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/*
// Copyright 2016 The Fuchsia Authors
// Copyright (c) 2009 Corey Tabaka
// Copyright (c) 2013 Travis Geiselbrecht
// Copyright (c) 2015 Intel Corporation
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT
*/
/*
* Symbols used in the kernel proper are defined with PROVIDE_HIDDEN:
* HIDDEN because everything in the kernel is STV_HIDDEN to make it
* clear that direct PC-relative references should be generated in PIC;
* PROVIDE because their only purpose is to satisfy kernel references.
*/
SECTIONS
{
. = KERNEL_BASE;
/*
* This symbol marks the beginning of the whole image, from here to _end.
* This name is chosen to match the built-in default in the linkers for
* this. (In normal ELF links __ehdr_start also points here, but in the
* GNU linkers __executable_start is defined in links without in-memory ELF
* headers, where __ehdr_start is not.)
*/
PROVIDE_HIDDEN(__executable_start = .);
/*
* This symbol marks the beginning of the executable segment, from here
* to __code_end. Future layouts will not necessarily put this first.
*/
PROVIDE_HIDDEN(__code_start = .);
/*
* This symbol is used by code the compiler generates.
* It serves no particular purpose in the kernel.
*/
PROVIDE_HIDDEN(__dso_handle = 0);
/*
* These are used by elf-kernel.ld and the kernel code ignores them if
* they're equal so they're defined away here. In this layout the RELRO
* data is just merged directly into the primary RODATA segment. The
* interim elf-kernel.ld layout has to do it differently.
*/
PROVIDE_HIDDEN(__relro_start = 0);
PROVIDE_HIDDEN(__relro_end = 0);
/*
* This just leaves space in the memory image for the boot headers.
* The actual boot header will be constructed in image.S, which see.
*/
.text.boot0 : {
/*
* Put some data in, or else the linker makes it a SHT_NOBITS
* section and that makes objcopy -O binary skip it in the image.
*/
LONG(0xdeadbeef);
. += BOOT_HEADER_SIZE - 4;
} :code
/*
* This is separate from .text just so gen-kaslr-fixups.sh can match
* it. The relocation processor skips this section because this code
* all runs before the boot-time fixups are applied and has its own
* special relationship with the memory layouts.
*/
.text.boot : {
*(.text.boot)
}
/*
* This is separate from .text just so gen-kaslr-fixups.sh can match
* it. This section contains movabs instructions that get 64-bit
* address fixups in place. This is safe because this code is never
* used until long after fixups have been applied. In general, the
* script will refuse to handle fixups in text (i.e. code) sections.
*/
.text.bootstrap16 : {
*(.text.bootstrap16)
}
.text : {
*(.text* .sram.text)
*(.gnu.linkonce.t.*)
}
PROVIDE_HIDDEN(__code_end = .);
/*
* The kernel's actual segments are aligned to the -z max-page-size=...
* value, which is 64k for ARM. But the exported VMOs within segments
* are only aligned to 4k, since that's still the user-visible page size.
*/
. = ALIGN(CONSTANT(MAXPAGESIZE));
PROVIDE_HIDDEN(__rodata_start = .);
/*
* These are page-aligned, so place them first.
*/
.rodata.rodso_image : {
*(.rodata.rodso_image.*)
} :rodata
/*
* The named sections starting with kcountdesc are sorted by name so that
* tools can provide binary search lookup for counters::Descriptor::name[]
* variables. This is page-aligned and padded out to page size so it can be
* exported as a VMO without exposing any other .rodata contents.
*/
.kcounter.desc : ALIGN(4096) {
PROVIDE_HIDDEN(k_counter_desc_vmo_begin = .);
*(.kcounter.desc.header)
ASSERT(. - k_counter_desc_vmo_begin == 16,
"lib/counters/counters.cc and kernel.ld mismatch");
QUAD(kcountdesc_end - kcountdesc_begin);
PROVIDE_HIDDEN(kcountdesc_begin = .);
ASSERT(kcountdesc_begin - k_counter_desc_vmo_begin == 24,
"lib/counters/counters.cc and kernel.ld mismatch");
*(SORT_BY_NAME(kcountdesc.*))
PROVIDE_HIDDEN(kcountdesc_end = .);
. = ALIGN(4096);
PROVIDE_HIDDEN(k_counter_desc_vmo_end = .);
}
.note.gnu.build-id : {
PROVIDE_HIDDEN(__build_id_note_start = .);
*(.note.gnu.build-id)
PROVIDE_HIDDEN(__build_id_note_end = .);
/*
* Record the build ID size, without the note header (including name)
* of 16 bytes. This is used below.
*/
HIDDEN(__build_id_size = ABSOLUTE(__build_id_note_end - __build_id_note_start) - 16);
} :rodata :note
.rodata : {
*(.rodata* .gnu.linkonce.r.*)
} :rodata
BootCpuidLeaf : {
PROVIDE_HIDDEN(__start_BootCpuidLeaf = .);
*(BootCpuidLeaf)
PROVIDE_HIDDEN(__stop_BootCpuidLeaf = .);
}
/*
* When compiling PIC, the compiler puts things into sections it
* thinks need to be writable until after dynamic relocation. In
* the kernel, these things all go into the read-only segment. But
* to the linker, they are writable and so the default "orphans"
* placement would put them after .data instead of here. That's bad
* both because we want these things in the read-only segment (the
* kernel's self-relocation applies before the read-only-ness starts
* being enforced anyway), and because the orphans would wind up
* being after the __data_end symbol (see below).
*
* Therefore, we have to list all the special-case sections created
* by SPECIAL_SECTION(...) uses in the kernel that are RELRO candidates,
* i.e. things that have address constants in their initializers.
* All such uses in the source use sections named ".data.rel.ro.foo"
* instead of just "foo" specifically to ensure we write them here.
* This avoids the magic linker behavior for an "orphan" section
* called "foo" of synthesizing "__start_foo" and "__stop_foo"
* symbols when the section name has no . characters in it, and so
* makes sure we'll get undefined symbol references if we omit such
* a section here. The magic linker behavior is nice, but it only
* goes for orphans, and we can't abide the default placement of
* orphans that should be RELRO.
*/
.data.rel.ro.commands : {
PROVIDE_HIDDEN(__start_commands = .);
*(.data.rel.ro.commands)
PROVIDE_HIDDEN(__stop_commands = .);
ASSERT(ALIGNOF(.data.rel.ro.commands) == 8 ||
SIZEOF(.data.rel.ro.commands) == 0,
".data.rel.ro.commands overalignment -> padding gaps");
}
.data.rel.ro.lk_init : {
PROVIDE_HIDDEN(__start_lk_init = .);
*(.data.rel.ro.lk_init)
PROVIDE_HIDDEN(__stop_lk_init = .);
ASSERT(ALIGNOF(.data.rel.ro.lk_init) == 8,
".data.rel.ro.lk_init overalignment -> padding gaps");
}
.data.rel.ro.unittest_testcases : {
PROVIDE_HIDDEN(__start_unittest_testcases = .);
*(.data.rel.ro.unittest_testcases)
PROVIDE_HIDDEN(__stop_unittest_testcases = .);
ASSERT(ALIGNOF(.data.rel.ro.unittest_testcases) == 8 ||
SIZEOF(.data.rel.ro.unittest_testcases) == 0,
".data.rel.ro.unittest_testcases overalignment -> padding gaps");
}
asan_globals : {
PROVIDE_HIDDEN(__start_asan_globals = .);
KEEP(*(asan_globals))
PROVIDE_HIDDEN(__stop_asan_globals = .);
}
.data.rel.ro : {
*(.data.rel.ro* .gnu.linkonce.d.rel.ro.*)
}
.init_array : {
PROVIDE_HIDDEN(__init_array_start = .);
KEEP(*(SORT_BY_INIT_PRIORITY(.init_array.*)
SORT_BY_INIT_PRIORITY(.ctors.*)))
KEEP(*(.init_array .ctors))
PROVIDE_HIDDEN(__init_array_end = .);
ASSERT(ALIGNOF(.init_array) == 8 || SIZEOF(.init_array) == 0,
".init_array overalignment -> maybe padding gaps");
}
/*
* When these instrumentation sections are emitted, they are
* read-only (possibly only after relocation).
*/
__llvm_prf_data : ALIGN(8) {
PROVIDE_HIDDEN(__start___llvm_prf_data = .);
*(__llvm_prf_data)
PROVIDE_HIDDEN(__stop___llvm_prf_data = .);
}
__llvm_prf_names : {
PROVIDE_HIDDEN(__start___llvm_prf_names = .);
*(__llvm_prf_names)
PROVIDE_HIDDEN(__stop___llvm_prf_names = .);
}
/*
* Any read-only data "orphan" sections will be inserted here.
* Ideally we'd put those into the .rodata output section, but
* there isn't a way to do that that guarantees all same-named
* input sections collect together as a contiguous unit, which
* is what we need them for. Linkers differ in how they'll
* place another empty section here relative to the orphans, so
* there's no good way to define __rodata_end to be exactly the
* end of all the orphans sections. But the only use we have
* for __rodata_end is to round it up to page size anyway, so
* just define it inside the writable section below, which is
* exactly the end of the orphans rounded up to the next page.
*/
.data : ALIGN(CONSTANT(MAXPAGESIZE)) {
PROVIDE_HIDDEN(__rodata_end = .);
PROVIDE_HIDDEN(__data_start = .);
/* Pull out any aligned data into a separate section to make sure
* individual variables do not alias with any unaligned vars.
*/
*(.data.cpu_align_exclusive)
. = ALIGN(128);
*(.data .data.* .gnu.linkonce.d.*)
}
/*
* Collects instances of fxt::InternedString and fxt::InternedCategory for
* registration during trace subsystem initialization, when string ids and
* category bits are allocated and instances are added to global lists.
*/
__fxt_interned_string_table : ALIGN(8) {
PROVIDE_HIDDEN(__start___fxt_interned_string_table = .);
*(__fxt_interned_string_table)
PROVIDE_HIDDEN(__stop___fxt_interned_string_table = .);
}
__fxt_interned_category_table : ALIGN(8) {
PROVIDE_HIDDEN(__start___fxt_interned_category_table = .);
*(__fxt_interned_category_table)
PROVIDE_HIDDEN(__stop___fxt_interned_category_table = .);
}
/*
* When these instrumentation sections are emitted, they are
* writable data that gets updated at runtime.
*/
__llvm_prf_cnts : ALIGN(8) {
PROVIDE_HIDDEN(__start___llvm_prf_cnts = .);
*(__llvm_prf_cnts)
PROVIDE_HIDDEN(__stop___llvm_prf_cnts = .);
}
__sancov_guards : ALIGN(4) {
PROVIDE_HIDDEN(__start___sancov_guards = .);
*(__sancov_guards)
PROVIDE_HIDDEN(__stop___sancov_guards = .);
}
/*
* Note that this end size might not be aligned. That's OK. It's
* not the actual end of the file size, because image.S adds on here
* and it's responsible for ZBI item alignment at its own end.
*
* What *is* crucial here is that __data_end (i.e., .) not be advanced
* without adding initialized data to fill! Everything depends on the
* __data_end address exactly matching the end of the raw kernel's
* load image for relative address arithmetic.
*/
PROVIDE_HIDDEN(__data_end = .);
/*
* Any writable orphan sections would be inserted here.
* But there's no way to put the __data_end symbol after
* them, so we cannot allow any such cases. There is no
* good way to assert that, though.
*/
.bss : ALIGN(CONSTANT(MAXPAGESIZE)) {
PROVIDE_HIDDEN(__bss_start = .);
/*
* See kernel/include/lib/counters.h; the KCOUNTER macro defines a
* kcounter.NAME array in the .bss.kcounter.NAME section that allocates
* SMP_MAX_CPUS counter slots. Here we collect all those together to
* make up the kcounters_arena contiguous array. There is no particular
* reason to sort these, but doing so makes them line up in parallel
* with the sorted .kcounter.desc section. Note that placement of the
* input sections in the arena has no actual bearing on how the space is
* used, because nothing ever refers to these arrays as variables--they
* exist only to get the right amount of space allocated in the arena.
* Instead, the order of the .kcounter.desc entries is what determines
* how the arena is used: each index in the desc table corresponds to an
* index in a per-CPU array, and the arena is a contiguous block of
* SMP_MAX_CPUS such arrays. The region containing the arena is
* page-aligned and padded out to page size so that it can be exported
* as a VMO without exposing any other .bss contents.
*/
. = ALIGN(4096);
PROVIDE_HIDDEN(kcounters_arena = .);
*(SORT_BY_NAME(.bss.kcounter.*))
PROVIDE_HIDDEN(kcounters_arena_end = .);
. = ALIGN(4096);
PROVIDE_HIDDEN(kcounters_arena_page_end = .);
/*
* Sanity check that the aggregate size of kcounters_arena SMP_MAX_CPUS
* slots for each counter. The counters::Descriptor structs in
* .kcounter.desc are 64 bytes each. (It's only for this sanity check
* that we need to care how big counters::Descriptor is.)
*/
ASSERT(kcounters_arena_end - kcounters_arena ==
(kcountdesc_end - kcountdesc_begin) * 8 * SMP_MAX_CPUS / 64,
"kcounters_arena size mismatch");
*(.bss*)
*(.gnu.linkonce.b.*)
*(COMMON)
}
/*
* Any SHT_NOBITS (.bss-like) sections would be inserted here.
*/
. = ALIGN(CONSTANT(MAXPAGESIZE));
PROVIDE_HIDDEN(_end = .);
/*
* Non-allocated section needs to be protected from GC with BFD ld.
*/
.code-patches 0 : {
KEEP(*(.code-patches))
}
}
PHDRS
{
code PT_LOAD FLAGS(5); /* PF_R|PF_X */
rodata PT_LOAD FLAGS(4); /* PF_R */
data PT_LOAD FLAGS(6); /* PF_R|PF_W */
note PT_NOTE FLAGS(4); /* PF_R */
}
/*
* This is not actually used since the entry point is set in image.ld,
* but it prevents the linker from warning about using a default address
* and it keeps --gc-sections from removing .text.boot.
*/
ENTRY(IMAGE_ELF_ENTRY)
/*
* These special symbols below are made public so they are visible via
* --just-symbols to the link of image.S.
*/
IMAGE_LOAD_START = __executable_start;
IMAGE_LOAD_KERNEL_END = __data_end;
IMAGE_MEMORY_END = _end;