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[ELF] Avoid adding an orphan section to a less suitable segment 

If segments are defined in a linker script, placing an orphan section
before the found closest-rank section can result in adding it in a
previous segment and changing flags of that segment. This happens if
the orphan section has a lower sort rank than the found section. To
avoid that, the patch forces orphan sections to be moved after the
found section if segments are explicitly defined.

Differential Revision: https://reviews.llvm.org/D111717
This commit is contained in:
Igor Kudrin 2021-10-21 11:37:52 +07:00
parent 66b650f3da
commit 1302fdc233
4 changed files with 70 additions and 17 deletions
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11
lld/ELF/Writer.cpp
View File

@ -1255,15 +1255,24 @@ findOrphanPos(std::vector<BaseCommand *>::iterator b,
});
if (i == e)
return e;
auto foundSec = dyn_cast<OutputSection>(*i);
if (!foundSec)
return e;
// Consider all existing sections with the same proximity.
int proximity = getRankProximity(sec, *i);
unsigned sortRank = sec->sortRank;
if (script->hasPhdrsCommands())
// Prevent the orphan section to be placed before the found section because
// that can result in adding it to a previous segment and changing flags of
// that segment, for example, making a read-only segment writable.
sortRank = std::max(sortRank, foundSec->sortRank);
for (; i != e; ++i) {
auto *curSec = dyn_cast<OutputSection>(*i);
if (!curSec || !curSec->hasInputSections)
continue;
if (getRankProximity(sec, curSec) != proximity ||
sec->sortRank < curSec->sortRank)
sortRank < curSec->sortRank)
break;
}

26
lld/test/ELF/aarch64-thunk-pi.s
View File

@ -15,7 +15,7 @@ low_target:
bl high_target
ret
// CHECK: <low_target>:
// CHECK-NEXT: d8: bl 0xec <__AArch64ADRPThunk_high_target>
// CHECK-NEXT: 0: bl 0x14 <__AArch64ADRPThunk_high_target>
// CHECK-NEXT: ret
.hidden low_target2
@ -28,23 +28,23 @@ low_target2:
bl .text_high+8
ret
// CHECK: <low_target2>:
// CHECK-NEXT: e0: bl 0xf8 <__AArch64ADRPThunk_high_target2>
// CHECK-NEXT: e4: bl 0x104 <__AArch64ADRPThunk_>
// CHECK-NEXT: 8: bl 0x20 <__AArch64ADRPThunk_high_target2>
// CHECK-NEXT: c: bl 0x2c <__AArch64ADRPThunk_>
// CHECK-NEXT: ret
// Expect range extension thunks for .text_low
// adrp calculation is (PC + signed immediate) & (!0xfff)
// CHECK: <__AArch64ADRPThunk_high_target>:
// CHECK-NEXT: ec: adrp x16, 0x10000000
// CHECK-NEXT: 14: adrp x16, 0x10000000
// CHECK-NEXT: add x16, x16, #0x40
// CHECK-NEXT: br x16
// CHECK: <__AArch64ADRPThunk_high_target2>:
// CHECK-NEXT: f8: adrp x16, 0x10000000
// CHECK-NEXT: 20: adrp x16, 0x10000000
// CHECK-NEXT: add x16, x16, #0x8
// CHECK-NEXT: br x16
/// Identical to the previous one, but for the target .text_high+8.
// CHECK: <__AArch64ADRPThunk_>:
// CHECK-NEXT: 104: adrp x16, 0x10000000
// CHECK-NEXT: 2c: adrp x16, 0x10000000
// CHECK-NEXT: add x16, x16, #0x8
// CHECK-NEXT: br x16
@ -75,7 +75,7 @@ high_target2:
// CHECK: <__AArch64ADRPThunk_low_target2>:
// CHECK-NEXT: 10000010: adrp x16, 0x0
// CHECK-NEXT: add x16, x16, #0xe0
// CHECK-NEXT: add x16, x16, #0x8
// CHECK-NEXT: br x16
// CHECK: Disassembly of section .plt:
@ -83,8 +83,8 @@ high_target2:
// CHECK-NEXT: <.plt>:
// CHECK-NEXT: 10000020: stp x16, x30, [sp, #-0x10]!
// CHECK-NEXT: adrp x16, 0x10000000
// CHECK-NEXT: ldr x17, [x16, #0x120]
// CHECK-NEXT: add x16, x16, #0x120
// CHECK-NEXT: ldr x17, [x16, #0x1f8]
// CHECK-NEXT: add x16, x16, #0x1f8
// CHECK-NEXT: br x17
// CHECK-NEXT: nop
// CHECK-NEXT: nop
@ -92,14 +92,14 @@ high_target2:
// CHECK-EMPTY:
// CHECK-NEXT: <high_target@plt>:
// CHECK-NEXT: 10000040: adrp x16, 0x10000000
// CHECK-NEXT: ldr x17, [x16, #0x128]
// CHECK-NEXT: add x16, x16, #0x128
// CHECK-NEXT: ldr x17, [x16, #0x200]
// CHECK-NEXT: add x16, x16, #0x200
// CHECK-NEXT: br x17
// CHECK-EMPTY:
// CHECK-NEXT: <low_target@plt>:
// CHECK-NEXT: 10000050: adrp x16, 0x10000000
// CHECK-NEXT: ldr x17, [x16, #0x130]
// CHECK-NEXT: add x16, x16, #0x130
// CHECK-NEXT: ldr x17, [x16, #0x208]
// CHECK-NEXT: add x16, x16, #0x208
// CHECK-NEXT: br x17
//--- lds

6
lld/test/ELF/linkerscript/implicit-program-header.test
View File

@ -7,9 +7,9 @@
# RUN: llvm-readelf -l %t1 | FileCheck %s
# CHECK: Segment Sections...
# CHECK-NEXT: 00 .dynsym .hash .dynstr .text
# CHECK-NEXT: 01 .foo .dynamic
# CHECK-NEXT: 02 .foo .dynamic
# CHECK-NEXT: 00 .text
# CHECK-NEXT: 01 .foo .dynsym .hash .dynstr .dynamic
# CHECK-NEXT: 02 .foo .dynsym .hash .dynstr .dynamic
PHDRS {
ph_write PT_LOAD FLAGS(2);

44
lld/test/ELF/linkerscript/orphan-phdrs2.test Normal file
View File

@ -0,0 +1,44 @@
# REQUIRES: x86
# RUN: split-file %s %ts
# RUN: llvm-mc -filetype=obj -triple=x86_64 %ts/s -o %t.o
# RUN: ld.lld -pie -o %t -T %ts/t %t.o
# RUN: llvm-readelf -l %t | FileCheck %s
## Check that an orphan section '.dynamic' is added to the same segment as
## its closest-rank section '.data', even though its sort rank is lower.
## Adding '.dynamic' to the first segment would make the segment writable.
# CHECK: Program Headers:
# CHECK-NEXT: Type {{.*}} Flg Align
# CHECK-NEXT: LOAD {{.*}} R E 0x
# CHECK-NEXT: LOAD {{.*}} RW 0x
# CHECK-MEXT: LOAD {{.*}} R 0x
# CHECK: Segment Sections...
# CHECK-NEXT: 00 .text {{$}}
# CHECK-NEXT: 01 .data .dynamic {{$}}
## Check that read-only non-PROGBITS orphan sections are placed after the
## closest-rank section '.rodata' despite their sort ranks are lower.
# CHECK-NEXT: 02 .rodata .dynsym .gnu.hash .hash .dynstr {{$}}
#--- s
.text
nop
.data
.quad 0
.rodata
.quad 0
#--- t
PHDRS {
exec PT_LOAD;
rw PT_LOAD;
ro PT_LOAD;
}
SECTIONS {
.text : { *(.text) } : exec
.data : { *(.data) } : rw
.rodata : { *(.rodata) } : ro
}