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/* Machine-dependent ELF startup code. PowerPC version.
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Copyright (C) 1995-2018 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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<http://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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/* Initial entry point code for the dynamic linker.
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The C function `_dl_start' is the real entry point;
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its return value is the user program's entry point. */
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ENTRY(_start)
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/* We start with the following on the stack, from top:
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argc (4 bytes);
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arguments for program (terminated by NULL);
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environment variables (terminated by NULL);
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arguments for the program loader. */
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/* Call _dl_start with one parameter pointing at argc */
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mr r3,r1
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/* (we have to frob the stack pointer a bit to allow room for
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_dl_start to save the link register). */
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li r4,0
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addi r1,r1,-16
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stw r4,0(r1)
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bl _dl_start@local
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/* FALLTHRU */
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_dl_start_user:
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/* Now, we do our main work of calling initialisation procedures.
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The ELF ABI doesn't say anything about parameters for these,
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so we just pass argc, argv, and the environment.
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Changing these is strongly discouraged (not least because argc is
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passed by value!). */
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/* Put our GOT pointer in r31, */
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SETUP_GOT_ACCESS(r31,got_label)
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addis r31,r31,_GLOBAL_OFFSET_TABLE_-got_label@ha
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addi r31,r31,_GLOBAL_OFFSET_TABLE_-got_label@l
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/* the address of _start in r30, */
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mr r30,r3
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/* &_dl_argc in 29, &_dl_argv in 27, and _dl_loaded in 28. */
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lwz r28,_rtld_local@got(r31)
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lwz r29,_dl_argc@got(r31)
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lwz r27,__GI__dl_argv@got(r31)
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/* Call _dl_init (_dl_loaded, _dl_argc, _dl_argv, _dl_argv+_dl_argc+1). */
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lwz r3,0(r28)
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lwz r4,0(r29)
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lwz r5,0(r27)
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slwi r6,r4,2
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add r6,r5,r6
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addi r6,r6,4
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bl _dl_init@local
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/* Now, to conform to the ELF ABI, we have to: */
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/* Pass argc (actually _dl_argc) in r3; */
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lwz r3,0(r29)
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/* pass argv (actually _dl_argv) in r4; */
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lwz r4,0(r27)
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/* pass envp (actually _dl_argv+_dl_argc+1) in r5; */
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slwi r5,r3,2
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add r6,r4,r5
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addi r5,r6,4
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/* pass the auxiliary vector in r6. This is passed to us just after _envp. */
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2: lwzu r0,4(r6)
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cmpwi r0,0
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bne 2b
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addi r6,r6,4
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/* Pass a termination function pointer (in this case _dl_fini) in r7. */
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lwz r7,_dl_fini@got(r31)
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/* Now, call the start function in r30... */
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mtctr r30
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/* Pass the stack pointer in r1 (so far so good), pointing to a NULL value.
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(This lets our startup code distinguish between a program linked statically,
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which linux will call with argc on top of the stack which will hopefully
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never be zero, and a dynamically linked program which will always have
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a NULL on the top of the stack).
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Take the opportunity to clear LR, so anyone who accidentally returns
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from _start gets SEGV. Also clear the next few words of the stack. */
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_dl_main_dispatch:
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li r31,0
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stw r31,0(r1)
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mtlr r31
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stw r31,4(r1)
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stw r31,8(r1)
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stw r31,12(r1)
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/* Go do it! */
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bctr
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END(_start)
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