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d6efcc118e
The PowerPC64 linker edits medium model toc-indirect code to toc-pointer relative: addis r9,r2,tc_entry_for_var@toc@ha ld r9,tc_entry_for_var@toc@l(r9) becomes addis r9,r2,(var-.TOC.)@ha addi r9,r9,(var-.TOC.)@l when "var" is known to be local to the binary. This isn't done for small-model toc-indirect code, because "var" is almost guaranteed to be too far away from .TOC. for a 16-bit signed offset. And, because the analysis of which .toc entry can be removed becomes much more complicated in objects that mix code models, they aren't removed if any small-model toc sequence appears in an object file. Unfortunately, glibc's build of ld.so smashes the needed objects together in a ld -r linking stage. This means the GOT/TOC is left with a whole lot of relative relocations which is untidy, but in itself is not a serious problem. However, static-pie on powerpc64 bombs due to a segfault caused by one of the small-model accesses before _dl_relocate_static_pie. (The very first one in rcrt1.o passing start_addresses in r8 to __libc_start_main.) So this patch makes all the toc/got accesses in assembly medium code model, and a couple of functions hidden. By itself this is not enough to give us working static-pie, but it is useful in isolation to enable better linker optimisation. There's a serious problem in libgcc too. libgcc ifuncs access the AT_HWCAP words stored in the tcb with an offset from the thread pointer (r13), but r13 isn't set at the time _dl_relocate_static_pie. A followup patch will fix that. Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
94 lines
3.2 KiB
ArmAsm
94 lines
3.2 KiB
ArmAsm
/* Startup code for programs linked with GNU libc. PowerPC64 version.
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Copyright (C) 1998-2022 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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In addition to the permissions in the GNU Lesser General Public
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License, the Free Software Foundation gives you unlimited
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permission to link the compiled version of this file with other
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programs, and to distribute those programs without any restriction
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coming from the use of this file. (The GNU Lesser General Public
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License restrictions do apply in other respects; for example, they
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cover modification of the file, and distribution when not linked
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into another program.)
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Note that people who make modified versions of this file are not
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obligated to grant this special exception for their modified
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versions; it is their choice whether to do so. The GNU Lesser
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General Public License gives permission to release a modified
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version without this exception; this exception also makes it
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possible to release a modified version which carries forward this
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exception.
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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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/* We do not want .eh_frame info for crt1.o since crt1.o is linked
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before crtbegin.o, the file defining __EH_FRAME_BEGIN__. */
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#undef cfi_startproc
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#define cfi_startproc
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#undef cfi_endproc
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#define cfi_endproc
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/* These are the various addresses we require. */
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#ifdef PIC
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.section ".data.rel.ro.local","aw"
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#else
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.section ".rodata"
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#endif
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.align 3
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L(start_addresses):
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.quad 0 /* was _SDA_BASE_ but not in 64-bit ABI*/
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/* function descriptors so don't need JUMPTARGET */
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.quad main
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.quad 0 /* Used to be init. */
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.quad 0 /* Used to be fini. */
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ASM_SIZE_DIRECTIVE(L(start_addresses))
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.section ".toc","aw"
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.L01:
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.tc L(start_addresses)[TC],L(start_addresses)
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.section ".text"
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ENTRY (_start)
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/* Save the stack pointer, in case we're statically linked under Linux. */
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mr r9,r1
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/* Set up an initial stack frame, and clear the LR. */
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clrrdi r1,r1,4
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li r0,0
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stdu r1,-128(r1)
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mtlr r0
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std r0,0(r1)
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/* put the address of start_addresses in r8... **
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** PPC64 ABI uses R13 for thread local, so we leave it alone */
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addis r8,r2,.L01@toc@ha
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ld r8,.L01@toc@l(r8)
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/* and continue in libc-start, in glibc. */
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b JUMPTARGET(__libc_start_main)
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/* Older versions of ld need this nop to recognize that it's OK to call via a
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TOC adjusting stub. */
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nop
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END(_start)
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/* Define a symbol for the first piece of initialized data. */
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.section ".data"
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.globl __data_start
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__data_start:
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.long 0
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weak_alias (__data_start, data_start)
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