_return,@function
	cfi_startproc
	.align 16
_dl_tlsdesc_return:
	_CET_ENDBR
	movl	4(%eax), %eax
	ret
	cfi_endproc
	.size	_dl_tlsdesc_return, .-_dl_tlsdesc_return

     /* This function is used for undefined weak TLS symbols, for
	which the base address (i.e., disregarding any addend) should
	resolve to NULL.

	%eax points to the TLS descriptor, such that 0(%eax) points to
	_dl_tlsdesc_undefweak itself, and 4(%eax) holds the addend.
	We return the addend minus the TP, such that, when the caller
	adds TP, it gets the addend back.  If that's zero, as usual,
	that's most likely a NULL pointer.  */

	.hidden _dl_tlsdesc_undefweak
	.global	_dl_tlsdesc_undefweak
	.type	_dl_tlsdesc_undefweak,@function
	cfi_startproc
	.align 16
_dl_tlsdesc_undefweak:
	_CET_ENDBR
	movl	4(%eax), %eax
	subl	%gs:0, %eax
	ret
	cfi_endproc
	.size	_dl_tlsdesc_undefweak, .-_dl_tlsdesc_undefweak

#ifdef SHARED
	.hidden _dl_tlsdesc_dynamic
	.global	_dl_tlsdesc_dynamic
	.type	_dl_tlsdesc_dynamic,@function

     /* This function is used for symbols that need dynamic TLS.

	%eax points to the TLS descriptor, such that 0(%eax) points to
	_dl_tlsdesc_dynamic itself, and 4(%eax) points to a struct
	tlsdesc_dynamic_arg object.  It must return in %eax the offset
	between the thread pointer and the object denoted by the
	argument, without clobbering any registers.

	The assembly code that follows is a rendition of the following
	C code, hand-optimized a little bit.

ptrdiff_t
__attribute__ ((__regparm__ (1)))
_dl_tlsdesc_dynamic (struct tlsdesc *tdp)
{
  struct tlsdesc_dynamic_arg *td = tdp->arg;
  dtv_t *dtv = *(dtv_t **)((char *)__thread_pointer + DTV_OFFSET);
  if (__builtin_expect (td->gen_count <= dtv[0].counter
			&& (dtv[td->tlsinfo.ti_module].pointer.val
			    != TLS_DTV_UNALLOCATED),
			1))
    return dtv[td->tlsinfo.ti_module].pointer.val + td->tlsinfo.ti_offset
      - __thread_pointer;

  return ___tls_get_addr (&td->tlsinfo) - __thread_pointer;
}
*/
	cfi_startproc
	.align 16
_dl_tlsdesc_dynamic:
	_CET_ENDBR
	/* Like all TLS resolvers, preserve call-clobbered registers.
	   We need two scratch regs anyway.  */
	subl	$28, %esp
	cfi_adjust_cfa_offset (28)
	movl	%ecx, 20(%esp)
	movl	%edx, 24(%esp)
	movl	TLSDESC_ARG(%eax), %eax
	movl	%gs:DTV_OFFSET, %edx
	movl	TLSDESC_GEN_COUNT(%eax), %ecx
	cmpl	(%edx), %ecx
	ja	.Lslow
	movl	TLSDESC_MODID(%eax), %ecx
	movl	(%edx,%ecx,8), %edx
	cmpl	$-1, %edx
	je	.Lslow
	movl	TLSDESC_MODOFF(%eax), %eax
	addl	%edx, %eax
.Lret:
	movl	20(%esp), %ecx
	subl	%gs:0, %eax
	movl	24(%esp), %edx
	addl	$28, %esp
	cfi_adjust_cfa_offset (-28)
	ret
	.p2align 4,,7
.Lslow:
	cfi_adjust_cfa_offset (28)
#ifdef NO_RTLD_HIDDEN
	call	JUMPTARGET (___tls_get_addr)
#else
	call	HIDDEN_JUMPTARGET (___tls_get_addr)
#endif
	jmp	.Lret
	cfi_endproc
	.size	_dl_tlsdesc_dynamic, .-_dl_tlsdesc_dynamic
#endif /* SHARED */

     /* This function is a wrapper for a lazy resolver for TLS_DESC
	REL relocations that reference the *ABS* segment in their own
	link maps.  %ebx points to the caller's GOT.  %eax points to a
	TLS descriptor, such that 0(%eax) holds the address of the
	resolver wrapper itself (unless some other thread beat us to
	it) and 4(%eax) holds the addend in the relocation.

	When the actual resolver returns, it will have adjusted the
	TLS descriptor such that we can tail-call it for it to return
	the TP offset of the symbol.  */

	.hidden _dl_tlsdesc_resolve_abs_plus_addend
	.global	_dl_tlsdesc_resolve_abs_plus_addend
	.type	_dl_tlsdesc_resolve_abs_plus_addend,@function
	cfi_startproc
	.align 16
_dl_tlsdesc_resolve_abs_plus_addend:
0:
	_CET_ENDBR
	pushl	%eax
	cfi_adjust_cfa_offset (4)
	pushl	%ecx
	cfi_adjust_cfa_offset (4)
	pushl	%edx
	cfi_adjust_cfa_offset (4)
	movl	$1f - 0b, %ecx
	movl	4(%ebx), %edx
	call	_dl_tlsdesc_resolve_abs_plus_addend_fixup
1:
	popl	%edx
	cfi_adjust_cfa_offset (-4)
	popl	%ecx
	cfi_adjust_cfa_offset (-4)
	popl	%eax
	cfi_adjust_cfa_offset (-4)
	jmp	*(%eax)
	cfi_endproc
	.size	_dl_tlsdesc_resolve_abs_plus_addend, .-_dl_tlsdesc_resolve_abs_plus_addend

     /* This function is a wrapper for a lazy resolver for TLS_DESC
	REL relocations that had zero addends.  %ebx points to the
	caller's GOT.  %eax points to a TLS descriptor, such that
	0(%eax) holds the address of the resolver wrapper itself
	(unless some other thread beat us to it) and 4(%eax) holds a
	pointer to the relocation.

	When the actual resolver returns, it will have adjusted the
	TLS descriptor such that we can tail-call it for it to return
	the TP offset of the symbol.  */

	.hidden _dl_tlsdesc_resolve_rel
	.global	_dl_tlsdesc_resolve_rel
	.type	_dl_tlsdesc_resolve_rel,@function
	cfi_startproc
	.align 16
_dl_tlsdesc_resolve_rel:
0:
	_CET_ENDBR
	pushl	%eax
	cfi_adjust_cfa_offset (4)
	pushl	%ecx
	cfi_adjust_cfa_offset (4)
	pushl	%edx
	cfi_adjust_cfa_offset (4)
	movl	$1f - 0b, %ecx
	movl	4(%ebx), %edx
	call	_dl_tlsdesc_resolve_rel_fixup
1:
	popl	%edx
	cfi_adjust_cfa_offset (-4)
	popl	%ecx
	cfi_adjust_cfa_offset (-4)
	popl	%eax
	cfi_adjust_cfa_offset (-4)
	jmp	*(%eax)
	cfi_endproc
	.size	_dl_tlsdesc_resolve_rel, .-_dl_tlsdesc_resolve_rel

     /* This function is a wrapper for a lazy resolver for TLS_DESC
	RELA relocations.  %ebx points to the caller's GOT.  %eax
	points to a TLS descriptor, such that 0(%eax) holds the
	address of the resolver wrapper itself (unless some other
	thread beat us to it) and 4(%eax) holds a pointer to the
	relocation.

	When the actual resolver returns, it will have adjusted the
	TLS descriptor such that we can tail-call it for it to return
	the TP offset of the symbol.  */

	.hidden _dl_tlsdesc_resolve_rela
	.global	_dl_tlsdesc_resolve_rela
	.type	_dl_tlsdesc_resolve_rela,@function
	cfi_startproc
	.align 16
_dl_tlsdesc_resolve_rela:
0:
	_CET_ENDBR
	pushl	%eax
	cfi_adjust_cfa_offset (4)
	pushl	%ecx
	cfi_adjust_cfa_offset (4)
	pushl	%edx
	cfi_adjust_cfa_offset (4)
	movl	$1f - 0b, %ecx
	movl	4(%ebx), %edx
	call	_dl_tlsdesc_resolve_rela_fixup
1:
	popl	%edx
	cfi_adjust_cfa_offset (-4)
	popl	%ecx
	cfi_adjust_cfa_offset (-4)
	popl	%eax
	cfi_adjust_cfa_offset (-4)
	jmp	*(%eax)
	cfi_endproc
	.size	_dl_tlsdesc_resolve_rela, .-_dl_tlsdesc_resolve_rela

     /* This function is a placeholder for lazy resolving of TLS
	relocations.  Once some thread starts resolving a TLS
	relocation, it sets up the TLS descriptor to use this
	resolver, such that other threads that would attempt to
	resolve it concurrently may skip the call to the original lazy
	resolver and go straight to a condition wait.

	When the actual resolver returns, it will have adjusted the
	TLS descriptor such that we can tail-call it for it to return
	the TP offset of the symbol.  */

	.hidden _dl_tlsdesc_resolve_hold
	.global	_dl_tlsdesc_resolve_hold
	.type	_dl_tlsdesc_resolve_hold,@function
	cfi_startproc
	.align 16
_dl_tlsdesc_resolve_hold:
0:
	_CET_ENDBR
	pushl	%eax
	cfi_adjust_cfa_offset (4)
	pushl	%ecx
	cfi_adjust_cfa_offset (4)
	pushl	%edx
	cfi_adjust_cfa_offset (4)
	movl	$1f - 0b, %ecx
	movl	4(%ebx), %edx
	call	_dl_tlsdesc_resolve_hold_fixup
1:
	popl	%edx
	cfi_adjust_cfa_offset (-4)
	popl	%ecx
	cfi_adjust_cfa_offset (-4)
	popl	%eax
	cfi_adjust_cfa_offset (-4)
	jmp	*(%eax)
	cfi_endproc
	.size	_dl_tlsdesc_resolve_hold, .-_dl_tlsdesc_resolve_hold