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WholeProgramDevirt: Teach the pass to respect the global's alignment.

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The bytes inserted before an overaligned global need to be padded according
to the alignment set on the original global in order for the initializer
to meet the global's alignment requirements. The previous implementation
that padded to the pointer width happened to be correct for vtables on most
platforms but may do the wrong thing if the vtable has a larger alignment.

This issue is visible with a prototype implementation of HWASAN for globals,
which will overalign all globals including vtables to 16 bytes.

There is also no padding requirement for the bytes inserted after the global
because they are never read from nor are they significant for alignment
purposes, so stop inserting padding there.

Differential Revision: https://reviews.llvm.org/D65031

llvm-svn: 366725
This commit is contained in:
Peter Collingbourne 2019-07-22 18:50:45 +00:00
parent ef51fda361
commit 25569f62e9
3 changed files with 23 additions and 18 deletions
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11
lib/Transforms/IPO/WholeProgramDevirt.cpp
View File

@ -1302,10 +1302,12 @@ void DevirtModule::rebuildGlobal(VTableBits &B) {
if (B.Before.Bytes.empty() && B.After.Bytes.empty())
return;
// Align each byte array to pointer width.
unsigned PointerSize = M.getDataLayout().getPointerSize();
B.Before.Bytes.resize(alignTo(B.Before.Bytes.size(), PointerSize));
B.After.Bytes.resize(alignTo(B.After.Bytes.size(), PointerSize));
// Align the before byte array to the global's minimum alignment so that we
// don't break any alignment requirements on the global.
unsigned Align = B.GV->getAlignment();
if (Align == 0)
Align = M.getDataLayout().getABITypeAlignment(B.GV->getValueType());
B.Before.Bytes.resize(alignTo(B.Before.Bytes.size(), Align));
// Before was stored in reverse order; flip it now.
for (size_t I = 0, Size = B.Before.Bytes.size(); I != Size / 2; ++I)
@ -1322,6 +1324,7 @@ void DevirtModule::rebuildGlobal(VTableBits &B) {
GlobalVariable::PrivateLinkage, NewInit, "", B.GV);
NewGV->setSection(B.GV->getSection());
NewGV->setComdat(B.GV->getComdat());
NewGV->setAlignment(B.GV->getAlignment());
// Copy the original vtable's metadata to the anonymous global, adjusting
// offsets as required.

14
test/Transforms/WholeProgramDevirt/virtual-const-prop-begin.ll
View File

@ -17,19 +17,19 @@ i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
i8* bitcast (i32 (i8*)* @vf2i32 to i8*)
], !type !0
; CHECK: [[VT3DATA:@[^ ]*]] = private constant { [8 x i8], [3 x i8*], [0 x i8] } { [8 x i8] c"\00\00\00\01\03\00\00\00", [3 x i8*] [i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf3i32 to i8*)], [0 x i8] zeroinitializer }, !type [[T8]]
; CHECK: [[VT3DATA:@[^ ]*]] = private constant { [5 x i8], [3 x i8*], [0 x i8] } { [5 x i8] c"\01\03\00\00\00", [3 x i8*] [i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf3i32 to i8*)], [0 x i8] zeroinitializer }, align 1, !type [[T5:![0-9]+]]
@vt3 = constant [3 x i8*] [
i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
i8* bitcast (i32 (i8*)* @vf3i32 to i8*)
], !type !0
], align 1, !type !0
; CHECK: [[VT4DATA:@[^ ]*]] = private constant { [8 x i8], [3 x i8*], [0 x i8] } { [8 x i8] c"\00\00\00\02\04\00\00\00", [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf4i32 to i8*)], [0 x i8] zeroinitializer }, !type [[T8]]
; CHECK: [[VT4DATA:@[^ ]*]] = private constant { [16 x i8], [3 x i8*], [0 x i8] } { [16 x i8] c"\00\00\00\00\00\00\00\00\00\00\00\02\04\00\00\00", [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf4i32 to i8*)], [0 x i8] zeroinitializer }, align 16, !type [[T16:![0-9]+]]
@vt4 = constant [3 x i8*] [
i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
i8* bitcast (i32 (i8*)* @vf4i32 to i8*)
], !type !0
], align 16, !type !0
; CHECK: @vt5 = {{.*}}, !type [[T0:![0-9]+]]
@vt5 = constant [3 x i8*] [
@ -40,8 +40,8 @@ i8* bitcast (void ()* @__cxa_pure_virtual to i8*)
; CHECK: @vt1 = alias [3 x i8*], getelementptr inbounds ({ [8 x i8], [3 x i8*], [0 x i8] }, { [8 x i8], [3 x i8*], [0 x i8] }* [[VT1DATA]], i32 0, i32 1)
; CHECK: @vt2 = alias [3 x i8*], getelementptr inbounds ({ [8 x i8], [3 x i8*], [0 x i8] }, { [8 x i8], [3 x i8*], [0 x i8] }* [[VT2DATA]], i32 0, i32 1)
; CHECK: @vt3 = alias [3 x i8*], getelementptr inbounds ({ [8 x i8], [3 x i8*], [0 x i8] }, { [8 x i8], [3 x i8*], [0 x i8] }* [[VT3DATA]], i32 0, i32 1)
; CHECK: @vt4 = alias [3 x i8*], getelementptr inbounds ({ [8 x i8], [3 x i8*], [0 x i8] }, { [8 x i8], [3 x i8*], [0 x i8] }* [[VT4DATA]], i32 0, i32 1)
; CHECK: @vt3 = alias [3 x i8*], getelementptr inbounds ({ [5 x i8], [3 x i8*], [0 x i8] }, { [5 x i8], [3 x i8*], [0 x i8] }* [[VT3DATA]], i32 0, i32 1)
; CHECK: @vt4 = alias [3 x i8*], getelementptr inbounds ({ [16 x i8], [3 x i8*], [0 x i8] }, { [16 x i8], [3 x i8*], [0 x i8] }* [[VT4DATA]], i32 0, i32 1)
define i1 @vf0i1(i8* %this) readnone {
ret i1 0
@ -134,6 +134,8 @@ declare void @llvm.assume(i1)
declare void @__cxa_pure_virtual()
; CHECK: [[T8]] = !{i32 8, !"typeid"}
; CHECK: [[T5]] = !{i32 5, !"typeid"}
; CHECK: [[T16]] = !{i32 16, !"typeid"}
; CHECK: [[T0]] = !{i32 0, !"typeid"}
!0 = !{i32 0, !"typeid"}

16
test/Transforms/WholeProgramDevirt/virtual-const-prop-end.ll
View File

@ -3,7 +3,7 @@
target datalayout = "e-p:64:64"
target triple = "x86_64-unknown-linux-gnu"
; CHECK: [[VT1DATA:@[^ ]*]] = private constant { [0 x i8], [4 x i8*], [8 x i8] } { [0 x i8] zeroinitializer, [4 x i8*] [i8* null, i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf1i32 to i8*)], [8 x i8] c"\01\00\00\00\01\00\00\00" }, !type [[T8:![0-9]+]]
; CHECK: [[VT1DATA:@[^ ]*]] = private constant { [0 x i8], [4 x i8*], [5 x i8] } { [0 x i8] zeroinitializer, [4 x i8*] [i8* null, i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf1i32 to i8*)], [5 x i8] c"\01\00\00\00\01" }, !type [[T8:![0-9]+]]
@vt1 = constant [4 x i8*] [
i8* null,
i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
@ -11,14 +11,14 @@ i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
i8* bitcast (i32 (i8*)* @vf1i32 to i8*)
], !type !1
; CHECK: [[VT2DATA:@[^ ]*]] = private constant { [0 x i8], [3 x i8*], [8 x i8] } { [0 x i8] zeroinitializer, [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf2i32 to i8*)], [8 x i8] c"\02\00\00\00\02\00\00\00" }, !type [[T0:![0-9]+]]
; CHECK: [[VT2DATA:@[^ ]*]] = private constant { [0 x i8], [3 x i8*], [5 x i8] } { [0 x i8] zeroinitializer, [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf2i32 to i8*)], [5 x i8] c"\02\00\00\00\02" }, !type [[T0:![0-9]+]]
@vt2 = constant [3 x i8*] [
i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
i8* bitcast (i32 (i8*)* @vf2i32 to i8*)
], !type !0
; CHECK: [[VT3DATA:@[^ ]*]] = private constant { [0 x i8], [4 x i8*], [8 x i8] } { [0 x i8] zeroinitializer, [4 x i8*] [i8* null, i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf3i32 to i8*)], [8 x i8] c"\03\00\00\00\01\00\00\00" }, !type [[T8]]
; CHECK: [[VT3DATA:@[^ ]*]] = private constant { [0 x i8], [4 x i8*], [5 x i8] } { [0 x i8] zeroinitializer, [4 x i8*] [i8* null, i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf3i32 to i8*)], [5 x i8] c"\03\00\00\00\01" }, !type [[T8]]
@vt3 = constant [4 x i8*] [
i8* null,
i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
@ -26,17 +26,17 @@ i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
i8* bitcast (i32 (i8*)* @vf3i32 to i8*)
], !type !1
; CHECK: [[VT4DATA:@[^ ]*]] = private constant { [0 x i8], [3 x i8*], [8 x i8] } { [0 x i8] zeroinitializer, [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf4i32 to i8*)], [8 x i8] c"\04\00\00\00\02\00\00\00" }, !type [[T0]]
; CHECK: [[VT4DATA:@[^ ]*]] = private constant { [0 x i8], [3 x i8*], [5 x i8] } { [0 x i8] zeroinitializer, [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf4i32 to i8*)], [5 x i8] c"\04\00\00\00\02" }, !type [[T0]]
@vt4 = constant [3 x i8*] [
i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
i8* bitcast (i32 (i8*)* @vf4i32 to i8*)
], !type !0
; CHECK: @vt1 = alias [4 x i8*], getelementptr inbounds ({ [0 x i8], [4 x i8*], [8 x i8] }, { [0 x i8], [4 x i8*], [8 x i8] }* [[VT1DATA]], i32 0, i32 1)
; CHECK: @vt2 = alias [3 x i8*], getelementptr inbounds ({ [0 x i8], [3 x i8*], [8 x i8] }, { [0 x i8], [3 x i8*], [8 x i8] }* [[VT2DATA]], i32 0, i32 1)
; CHECK: @vt3 = alias [4 x i8*], getelementptr inbounds ({ [0 x i8], [4 x i8*], [8 x i8] }, { [0 x i8], [4 x i8*], [8 x i8] }* [[VT3DATA]], i32 0, i32 1)
; CHECK: @vt4 = alias [3 x i8*], getelementptr inbounds ({ [0 x i8], [3 x i8*], [8 x i8] }, { [0 x i8], [3 x i8*], [8 x i8] }* [[VT4DATA]], i32 0, i32 1)
; CHECK: @vt1 = alias [4 x i8*], getelementptr inbounds ({ [0 x i8], [4 x i8*], [5 x i8] }, { [0 x i8], [4 x i8*], [5 x i8] }* [[VT1DATA]], i32 0, i32 1)
; CHECK: @vt2 = alias [3 x i8*], getelementptr inbounds ({ [0 x i8], [3 x i8*], [5 x i8] }, { [0 x i8], [3 x i8*], [5 x i8] }* [[VT2DATA]], i32 0, i32 1)
; CHECK: @vt3 = alias [4 x i8*], getelementptr inbounds ({ [0 x i8], [4 x i8*], [5 x i8] }, { [0 x i8], [4 x i8*], [5 x i8] }* [[VT3DATA]], i32 0, i32 1)
; CHECK: @vt4 = alias [3 x i8*], getelementptr inbounds ({ [0 x i8], [3 x i8*], [5 x i8] }, { [0 x i8], [3 x i8*], [5 x i8] }* [[VT4DATA]], i32 0, i32 1)
define i1 @vf0i1(i8* %this) readnone {
ret i1 0