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119 lines
4.6 KiB
ArmAsm
119 lines
4.6 KiB
ArmAsm
/* ARM support code for fibers and multithreading.
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Copyright (C) 2019 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free
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Software Foundation; either version 3, or (at your option) any later
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version.
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GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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#include "../common/threadasm.S"
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#if defined(__ARM_EABI__)
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/**
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* Performs a context switch.
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*
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* Parameters:
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* r0 - void** - ptr to old stack pointer
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* r1 - void* - new stack pointer
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*
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* ARM EABI registers:
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* r0-r3 : argument/scratch registers
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* r4-r10 : callee-save registers
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* r11 : frame pointer (or a callee save register if fp isn't needed)
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* r12 =ip : inter procedure register. We can treat it like any other scratch
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* register
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* r13 =sp : stack pointer
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* r14 =lr : link register, it contains the return address (belonging to the
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* function which called us)
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* r15 =pc : program counter
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*
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* For floating point registers:
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* According to AAPCS (version 2.09, section 5.1.2) only the d8-d15 registers
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* need to be preserved across method calls. This applies to all ARM FPU
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* variants, whether they have 16 or 32 double registers NEON support or not,
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* half-float support or not and so on does not matter.
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*
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* Note: If this file was compiled with -mfloat-abi=soft but the code runs on a
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* softfp system with fpu the d8-d15 registers won't be saved (we do not know
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* that the system has got a fpu in that case) but the registers might actually
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* be used by other code if it was compiled with -mfloat-abi=softfp.
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*
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* Interworking is only supported on ARMv5+, not on ARM v4T as ARM v4t requires
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* special stubs when changing from thumb to arm mode or the other way round.
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*/
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.text
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#if defined(__ARM_PCS_VFP) || (defined(__ARM_PCS) && !defined(__SOFTFP__))
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.fpu vfp
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#endif
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.global CSYM(fiber_switchContext)
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.type CSYM(fiber_switchContext), %function
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.align 4
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CSYM(fiber_switchContext):
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.cfi_sections .debug_frame
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.cfi_startproc
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.fnstart
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push {r4-r11}
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// update the oldp pointer. Link register and floating point registers
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// stored later to prevent the GC from scanning them.
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str sp, [r0]
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// push r0 (or any other register) as well to keep stack 8byte aligned
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push {r0, lr}
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// ARM_HardFloat || ARM_SoftFP
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#if defined(__ARM_PCS_VFP) || (defined(__ARM_PCS) && !defined(__SOFTFP__))
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vpush {d8-d15}
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// now switch over to the new stack.
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// Need to subtract (8*8[d8-d15]+2*4[r0, lr]) to position stack pointer
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// below the last saved register. Remember we saved the SP before pushing
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// [r0, lr, d8-d15].
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sub sp, r1, #72
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vpop {d8-d15}
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#else
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sub sp, r1, #8
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#endif
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// we don't really care about r0, we only used that for padding.
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// r1 is now what used to be in the link register when saving.
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pop {r0, r1, r4-r11}
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/**
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* The link register for the initial jump to fiber_entryPoint must be zero:
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* The jump actually looks like a normal method call as we jump to the
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* start of the fiber_entryPoint function. Although fiber_entryPoint never
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* returns and therefore never accesses lr, it saves lr to the stack.
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* ARM unwinding will then look at the stack, find lr and think that
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* fiber_entryPoint was called by the function in lr! So if we have some
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* address in lr the unwinder will try to continue stack unwinding,
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* although it's already at the stack base and crash.
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* In all other cases the content of lr doesn't matter.
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* Note: If we simply loaded into lr above and then moved lr into pc, the
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* initial method call to fiber_entryPoint would look as if it was called
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* from fiber_entryPoint itself, as the fiber_entryPoint address is in lr
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* on the initial context switch.
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*/
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mov lr, #0
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// return by writing lr into pc
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mov pc, r1
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.fnend
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.cfi_endproc
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.size CSYM(fiber_switchContext),.-CSYM(fiber_switchContext)
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#endif
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