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[asan] Move instrumented null-terminated strings to a special section, LLVM part 

On Darwin, simple C null-terminated constant strings normally end up in the __TEXT,__cstring section of the resulting Mach-O binary. When instrumented with ASan, these strings are transformed in a way that they cannot be in __cstring (the linker unifies the content of this section and strips extra NUL bytes, which would break instrumentation), and are put into a generic __const section. This breaks some of the tools that we have: Some tools need to scan all C null-terminated strings in Mach-O binaries, and scanning all the contents of __const has a large performance penalty. This patch instead introduces a special section, __asan_cstring which will now hold the instrumented null-terminated strings.

Differential Revision: https://reviews.llvm.org/D25026

llvm-svn: 285619
This commit is contained in:
Kuba Brecka 2016-10-31 18:51:58 +00:00
parent e7b54c2ea5
commit a28c9e8f09
2 changed files with 29 additions and 0 deletions
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8
llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
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@ -1535,6 +1535,14 @@ bool AddressSanitizerModule::InstrumentGlobals(IRBuilder<> &IRB, Module &M) {
NewGlobal->copyAttributesFrom(G);
NewGlobal->setAlignment(MinRZ);
// Move null-terminated C strings to "__asan_cstring" section on Darwin.
if (TargetTriple.isOSBinFormatMachO() && !G->hasSection() &&
G->isConstant()) {
auto Seq = dyn_cast<ConstantDataSequential>(G->getInitializer());
if (Seq && Seq->isCString())
NewGlobal->setSection("__TEXT,__asan_cstring,regular");
}
// Transfer the debug info. The payload starts at offset zero so we can
// copy the debug info over as is.
SmallVector<DIGlobalVariable *, 1> GVs;

21
llvm/test/Instrumentation/AddressSanitizer/global_cstring_darwin.ll Normal file
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@ -0,0 +1,21 @@
; This test checks that instrumented global C (null terminated) strings are put into a special section on Darwin.
; RUN: opt < %s -asan -asan-module -S | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.10.0"
; Should be put into __asan_cstring section:
@.str.1 = private unnamed_addr constant [13 x i8] c"Hello world.\00", align 1
@.str.2 = private unnamed_addr constant [4 x i8] c"%s\0A\00", align 1
; CHECK: @.str.1 = internal unnamed_addr constant { [13 x i8], [51 x i8] } { [13 x i8] c"Hello world.\00", [51 x i8] zeroinitializer }, section "__TEXT,__asan_cstring,regular", align 32
; CHECK: @.str.2 = internal unnamed_addr constant { [4 x i8], [60 x i8] } { [4 x i8] c"%s\0A\00", [60 x i8] zeroinitializer }, section "__TEXT,__asan_cstring,regular", align 32
; Shouldn't be put into special section:
@.str.3 = private unnamed_addr constant [4 x i8] c"\00\01\02\03", align 1
@.str.4 = private unnamed_addr global [7 x i8] c"Hello.\00", align 1
@.str.5 = private unnamed_addr constant [8 x i8] c"Hello.\00\00", align 1
; CHECK: @.str.3 = internal unnamed_addr constant { [4 x i8], [60 x i8] } { [4 x i8] c"\00\01\02\03", [60 x i8] zeroinitializer }, align 32
; CHECK: @.str.4 = private unnamed_addr global { [7 x i8], [57 x i8] } { [7 x i8] c"Hello.\00", [57 x i8] zeroinitializer }, align 32
; CHECK: @.str.5 = internal unnamed_addr constant { [8 x i8], [56 x i8] } { [8 x i8] c"Hello.\00\00", [56 x i8] zeroinitializer }, align 32