Add support for #pragma clang section

This patch provides a means to specify section-names for global variables, 
functions and static variables, using #pragma directives. 
This feature is only defined to work sensibly for ELF targets.
One can specify section names as:
#pragma clang section bss="myBSS" data="myData" rodata="myRodata" text="myText"
One can "unspecify" a section name with empty string e.g.
#pragma clang section bss="" data="" text="" rodata=""

Reviewers: Roger Ferrer, Jonathan Roelofs, Reid Kleckner
Differential Revision: https://reviews.llvm.org/D33412

llvm-svn: 304705
This commit is contained in:
Javed Absar 2017-06-05 10:11:57 +00:00
parent b16d146838
commit 2a67c9ee39
13 changed files with 409 additions and 1 deletions

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@ -2521,3 +2521,45 @@ whether or not an attribute is supported by the pragma by referring to the
The attributes are applied to all matching declarations individually, even when
the attribute is semantically incorrect. The attributes that aren't applied to
any declaration are not verified semantically.
Specifying section names for global objects (#pragma clang section)
===================================================================
The ``#pragma clang section`` directive provides a means to assign section-names
to global variables, functions and static variables.
The section names can be specified as:
.. code-block:: c++
#pragma clang section bss="myBSS" data="myData" rodata="myRodata" text="myText"
The section names can be reverted back to default name by supplying an empty
string to the section kind, for example:
.. code-block:: c++
#pragma clang section bss="" data="" text="" rodata=""
The ``#pragma clang section`` directive obeys the following rules:
* The pragma applies to all global variable, statics and function declarations
from the pragma to the end of the translation unit.
* The pragma clang section is enabled automatically, without need of any flags.
* This feature is only defined to work sensibly for ELF targets.
* If section name is specified through _attribute_((section("myname"))), then
the attribute name gains precedence.
* Global variables that are initialized to zero will be placed in the named
bss section, if one is present.
* The ``#pragma clang section`` directive does not does try to infer section-kind
from the name. For example, naming a section "``.bss.mySec``" does NOT mean
it will be a bss section name.
* The decision about which section-kind applies to each global is taken in the back-end.
Once the section-kind is known, appropriate section name, as specified by the user using
``#pragma clang section`` directive, is applied to that global.

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@ -1683,6 +1683,42 @@ def Section : InheritableAttr {
let Documentation = [SectionDocs];
}
def PragmaClangBSSSection : InheritableAttr {
// This attribute has no spellings as it is only ever created implicitly.
let Spellings = [];
let Args = [StringArgument<"Name">];
let Subjects = SubjectList<[GlobalVar], ErrorDiag,
"ExpectedFunctionMethodOrGlobalVar">;
let Documentation = [Undocumented];
}
def PragmaClangDataSection : InheritableAttr {
// This attribute has no spellings as it is only ever created implicitly.
let Spellings = [];
let Args = [StringArgument<"Name">];
let Subjects = SubjectList<[GlobalVar], ErrorDiag,
"ExpectedFunctionMethodOrGlobalVar">;
let Documentation = [Undocumented];
}
def PragmaClangRodataSection : InheritableAttr {
// This attribute has no spellings as it is only ever created implicitly.
let Spellings = [];
let Args = [StringArgument<"Name">];
let Subjects = SubjectList<[GlobalVar], ErrorDiag,
"ExpectedFunctionMethodOrGlobalVar">;
let Documentation = [Undocumented];
}
def PragmaClangTextSection : InheritableAttr {
// This attribute has no spellings as it is only ever created implicitly.
let Spellings = [];
let Args = [StringArgument<"Name">];
let Subjects = SubjectList<[Function], ErrorDiag,
"ExpectedFunctionMethodOrGlobalVar">;
let Documentation = [Undocumented];
}
def Sentinel : InheritableAttr {
let Spellings = [GCC<"sentinel">];
let Args = [DefaultIntArgument<"Sentinel", 0>,

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@ -887,9 +887,18 @@ def warn_pragma_expected_rparen : Warning<
"missing ')' after '#pragma %0' - ignoring">, InGroup<IgnoredPragmas>;
def warn_pragma_expected_identifier : Warning<
"expected identifier in '#pragma %0' - ignored">, InGroup<IgnoredPragmas>;
// '#pragma clang section' related errors
def err_pragma_expected_clang_section_name : Error<
"expected one of [bss|data|rodata|text] section kind in '#pragma %0'">;
def err_pragma_clang_section_expected_equal : Error<
"expected '=' following '#pragma clang section %select{invalid|bss|data|rodata|text}0'">;
def err_pragma_clang_section_expected_name_or_clear : Error<
"expected section name or '\"\"' following '#pragma clang section %select{invalid|bss|data|rodata|text}0'">;
def warn_pragma_expected_section_name : Warning<
"expected a string literal for the section name in '#pragma %0' - ignored">,
InGroup<IgnoredPragmas>;
def warn_pragma_expected_section_push_pop_or_name : Warning<
"expected push, pop or a string literal for the section name in '#pragma %0' - ignored">,
InGroup<IgnoredPragmas>;

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@ -166,6 +166,7 @@ class Parser : public CodeCompletionHandler {
std::unique_ptr<PragmaHandler> FPContractHandler;
std::unique_ptr<PragmaHandler> OpenCLExtensionHandler;
std::unique_ptr<PragmaHandler> OpenMPHandler;
std::unique_ptr<PragmaHandler> PCSectionHandler;
std::unique_ptr<PragmaHandler> MSCommentHandler;
std::unique_ptr<PragmaHandler> MSDetectMismatchHandler;
std::unique_ptr<PragmaHandler> MSPointersToMembers;

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@ -336,6 +336,35 @@ public:
/// \brief Source location for newly created implicit MSInheritanceAttrs
SourceLocation ImplicitMSInheritanceAttrLoc;
/// \brief pragma clang section kind
enum PragmaClangSectionKind {
PCSK_Invalid = 0,
PCSK_BSS = 1,
PCSK_Data = 2,
PCSK_Rodata = 3,
PCSK_Text = 4
};
enum PragmaClangSectionAction {
PCSA_Set = 0,
PCSA_Clear = 1
};
struct PragmaClangSection {
std::string SectionName;
bool Valid = false;
SourceLocation PragmaLocation;
void Act(SourceLocation PragmaLocation,
PragmaClangSectionAction Action,
StringLiteral* Name);
};
PragmaClangSection PragmaClangBSSSection;
PragmaClangSection PragmaClangDataSection;
PragmaClangSection PragmaClangRodataSection;
PragmaClangSection PragmaClangTextSection;
enum PragmaMsStackAction {
PSK_Reset = 0x0, // #pragma ()
PSK_Set = 0x1, // #pragma (value)
@ -8117,6 +8146,11 @@ public:
POAK_Reset // #pragma options align=reset
};
/// ActOnPragmaClangSection - Called on well formed \#pragma clang section
void ActOnPragmaClangSection(SourceLocation PragmaLoc,
PragmaClangSectionAction Action,
PragmaClangSectionKind SecKind, StringRef SecName);
/// ActOnPragmaOptionsAlign - Called on well formed \#pragma options align.
void ActOnPragmaOptionsAlign(PragmaOptionsAlignKind Kind,
SourceLocation PragmaLoc);

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@ -406,6 +406,13 @@ void CodeGenFunction::EmitStaticVarDecl(const VarDecl &D,
if (D.hasAttr<AnnotateAttr>())
CGM.AddGlobalAnnotations(&D, var);
if (auto *SA = D.getAttr<PragmaClangBSSSectionAttr>())
var->addAttribute("bss-section", SA->getName());
if (auto *SA = D.getAttr<PragmaClangDataSectionAttr>())
var->addAttribute("data-section", SA->getName());
if (auto *SA = D.getAttr<PragmaClangRodataSectionAttr>())
var->addAttribute("rodata-section", SA->getName());
if (const SectionAttr *SA = D.getAttr<SectionAttr>())
var->setSection(SA->getName());

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@ -1026,9 +1026,25 @@ void CodeGenModule::setNonAliasAttributes(const Decl *D,
llvm::GlobalObject *GO) {
SetCommonAttributes(D, GO);
if (D)
if (D) {
if (auto *GV = dyn_cast<llvm::GlobalVariable>(GO)) {
if (auto *SA = D->getAttr<PragmaClangBSSSectionAttr>())
GV->addAttribute("bss-section", SA->getName());
if (auto *SA = D->getAttr<PragmaClangDataSectionAttr>())
GV->addAttribute("data-section", SA->getName());
if (auto *SA = D->getAttr<PragmaClangRodataSectionAttr>())
GV->addAttribute("rodata-section", SA->getName());
}
if (auto *F = dyn_cast<llvm::Function>(GO)) {
if (auto *SA = D->getAttr<PragmaClangTextSectionAttr>())
if (!D->getAttr<SectionAttr>())
F->addFnAttr("implicit-section-name", SA->getName());
}
if (const SectionAttr *SA = D->getAttr<SectionAttr>())
GO->setSection(SA->getName());
}
getTargetCodeGenInfo().setTargetAttributes(D, GO, *this);
}
@ -1127,6 +1143,10 @@ void CodeGenModule::SetFunctionAttributes(GlobalDecl GD, llvm::Function *F,
setLinkageAndVisibilityForGV(F, FD);
if (FD->getAttr<PragmaClangTextSectionAttr>()) {
F->addFnAttr("implicit-section-name");
}
if (const SectionAttr *SA = FD->getAttr<SectionAttr>())
F->setSection(SA->getName());
@ -2828,6 +2848,14 @@ static bool isVarDeclStrongDefinition(const ASTContext &Context,
if (D->hasAttr<SectionAttr>())
return true;
// A variable cannot be both common and exist in a section.
// We dont try to determine which is the right section in the front-end.
// If no specialized section name is applicable, it will resort to default.
if (D->hasAttr<PragmaClangBSSSectionAttr>() ||
D->hasAttr<PragmaClangDataSectionAttr>() ||
D->hasAttr<PragmaClangRodataSectionAttr>())
return true;
// Thread local vars aren't considered common linkage.
if (D->getTLSKind())
return true;

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@ -49,6 +49,15 @@ struct PragmaPackHandler : public PragmaHandler {
Token &FirstToken) override;
};
struct PragmaClangSectionHandler : public PragmaHandler {
explicit PragmaClangSectionHandler(Sema &S)
: PragmaHandler("section"), Actions(S) {}
void HandlePragma(Preprocessor &PP, PragmaIntroducerKind Introducer,
Token &FirstToken) override;
private:
Sema &Actions;
};
struct PragmaMSStructHandler : public PragmaHandler {
explicit PragmaMSStructHandler() : PragmaHandler("ms_struct") {}
void HandlePragma(Preprocessor &PP, PragmaIntroducerKind Introducer,
@ -224,6 +233,9 @@ void Parser::initializePragmaHandlers() {
FPContractHandler.reset(new PragmaFPContractHandler());
PP.AddPragmaHandler("STDC", FPContractHandler.get());
PCSectionHandler.reset(new PragmaClangSectionHandler(Actions));
PP.AddPragmaHandler("clang", PCSectionHandler.get());
if (getLangOpts().OpenCL) {
OpenCLExtensionHandler.reset(new PragmaOpenCLExtensionHandler());
PP.AddPragmaHandler("OPENCL", OpenCLExtensionHandler.get());
@ -323,6 +335,9 @@ void Parser::resetPragmaHandlers() {
MSCommentHandler.reset();
}
PP.RemovePragmaHandler("clang", PCSectionHandler.get());
PCSectionHandler.reset();
if (getLangOpts().MicrosoftExt) {
PP.RemovePragmaHandler(MSDetectMismatchHandler.get());
MSDetectMismatchHandler.reset();
@ -1614,6 +1629,51 @@ void PragmaMSStructHandler::HandlePragma(Preprocessor &PP,
PP.EnterTokenStream(Toks, /*DisableMacroExpansion=*/true);
}
// #pragma clang section bss="abc" data="" rodata="def" text=""
void PragmaClangSectionHandler::HandlePragma(Preprocessor &PP,
PragmaIntroducerKind Introducer, Token &FirstToken) {
Token Tok;
auto SecKind = Sema::PragmaClangSectionKind::PCSK_Invalid;
PP.Lex(Tok); // eat 'section'
while (Tok.isNot(tok::eod)) {
if (Tok.isNot(tok::identifier)) {
PP.Diag(Tok.getLocation(), diag::err_pragma_expected_clang_section_name) << "clang section";
return;
}
const IdentifierInfo *SecType = Tok.getIdentifierInfo();
if (SecType->isStr("bss"))
SecKind = Sema::PragmaClangSectionKind::PCSK_BSS;
else if (SecType->isStr("data"))
SecKind = Sema::PragmaClangSectionKind::PCSK_Data;
else if (SecType->isStr("rodata"))
SecKind = Sema::PragmaClangSectionKind::PCSK_Rodata;
else if (SecType->isStr("text"))
SecKind = Sema::PragmaClangSectionKind::PCSK_Text;
else {
PP.Diag(Tok.getLocation(), diag::err_pragma_expected_clang_section_name) << "clang section";
return;
}
PP.Lex(Tok); // eat ['bss'|'data'|'rodata'|'text']
if (Tok.isNot(tok::equal)) {
PP.Diag(Tok.getLocation(), diag::err_pragma_clang_section_expected_equal) << SecKind;
return;
}
std::string SecName;
if (!PP.LexStringLiteral(Tok, SecName, "pragma clang section", false))
return;
Actions.ActOnPragmaClangSection(Tok.getLocation(),
(SecName.size()? Sema::PragmaClangSectionAction::PCSA_Set :
Sema::PragmaClangSectionAction::PCSA_Clear),
SecKind, SecName);
}
}
// #pragma 'align' '=' {'native','natural','mac68k','power','reset'}
// #pragma 'options 'align' '=' {'native','natural','mac68k','power','reset'}
static void ParseAlignPragma(Preprocessor &PP, Token &FirstTok,

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@ -126,6 +126,36 @@ void Sema::ActOnPragmaOptionsAlign(PragmaOptionsAlignKind Kind,
PackStack.Act(PragmaLoc, Action, StringRef(), Alignment);
}
void Sema::ActOnPragmaClangSection(SourceLocation PragmaLoc, PragmaClangSectionAction Action,
PragmaClangSectionKind SecKind, StringRef SecName) {
PragmaClangSection *CSec;
switch (SecKind) {
case PragmaClangSectionKind::PCSK_BSS:
CSec = &PragmaClangBSSSection;
break;
case PragmaClangSectionKind::PCSK_Data:
CSec = &PragmaClangDataSection;
break;
case PragmaClangSectionKind::PCSK_Rodata:
CSec = &PragmaClangRodataSection;
break;
case PragmaClangSectionKind::PCSK_Text:
CSec = &PragmaClangTextSection;
break;
default:
llvm_unreachable("invalid clang section kind");
}
if (Action == PragmaClangSectionAction::PCSA_Clear) {
CSec->Valid = false;
return;
}
CSec->Valid = true;
CSec->SectionName = SecName;
CSec->PragmaLocation = PragmaLoc;
}
void Sema::ActOnPragmaPack(SourceLocation PragmaLoc, PragmaMsStackAction Action,
StringRef SlotLabel, Expr *alignment) {
Expr *Alignment = static_cast<Expr *>(alignment);

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@ -8651,6 +8651,14 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
NewFD->setInvalidDecl();
}
// Apply an implicit SectionAttr if '#pragma clang section text' is active
if (PragmaClangTextSection.Valid && D.isFunctionDefinition() &&
!NewFD->hasAttr<SectionAttr>()) {
NewFD->addAttr(PragmaClangTextSectionAttr::CreateImplicit(Context,
PragmaClangTextSection.SectionName,
PragmaClangTextSection.PragmaLocation));
}
// Apply an implicit SectionAttr if #pragma code_seg is active.
if (CodeSegStack.CurrentValue && D.isFunctionDefinition() &&
!NewFD->hasAttr<SectionAttr>()) {
@ -11175,6 +11183,23 @@ void Sema::FinalizeDeclaration(Decl *ThisDecl) {
if (!VD)
return;
// Apply an implicit SectionAttr if '#pragma clang section bss|data|rodata' is active
if (VD->hasGlobalStorage() && VD->isThisDeclarationADefinition() &&
!inTemplateInstantiation() && !VD->hasAttr<SectionAttr>()) {
if (PragmaClangBSSSection.Valid)
VD->addAttr(PragmaClangBSSSectionAttr::CreateImplicit(Context,
PragmaClangBSSSection.SectionName,
PragmaClangBSSSection.PragmaLocation));
if (PragmaClangDataSection.Valid)
VD->addAttr(PragmaClangDataSectionAttr::CreateImplicit(Context,
PragmaClangDataSection.SectionName,
PragmaClangDataSection.PragmaLocation));
if (PragmaClangRodataSection.Valid)
VD->addAttr(PragmaClangRodataSectionAttr::CreateImplicit(Context,
PragmaClangRodataSection.SectionName,
PragmaClangRodataSection.PragmaLocation));
}
if (auto *DD = dyn_cast<DecompositionDecl>(ThisDecl)) {
for (auto *BD : DD->bindings()) {
FinalizeDeclaration(BD);

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@ -0,0 +1,41 @@
// RUN: %clang_cc1 -x c -emit-llvm -triple arm-none-eabi -o - %s | FileCheck %s
// Test that section attributes are attached to C tentative definitions as per
// '#pragma clang section' directives.
#pragma clang section bss = ".bss.1"
int x; // bss.1
#pragma clang section bss = ""
int x; // stays in .bss.1
int y; // not assigned a section attribute
int z; // not assigned a section attribute
#pragma clang section bss = ".bss.2"
int x; // stays in .bss.1
int y; // .bss.2
// Test the same for `const` declarations.
#pragma clang section rodata = ".rodata.1"
const int cx; // rodata.1
#pragma clang section rodata = ""
const int cx; // stays in .rodata.1
const int cy; // not assigned a section attribute
const int cz; // not assigned a rodata section attribute
#pragma clang section rodata = ".rodata.2"
const int cx; // stays in .rodata.1
const int cy; // .rodata.2
// CHECK: @x = global i32 0, align 4 #0
// CHECK: @y = global i32 0, align 4 #1
// CHECK: @z = common global i32 0, align 4
// CHECK: @cx = constant i32 0, align 4 #2
// CHECK: @cy = constant i32 0, align 4 #3
// CHECK: @cz = constant i32 0, align 4 #1
// CHECK: attributes #0 = { "bss-section"=".bss.1" }
// CHECK: attributes #1 = { "bss-section"=".bss.2" }
// CHECK: attributes #2 = { "bss-section"=".bss.2" "rodata-section"=".rodata.1" }
// CHECK: attributes #3 = { "bss-section"=".bss.2" "rodata-section"=".rodata.2" }

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@ -0,0 +1,78 @@
// RUN: %clang_cc1 -emit-llvm -triple arm-none-eabi -o - %s | FileCheck %s
// Test that global variables, statics and functions are attached section-attributes
// as per '#pragma clang section' directives.
extern "C" {
// test with names for each section
#pragma clang section bss="my_bss.1" data="my_data.1" rodata="my_rodata.1"
#pragma clang section text="my_text.1"
int a; // my_bss.1
int b = 1; // my_data.1
int c[4]; // my_bss.1
short d[5] = {0}; // my_bss.1
short e[6] = {0, 0, 1}; // my_data.1
extern const int f;
const int f = 2; // my_rodata.1
int foo(void) { // my_text.1
return b;
}
static int g[2]; // my_bss.1
#pragma clang section bss=""
int h; // default - .bss
#pragma clang section data="" bss="my_bss.2" text="my_text.2"
int i = 0; // my_bss.2
extern const int j;
const int j = 4; // default - .rodata
int k; // my_bss.2
extern int zoo(int *x, int *y);
int goo(void) { // my_text.2
static int lstat_h; // my_bss.2
return zoo(g, &lstat_h);
}
#pragma clang section rodata="my_rodata.2" data="my_data.2"
int l = 5; // my_data.2
extern const int m;
const int m = 6; // my_rodata.2
#pragma clang section rodata="" data="" bss="" text=""
int n; // default
int o = 6; // default
extern const int p;
const int p = 7; // default
int hoo(void) {
return b;
}
}
//CHECK: @a = global i32 0, align 4 #0
//CHECK: @b = global i32 1, align 4 #0
//CHECK: @c = global [4 x i32] zeroinitializer, align 4 #0
//CHECK: @d = global [5 x i16] zeroinitializer, align 2 #0
//CHECK: @e = global [6 x i16] [i16 0, i16 0, i16 1, i16 0, i16 0, i16 0], align 2 #0
//CHECK: @f = constant i32 2, align 4 #0
//CHECK: @h = global i32 0, align 4 #1
//CHECK: @i = global i32 0, align 4 #2
//CHECK: @j = constant i32 4, align 4 #2
//CHECK: @k = global i32 0, align 4 #2
//CHECK: @_ZZ3gooE7lstat_h = internal global i32 0, align 4 #2
//CHECK: @_ZL1g = internal global [2 x i32] zeroinitializer, align 4 #0
//CHECK: @l = global i32 5, align 4 #3
//CHECK: @m = constant i32 6, align 4 #3
//CHECK: @n = global i32 0, align 4
//CHECK: @o = global i32 6, align 4
//CHECK: @p = constant i32 7, align 4
//CHECK: define i32 @foo() #4 {
//CHECK: define i32 @goo() #5 {
//CHECK: declare i32 @zoo(i32*, i32*) #6
//CHECK: define i32 @hoo() #7 {
//CHECK: attributes #0 = { "bss-section"="my_bss.1" "data-section"="my_data.1" "rodata-section"="my_rodata.1" }
//CHECK: attributes #1 = { "data-section"="my_data.1" "rodata-section"="my_rodata.1" }
//CHECK: attributes #2 = { "bss-section"="my_bss.2" "rodata-section"="my_rodata.1" }
//CHECK: attributes #3 = { "bss-section"="my_bss.2" "data-section"="my_data.2" "rodata-section"="my_rodata.2" }
//CHECK: attributes #4 = { {{.*"implicit-section-name"="my_text.1".*}} }
//CHECK: attributes #5 = { {{.*"implicit-section-name"="my_text.2".*}} }
//CHECK-NOT: attributes #6 = { {{.*"implicit-section-name".*}} }
//CHECK-NOT: attributes #7 = { {{.*"implicit-section-name".*}} }

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@ -0,0 +1,17 @@
// RUN: %clang_cc1 -fsyntax-only -verify %s -triple arm-none-eabi
#pragma clang section bss="mybss.1" data="mydata.1" rodata="myrodata.1" text="mytext.1"
#pragma clang section bss="" data="" rodata="" text=""
#pragma clang section
#pragma clang section dss="mybss.2" // expected-error {{expected one of [bss|data|rodata|text] section kind in '#pragma clang section'}}
#pragma clang section deta="mydata.2" // expected-error {{expected one of [bss|data|rodata|text] section kind in '#pragma clang section'}}
#pragma clang section rodeta="rodata.2" // expected-error {{expected one of [bss|data|rodata|text] section kind in '#pragma clang section'}}
#pragma clang section taxt="text.2" // expected-error {{expected one of [bss|data|rodata|text] section kind in '#pragma clang section'}}
#pragma clang section section bss="mybss.2" // expected-error {{expected one of [bss|data|rodata|text] section kind in '#pragma clang section'}}
#pragma clang section bss "mybss.2" // expected-error {{expected '=' following '#pragma clang section bss'}}
#pragma clang section data "mydata.2" // expected-error {{expected '=' following '#pragma clang section data'}}
#pragma clang section rodata "myrodata.2" // expected-error {{expected '=' following '#pragma clang section rodata'}}
#pragma clang section bss="" data="" rodata="" text="" more //expected-error {{expected one of [bss|data|rodata|text] section kind in '#pragma clang section'}}
int a;