Commit 7b44f042 authored by Rafael Ávila de Espíndola's avatar Rafael Ávila de Espíndola Committed by Fangrui Song
Browse files

Add a llvm::shuffle and use it in lld 

With this --shuffle-sections=seed produces the same result in every
host.

Reviewed By: grimar, MaskRay

Differential Revision: https://reviews.llvm.org/D74971
parent e48849a2

lld/ELF/Writer.cpp

+1 −1
Original line number Diff line number Diff line
@@ -1218,7 +1218,7 @@ static void maybeShuffle(DenseMap<const InputSectionBase *, int> &order) { 
    prio = curPrio++;

  uint32_t seed = *config->shuffleSectionSeed;

  std::mt19937 g(seed ? seed : std::random_device()());

  std::shuffle(priorities.begin(), priorities.end(), g);

  llvm::shuffle(priorities.begin(), priorities.end(), g);

  int prioIndex = 0;

  for (InputSectionBase *sec : inputSections) {

    if (order.try_emplace(sec, priorities[prioIndex]).second)

lld/test/ELF/shuffle-sections-init-fini.s

+4 −7
Original line number Diff line number Diff line
@@ -21,12 +21,12 @@ 
# CHECK:      Hex dump of section '.init_array'

# CHECK-NEXT: 0x{{[0-9a-f]+}} ff

# ORDERED-SAME: 000102 03040506 0708090a 0b

# SHUFFLED-NOT: 000102 03040506 0708090a 0b

# SHUFFLED-SAME: 04000b 06010a08 09070203 05



# CHECK:      Hex dump of section '.fini_array'

# CHECK-NEXT: 0x{{[0-9a-f]+}} ff

# ORDERED-SAME:  000102 03040506 0708090a 0b

# SHUFFLED-NOT: 000102 03040506 0708090a 0b

# SHUFFLED-SAME: 090401 070b0003 080a0605 02



## With a SECTIONS command, SHT_INIT_ARRAY prirotities are ignored.

## All .init_array* are shuffled together.
@@ -40,11 +40,8 @@ 


# CHECK2:       Hex dump of section '.init_array'

# ORDERED2-NEXT:  0x{{[0-9a-f]+}} 00010203 04050607 08090a0b ff

# SHUFFLED2-NOT:  0x{{[0-9a-f]+}} 00010203 04050607 08090a0b ff

# SHUFFLED2-NEXT: 0x{{[0-9a-f]+}} 04000b06 010a0809 07ff0203 05



## std::shuffle have different implementations.

## When the number of input sections are large, it is almost guaranteed

## to have an unordered result with --shuffle-sections=.

.irp i,0,1,2,3,4,5,6,7,8,9,10,11

  .section .init,"ax",@progbits,unique,\i

  .byte \i

lld/test/ELF/shuffle-sections.s

+8 −2
Original line number Diff line number Diff line
@@ -6,6 +6,12 @@ 
# CHECK: Hex dump of section '.text':

# CHECK-NEXT: 01020304



## --shuffle-sections= shuffles input sections.

# RUN: ld.lld --shuffle-sections=1 %t.o -o %t1.out

# RUN: llvm-readelf -x .text %t1.out | FileCheck %s --check-prefix=SHUFFLE1

# SHUFFLE1: Hex dump of section '.text':

# SHUFFLE1-NEXT: 0204cccc 0103



## Test that --shuffle-sections= can be used with --symbol-ordering-file

# RUN: echo "foo" > %t_order.txt

# RUN: echo "_start " >> %t_order.txt
@@ -13,12 +19,12 @@ 
# RUN: ld.lld --symbol-ordering-file %t_order.txt --shuffle-sections=2 %t.o -o %t2.out

# RUN: llvm-readelf -x .text %t2.out | FileCheck %s --check-prefix=SHUFFLE2

# SHUFFLE2: Hex dump of section '.text':

# SHUFFLE2-NEXT: 02cccccc 01{{....}}

# SHUFFLE2-NEXT: 02cccccc 010304



# RUN: ld.lld --symbol-ordering-file %t_order.txt --shuffle-sections=3 %t.o -o %t3.out

# RUN: llvm-readelf -x .text %t3.out | FileCheck %s --check-prefix=SHUFFLE3

# SHUFFLE3: Hex dump of section '.text':

# SHUFFLE3-NEXT: 02cccccc 01{{....}}

# SHUFFLE3-NEXT: 02cccccc 010403



## .text has an alignment of 4.

.global _start

llvm/include/llvm/ADT/STLExtras.h

+10 −0
Original line number Diff line number Diff line
@@ -1007,6 +1007,16 @@ struct are_base_of<T, U, Ts...> { 
//     Extra additions for arrays

//===----------------------------------------------------------------------===//



// We have a copy here so that LLVM behaves the same when using different

// standard libraries.

template <class Iterator, class RNG>

void shuffle(Iterator first, Iterator last, RNG &&g) {

  // It would be better to use a std::uniform_int_distribution,

  // but that would be stdlib dependent.

  for (auto size = last - first; size > 1; ++first, (void)--size)

    std::iter_swap(first, first + g() % size);

}



/// Find the length of an array.

template <class T, std::size_t N>

constexpr inline size_t array_lengthof(T (&)[N]) {