diff options
Diffstat (limited to 'elf/dl-map-segments.h')
| -rw-r--r-- | elf/dl-map-segments.h | 153 |
1 files changed, 153 insertions, 0 deletions
diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h new file mode 100644 index 0000000..71671cd --- /dev/null +++ b/elf/dl-map-segments.h @@ -0,0 +1,153 @@ +/* Map in a shared object's segments. Generic version. + Copyright (C) 1995-2014 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <http://www.gnu.org/licenses/>. */ + +#include <dl-load.h> + +/* This implementation assumes (as does the corresponding implementation + of _dl_unmap_segments, in dl-unmap-segments.h) that shared objects + are always laid out with all segments contiguous (or with gaps + between them small enough that it's preferable to reserve all whole + pages inside the gaps with PROT_NONE mappings rather than permitting + other use of those parts of the address space). */ + +static __always_inline const char * +_dl_map_segments (struct link_map *l, int fd, + const ElfW(Ehdr) *header, int type, + const struct loadcmd loadcmds[], size_t nloadcmds, + const size_t maplength, bool has_holes, + struct link_map *loader) +{ + const struct loadcmd *c = loadcmds; + + if (__glibc_likely (type == ET_DYN)) + { + /* This is a position-independent shared object. We can let the + kernel map it anywhere it likes, but we must have space for all + the segments in their specified positions relative to the first. + So we map the first segment without MAP_FIXED, but with its + extent increased to cover all the segments. Then we remove + access from excess portion, and there is known sufficient space + there to remap from the later segments. + + As a refinement, sometimes we have an address that we would + prefer to map such objects at; but this is only a preference, + the OS can do whatever it likes. */ + ElfW(Addr) mappref + = (ELF_PREFERRED_ADDRESS (loader, maplength, + c->mapstart & GLRO(dl_use_load_bias)) + - MAP_BASE_ADDR (l)); + + /* Remember which part of the address space this object uses. */ + l->l_map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength, + c->prot, + MAP_COPY|MAP_FILE, + fd, c->mapoff); + if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED)) + return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT; + + l->l_map_end = l->l_map_start + maplength; + l->l_addr = l->l_map_start - c->mapstart; + + if (has_holes) + /* Change protection on the excess portion to disallow all access; + the portions we do not remap later will be inaccessible as if + unallocated. Then jump into the normal segment-mapping loop to + handle the portion of the segment past the end of the file + mapping. */ + __mprotect ((caddr_t) (l->l_addr + c->mapend), + loadcmds[nloadcmds - 1].mapstart - c->mapend, + PROT_NONE); + + l->l_contiguous = 1; + + goto postmap; + } + + /* Remember which part of the address space this object uses. */ + l->l_map_start = c->mapstart + l->l_addr; + l->l_map_end = l->l_map_start + maplength; + l->l_contiguous = !has_holes; + + while (c < &loadcmds[nloadcmds]) + { + if (c->mapend > c->mapstart + /* Map the segment contents from the file. */ + && (__mmap ((void *) (l->l_addr + c->mapstart), + c->mapend - c->mapstart, c->prot, + MAP_FIXED|MAP_COPY|MAP_FILE, + fd, c->mapoff) + == MAP_FAILED)) + return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT; + + postmap: + _dl_postprocess_loadcmd (l, header, c); + + if (c->allocend > c->dataend) + { + /* Extra zero pages should appear at the end of this segment, + after the data mapped from the file. */ + ElfW(Addr) zero, zeroend, zeropage; + + zero = l->l_addr + c->dataend; + zeroend = l->l_addr + c->allocend; + zeropage = ((zero + GLRO(dl_pagesize) - 1) + & ~(GLRO(dl_pagesize) - 1)); + + if (zeroend < zeropage) + /* All the extra data is in the last page of the segment. + We can just zero it. */ + zeropage = zeroend; + + if (zeropage > zero) + { + /* Zero the final part of the last page of the segment. */ + if (__glibc_unlikely ((c->prot & PROT_WRITE) == 0)) + { + /* Dag nab it. */ + if (__mprotect ((caddr_t) (zero + & ~(GLRO(dl_pagesize) - 1)), + GLRO(dl_pagesize), c->prot|PROT_WRITE) < 0) + return DL_MAP_SEGMENTS_ERROR_MPROTECT; + } + memset ((void *) zero, '\0', zeropage - zero); + if (__glibc_unlikely ((c->prot & PROT_WRITE) == 0)) + __mprotect ((caddr_t) (zero & ~(GLRO(dl_pagesize) - 1)), + GLRO(dl_pagesize), c->prot); + } + + if (zeroend > zeropage) + { + /* Map the remaining zero pages in from the zero fill FD. */ + caddr_t mapat; + mapat = __mmap ((caddr_t) zeropage, zeroend - zeropage, + c->prot, MAP_ANON|MAP_PRIVATE|MAP_FIXED, + -1, 0); + if (__glibc_unlikely (mapat == MAP_FAILED)) + return DL_MAP_SEGMENTS_ERROR_MAP_ZERO_FILL; + } + } + + ++c; + } + + /* Notify ELF_PREFERRED_ADDRESS that we have to load this one + fixed. */ + ELF_FIXED_ADDRESS (loader, c->mapstart); + + return NULL; +} |