| /* Copyright (c) 2011 The Chromium Authors. All rights reserved. |
| * Use of this source code is governed by a BSD-style license that can be |
| * found in the LICENSE file. |
| * |
| * This is a custom linker script used to build nacl_helper_bootstrap. |
| * It has a very special layout. This script will only work with input |
| * that is kept extremely minimal. If there are unexpected input sections |
| * not named here, the result will not be correct. |
| * |
| * We need to use a standalone loader program rather than just using a |
| * dynamically-linked program here because its entire address space will be |
| * taken over for the NaCl untrusted address space. A normal program would |
| * cause dynamic linker data structures to point to its .dynamic section, |
| * which is no longer available after startup. |
| * |
| * We need this special layout (and the nacl_helper_bootstrap_munge_phdr |
| * step) because simply having bss space large enough to reserve the |
| * address space would cause the kernel loader to think we're using that |
| * much anonymous memory and refuse to execute the program on a machine |
| * with not much memory available. |
| */ |
| |
| /* |
| * Set the entry point to the symbol called _start, which we define in assembly. |
| */ |
| ENTRY(_start) |
| |
| /* |
| * This is the address where the program text starts. |
| * We set this as low as we think we can get away with. |
| * The common settings for sysctl vm.mmap_min_addr range from 4k to 64k. |
| */ |
| TEXT_START = 0x10000; |
| |
| /* |
| * This is the top of the range we are trying to reserve, which is 1G |
| * for x86-32 and ARM. For an x86-64 zero-based sandbox, this really |
| * needs to be 36G. |
| */ |
| RESERVE_TOP = 1 << 30; |
| |
| /* |
| * We specify the program headers we want explicitly, to get the layout |
| * exactly right and to give the "reserve" segment p_flags of zero, so |
| * that it gets mapped as PROT_NONE. |
| */ |
| PHDRS { |
| text PT_LOAD FILEHDR PHDRS; |
| data PT_LOAD; |
| reserve PT_LOAD FLAGS(0); |
| note PT_NOTE; |
| stack PT_GNU_STACK FLAGS(6); /* RW, no E */ |
| } |
| |
| /* |
| * Now we lay out the sections across those segments. |
| */ |
| SECTIONS { |
| . = TEXT_START + SIZEOF_HEADERS; |
| |
| /* |
| * The build ID note usually comes first. |
| * It's both part of the text PT_LOAD segment (like other rodata) and |
| * it's what the PT_NOTE header points to. |
| */ |
| .note.gnu.build-id : { |
| *(.note.gnu.build-id) |
| } :text :note |
| |
| /* |
| * Here is the program itself. |
| */ |
| .text : { |
| *(.text*) |
| } :text |
| .rodata : { |
| *(.rodata*) |
| *(.eh_frame*) |
| } |
| |
| etext = .; |
| |
| /* |
| * Adjust the address for the data segment. We want to adjust up to |
| * the same address within the page on the next page up. |
| */ |
| . = (ALIGN(CONSTANT(MAXPAGESIZE)) - |
| ((CONSTANT(MAXPAGESIZE) - .) & (CONSTANT(MAXPAGESIZE) - 1))); |
| . = DATA_SEGMENT_ALIGN(CONSTANT(MAXPAGESIZE), CONSTANT(COMMONPAGESIZE)); |
| |
| .data : { |
| *(.data*) |
| } :data |
| .bss : { |
| *(.bss*) |
| } |
| |
| /* |
| * Now we move up to the next p_align increment, and place the dummy |
| * segment there. The linker emits this segment with the p_vaddr and |
| * p_memsz we want, which reserves the address space. But the linker |
| * gives it a p_filesz of zero. We have to edit the phdr after link |
| * time to give it a p_filesz matching its p_memsz. That way, the |
| * kernel doesn't think we are preallocating a huge amount of memory. |
| * It just maps it from the file, i.e. way off the end of the file, |
| * which is perfect for reserving the address space. |
| */ |
| . = ALIGN(CONSTANT(COMMONPAGESIZE)); |
| RESERVE_START = .; |
| .reserve : { |
| . = RESERVE_TOP - RESERVE_START; |
| } :reserve |
| |
| /* |
| * These are empty input sections the linker generates. |
| * If we don't discard them, they pollute the flags in the output segment. |
| */ |
| /DISCARD/ : { |
| *(.iplt) |
| *(.rel*) |
| *(.igot.plt) |
| } |
| } |