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[COFF] Implement llvm.global_ctors priorities for MSVC COFF targets 

Summary:
MSVC and LLD sort sections ASCII-betically, so we need to use section
names that sort between .CRT$XCA (the start) and .CRT$XCU (the default
priority).

In the general case, use .CRT$XCT12345 as the section name, and let the
linker sort the zero-padded digits.

Users with low priorities typically want to initialize as early as
possible, so use .CRT$XCA00199 for prioties less than 200. This number
is arbitrary.

Implements PR38552.

Reviewers: majnemer, mstorsjo

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D51820

llvm-svn: 341727
This commit is contained in:
Reid Kleckner 2018-09-07 23:07:55 +00:00
parent c30dfb2dfc
commit f803b23879
2 changed files with 78 additions and 2 deletions
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21
llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
View File

@ -1456,8 +1456,25 @@ static MCSectionCOFF *getCOFFStaticStructorSection(MCContext &Ctx,
unsigned Priority,
const MCSymbol *KeySym,
MCSectionCOFF *Default) {
if (T.isKnownWindowsMSVCEnvironment() || T.isWindowsItaniumEnvironment())
return Ctx.getAssociativeCOFFSection(Default, KeySym, 0);
if (T.isKnownWindowsMSVCEnvironment() || T.isWindowsItaniumEnvironment()) {
// If the priority is the default, use .CRT$XCU, possibly associative.
if (Priority == 65535)
return Ctx.getAssociativeCOFFSection(Default, KeySym, 0);
// Otherwise, we need to compute a new section name. Low priorities should
// run earlier. The linker will sort sections ASCII-betically, and we need a
// string that sorts between .CRT$XCA and .CRT$XCU. In the general case, we
// make a name like ".CRT$XCT12345", since that runs before .CRT$XCU. Really
// low priorities need to sort before 'L', since the CRT uses that
// internally, so we use ".CRT$XCA00001" for them.
SmallString<24> Name;
raw_svector_ostream OS(Name);
OS << ".CRT$XC" << (Priority < 200 ? 'A' : 'T') << format("%05u", Priority);
MCSectionCOFF *Sec = Ctx.getCOFFSection(
Name, COFF::IMAGE_SCN_CNT_INITIALIZED_DATA | COFF::IMAGE_SCN_MEM_READ,
SectionKind::getReadOnly());
return Ctx.getAssociativeCOFFSection(Sec, KeySym, 0);
}
std::string Name = IsCtor ? ".ctors" : ".dtors";
if (Priority != 65535)

59
llvm/test/CodeGen/X86/ctor-priority-coff.ll Normal file
View File

@ -0,0 +1,59 @@
; RUN: llc < %s | FileCheck %s
; Check that we come up with appropriate section names that link.exe sorts
; well.
; CHECK: .section .CRT$XCA00042,"dr"
; CHECK: .p2align 3
; CHECK: .quad f
; CHECK: .section .CRT$XCT12345,"dr"
; CHECK: .p2align 3
; CHECK: .quad g
; CHECK: .section .CRT$XCT23456,"dr",associative,h
; CHECK: .p2align 3
; CHECK: .quad init_h
target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-windows-msvc19.14.26433"
$h = comdat any
@h = linkonce_odr global i8 55, comdat, align 1
@str0 = private dso_local unnamed_addr constant [6 x i8] c"later\00", align 1
@str1 = private dso_local unnamed_addr constant [6 x i8] c"first\00", align 1
@str2 = private dso_local unnamed_addr constant [5 x i8] c"main\00", align 1
@llvm.global_ctors = appending global [3 x { i32, void ()*, i8* }] [
{ i32, void ()*, i8* } { i32 12345, void ()* @g, i8* null },
{ i32, void ()*, i8* } { i32 42, void ()* @f, i8* null },
{ i32, void ()*, i8* } { i32 23456, void ()* @init_h, i8* @h }
]
declare dso_local i32 @puts(i8* nocapture readonly) local_unnamed_addr
define dso_local void @g() {
entry:
%call = tail call i32 @puts(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @str0, i64 0, i64 0))
ret void
}
define dso_local void @f() {
entry:
%call = tail call i32 @puts(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @str1, i64 0, i64 0))
ret void
}
define dso_local void @init_h() {
entry:
store i8 42, i8* @h
ret void
}
; Function Attrs: nounwind uwtable
define dso_local i32 @main() local_unnamed_addr {
entry:
%call = tail call i32 @puts(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @str2, i64 0, i64 0))
ret i32 0
}