/
elf.cc
1968 lines (1783 loc) · 58.5 KB
/
elf.cc
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
/*
* Copyright (C) 2013 Cloudius Systems, Ltd.
*
* This work is open source software, licensed under the terms of the
* BSD license as described in the LICENSE file in the top-level directory.
*/
#include <osv/elf.hh>
#include <osv/app.hh>
#include <osv/mmu.hh>
#include <boost/format.hpp>
#include <exception>
#include <memory>
#include <string.h>
#include <osv/align.hh>
#include <osv/debug.hh>
#include <stdlib.h>
#include <unistd.h>
#include <boost/algorithm/string.hpp>
#include <boost/range/algorithm/find.hpp>
#include <functional>
#include <iterator>
#include <osv/sched.hh>
#include <osv/trace.hh>
#include <osv/version.hh>
#include <osv/stubbing.hh>
#include <sys/utsname.h>
#include <osv/demangle.hh>
#include <osv/export.h>
#include <boost/version.hpp>
#include <deque>
#include "arch.hh"
#include "arch-elf.hh"
#include "cpuid.hh"
#if CONF_debug_elf
#define elf_debug(format,...) kprintf("ELF [tid:%d, mod:%d, %s]: " format, sched::thread::current()->id(), _module_index, _pathname.c_str(), ##__VA_ARGS__)
#else
#define elf_debug(...)
#endif
TRACEPOINT(trace_elf_load, "%s", const char *);
TRACEPOINT(trace_elf_unload, "%s", const char *);
TRACEPOINT(trace_elf_lookup, "%s", const char *);
TRACEPOINT(trace_elf_lookup_next, "%s", const char *);
TRACEPOINT(trace_elf_lookup_addr, "%p", const void *);
extern void* elf_start;
extern size_t elf_size;
using namespace boost::range;
namespace {
typedef boost::format fmt;
}
namespace elf {
const ulong program::core_module_index = 0;
namespace {
unsigned symbol_type(Elf64_Sym& sym)
{
return sym.st_info & 15;
}
unsigned symbol_binding(Elf64_Sym& sym)
{
return sym.st_info >> 4;
}
}
symbol_module::symbol_module()
: symbol()
, obj()
{
}
symbol_module::symbol_module(Elf64_Sym* _sym, object* _obj)
: symbol(_sym)
, obj(_obj)
{
}
void* symbol_module::relocated_addr() const
{
void* base = obj->base();
if (symbol->st_shndx == SHN_UNDEF || symbol->st_shndx == SHN_ABS) {
base = 0;
}
switch (symbol_type(*symbol)) {
case STT_NOTYPE:
case STT_OBJECT:
case STT_FUNC:
return base + symbol->st_value;
break;
case STT_IFUNC:
return reinterpret_cast<void *(*)()>(base + symbol->st_value)();
default:
abort("Unknown symbol type %d\n", symbol_type(*symbol));
}
}
u64 symbol_module::size() const
{
return symbol->st_size;
}
std::atomic<ptrdiff_t> object::_static_tls_alloc;
object::object(program& prog, std::string pathname)
: _prog(prog)
, _pathname(pathname)
, _tls_segment()
, _tls_init_size()
, _tls_uninit_size()
, _static_tls(false)
, _static_tls_offset(0)
, _initial_tls_size(0)
, _dynamic_table(nullptr)
, _module_index(_prog.register_dtv(this))
, _is_executable(false)
, _init_called(false)
, _eh_frame(0)
, _visibility_thread(nullptr)
, _visibility_level(VisibilityLevel::Public)
{
elf_debug("Instantiated\n");
}
object::~object()
{
elf_debug("Removed\n");
_prog.free_dtv(this);
}
ulong object::module_index() const
{
return _module_index;
}
bool object::visible(void) const
{
auto level = _visibility_level.load(std::memory_order_acquire);
if (level == VisibilityLevel::Public) {
return true;
}
auto thread = _visibility_thread.load(std::memory_order_acquire);
if (!thread) { //Unlikely, but ...
return true;
}
auto current_thread = sched::thread::current();
if (level == VisibilityLevel::ThreadOnly) {
return thread == current_thread;
}
// Is current thread the same as "thread" or is it a child of it?
if (thread == current_thread) {
return true;
}
bool visible = false;
auto next_parent_id = current_thread->parent_id();
while (next_parent_id) {
sched::with_thread_by_id(next_parent_id, [&next_parent_id, &visible, thread] (sched::thread *t) {
if (t == thread) {
visible = true;
next_parent_id = 0;
} else {
next_parent_id = t ? t->parent_id() : 0;
}
});
}
return visible;
}
void object::set_visibility(elf::VisibilityLevel visibilityLevel)
{
_visibility_thread.store(visibilityLevel == VisibilityLevel::Public ? nullptr : sched::thread::current(),
std::memory_order_release);
_visibility_level.store(visibilityLevel, std::memory_order_release);
}
template <>
void* object::lookup(const char* symbol)
{
symbol_module sm{lookup_symbol(symbol, false), this};
if (!sm.symbol || sm.symbol->st_shndx == SHN_UNDEF) {
return nullptr;
}
return sm.relocated_addr();
}
void* object::cached_lookup(const std::string& name)
{
auto cached_address_it = _cached_symbols.find(name);
if (cached_address_it != _cached_symbols.end()) {
return cached_address_it->second;
}
else {
void *symbol_address = lookup(name.c_str());
_cached_symbols[name] = symbol_address;
return symbol_address;
}
}
std::vector<Elf64_Shdr> object::sections()
{
size_t bytes = size_t(_ehdr.e_shentsize) * _ehdr.e_shnum;
std::unique_ptr<char[]> tmp(new char[bytes]);
read(_ehdr.e_shoff, tmp.get(), bytes);
auto p = tmp.get();
std::vector<Elf64_Shdr> ret;
for (unsigned i = 0; i < _ehdr.e_shnum; ++i, p += _ehdr.e_shentsize) {
ret.push_back(*reinterpret_cast<Elf64_Shdr*>(p));
}
return ret;
}
std::string object::section_name(const Elf64_Shdr& shdr)
{
if (_ehdr.e_shstrndx == SHN_UNDEF) {
return {};
}
if (!_section_names_cache) {
auto s = sections().at(_ehdr.e_shstrndx);
std::unique_ptr<char[]> p(new char[s.sh_size]);
read(s.sh_offset, p.get(), s.sh_size);
_section_names_cache = std::move(p);
}
return _section_names_cache.get() + shdr.sh_name;
}
std::vector<Elf64_Sym> object::symbols() {
auto symtab = dynamic_ptr<Elf64_Sym>(DT_SYMTAB);
auto len = symtab_len();
return std::vector<Elf64_Sym>(symtab, symtab + len);
}
const char * object::symbol_name(const Elf64_Sym * sym) {
auto strtab = dynamic_ptr<char>(DT_STRTAB);
return strtab + sym->st_name;
}
void* object::entry_point() const {
if (!_is_executable) {
return nullptr;
}
return _base + _ehdr.e_entry;
}
file::file(program& prog, ::fileref f, std::string pathname)
: object(prog, pathname)
, _f(f)
{
load_elf_header();
load_program_headers();
}
file::~file()
{
}
memory_image::memory_image(program& prog, void* base)
: object(prog, "")
{
_ehdr = *static_cast<Elf64_Ehdr*>(base);
auto p = static_cast<Elf64_Phdr*>(base + _ehdr.e_phoff);
assert(_ehdr.e_phentsize == sizeof(*p));
_phdrs.assign(p, p + _ehdr.e_phnum);
}
void memory_image::load_segment(const Elf64_Phdr& phdr)
{
}
void memory_image::unload_segment(const Elf64_Phdr& phdr)
{
}
void memory_image::read(Elf64_Off offset, void* data, size_t size)
{
throw std::runtime_error("cannot load from Elf memory image");
}
void file::load_elf_header()
{
try {
read(0, &_ehdr, sizeof(_ehdr));
} catch(error &e) {
throw osv::invalid_elf_error(
std::string("can't read elf header: ") + strerror(e.get()));
}
if (!(_ehdr.e_ident[EI_MAG0] == '\x7f'
&& _ehdr.e_ident[EI_MAG1] == 'E'
&& _ehdr.e_ident[EI_MAG2] == 'L'
&& _ehdr.e_ident[EI_MAG3] == 'F')) {
throw osv::invalid_elf_error("bad elf header");
}
if (!(_ehdr.e_ident[EI_CLASS] == ELFCLASS64)) {
throw osv::invalid_elf_error("bad elf class");
}
if (!(_ehdr.e_ident[EI_DATA] == ELFDATA2LSB)) {
throw osv::invalid_elf_error("bad elf endianness");
}
if (!(_ehdr.e_ident[EI_VERSION] == EV_CURRENT)) {
throw osv::invalid_elf_error("bad elf version");
}
if (!(_ehdr.e_ident[EI_OSABI] == ELFOSABI_LINUX
|| _ehdr.e_ident[EI_OSABI] == 0)) {
throw osv::invalid_elf_error("bad os abi");
}
if (!(_ehdr.e_type == ET_DYN || _ehdr.e_type == ET_EXEC)) {
throw osv::invalid_elf_error(
"bad executable type (only shared-object, PIE or non-PIE executable supported)");
}
if(_ehdr.e_machine != ELF_KERNEL_MACHINE_TYPE) {
throw osv::invalid_elf_error("machine type for " + _pathname + " differs from the kernel");
}
}
void file::read(Elf64_Off offset, void* data, size_t size)
{
// read(fileref, ...) is void, and crashes with assertion failure if the
// file is not long enough. So we need to check first.
if (::size(_f) < offset + size) {
throw osv::invalid_elf_error("executable too short");
}
::read(_f, data, offset, size);
}
namespace {
void* align(void* addr, ulong align, ulong offset)
{
return align_up(addr - offset, align) + offset;
}
}
static bool intersects_with_kernel(Elf64_Addr elf_addr)
{
void *addr = reinterpret_cast<void*>(elf_addr);
return addr >= elf_start && addr < elf_start + elf_size;
}
void object::set_base(void* base)
{
std::vector<const Elf64_Phdr*> pt_load_headers;
for (auto& p : _phdrs) {
if (p.p_type == PT_LOAD) {
pt_load_headers.push_back(&p);
}
}
auto p = *std::min_element(pt_load_headers.begin(), pt_load_headers.end(),
[](const Elf64_Phdr* a, const Elf64_Phdr* b)
{ return a->p_vaddr < b->p_vaddr; });
auto q = *std::max_element(pt_load_headers.begin(), pt_load_headers.end(),
[](const Elf64_Phdr* a, const Elf64_Phdr* b)
{ return a->p_vaddr < b->p_vaddr; });
if (!is_core() && is_non_pie_executable()) {
// Verify non-PIE executable does not collide with the kernel
if (intersects_with_kernel(p->p_vaddr) || intersects_with_kernel(q->p_vaddr + q->p_memsz)) {
abort("Non-PIE executable [%s] collides with kernel: [%p-%p] !\n",
pathname().c_str(), p->p_vaddr, q->p_vaddr + q->p_memsz);
}
// Override the passed in value as the base for non-PIEs (Position Dependant Executables)
// needs to be set to 0 because all the addresses in it are absolute
_base = 0x0;
} else {
// Otherwise for kernel, PIEs and shared libraries set the base as requested by caller
_base = align(base, p->p_align, p->p_vaddr & (p->p_align - 1)) - p->p_vaddr;
}
_end = _base + q->p_vaddr + q->p_memsz;
elf_debug("The base set to: %018p and end: %018p\n", _base, _end);
}
void* object::base() const
{
return _base;
}
void* object::end() const
{
return _end;
}
void file::load_program_headers()
{
_phdrs.resize(_ehdr.e_phnum);
for (unsigned i = 0; i < _ehdr.e_phnum; ++i) {
read(_ehdr.e_phoff + i * _ehdr.e_phentsize,
&_phdrs[i],
_ehdr.e_phentsize);
}
}
void file::load_segment(const Elf64_Phdr& phdr)
{
ulong vstart = align_down(phdr.p_vaddr, mmu::page_size);
ulong filesz_unaligned = phdr.p_vaddr + phdr.p_filesz - vstart;
ulong filesz = align_up(filesz_unaligned, mmu::page_size);
ulong memsz = align_up(phdr.p_vaddr + phdr.p_memsz, mmu::page_size) - vstart;
unsigned perm = get_segment_mmap_permissions(phdr);
auto flag = mmu::mmap_fixed | (mlocked() ? mmu::mmap_populate : 0);
mmu::map_file(_base + vstart, filesz, flag, perm, _f, align_down(phdr.p_offset, mmu::page_size));
if (phdr.p_filesz != phdr.p_memsz) {
assert(perm & mmu::perm_write);
memset(_base + vstart + filesz_unaligned, 0, filesz - filesz_unaligned);
if (memsz != filesz) {
mmu::map_anon(_base + vstart + filesz, memsz - filesz, flag, perm);
}
}
elf_debug("Loaded and mapped PT_LOAD segment at: %018p of size: 0x%x\n", _base + vstart, filesz);
}
bool object::mlocked()
{
for (auto&& s : sections()) {
if (section_name(s) == ".note.osv-mlock") {
return true;
}
}
return false;
}
bool object::has_non_writable_text_relocations()
{
return dynamic_exists(DT_TEXTREL);
}
Elf64_Note::Elf64_Note(void *_base, char *str)
{
Elf64_Word *base = reinterpret_cast<Elf64_Word *>(_base);
n_type = base[2];
n_owner.reserve(base[0]);
n_value.reserve(base[1]);
// The note section strings will include the trailing 0. std::string
// doesn't like that very much, and comparisons against a string that is
// constructed from this string will fail. Therefore the - 1 at the end
if (base[0] > 0) {
n_owner.assign(str, base[0] -1);
}
str = align_up(str + base[0], 4);
if (base[1] > 0) {
n_value.assign(str, base[1] - 1);
}
}
extern "C" char _pie_static_tls_start, _pie_static_tls_end;
void object::load_segments()
{
elf_debug("Loading segments\n");
for (unsigned i = 0; i < _ehdr.e_phnum; ++i) {
auto &phdr = _phdrs[i];
if (phdr.p_type == PT_LOAD) {
load_segment(phdr);
}
}
}
void object::process_headers()
{
elf_debug("Processing headers\n");
for (unsigned i = 0; i < _ehdr.e_phnum; ++i) {
auto &phdr = _phdrs[i];
switch (phdr.p_type) {
case PT_NULL:
break;
case PT_DYNAMIC:
_dynamic_table = reinterpret_cast<Elf64_Dyn*>(_base + phdr.p_vaddr);
break;
case PT_INTERP:
_is_executable = true;
break;
case PT_NOTE: {
if (phdr.p_memsz < 16) {
/* we have the PT_NOTE segment in the linker scripts,
* but if we have no note sections we will end up with
* a zero length segment. Handle this case by validating
* the phdr length.
*/
break;
}
void *start = _base + phdr.p_vaddr;
char *str = align_up((char *)start + 3 * sizeof(Elf64_Word), 4);
struct Elf64_Note header(start, str);
if (header.n_type != NT_VERSION) {
break;
}
if (header.n_owner != "OSv") {
break;
}
// FIXME: In the future, we should probably prevent loading of libosv.so in this
// situation.
if (header.n_value != osv::version()) {
printf("WARNING: libosv.so version mismatch. Kernel is %s, lib is %s\n",
osv::version().c_str(), header.n_value.c_str());
}
break;
}
case PT_LOAD:
case PT_PHDR:
case PT_GNU_STACK:
case PT_GNU_RELRO:
case PT_PAX_FLAGS:
case PT_GNU_PROPERTY:
break;
case PT_GNU_EH_FRAME:
_eh_frame = _base + phdr.p_vaddr;
break;
case PT_TLS:
_tls_segment = _base + phdr.p_vaddr;
_tls_init_size = phdr.p_filesz;
_tls_uninit_size = phdr.p_memsz - phdr.p_filesz;
_tls_alignment = phdr.p_align;
elf_debug("Found TLS segment at %018p of aligned size: 0x%x\n", _tls_segment, get_aligned_tls_size());
break;
default:
abort("Unknown p_type in executable %s: %d\n", pathname(), phdr.p_type);
}
}
if (!is_core() && _ehdr.e_type == ET_EXEC && !_is_executable) {
abort("Statically linked executables are not supported!\n");
}
if (_is_executable && _tls_segment) {
auto app_tls_size = get_aligned_tls_size();
ulong pie_static_tls_maximum_size = &_pie_static_tls_end - &_pie_static_tls_start;
if (app_tls_size > pie_static_tls_maximum_size) {
// The reservation at the end of the kernel TLS is NOT big enough
// to hold the app static TLS. Let us calculate what the reservation should be
// and inform user how to relink kernel
auto kernel_tls_size = sched::kernel_tls_size();
auto kernel_tls_used_size = kernel_tls_size - pie_static_tls_maximum_size;
auto kernel_tls_needed_size = align_up(kernel_tls_used_size + app_tls_size, 64UL);
auto app_tls_needed_size = kernel_tls_needed_size - kernel_tls_used_size;
std::cout << "WARNING: " << pathname() << " is a PIE using TLS of size " << app_tls_size
<< " which is greater than the " << pie_static_tls_maximum_size << " bytes limit. "
<< "Either re-link the kernel by adding 'app_local_exec_tls_size=" << app_tls_needed_size
<< "' to ./scripts/build or re-link the app with '-shared' instead of '-pie'.\n";
}
}
}
void file::unload_segment(const Elf64_Phdr& phdr)
{
ulong vstart = align_down(phdr.p_vaddr, mmu::page_size);
ulong filesz_unaligned = phdr.p_vaddr + phdr.p_filesz - vstart;
ulong filesz = align_up(filesz_unaligned, mmu::page_size);
ulong memsz = align_up(phdr.p_vaddr + phdr.p_memsz, mmu::page_size) - vstart;
mmu::munmap(_base + vstart, filesz);
mmu::munmap(_base + vstart + filesz, memsz - filesz);
}
void object::unload_segments()
{
for (unsigned i = 0; i < _ehdr.e_phnum; ++i) {
auto &phdr = _phdrs[i];
switch (phdr.p_type) {
case PT_LOAD:
unload_segment(phdr);
break;
default:
break;
}
}
}
unsigned object::get_segment_mmap_permissions(const Elf64_Phdr& phdr)
{
unsigned perm = 0;
if (phdr.p_flags & PF_X)
perm |= mmu::perm_exec;
if (phdr.p_flags & PF_W)
perm |= mmu::perm_write;
if (phdr.p_flags & PF_R)
perm |= mmu::perm_read;
return perm;
}
void object::fix_permissions()
{
if(has_non_writable_text_relocations()) {
make_text_writable(false);
}
for (auto&& phdr : _phdrs) {
if (phdr.p_type != PT_GNU_RELRO)
continue;
ulong vstart = align_down(phdr.p_vaddr, mmu::page_size);
ulong memsz = align_up(phdr.p_vaddr + phdr.p_memsz, mmu::page_size) - vstart;
mmu::mprotect(_base + vstart, memsz, mmu::perm_read);
}
}
void object::make_text_writable(bool flag)
{
for (auto&& phdr : _phdrs) {
if (phdr.p_type != PT_LOAD)
continue;
ulong vstart = align_down(phdr.p_vaddr, mmu::page_size);
ulong memsz = align_up(phdr.p_vaddr + phdr.p_memsz, mmu::page_size) - vstart;
unsigned perm = get_segment_mmap_permissions(phdr);
mmu::mprotect(_base + vstart, memsz, flag ? perm | mmu::perm_write : perm);
}
}
template <typename T>
T* object::dynamic_ptr(unsigned tag)
{
return static_cast<T*>(_base + dynamic_tag(tag).d_un.d_ptr);
}
Elf64_Xword object::dynamic_val(unsigned tag)
{
return dynamic_tag(tag).d_un.d_val;
}
const char* object::dynamic_str(unsigned tag)
{
return dynamic_ptr<const char>(DT_STRTAB) + dynamic_val(tag);
}
bool object::dynamic_exists(unsigned tag)
{
return _dynamic_tag(tag);
}
Elf64_Dyn* object::_dynamic_tag(unsigned tag)
{
if (!_dynamic_table) {
return nullptr;
}
for (auto p = _dynamic_table; p->d_tag != DT_NULL; ++p) {
if (p->d_tag == tag) {
return p;
}
}
return nullptr;
}
Elf64_Dyn& object::dynamic_tag(unsigned tag)
{
auto r = _dynamic_tag(tag);
if (!r) {
throw osv::invalid_elf_error("missing tag");
}
return *r;
}
std::vector<const char *>
object::dynamic_str_array(unsigned tag)
{
auto strtab = dynamic_ptr<const char>(DT_STRTAB);
std::vector<const char *> r;
for (auto p = _dynamic_table; p->d_tag != DT_NULL; ++p) {
if (p->d_tag == tag) {
r.push_back(strtab + p->d_un.d_val);
}
}
return r;
}
static std::string demangle(const char *name) {
auto demangled = osv::demangle(name);
std::string ret(name);
if (demangled) {
ret += " (";
ret += demangled.get();
ret += ")";
}
return ret;
}
symbol_module object::symbol(unsigned idx, bool ignore_missing)
{
auto symtab = dynamic_ptr<Elf64_Sym>(DT_SYMTAB);
assert(dynamic_val(DT_SYMENT) == sizeof(Elf64_Sym));
auto sym = &symtab[idx];
auto binding = symbol_binding(*sym);
if (binding == STB_LOCAL) {
return symbol_module(sym, this);
}
auto nameidx = sym->st_name;
auto name = dynamic_ptr<const char>(DT_STRTAB) + nameidx;
auto ret = _prog.lookup(name, this);
if (!ret.symbol && binding == STB_WEAK) {
return symbol_module(sym, this);
}
if (!ret.symbol) {
if (ignore_missing) {
debug("%s: ignoring missing symbol %s\n", pathname().c_str(), demangle(name).c_str());
} else {
abort("%s: failed looking up symbol %s\n", pathname().c_str(), demangle(name).c_str());
}
}
return ret;
}
// symbol_other(idx) is similar to symbol(idx), except that the symbol is not
// looked up in the object itself, just in the other objects.
symbol_module object::symbol_other(unsigned idx)
{
auto symtab = dynamic_ptr<Elf64_Sym>(DT_SYMTAB);
assert(dynamic_val(DT_SYMENT) == sizeof(Elf64_Sym));
auto sym = &symtab[idx];
auto nameidx = sym->st_name;
auto name = dynamic_ptr<const char>(DT_STRTAB) + nameidx;
symbol_module ret(nullptr,nullptr);
_prog.with_modules([&](const elf::program::modules_list &ml) {
for (auto module : ml.objects) {
if (module == this)
continue; // do not match this module
if (auto sym = module->lookup_symbol(name, false)) {
ret = symbol_module(sym, module);
break;
}
}
});
if (!ret.symbol) {
abort("%s: failed looking up symbol %s in other objects\n",
pathname().c_str(), demangle(name).c_str());
}
return ret;
}
void object::relocate_rela()
{
if(has_non_writable_text_relocations()) {
make_text_writable(true);
}
auto rela = dynamic_ptr<Elf64_Rela>(DT_RELA);
assert(dynamic_val(DT_RELAENT) == sizeof(Elf64_Rela));
unsigned nb = dynamic_val(DT_RELASZ) / sizeof(Elf64_Rela);
for (auto p = rela; p < rela + nb; ++p) {
auto info = p->r_info;
u32 sym = info >> 32;
u32 type = info & 0xffffffff;
void *addr = _base + p->r_offset;
auto addend = p->r_addend;
if (!arch_relocate_rela(type, sym, addr, addend)) {
debug_early_u64("relocate_rela(): unknown relocation type ", type);
abort();
}
}
elf_debug("Relocated %d symbols in DT_RELA\n", nb);
}
extern "C" { void __elf_resolve_pltgot(void); }
void object::relocate_pltgot()
{
auto pltgot = dynamic_ptr<void*>(DT_PLTGOT);
void *original_plt = nullptr;
if (pltgot[1]) {
// The library was prelinked before being copied to OSV, so the
// .GOT.PLT entries point not to the .PLT but to a prelinked address
// of the actual function. We'll need to return the link to the .PLT.
// The prelinker saved us in pltgot[1] the address of .plt + 0x16.
#ifdef AARCH64_PORT_STUB
assert(0);
#endif /* AARCH64_PORT_STUB */
original_plt = static_cast<void*>(_base + (u64)pltgot[1]);
}
bool bind_now = dynamic_exists(DT_BIND_NOW) || mlocked() ||
(dynamic_exists(DT_FLAGS) && (dynamic_val(DT_FLAGS) & DF_BIND_NOW)) ||
(dynamic_exists(DT_FLAGS_1) && (dynamic_val(DT_FLAGS_1) & DF_1_NOW));
auto rel = dynamic_ptr<Elf64_Rela>(DT_JMPREL);
auto nrel = dynamic_val(DT_PLTRELSZ) / sizeof(*rel);
for (auto p = rel; p < rel + nrel; ++p) {
auto info = p->r_info;
u32 type = info & 0xffffffff;
void *addr = _base + p->r_offset;
assert(type == ARCH_JUMP_SLOT || type == ARCH_TLSDESC);
if (type == ARCH_JUMP_SLOT) {
if (bind_now) {
// If on-load binding is requested (instead of the default lazy
// binding), try to resolve all the PLT entries now.
// If symbol cannot be resolved warn about it instead of aborting
u32 sym = info >> 32;
auto _sym = symbol(sym, true);
if (arch_relocate_jump_slot(_sym, addr, p->r_addend))
continue;
}
if (original_plt) {
// Restore the link to the original plt.
// We know the JUMP_SLOT entries are in plt order, and that
// each plt entry is 16 bytes.
*static_cast<void**>(addr) = original_plt + (p-rel)*16;
} else {
// The JUMP_SLOT entry already points back to the PLT, just
// make sure it is relocated relative to the object base.
*static_cast<u64*>(addr) += reinterpret_cast<u64>(_base);
}
} else {
u32 sym = info >> 32;
arch_relocate_tls_desc(sym, addr, p->r_addend);
}
}
elf_debug("Relocated %d PLT symbols\n", nrel);
// PLTGOT resolution has a special calling convention,
// for x64 the symbol index and some word is pushed on the stack,
// for AArch64 &pltgot[n] and LR are pushed on the stack,
// so we need an assembly stub to convert it back to the
// standard calling convention.
pltgot[1] = this;
pltgot[2] = reinterpret_cast<void*>(__elf_resolve_pltgot);
}
void* object::resolve_pltgot(unsigned index)
{
assert(sched::preemptable());
auto rel = dynamic_ptr<Elf64_Rela>(DT_JMPREL);
auto slot = rel[index];
auto info = slot.r_info;
u32 sym = info >> 32;
u32 type = info & 0xffffffff;
assert(type == ARCH_JUMP_SLOT);
void *addr = _base + slot.r_offset;
auto sm = symbol(sym);
if (sm.obj != this) {
WITH_LOCK(_used_by_resolve_plt_got_mutex) {
_used_by_resolve_plt_got.insert(sm.obj->shared_from_this());
}
}
if (!arch_relocate_jump_slot(sm, addr, slot.r_addend)) {
debug_early("resolve_pltgot(): failed jump slot relocation\n");
abort();
}
return *static_cast<void**>(addr);
}
void object::relocate()
{
assert(!dynamic_exists(DT_REL));
if (dynamic_exists(DT_RELA)) {
relocate_rela();
}
if (dynamic_exists(DT_JMPREL)) {
relocate_pltgot();
}
}
unsigned long
elf64_hash(const char *name)
{
unsigned long h = 0, g;
while (*name) {
h = (h << 4) + (unsigned char)(*name++);
if ((g = h & 0xf0000000)) {
h ^= g >> 24;
}
h &= 0x0fffffff;
}
return h;
}
constexpr Elf64_Versym old_version_symbol_mask = Elf64_Versym(1) << 15;
Elf64_Sym* object::lookup_symbol_old(const char* name)
{
auto symtab = dynamic_ptr<Elf64_Sym>(DT_SYMTAB);
auto strtab = dynamic_ptr<char>(DT_STRTAB);
auto hashtab = dynamic_ptr<Elf64_Word>(DT_HASH);
auto nbucket = hashtab[0];
auto buckets = hashtab + 2;
auto chain = buckets + nbucket;
for (auto ent = buckets[elf64_hash(name) % nbucket];
ent != STN_UNDEF;
ent = chain[ent]) {
auto &sym = symtab[ent];
if (strcmp(name, &strtab[sym.st_name]) == 0) {
return &sym;
}
}
return nullptr;
}
uint_fast32_t
dl_new_hash(const char *s)
{
uint_fast32_t h = 5381;
for (unsigned char c = *s; c != '\0'; c = *++s) {
h = h * 33 + c;
}
return h & 0xffffffff;
}
Elf64_Sym* object::lookup_symbol_gnu(const char* name, bool self_lookup)
{
auto symtab = dynamic_ptr<Elf64_Sym>(DT_SYMTAB);
auto strtab = dynamic_ptr<char>(DT_STRTAB);
auto hashtab = dynamic_ptr<Elf64_Word>(DT_GNU_HASH);
auto nbucket = hashtab[0];
auto symndx = hashtab[1];
auto maskwords = hashtab[2];
auto shift2 = hashtab[3];
auto bloom = reinterpret_cast<const Elf64_Xword*>(hashtab + 4);
auto C = sizeof(*bloom) * 8;
auto hashval = dl_new_hash(name);
auto bword = bloom[(hashval / C) % maskwords];
auto hashbit1 = hashval % C;
auto hashbit2 = (hashval >> shift2) % C;
if ((bword >> hashbit1) == 0 || (bword >> hashbit2) == 0) {
return nullptr;
}
auto buckets = reinterpret_cast<const Elf64_Word*>(bloom + maskwords);
auto chains = buckets + nbucket - symndx;
auto idx = buckets[hashval % nbucket];
if (idx == 0) {
return nullptr;
}
auto version_symtab = (!self_lookup && dynamic_exists(DT_VERSYM)) ? dynamic_ptr<Elf64_Versym>(DT_VERSYM) : nullptr;
do {
if ((chains[idx] & ~1) != (hashval & ~1)) {
continue;
}
if (version_symtab && version_symtab[idx] & old_version_symbol_mask) { //Ignore old version symbols
continue;
}
if (strcmp(&strtab[symtab[idx].st_name], name) == 0) {
return &symtab[idx];
}
} while ((chains[idx++] & 1) == 0);
return nullptr;
}
Elf64_Sym* object::lookup_symbol(const char* name, bool self_lookup)
{
if (!visible()) {
return nullptr;
}
Elf64_Sym* sym;
if (dynamic_exists(DT_GNU_HASH)) {
sym = lookup_symbol_gnu(name, self_lookup);
} else {
sym = lookup_symbol_old(name);
}
if (sym && sym->st_shndx == SHN_UNDEF) {
sym = nullptr;
}
return sym;
}
symbol_module object::lookup_symbol_deep(const char* name)
{
symbol_module sym = { lookup_symbol(name, false), this };
if (!sym.symbol) {
auto deps = this->collect_dependencies_bfs();
for (auto&& _obj : deps) {
auto symbol = _obj->lookup_symbol(name, false);
if (symbol) {
sym = { symbol, _obj };
break;
}
}
}
return sym;
}
unsigned object::symtab_len()
{
if (dynamic_exists(DT_HASH)) {
auto hashtab = dynamic_ptr<Elf64_Word>(DT_HASH);
return hashtab[1];
}
auto hashtab = dynamic_ptr<Elf64_Word>(DT_GNU_HASH);
auto nbucket = hashtab[0];
auto symndx = hashtab[1];
auto maskwords = hashtab[2];
auto bloom = reinterpret_cast<const Elf64_Xword*>(hashtab + 4);
auto buckets = reinterpret_cast<const Elf64_Word*>(bloom + maskwords);
auto chains = buckets + nbucket - symndx;
unsigned len = 0;