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