202 lines
6.5 KiB
ArmAsm
202 lines
6.5 KiB
ArmAsm
// crt1-sim.S
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// For the Xtensa simulator target, this code sets up the C calling context
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// and calls main() (via __clibrary_start).
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// Control arrives here at _start from the reset vector or from crt0-app.S.
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// Copyright (c) 1998-2012 Tensilica Inc.
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//
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// Permission is hereby granted, free of charge, to any person obtaining
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// a copy of this software and associated documentation files (the
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// "Software"), to deal in the Software without restriction, including
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// without limitation the rights to use, copy, modify, merge, publish,
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// distribute, sublicense, and/or sell copies of the Software, and to
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// permit persons to whom the Software is furnished to do so, subject to
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// the following conditions:
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//
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// The above copyright notice and this permission notice shall be included
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// in all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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#include <xtensa/config/core-isa.h>
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#include <xtensa/corebits.h>
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#include <syscalls.h>
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// Exports
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.global _start
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// Imports
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// __clibrary_init from C library (eg. newlib or uclibc)
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// exit from C library
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// main from user application
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// __stack from linker script (see LSP Ref Manual)
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.type __clibrary_init, @function
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.type main, @function
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.type exit, @function
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# define CALL call4
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# define CALLX callx4
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# define ARG1 a6 /* 1st outgoing call argument */
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# define ARG2 a7 /* 2nd outgoing call argument */
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# define ARG3 a8 /* 3rd outgoing call argument */
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# define ARG4 a9 /* 4th outgoing call argument */
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# define ARG5 a10 /* 5th outgoing call argument */
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.data
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.weak _start_envp // allow overriding
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.align 4
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_start_envp: .word 0 // empty environ
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.text
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.align 4
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_start:
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// _start is typically NOT at the beginning of the text segment --
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// it is always called from either the reset vector or other code
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// that does equivalent initialization (such as crt0-app.S).
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//
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// Assumptions on entry to _start:
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// - low (level-one) and medium priority interrupts are disabled
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// via PS.INTLEVEL and/or INTENABLE (PS.INTLEVEL is expected to
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// be zeroed, to potentially enable them, before calling main)
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// - C calling context not initialized:
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// - PS not initialized
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// - SP not initialized
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// - the following are initialized:
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// - LITBASE, cache attributes, WindowBase, WindowStart,
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// CPENABLE, FP's FCR and FSR, EXCSAVE[n]
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// Keep a0 zero. It is used to initialize a few things.
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// It is also the return address, where zero indicates
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// that the frame used by _start is the bottommost frame.
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//
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movi a0, 0 // keep this register zero.
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wsr a0, INTENABLE // INTENABLE value is not defined after reset.
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//make sure that interrupts are shut off (*before* we lower PS.INTLEVEL and PS.EXCM!)
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// Windowed register init, so we can call windowed code (eg. C code).
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movi a1, 1
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wsr a1, WINDOWSTART
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// The processor always clears WINDOWBASE at reset, so no need to clear it here.
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// It resets WINDOWSTART to 1 starting with LX2.0/X7.0 (RB-2006.0).
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// However, assuming hard reset is not yet always practical, so do this anyway:
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wsr a0, WINDOWBASE
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rsync
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// Set VECBASE to use our vectors instead vectors in ROM
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movi a1, _vector_table
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wsr a1, VECBASE
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// Run only one core
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// Multi-threading could be supported in future
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rsr.prid a1 // core and multiprocessor ID
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extui a1, a1, 13, 1 // extract core ID
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beqz a1, .Lcore0 // goto Lcore0 for core0 only
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.Lsuspend: // other cores are suspended
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waiti 0
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j .Lsuspend
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.Lcore0:
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// Initialize the stack pointer.
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// See the "ABI and Software Conventions" chapter in the
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// Xtensa ISA Reference manual for details.
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// NOTE: Because the _start routine does not use any memory in its
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// stack frame, and because all of its CALL instructions use a
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// window size of 4, the stack frame for _start can be empty.
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movi sp, __stack
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// reserve stack space for
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// - argv array
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// - argument strings
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movi a2, SYS_argv_size
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simcall // returns size of argv[] + its strings in a2
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// The stack only needs 16-byte alignment.
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// However, here we round up the argv size further to 128 byte multiples
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// so that in most cases, variations in argv[0]'s path do not result in
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// different stack allocation. Otherwise, such variations can impact
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// execution timing (eg. due to cache effects etc) for the same code and data.
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// If we have a PIF, it's more likely the extra required space is okay.
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addi a2, a2, 127
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srli a2, a2, 7
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slli a2, a2, 7
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// No need to use MOVSP because we have no caller (we're the
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// base caller); in fact it's better not to use MOVSP in this
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// context, to avoid unnecessary ALLOCA exceptions and copying
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// from undefined memory:
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// sub a3, sp, a2
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// movsp sp, a3
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sub sp, sp, a2
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/*
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* Now that sp (a1) is set, we can set PS as per the application
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* (user vector mode, enable interrupts, enable window exceptions if applicable).
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*/
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movi a3, PS_UM|PS_WOE // PS.WOE = 1, PS.UM = 1, PS.EXCM = 0, PS.INTLEVEL = 0
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wsr a3, PS
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rsync
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#if XCHAL_HAVE_FP || XCHAL_HAVE_DFP
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movi a3, 1
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wsr a3, CPENABLE
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#endif
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1:
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/*
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* Clear the BSS (uninitialized data) segments.
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* This code supports multiple zeroed sections (*.bss).
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* For speed, we clear memory using an ISS simcall
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* (see crt1-boards.S for more generic BSS clearing code).
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*/
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movi a6, __bss_start
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movi a7, _end
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bgeu a6, a7, .Lnobss
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.Lbssloop:
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movi a2, SYS_memset
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l32i a3, a6, 0 // arg1 = fill start address
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movi a4, 0 // arg2 = fill pattern
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l32i a5, a6, 4 // get end address
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addi a6, a6, 8 // next bss table entry
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sub a5, a5, a3 // arg3 = fill size in bytes
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simcall // memset(a3,a4,a5)
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bltu a6, a7, .Lbssloop // loop until end of bss table
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.Lnobss:
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mov a3, sp // tell simcall where to write argv[]
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movi a2, SYS_argv
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simcall // write argv[] array at a3
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movi a2, SYS_argc
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simcall // put argc in a2
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.weak _init
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.weak _fini
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mov ARG2, sp // argv
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movi ARG3, _start_envp // envp
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movi ARG4, _init // _init
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movi ARG5, _fini // _fini
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CALL __clibrary_init
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mov ARG1, a2 // argc
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mov ARG2, sp // argv
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CALL main
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// The return value is the same register as the first outgoing argument.
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CALL exit // exit with main's return value
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// Does not return here.
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.size _start, . - _start
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