1 /* Subroutine for function pointer canonicalization on PA-RISC with ELF32. 2 Copyright (C) 2002-2015 Free Software Foundation, Inc. 3 Contributed by John David Anglin (dave.anglin@nrc.ca). 4 5 This file is part of GCC. 6 7 GCC is free software; you can redistribute it and/or modify it under 8 the terms of the GNU General Public License as published by the Free 9 Software Foundation; either version 3, or (at your option) any later 10 version. 11 12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY 13 WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 for more details. 16 17 Under Section 7 of GPL version 3, you are granted additional 18 permissions described in the GCC Runtime Library Exception, version 19 3.1, as published by the Free Software Foundation. 20 21 You should have received a copy of the GNU General Public License and 22 a copy of the GCC Runtime Library Exception along with this program; 23 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 24 <http://www.gnu.org/licenses/>. */ 25 26 27 /* WARNING: The code is this function depends on internal and undocumented 28 details of the GNU linker and dynamic loader as implemented for parisc 29 linux. */ 30 31 /* This MUST match the defines sysdeps/hppa/dl-machine.h and 32 bfd/elf32-hppa.c. */ 33 #define GOT_FROM_PLT_STUB (4*4) 34 35 /* List of byte offsets in _dl_runtime_resolve to search for "bl" branches. 36 The first "bl" branch instruction found MUST be a call to fixup. See 37 the define for TRAMPOLINE_TEMPLATE in sysdeps/hppa/dl-machine.h. If 38 the trampoline template is changed, the list must be appropriately 39 updated. The offset of -4 allows for a magic branch at the start of 40 the template should it be necessary to change the current branch 41 position. */ 42 #define NOFFSETS 2 43 static int fixup_branch_offset[NOFFSETS] = { -4, 32 }; 44 45 #define GET_FIELD(X, FROM, TO) \ 46 ((X) >> (31 - (TO)) & ((1 << ((TO) - (FROM) + 1)) - 1)) 47 #define SIGN_EXTEND(VAL,BITS) \ 48 ((int) ((VAL) >> ((BITS) - 1) ? (-1 << (BITS)) | (VAL) : (VAL))) 49 50 struct link_map; 51 typedef int (*fptr_t) (void); 52 typedef int (*fixup_t) (struct link_map *, unsigned int); 53 extern unsigned int _GLOBAL_OFFSET_TABLE_; 54 55 /* __canonicalize_funcptr_for_compare must be hidden so that it is not 56 placed in the dynamic symbol table. Like millicode functions, it 57 must be linked into all binaries in order access the got table of 58 that binary. However, we don't use the millicode calling convention 59 and the routine must be a normal function so that it can be compiled 60 as pic code. */ 61 unsigned int __canonicalize_funcptr_for_compare (fptr_t) 62 __attribute__ ((visibility ("hidden"))); 63 64 unsigned int 65 __canonicalize_funcptr_for_compare (fptr_t fptr) 66 { 67 static unsigned int fixup_plabel[2] __attribute__((used)); 68 fixup_t fixup; 69 unsigned int *got, *iptr, *plabel; 70 int i; 71 72 /* -1 and page 0 are special. -1 is used in crtend to mark the end of 73 a list of function pointers. Also return immediately if the plabel 74 bit is not set in the function pointer. In this case, the function 75 pointer points directly to the function. */ 76 if ((int) fptr == -1 || (unsigned int) fptr < 4096 || !((int) fptr & 2)) 77 return (unsigned int) fptr; 78 79 /* The function pointer points to a function descriptor (plabel). If 80 the plabel hasn't been resolved, the first word of the plabel points 81 to the entry of the PLT stub just before the global offset table. 82 The second word in the plabel contains the relocation offset for the 83 function. */ 84 plabel = (unsigned int *) ((unsigned int) fptr & ~3); 85 got = (unsigned int *) (plabel[0] + GOT_FROM_PLT_STUB); 86 87 /* Return the address of the function if the plabel has been resolved. */ 88 if (got != &_GLOBAL_OFFSET_TABLE_) 89 return plabel[0]; 90 91 /* Find the first "bl" branch in the offset search list. This is a 92 call to _dl_fixup or a magic branch to fixup at the beginning of the 93 trampoline template. The fixup function does the actual runtime 94 resolution of function descriptors. We only look for "bl" branches 95 with a 17-bit pc-relative displacement. */ 96 for (i = 0; i < NOFFSETS; i++) 97 { 98 iptr = (unsigned int *) (got[-2] + fixup_branch_offset[i]); 99 if ((*iptr & 0xfc00e000) == 0xe8000000) 100 break; 101 } 102 103 /* This should not happen... */ 104 if (i == NOFFSETS) 105 return ~0; 106 107 /* Extract the 17-bit displacement from the instruction. */ 108 iptr += SIGN_EXTEND (GET_FIELD (*iptr, 19, 28) | 109 GET_FIELD (*iptr, 29, 29) << 10 | 110 GET_FIELD (*iptr, 11, 15) << 11 | 111 GET_FIELD (*iptr, 31, 31) << 16, 17); 112 113 /* Build a plabel for an indirect call to _dl_fixup. */ 114 fixup_plabel[0] = (unsigned int) iptr + 8; /* address of fixup */ 115 fixup_plabel[1] = got[-1]; /* ltp for fixup */ 116 fixup = (fixup_t) ((int) fixup_plabel | 3); 117 118 /* Call fixup to resolve the function address. got[1] contains the 119 link_map pointer and plabel[1] the relocation offset. */ 120 fixup ((struct link_map *) got[1], plabel[1]); 121 122 return plabel[0]; 123 } 124