From bc1d58a6b1cfe13e4b7f24de505bbb286febc73e Mon Sep 17 00:00:00 2001
From: George Rimar <grimar@accesssoftek.com>
Date: Tue, 3 Apr 2018 12:19:04 +0000
Subject: [PATCH] [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
---
 lld/ELF/Arch/X86.cpp                      |  4 ++--
 lld/test/ELF/i386-reloc-16-large-addend.s | 12 ++++++++++++
 lld/test/ELF/i386-reloc-16.s              |  2 +-
 lld/test/ELF/i386-reloc-8-large-addend.s  | 12 ++++++++++++
 lld/test/ELF/i386-reloc-8.s               |  2 +-
 5 files changed, 28 insertions(+), 4 deletions(-)
 create mode 100644 lld/test/ELF/i386-reloc-16-large-addend.s
 create mode 100644 lld/test/ELF/i386-reloc-8-large-addend.s

diff --git a/lld/ELF/Arch/X86.cpp b/lld/ELF/Arch/X86.cpp
index 87c84ad..b2d9007 100644
--- a/lld/ELF/Arch/X86.cpp
+++ b/lld/ELF/Arch/X86.cpp
@@ -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:
diff --git a/lld/test/ELF/i386-reloc-16-large-addend.s b/lld/test/ELF/i386-reloc-16-large-addend.s
new file mode 100644
index 0000000..ceb4862
--- /dev/null
+++ b/lld/test/ELF/i386-reloc-16-large-addend.s
@@ -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
diff --git a/lld/test/ELF/i386-reloc-16.s b/lld/test/ELF/i386-reloc-16.s
index e9d4fbb..33b6c44 100644
--- a/lld/test/ELF/i386-reloc-16.s
+++ b/lld/test/ELF/i386-reloc-16.s
@@ -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
diff --git a/lld/test/ELF/i386-reloc-8-large-addend.s b/lld/test/ELF/i386-reloc-8-large-addend.s
new file mode 100644
index 0000000..61d6380
--- /dev/null
+++ b/lld/test/ELF/i386-reloc-8-large-addend.s
@@ -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
diff --git a/lld/test/ELF/i386-reloc-8.s b/lld/test/ELF/i386-reloc-8.s
index e0e255b..9e9f0cc 100644
--- a/lld/test/ELF/i386-reloc-8.s
+++ b/lld/test/ELF/i386-reloc-8.s
@@ -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
-- 
2.7.4