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[ELF] - Relax checks for R_386_8/R_386_16 relocations. 

This fixes PR36927.

The issue is next. Imagine we have -Ttext 0x7c and code below.

.code16
.global _start
_start:
movb $_start+0x83,%ah

So we have R_386_8 relocation and _start at 0x7C.
Addend is 0x83 == 131. We will sign extend it to 0xffffffffffffff83.

Now, 0xffffffffffffff83 + 0x7c gives us 0xFFFFFFFFFFFFFFFF.
Techically 0x83 + 0x7c == 0xFF, we do not exceed 1 byte value, but
currently LLD errors out, because we use checkUInt<8>.

Let's try to use checkInt<8> now and the following code to see if it can help (no):
main.s:
.byte foo

input.s:
.globl foo
.hidden foo
foo = 0xff

Here, foo is 0xFF. And addend is 0x0. Final value is 0x00000000000000FF.
Again, it fits one byte well, but with checkInt<8>,
we would error out it, so we can't use it.

What we want to do is to check that the result fits 1 byte well.
Patch changes the check to checkIntUInt to fix the issue.

Differential revision: https://reviews.llvm.org/D45051

llvm-svn: 329061
This commit is contained in:
George Rimar 2018-04-03 12:19:04 +00:00
parent bfbeecdc5d
commit bc1d58a6b1
5 changed files with 28 additions and 4 deletions
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4
lld/ELF/Arch/X86.cpp
View File

@ -255,7 +255,7 @@ void X86::relocateOne(uint8_t *Loc, RelType Type, uint64_t Val) const {
// R_386_{PC,}{8,16} are not part of the i386 psABI, but they are
// being used for some 16-bit programs such as boot loaders, so
// we want to support them.
checkUInt(Loc, Val, 8, Type);
checkIntUInt(Loc, Val, 8, Type);
*Loc = Val;
break;
case R_386_PC8:
@ -263,7 +263,7 @@ void X86::relocateOne(uint8_t *Loc, RelType Type, uint64_t Val) const {
*Loc = Val;
break;
case R_386_16:
checkUInt(Loc, Val, 16, Type);
checkIntUInt(Loc, Val, 16, Type);
write16le(Loc, Val);
break;
case R_386_PC16:

12
lld/test/ELF/i386-reloc-16-large-addend.s Normal file
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@ -0,0 +1,12 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=i386-pc-linux %s -o %t
# RUN: ld.lld -Ttext 0x7c00 %t -o %t2
# RUN: llvm-objdump -s %t2 | FileCheck %s
# CHECK: Contents of section .text:
# CHECK-NEXT: 7c00 b800ff
.code16
.global _start
_start:
movw $_start+0x8300,%ax

2
lld/test/ELF/i386-reloc-16.s
View File

@ -10,6 +10,6 @@
// CHECK-NEXT: 1000 42
// RUN: not ld.lld -shared %t %t2 -o %t4 2>&1 | FileCheck --check-prefix=ERROR %s
// ERROR: relocation R_386_16 out of range: 65536 is not in [0, 65535]
// ERROR: relocation R_386_16 out of range: 65536 is not in [-32768, 32767]
.short foo

12
lld/test/ELF/i386-reloc-8-large-addend.s Normal file
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@ -0,0 +1,12 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=i386-pc-linux %s -o %t
# RUN: ld.lld -Ttext 0x7c %t -o %t2
# RUN: llvm-objdump -s %t2 | FileCheck %s
# CHECK: Contents of section .text:
# CHECK-NEXT: 007c b4ff
.code16
.global _start
_start:
movb $_start+0x83,%ah

2
lld/test/ELF/i386-reloc-8.s
View File

@ -10,6 +10,6 @@
// CHECK-NEXT: 1000 ff
// RUN: not ld.lld -shared %t %t2 -o %t4 2>&1 | FileCheck --check-prefix=ERROR %s
// ERROR: relocation R_386_8 out of range: 256 is not in [0, 255]
// ERROR: relocation R_386_8 out of range: 256 is not in [-128, 127]
.byte foo