[llvm] acc6bcd - Support alternative sections for patchable function entries (#131230)
via llvm-commits
llvm-commits at lists.llvm.org
Wed Apr 2 14:53:59 PDT 2025
Author: Sami Tolvanen
Date: 2025-04-02T21:53:55Z
New Revision: acc6bcdc504ad2e8c09a628dc18de0067f7344b8
URL: https://github.com/llvm/llvm-project/commit/acc6bcdc504ad2e8c09a628dc18de0067f7344b8
DIFF: https://github.com/llvm/llvm-project/commit/acc6bcdc504ad2e8c09a628dc18de0067f7344b8.diff
LOG: Support alternative sections for patchable function entries (#131230)
With -fpatchable-function-entry (or the patchable_function_entry
function attribute), we emit records of patchable entry locations to the
__patchable_function_entries section. Add an additional parameter to the
command line option that allows one to specify a different default
section name for the records, and an identical parameter to the function
attribute that allows one to override the section used.
The main use case for this change is the Linux kernel using prefix NOPs
for ftrace, and thus depending on__patchable_function_entries to locate
traceable functions. Functions that are not traceable currently disable
entry NOPs using the function attribute, but this creates a
compatibility issue with -fsanitize=kcfi, which expects all indirectly
callable functions to have a type hash prefix at the same offset from
the function entry.
Adding a section parameter would allow the kernel to distinguish between
traceable and non-traceable functions by adding entry records to
separate sections while maintaining a stable function prefix layout for
all functions. LKML discussion:
https://lore.kernel.org/lkml/Y1QEzk%2FA41PKLEPe@hirez.programming.kicks-ass.net/
Added:
clang/test/CodeGen/patchable-function-entry-section.c
Modified:
clang/include/clang/Basic/Attr.td
clang/include/clang/Basic/AttrDocs.td
clang/include/clang/Basic/CodeGenOptions.h
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/include/clang/Driver/Options.td
clang/lib/CodeGen/CodeGenFunction.cpp
clang/lib/Driver/ToolChains/Clang.cpp
clang/lib/Sema/SemaDeclAttr.cpp
clang/test/Driver/fpatchable-function-entry.c
clang/test/Sema/patchable-function-entry-attr.c
llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
llvm/lib/IR/Verifier.cpp
llvm/test/CodeGen/X86/patchable-function-entry.ll
llvm/test/Verifier/invalid-patchable-function-entry.ll
Removed:
################################################################################
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 0999d8065e9f5..fd9e686485552 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -936,7 +936,8 @@ def PatchableFunctionEntry
"riscv64", "x86", "x86_64", "ppc", "ppc64"]>> {
let Spellings = [GCC<"patchable_function_entry">];
let Subjects = SubjectList<[Function, ObjCMethod]>;
- let Args = [UnsignedArgument<"Count">, DefaultIntArgument<"Offset", 0>];
+ let Args = [UnsignedArgument<"Count">, DefaultIntArgument<"Offset", 0>,
+ StringArgument<"Section", /* optional */ 1>];
let Documentation = [PatchableFunctionEntryDocs];
}
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index a52ece467ec70..c8b371280e35d 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -6502,10 +6502,12 @@ only N==1 is supported.
def PatchableFunctionEntryDocs : Documentation {
let Category = DocCatFunction;
let Content = [{
-``__attribute__((patchable_function_entry(N,M)))`` is used to generate M NOPs
-before the function entry and N-M NOPs after the function entry. This attribute
-takes precedence over the command line option ``-fpatchable-function-entry=N,M``.
-``M`` defaults to 0 if omitted.
+``__attribute__((patchable_function_entry(N,M,Section)))`` is used to generate M
+NOPs before the function entry and N-M NOPs after the function entry, with a record of
+the entry stored in section ``Section``. This attribute takes precedence over the
+command line option ``-fpatchable-function-entry=N,M,Section``. ``M`` defaults to 0
+if omitted.``Section`` defaults to the ``-fpatchable-function-entry`` section name if
+set, or to ``__patchable_function_entries`` otherwise.
This attribute is only supported on
aarch64/aarch64-be/loongarch32/loongarch64/riscv32/riscv64/i386/x86-64/ppc/ppc64 targets.
diff --git a/clang/include/clang/Basic/CodeGenOptions.h b/clang/include/clang/Basic/CodeGenOptions.h
index c531c656f42b7..e39a73bdb13ac 100644
--- a/clang/include/clang/Basic/CodeGenOptions.h
+++ b/clang/include/clang/Basic/CodeGenOptions.h
@@ -281,6 +281,10 @@ class CodeGenOptions : public CodeGenOptionsBase {
/// -fprofile-generate, and -fcs-profile-generate.
std::string InstrProfileOutput;
+ /// Name of the patchable function entry section with
+ /// -fpatchable-function-entry.
+ std::string PatchableFunctionEntrySection;
+
/// Name of the profile file to use with -fprofile-sample-use.
std::string SampleProfileFile;
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 10568a5ee87fc..3f9ba933582da 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3550,6 +3550,10 @@ def err_conflicting_codeseg_attribute : Error<
def warn_duplicate_codeseg_attribute : Warning<
"duplicate code segment specifiers">, InGroup<Section>;
+def err_attribute_patchable_function_entry_invalid_section
+ : Error<"section argument to 'patchable_function_entry' attribute is not "
+ "valid for this target: %0">;
+
def err_anonymous_property: Error<
"anonymous property is not supported">;
def err_property_is_variably_modified : Error<
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 534631e43d26d..e69b804de63b5 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3759,10 +3759,16 @@ defm pascal_strings : BoolFOption<"pascal-strings",
// Note: This flag has
diff erent semantics in the driver and in -cc1. The driver accepts -fpatchable-function-entry=M,N
// and forwards it to -cc1 as -fpatchable-function-entry=M and -fpatchable-function-entry-offset=N. In -cc1, both flags
// are treated as a single integer.
-def fpatchable_function_entry_EQ : Joined<["-"], "fpatchable-function-entry=">, Group<f_Group>,
- Visibility<[ClangOption, CC1Option]>,
- MetaVarName<"<N,M>">, HelpText<"Generate M NOPs before function entry and N-M NOPs after function entry">,
- MarshallingInfoInt<CodeGenOpts<"PatchableFunctionEntryCount">>;
+def fpatchable_function_entry_EQ
+ : Joined<["-"], "fpatchable-function-entry=">,
+ Group<f_Group>,
+ Visibility<[ClangOption, CC1Option]>,
+ MetaVarName<"<N,M,Section>">,
+ HelpText<"Generate M NOPs before function entry and N-M NOPs after "
+ "function entry. "
+ "If section is specified, use it instead of "
+ "__patchable_function_entries.">,
+ MarshallingInfoInt<CodeGenOpts<"PatchableFunctionEntryCount">>;
def fms_hotpatch : Flag<["-"], "fms-hotpatch">, Group<f_Group>,
Visibility<[ClangOption, CC1Option, CLOption]>,
HelpText<"Ensure that all functions can be hotpatched at runtime">,
@@ -7593,6 +7599,11 @@ def fpatchable_function_entry_offset_EQ
: Joined<["-"], "fpatchable-function-entry-offset=">, MetaVarName<"<M>">,
HelpText<"Generate M NOPs before function entry">,
MarshallingInfoInt<CodeGenOpts<"PatchableFunctionEntryOffset">>;
+def fpatchable_function_entry_section_EQ
+ : Joined<["-"], "fpatchable-function-entry-section=">,
+ MetaVarName<"<Section>">,
+ HelpText<"Use Section instead of __patchable_function_entries">,
+ MarshallingInfoString<CodeGenOpts<"PatchableFunctionEntrySection">>;
def fprofile_instrument_EQ : Joined<["-"], "fprofile-instrument=">,
HelpText<"Enable PGO instrumentation">, Values<"none,clang,llvm,csllvm">,
NormalizedValuesScope<"CodeGenOptions">,
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index dcf523f56bf1e..b55003b9b0bbb 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -965,18 +965,24 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
}
unsigned Count, Offset;
+ StringRef Section;
if (const auto *Attr =
D ? D->getAttr<PatchableFunctionEntryAttr>() : nullptr) {
Count = Attr->getCount();
Offset = Attr->getOffset();
+ Section = Attr->getSection();
} else {
Count = CGM.getCodeGenOpts().PatchableFunctionEntryCount;
Offset = CGM.getCodeGenOpts().PatchableFunctionEntryOffset;
}
+ if (Section.empty())
+ Section = CGM.getCodeGenOpts().PatchableFunctionEntrySection;
if (Count && Offset <= Count) {
Fn->addFnAttr("patchable-function-entry", std::to_string(Count - Offset));
if (Offset)
Fn->addFnAttr("patchable-function-prefix", std::to_string(Offset));
+ if (!Section.empty())
+ Fn->addFnAttr("patchable-function-entry-section", Section);
}
// Instruct that functions for COFF/CodeView targets should start with a
// patchable instruction, but only on x86/x64. Don't forward this to ARM/ARM64
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 5f45cf0865b9e..db4f50fc98f7c 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -6917,8 +6917,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
D.Diag(diag::err_drv_unsupported_opt_for_target)
<< A->getAsString(Args) << TripleStr;
else if (S.consumeInteger(10, Size) ||
- (!S.empty() && (!S.consume_front(",") ||
- S.consumeInteger(10, Offset) || !S.empty())))
+ (!S.empty() &&
+ (!S.consume_front(",") || S.consumeInteger(10, Offset))) ||
+ (!S.empty() && (!S.consume_front(",") || S.empty())))
D.Diag(diag::err_drv_invalid_argument_to_option)
<< S0 << A->getOption().getName();
else if (Size < Offset)
@@ -6927,6 +6928,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
CmdArgs.push_back(Args.MakeArgString(A->getSpelling() + Twine(Size)));
CmdArgs.push_back(Args.MakeArgString(
"-fpatchable-function-entry-offset=" + Twine(Offset)));
+ if (!S.empty())
+ CmdArgs.push_back(
+ Args.MakeArgString("-fpatchable-function-entry-section=" + S));
}
}
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 6cb6f6d105a32..0b844b44930b9 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -5833,9 +5833,10 @@ static void handlePatchableFunctionEntryAttr(Sema &S, Decl *D,
return;
}
uint32_t Count = 0, Offset = 0;
+ StringRef Section;
if (!S.checkUInt32Argument(AL, AL.getArgAsExpr(0), Count, 0, true))
return;
- if (AL.getNumArgs() == 2) {
+ if (AL.getNumArgs() >= 2) {
Expr *Arg = AL.getArgAsExpr(1);
if (!S.checkUInt32Argument(AL, Arg, Offset, 1, true))
return;
@@ -5845,8 +5846,25 @@ static void handlePatchableFunctionEntryAttr(Sema &S, Decl *D,
return;
}
}
- D->addAttr(::new (S.Context)
- PatchableFunctionEntryAttr(S.Context, AL, Count, Offset));
+ if (AL.getNumArgs() == 3) {
+ SourceLocation LiteralLoc;
+ if (!S.checkStringLiteralArgumentAttr(AL, 2, Section, &LiteralLoc))
+ return;
+ if (llvm::Error E = S.isValidSectionSpecifier(Section)) {
+ S.Diag(LiteralLoc,
+ diag::err_attribute_patchable_function_entry_invalid_section)
+ << toString(std::move(E));
+ return;
+ }
+ if (Section.empty()) {
+ S.Diag(LiteralLoc,
+ diag::err_attribute_patchable_function_entry_invalid_section)
+ << "section must not be empty";
+ return;
+ }
+ }
+ D->addAttr(::new (S.Context) PatchableFunctionEntryAttr(S.Context, AL, Count,
+ Offset, Section));
}
static void handleBuiltinAliasAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
diff --git a/clang/test/CodeGen/patchable-function-entry-section.c b/clang/test/CodeGen/patchable-function-entry-section.c
new file mode 100644
index 0000000000000..4c0d2a1baf77b
--- /dev/null
+++ b/clang/test/CodeGen/patchable-function-entry-section.c
@@ -0,0 +1,41 @@
+// RUN: %clang_cc1 -triple aarch64 -emit-llvm %s -o - | FileCheck --check-prefixes=COMMON,NODEFAULT %s
+// RUN: %clang_cc1 -triple x86_64 -emit-llvm %s -fpatchable-function-entry=1 -fpatchable-function-entry-section=__default_section -o - | FileCheck --check-prefixes=COMMON,DEFAULT %s
+
+// COMMON: define{{.*}} void @f0() #0
+__attribute__((patchable_function_entry(0))) void f0(void) {}
+
+// COMMON: define{{.*}} void @f00() #0
+__attribute__((patchable_function_entry(0, 0, "__unused_section"))) void f00(void) {}
+
+// COMMON: define{{.*}} void @f2() #1
+__attribute__((patchable_function_entry(2))) void f2(void) {}
+
+// COMMON: define{{.*}} void @f20() #2
+__attribute__((patchable_function_entry(2, 0, "__attr_section"))) void f20(void) {}
+
+// COMMON: define{{.*}} void @f44() #3
+__attribute__((patchable_function_entry(4, 4))) void f44(void) {}
+
+// COMMON: define{{.*}} void @f52() #4
+__attribute__((patchable_function_entry(5, 2, "__attr_section"))) void f52(void) {}
+
+// OPT: define{{.*}} void @f() #5
+void f(void) {}
+
+/// No need to emit "patchable-function-entry" and thus also "patchable-function-entry-section"
+// COMMON: attributes #0 = { {{.*}}
+// COMMON-NOT: "patchable-function-entry-section"
+
+// NODEFAULT: attributes #1 = { {{.*}} "patchable-function-entry"="2"
+// NODEFAULT-NOT: "patchable-function-entry-section"
+// DEFAULT: attributes #1 = { {{.*}} "patchable-function-entry"="2" "patchable-function-entry-section"="__default_section"
+
+// COMMON: attributes #2 = { {{.*}} "patchable-function-entry"="2" "patchable-function-entry-section"="__attr_section"
+
+// NODEFAULT: attributes #3 = { {{.*}} "patchable-function-entry"="0" "patchable-function-prefix"="4"
+// NODEFAULT-NOT: "patchable-function-entry-section"
+// DEFAULT: attributes #3 = { {{.*}} "patchable-function-entry"="0" "patchable-function-entry-section"="__default_section" "patchable-function-prefix"="4"
+
+// COMMON: attributes #4 = { {{.*}} "patchable-function-entry"="3" "patchable-function-entry-section"="__attr_section" "patchable-function-prefix"="2"
+
+// DEFAULT: attributes #5 = { {{.*}} "patchable-function-entry"="1" "patchable-function-entry-section"="__default_section"
diff --git a/clang/test/Driver/fpatchable-function-entry.c b/clang/test/Driver/fpatchable-function-entry.c
index 5f07ca99a69de..43be6c5a47e47 100644
--- a/clang/test/Driver/fpatchable-function-entry.c
+++ b/clang/test/Driver/fpatchable-function-entry.c
@@ -15,6 +15,9 @@
// RUN: %clang --target=aarch64 -fsyntax-only %s -fpatchable-function-entry=2,1 -c -### 2>&1 | FileCheck --check-prefix=21 %s
// 21: "-fpatchable-function-entry=2" "-fpatchable-function-entry-offset=1"
+// RUN: %clang --target=aarch64 -fsyntax-only %s -fpatchable-function-entry=1,1,__section_name -c -### 2>&1 | FileCheck --check-prefix=SECTION %s
+// SECTION: "-fpatchable-function-entry=1" "-fpatchable-function-entry-offset=1" "-fpatchable-function-entry-section=__section_name"
+
// RUN: not %clang --target=powerpc64-ibm-aix-xcoff -fsyntax-only %s -fpatchable-function-entry=1 2>&1 | FileCheck --check-prefix=AIX64 %s
// AIX64: error: unsupported option '-fpatchable-function-entry=1' for target 'powerpc64-ibm-aix-xcoff'
diff --git a/clang/test/Sema/patchable-function-entry-attr.c b/clang/test/Sema/patchable-function-entry-attr.c
index 89e4380c36230..f453e134ab625 100644
--- a/clang/test/Sema/patchable-function-entry-attr.c
+++ b/clang/test/Sema/patchable-function-entry-attr.c
@@ -3,9 +3,15 @@
// expected-error at +1 {{'patchable_function_entry' attribute takes at least 1 argument}}
__attribute__((patchable_function_entry)) void f(void);
-// expected-error at +1 {{'patchable_function_entry' attribute takes no more than 2 arguments}}
+// expected-error at +1 {{expected string literal as argument of 'patchable_function_entry' attribute}}
__attribute__((patchable_function_entry(0, 0, 0))) void f(void);
+// expected-error at +1 {{section argument to 'patchable_function_entry' attribute is not valid for this target}}
+__attribute__((patchable_function_entry(0, 0, ""))) void f(void);
+
+// expected-error at +1 {{'patchable_function_entry' attribute takes no more than 3 arguments}}
+__attribute__((patchable_function_entry(0, 0, "__section", 0))) void f(void);
+
// expected-error at +1 {{'patchable_function_entry' attribute requires a non-negative integral compile time constant expression}}
__attribute__((patchable_function_entry(-1))) void f(void);
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 2d76aa5488333..0deaf94502b11 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -4602,7 +4602,13 @@ void AsmPrinter::emitPatchableFunctionEntries() {
if (TM.getTargetTriple().isOSBinFormatELF()) {
auto Flags = ELF::SHF_WRITE | ELF::SHF_ALLOC;
const MCSymbolELF *LinkedToSym = nullptr;
- StringRef GroupName;
+ StringRef GroupName, SectionName;
+
+ if (F.hasFnAttribute("patchable-function-entry-section"))
+ SectionName = F.getFnAttribute("patchable-function-entry-section")
+ .getValueAsString();
+ if (SectionName.empty())
+ SectionName = "__patchable_function_entries";
// GNU as < 2.35 did not support section flag 'o'. GNU ld < 2.36 did not
// support mixed SHF_LINK_ORDER and non-SHF_LINK_ORDER sections.
@@ -4615,8 +4621,8 @@ void AsmPrinter::emitPatchableFunctionEntries() {
LinkedToSym = cast<MCSymbolELF>(CurrentFnSym);
}
OutStreamer->switchSection(OutContext.getELFSection(
- "__patchable_function_entries", ELF::SHT_PROGBITS, Flags, 0, GroupName,
- F.hasComdat(), MCSection::NonUniqueID, LinkedToSym));
+ SectionName, ELF::SHT_PROGBITS, Flags, 0, GroupName, F.hasComdat(),
+ MCSection::NonUniqueID, LinkedToSym));
emitAlignment(Align(PointerSize));
OutStreamer->emitSymbolValue(CurrentPatchableFunctionEntrySym, PointerSize);
}
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 95dd3aa86b428..7c6cd414554e3 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -2409,6 +2409,11 @@ void Verifier::verifyFunctionAttrs(FunctionType *FT, AttributeList Attrs,
checkUnsignedBaseTenFuncAttr(Attrs, "patchable-function-prefix", V);
checkUnsignedBaseTenFuncAttr(Attrs, "patchable-function-entry", V);
+ if (Attrs.hasFnAttr("patchable-function-entry-section"))
+ Check(!Attrs.getFnAttr("patchable-function-entry-section")
+ .getValueAsString()
+ .empty(),
+ "\"patchable-function-entry-section\" must not be empty");
checkUnsignedBaseTenFuncAttr(Attrs, "warn-stack-size", V);
if (auto A = Attrs.getFnAttr("sign-return-address"); A.isValid()) {
diff --git a/llvm/test/CodeGen/X86/patchable-function-entry.ll b/llvm/test/CodeGen/X86/patchable-function-entry.ll
index 54ecd8b1e5daf..d6dfe00c74991 100644
--- a/llvm/test/CodeGen/X86/patchable-function-entry.ll
+++ b/llvm/test/CodeGen/X86/patchable-function-entry.ll
@@ -98,3 +98,16 @@ define void @f3_2() "patchable-function-entry"="1" "patchable-function-prefix"="
%frame = alloca i8, i32 16
ret void
}
+
+define void @s1() "patchable-function-entry"="1" "patchable-function-entry-section"=".entries" {
+; CHECK-LABEL: s1:
+; CHECK-NEXT: .Lfunc_begin6:
+; CHECK: nop
+; CHECK-NEXT: ret
+; CHECK: .section .entries,"awo", at progbits,s1{{$}}
+; X86: .p2align 2
+; X86-NEXT: .long .Lfunc_begin6
+; X64: .p2align 3
+; X64-NEXT: .quad .Lfunc_begin6
+ ret void
+}
diff --git a/llvm/test/Verifier/invalid-patchable-function-entry.ll b/llvm/test/Verifier/invalid-patchable-function-entry.ll
index e74037a28abe6..a86cd89ae7ef9 100644
--- a/llvm/test/Verifier/invalid-patchable-function-entry.ll
+++ b/llvm/test/Verifier/invalid-patchable-function-entry.ll
@@ -19,3 +19,7 @@ define void @g() "patchable-function-prefix" { ret void }
define void @ga() "patchable-function-prefix"="a" { ret void }
define void @g_1() "patchable-function-prefix"="-1" { ret void }
define void @g3comma() "patchable-function-prefix"="3," { ret void }
+
+; CHECK: "patchable-function-entry-section" must not be empty
+
+define void @s1() "patchable-function-entry"="1" "patchable-function-entry-section" { ret void }
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