Commit 501ad1d7 authored by Hans Wennborg's avatar Hans Wennborg
Browse files

Merging r369828: 

------------------------------------------------------------------------
r369828 | maskray | 2019-08-24 02:41:15 +0200 (Sat, 24 Aug 2019) | 18 lines

[ELF] Align the first section of a PT_LOAD even if its type is SHT_NOBITS

Reported at https://reviews.llvm.org/D64930#1642223

If the only section of a PT_LOAD is a SHT_NOBITS section (e.g. .bss), we
may not align its sh_offset. p_offset of the PT_LOAD will be set to
sh_offset, and we will get p_offset!=p_vaddr (mod p_align).  If such
executable is mapped by the Linux kernel, it will segfault.

After D64906, this may happen the non-linker script case.

The linker script case has had this issue for a long time.
This was fixed by rL321657 (but the test linkerscript/nobits-offset.s
failed to test a SHT_NOBITS section), but broken by rL345154.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D66658
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llvm-svn: 371196
parent 5fc03679

lld/ELF/Writer.cpp

+12 −11
Original line number Diff line number Diff line
@@ -2230,8 +2230,16 @@ template <class ELFT> void Writer<ELFT>::fixSectionAlignments() { 
// same with its virtual address modulo the page size, so that the loader can

// load executables without any address adjustment.

static uint64_t computeFileOffset(OutputSection *os, uint64_t off) {

  // File offsets are not significant for .bss sections. By convention, we keep

  // section offsets monotonically increasing rather than setting to zero.

  // The first section in a PT_LOAD has to have congruent offset and address

  // module the page size.

  if (os->ptLoad && os->ptLoad->firstSec == os) {

    uint64_t alignment = std::max<uint64_t>(os->alignment, config->maxPageSize);

    return alignTo(off, alignment, os->addr);

  }



  // File offsets are not significant for .bss sections other than the first one

  // in a PT_LOAD. By convention, we keep section offsets monotonically

  // increasing rather than setting to zero.

   if (os->type == SHT_NOBITS)

     return off;
@@ -2239,16 +2247,9 @@ static uint64_t computeFileOffset(OutputSection *os, uint64_t off) { 
  if (!os->ptLoad)

    return alignTo(off, os->alignment);



  // The first section in a PT_LOAD has to have congruent offset and address

  // module the page size.

  OutputSection *first = os->ptLoad->firstSec;

  if (os == first) {

    uint64_t alignment = std::max<uint64_t>(os->alignment, config->maxPageSize);

    return alignTo(off, alignment, os->addr);

  }



  // If two sections share the same PT_LOAD the file offset is calculated

  // using this formula: Off2 = Off1 + (VA2 - VA1).

  OutputSection *first = os->ptLoad->firstSec;

  return first->offset + os->addr - first->addr;

}

lld/test/ELF/basic-ppc64.s

+6 −6
Original line number Diff line number Diff line
@@ -35,7 +35,7 @@ 
// CHECK-NEXT:  Version: 1

// CHECK-NEXT:  Entry: 0x10000

// CHECK-NEXT:  ProgramHeaderOffset: 0x40

// CHECK-NEXT:  SectionHeaderOffset: 0x200F8

// CHECK-NEXT:  SectionHeaderOffset: 0x30098

// CHECK-NEXT:  Flags [ (0x2)

// CHECK-NEXT:    0x2

// CHECK-NEXT:  ]
@@ -178,7 +178,7 @@ 
// CHECK-NEXT:      SHF_WRITE (0x1)

// CHECK-NEXT:    ]

// CHECK-NEXT:    Address: 0x30000

// CHECK-NEXT:    Offset: 0x20060

// CHECK-NEXT:    Offset: 0x30000

// CHECK-NEXT:    Size: 0

// CHECK-NEXT:    Link: 0

// CHECK-NEXT:    Info: 0
@@ -194,7 +194,7 @@ 
// CHECK-NEXT:      SHF_STRINGS (0x20)

// CHECK-NEXT:    ]

// CHECK-NEXT:    Address: 0x0

// CHECK-NEXT:    Offset: 0x20060

// CHECK-NEXT:    Offset: 0x30000

// CHECK-NEXT:    Size: 8

// CHECK-NEXT:    Link: 0

// CHECK-NEXT:    Info: 0
@@ -211,7 +211,7 @@ 
// CHECK-NEXT:    Flags [ (0x0)

// CHECK-NEXT:    ]

// CHECK-NEXT:    Address: 0x0

// CHECK-NEXT:    Offset: 0x20068

// CHECK-NEXT:    Offset: 0x30008

// CHECK-NEXT:    Size: 48

// CHECK-NEXT:    Link: 10

// CHECK-NEXT:    Info: 2
@@ -233,7 +233,7 @@ 
// CHECK-NEXT:    Flags [ (0x0)

// CHECK-NEXT:    ]

// CHECK-NEXT:    Address: 0x0

// CHECK-NEXT:    Offset: 0x20098

// CHECK-NEXT:    Offset: 0x30038

// CHECK-NEXT:    Size: 84

// CHECK-NEXT:    Link: 0

// CHECK-NEXT:    Info: 0
@@ -255,7 +255,7 @@ 
// CHECK-NEXT:    Flags [ (0x0)

// CHECK-NEXT:    ]

// CHECK-NEXT:    Address: 0x0

// CHECK-NEXT:    Offset: 0x200EC

// CHECK-NEXT:    Offset: 0x3008C

// CHECK-NEXT:    Size: 10

// CHECK-NEXT:    Link: 0

// CHECK-NEXT:    Info: 0

lld/test/ELF/linkerscript/nobits-offset.s

+16 −9
Original line number Diff line number Diff line
@@ -2,17 +2,24 @@ 
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o

# RUN: echo "SECTIONS { \

# RUN:         .sec1 (NOLOAD) : { . += 1; } \

# RUN:         .text          : { *(.text) } \

# RUN:         .bss           : { *(.bss) } \

# RUN:       };" > %t.script

# RUN: ld.lld %t.o -T %t.script -o %t

# RUN: llvm-readelf --sections %t | FileCheck %s

# RUN: llvm-readelf -S -l %t | FileCheck %s



# We used to misalign section offsets if the first section in a

# PT_LOAD was SHT_NOBITS.

## If a SHT_NOBITS section is the only section of a PT_LOAD segment,

## p_offset will be set to the sh_offset field of the section. Check we align

## sh_offset to sh_addr modulo max-page-size, so that p_vaddr=p_offset (mod

## p_align).



# CHECK: [ 2] .text  PROGBITS  0000000000000010 001010 000010 00  AX  0   0 16

# CHECK: Name Type   Address          Off     Size   ES Flg Lk Inf Al

# CHECK: .bss NOBITS 0000000000000400 001400  000001 00  WA  0   0 1024



.global _start

_start:

  nop

.p2align 4
 
# CHECK: Type Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align

# CHECK: LOAD 0x001400 0x0000000000000400 0x0000000000000400 0x000000 0x000001 RW  0x1000



# CHECK: 00 .bss



.bss

.p2align 10

.byte 0

lld/test/ELF/nobits-offset.s

0 → 100644
+21 −0
Original line number Diff line number Diff line 
# REQUIRES: aarch64

# RUN: llvm-mc -filetype=obj -triple=aarch64 %s -o %t.o

# RUN: ld.lld %t.o -o %t

# RUN: llvm-readelf -S -l %t | FileCheck %s



## If a SHT_NOBITS section is the only section of a PT_LOAD segment,

## p_offset will be set to the sh_offset field of the section. Check we align

## sh_offset to sh_addr modulo max-page-size, so that p_vaddr=p_offset (mod

## p_align).



# CHECK: Name Type   Address          Off     Size   ES Flg Lk Inf Al

# CHECK: .bss NOBITS 0000000000210000 010000  000001 00  WA  0   0 4096



# CHECK: Type Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align

# CHECK: LOAD 0x010000 0x0000000000210000 0x0000000000210000 0x000000 0x000001 RW  0x10000



# CHECK: 02 .bss



.bss

.p2align 12

.byte 0

lld/test/ELF/relocation-copy-align-common.s

+1 −1
Original line number Diff line number Diff line
@@ -15,7 +15,7 @@ 
# CHECK-NEXT:     SHF_WRITE

# CHECK-NEXT:   ]

# CHECK-NEXT:   Address: 0x203000

# CHECK-NEXT:   Offset: 0x20B0

# CHECK-NEXT:   Offset: 0x3000

# CHECK-NEXT:   Size: 16

# CHECK-NEXT:   Link: 0

# CHECK-NEXT:   Info: 0