124 lines
5.0 KiB
C
124 lines
5.0 KiB
C
/* Subroutine for function pointer canonicalization on PA-RISC with ELF32.
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Copyright (C) 2002-2017 Free Software Foundation, Inc.
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Contributed by John David Anglin (dave.anglin@nrc.ca).
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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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/* WARNING: The code is this function depends on internal and undocumented
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details of the GNU linker and dynamic loader as implemented for parisc
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linux. */
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/* This MUST match the defines sysdeps/hppa/dl-machine.h and
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bfd/elf32-hppa.c. */
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#define GOT_FROM_PLT_STUB (4*4)
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/* List of byte offsets in _dl_runtime_resolve to search for "bl" branches.
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The first "bl" branch instruction found MUST be a call to fixup. See
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the define for TRAMPOLINE_TEMPLATE in sysdeps/hppa/dl-machine.h. If
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the trampoline template is changed, the list must be appropriately
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updated. The offset of -4 allows for a magic branch at the start of
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the template should it be necessary to change the current branch
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position. */
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#define NOFFSETS 2
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static int fixup_branch_offset[NOFFSETS] = { -4, 32 };
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#define GET_FIELD(X, FROM, TO) \
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((X) >> (31 - (TO)) & ((1 << ((TO) - (FROM) + 1)) - 1))
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#define SIGN_EXTEND(VAL,BITS) \
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((int) ((VAL) >> ((BITS) - 1) ? ((unsigned)(-1) << (BITS)) | (VAL) : (VAL)))
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struct link_map;
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typedef int (*fptr_t) (void);
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typedef int (*fixup_t) (struct link_map *, unsigned int);
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extern unsigned int _GLOBAL_OFFSET_TABLE_;
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/* __canonicalize_funcptr_for_compare must be hidden so that it is not
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placed in the dynamic symbol table. Like millicode functions, it
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must be linked into all binaries in order access the got table of
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that binary. However, we don't use the millicode calling convention
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and the routine must be a normal function so that it can be compiled
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as pic code. */
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unsigned int __canonicalize_funcptr_for_compare (fptr_t)
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__attribute__ ((visibility ("hidden")));
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unsigned int
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__canonicalize_funcptr_for_compare (fptr_t fptr)
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{
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static unsigned int fixup_plabel[2] __attribute__((used));
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fixup_t fixup;
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unsigned int *got, *iptr, *plabel;
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int i;
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/* -1 and page 0 are special. -1 is used in crtend to mark the end of
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a list of function pointers. Also return immediately if the plabel
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bit is not set in the function pointer. In this case, the function
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pointer points directly to the function. */
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if ((int) fptr == -1 || (unsigned int) fptr < 4096 || !((int) fptr & 2))
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return (unsigned int) fptr;
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/* The function pointer points to a function descriptor (plabel). If
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the plabel hasn't been resolved, the first word of the plabel points
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to the entry of the PLT stub just before the global offset table.
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The second word in the plabel contains the relocation offset for the
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function. */
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plabel = (unsigned int *) ((unsigned int) fptr & ~3);
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got = (unsigned int *) (plabel[0] + GOT_FROM_PLT_STUB);
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/* Return the address of the function if the plabel has been resolved. */
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if (got != &_GLOBAL_OFFSET_TABLE_)
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return plabel[0];
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/* Find the first "bl" branch in the offset search list. This is a
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call to _dl_fixup or a magic branch to fixup at the beginning of the
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trampoline template. The fixup function does the actual runtime
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resolution of function descriptors. We only look for "bl" branches
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with a 17-bit pc-relative displacement. */
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for (i = 0; i < NOFFSETS; i++)
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{
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iptr = (unsigned int *) (got[-2] + fixup_branch_offset[i]);
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if ((*iptr & 0xfc00e000) == 0xe8000000)
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break;
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}
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/* This should not happen... */
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if (i == NOFFSETS)
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return ~0;
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/* Extract the 17-bit displacement from the instruction. */
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iptr += SIGN_EXTEND (GET_FIELD (*iptr, 19, 28) |
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GET_FIELD (*iptr, 29, 29) << 10 |
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GET_FIELD (*iptr, 11, 15) << 11 |
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GET_FIELD (*iptr, 31, 31) << 16, 17);
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/* Build a plabel for an indirect call to _dl_fixup. */
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fixup_plabel[0] = (unsigned int) iptr + 8; /* address of fixup */
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fixup_plabel[1] = got[-1]; /* ltp for fixup */
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fixup = (fixup_t) ((int) fixup_plabel | 2);
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/* Call fixup to resolve the function address. got[1] contains the
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link_map pointer and plabel[1] the relocation offset. */
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fixup ((struct link_map *) got[1], plabel[1]);
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return plabel[0];
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}
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