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9e7e5fda38
The current getcontext return trampoline is overly complex and it unnecessarily clobbers several registers. By saving the context pointer (r26) in the context, __getcontext_ret can restore any registers not restored by setcontext. This allows getcontext to save and restore the entire register context present when getcontext is entered. We use the unused oR0 context slot for the return from __getcontext_ret. While this is not directly useful in C, it can be exploited in assembly code. Registers r20, r23, r24 and r25 are not clobbered in the call path to getcontext. This allows a small simplification of swapcontext. It also allows saving and restoring the 6-bit SAR register in the LSB of the oSAR context slot. The getcontext flag value can be stored in the MSB of the oSAR slot.
170 lines
4.1 KiB
ArmAsm
170 lines
4.1 KiB
ArmAsm
/* Install given context.
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Copyright (C) 2008-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library. If not, see
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<https://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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#include <libc-symbols.h>
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#include "ucontext_i.h"
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ENTRY(__setcontext)
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/* Prologue */
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stw %r2, -20(%sp)
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.cfi_offset 2, -20
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stwm %r3, 64(%sp)
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.cfi_def_cfa_offset -64
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.cfi_offset 3, 0
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#ifdef PIC
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stw %r19, -32(%sp)
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.cfi_offset 19, 32
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#endif
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stw %ret1, -60(%sp)
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.cfi_offset 29, 4
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/* Save ucp. */
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copy %r26, %r3
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.Lagain:
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/* Set the current signal mask. */
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/* sigprocmask(SIG_BLOCK, &ucp->uc_sigmask, NULL); */
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copy %r0, %r24
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ldo oSIGMASK(%r3), %r25
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bl __sigprocmask, %r2
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ldi SIG_SETMASK, %r26
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comib,<>,n 0,%ret0,.Lerror
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/* Save %sp, %dp. */
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copy %sp, %r4
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copy %dp, %r5
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copy %r19, %r6
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/* Get the registers. */
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ldw oR1(%r3), %r1
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ldw oR2(%r3), %r2
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/* ldw oR3(%r3), %r3 - used for ucp pointer. */
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/* ldw oR4(%r3), %r4 - used for original %sp. */
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/* ldw oR5(%r3), %r5 - used for %dp / %r27. */
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/* ldw oR6(%r3), %r6 - used for %r19. */
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ldw oR7(%r3), %r7
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ldw oR8(%r3), %r8
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ldw oR9(%r3), %r9
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ldw oR10(%r3), %r10
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ldw oR11(%r3), %r11
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ldw oR12(%r3), %r12
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ldw oR13(%r3), %r13
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ldw oR14(%r3), %r14
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ldw oR15(%r3), %r15
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ldw oR16(%r3), %r16
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ldw oR17(%r3), %r17
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ldw oR18(%r3), %r18
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ldw oR19(%r3), %r19
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ldw oR20(%r3), %r20
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ldw oR21(%r3), %r21 /* maybe clobbered by dyncall */
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/* ldw oR22(%r3), %r22 - dyncall arg. */
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ldw oR23(%r3), %r23
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ldw oR24(%r3), %r24
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ldw oR25(%r3), %r25
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ldw oR26(%r3), %r26
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ldw oR27(%r3), %r27
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ldw oR28(%r3), %r28
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ldw oR29(%r3), %r29
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ldw oR30(%r3), %sp
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/* ldw oR31(%r3), %r31 - dyncall scratch register */
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/* Restore SAR register. */
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ldw oSAR(%r3), %r22
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mtsar %r22
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/* Restore floating-point registers. */
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ldo oFPREGS31(%r3), %r22
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fldds 0(%r22), %fr31
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fldds,mb -8(%r22), %fr30
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fldds,mb -8(%r22), %fr29
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fldds,mb -8(%r22), %fr28
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fldds,mb -8(%r22), %fr27
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fldds,mb -8(%r22), %fr26
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fldds,mb -8(%r22), %fr25
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fldds,mb -8(%r22), %fr24
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fldds,mb -8(%r22), %fr23
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fldds,mb -8(%r22), %fr22
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fldds,mb -8(%r22), %fr21
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fldds,mb -8(%r22), %fr20
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fldds,mb -8(%r22), %fr19
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fldds,mb -8(%r22), %fr18
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fldds,mb -8(%r22), %fr17
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fldds,mb -8(%r22), %fr16
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fldds,mb -8(%r22), %fr15
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fldds,mb -8(%r22), %fr14
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fldds,mb -8(%r22), %fr13
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fldds,mb -8(%r22), %fr12
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fldds,mb -8(%r22), %fr11
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fldds,mb -8(%r22), %fr10
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fldds,mb -8(%r22), %fr9
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fldds,mb -8(%r22), %fr8
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fldds,mb -8(%r22), %fr7
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fldds,mb -8(%r22), %fr6
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fldds,mb -8(%r22), %fr5
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fldds,mb -8(%r22), %fr4
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fldds,mb -8(%r22), %fr3
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fldds,mb -8(%r22), %fr2
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fldds,mb -8(%r22), %fr1
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fldds,mb -8(%r22), %fr0
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/* Do not load oSS_SP into %sp. The value of oSS_SP indicates
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the start of the user allocated stack, but not the sp that
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should be used by the new context. In fact makecontext
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will create a frame, and adjust sp as required. We do not
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support calling getcontext and modifying ss_sp without
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a call to makecontext to synchronize ss_sp into the machine
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context. */
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/* Call external function. */
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copy %r2, %r22
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bl $$dyncall, %r31
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copy %r31, %r2
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/* We return here. Get new ucp in %r3, reload %sp. */
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ldw oUC_LINK(%r3), %r3
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copy %r4, %sp
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copy %r5, %dp
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copy %r6, %r19
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/* Continue until ucp == NULL. */
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comib,<> 0,%r3,.Lagain
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nop
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/* No further context available. Exit now. */
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bl HIDDEN_JUMPTARGET(exit), %r2
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ldi 0, %r26
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.Lerror:
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/* Epilogue */
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ldw -84(%r30), %r2
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#ifdef PIC
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ldw -32(%r30), %r19
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#endif
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ldw -60(%r30), %ret1
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bv %r0(%r2)
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ldwm -64(%r30), %r3
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L(pseudo_end):
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PSEUDO_END(__setcontext)
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weak_alias(__setcontext, setcontext)
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