[llvm] [LLVM][AArch64] Build attributes: Support switching to a defined subsection by name only (PR #154159)
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Mon Aug 18 10:02:59 PDT 2025
https://github.com/sivan-shani created https://github.com/llvm/llvm-project/pull/154159
The AArch64 build attribute specification now allows switching to an already-defined subsection using its name alone, without repeating the optionality and type parameters.
This patch updates the parser to support that behavior.
Spec reference: https://github.com/ARM-software/abi-aa/pull/230/files
>From ad6bc39fe3425baead1f36722cd7b7e572e2da23 Mon Sep 17 00:00:00 2001
From: Sivan Shani <sivan.shani at arm.com>
Date: Mon, 18 Aug 2025 17:48:07 +0100
Subject: [PATCH] [LLVM][AArch64] Build attributes: Support switching to a
defined subsection by name only
The AArch64 build attribute specification now allows switching to an already-defined subsection
using its name alone, without repeating the optionality and type parameters.
This patch updates the parser to support that behavior.
Spec reference: https://github.com/ARM-software/abi-aa/pull/230/files
---
.../AArch64/AsmParser/AArch64AsmParser.cpp | 28 +++++++++++--
.../MCTargetDesc/AArch64TargetStreamer.cpp | 19 ++++++---
.../MCTargetDesc/AArch64TargetStreamer.h | 1 +
...ributes-asm-aeabi-switch_using_name_only.s | 39 +++++++++++++++++++
4 files changed, 77 insertions(+), 10 deletions(-)
create mode 100644 llvm/test/MC/AArch64/build-attributes-asm-aeabi-switch_using_name_only.s
diff --git a/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp b/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
index 1ca61f5c6b349..82d295d8d9c30 100644
--- a/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
+++ b/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
@@ -7909,9 +7909,11 @@ bool AArch64AsmParser::parseDirectiveSEHSavePReg(SMLoc L) {
}
bool AArch64AsmParser::parseDirectiveAeabiSubSectionHeader(SMLoc L) {
- // Expecting 3 AsmToken::Identifier after '.aeabi_subsection', a name and 2
- // parameters, e.g.: .aeabi_subsection (1)aeabi_feature_and_bits, (2)optional,
- // (3)uleb128 separated by 2 commas.
+ // Handle parsing of .aeabi_subsection directives
+ // - On first declaration of a subsection, expect exactly three identifiers
+ // after `.aeabi_subsection`: the subsection name and two parameters.
+ // - When switching to an existing subsection, it is valid to provide only
+ // the subsection name, or the name together with the two parameters.
MCAsmParser &Parser = getParser();
// Consume the name (subsection name)
@@ -7925,7 +7927,25 @@ bool AArch64AsmParser::parseDirectiveAeabiSubSectionHeader(SMLoc L) {
return true;
}
Parser.Lex();
- // consume a comma
+
+ // Check whether only the subsection name was provided.
+ // If so, the user is trying to switch to a subsection that should have been
+ // declared before.
+ if (Parser.getTok().is(llvm::AsmToken::EndOfStatement)) {
+ // If subsection does not exists, report error.
+ if (!getTargetStreamer().hasSubsection(SubsectionName)) {
+ Error(Parser.getTok().getLoc(),
+ "Could not switch to subsection '" + SubsectionName +
+ "' using subsection name, subsection has not been defined");
+ return true;
+ }
+ // Since subsection exists, no need to call
+ // AArch64TargetStreamer::emitAttributesSubsection(...)
+ getTargetStreamer().activateAttributesSubsection(SubsectionName);
+ return false;
+ }
+
+ // Otherwise, expecting 2 more parameters: consume a comma
// parseComma() return *false* on success, and call Lex(), no need to call
// Lex() again.
if (Parser.parseComma()) {
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.cpp
index d742b282b617c..6d504a8bce3ea 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.cpp
@@ -153,17 +153,24 @@ MCTargetStreamer *llvm::createAArch64NullTargetStreamer(MCStreamer &S) {
return new AArch64TargetStreamer(S);
}
+bool AArch64TargetStreamer::hasSubsection(StringRef SubSectionName) {
+ for (MCELFStreamer::AttributeSubSection &SubSection : AttributeSubSections) {
+ if (SubSection.VendorName == SubSectionName)
+ return true;
+ }
+ return false;
+}
+
void AArch64TargetStreamer::emitAttributesSubsection(
StringRef VendorName, AArch64BuildAttributes::SubsectionOptional IsOptional,
AArch64BuildAttributes::SubsectionType ParameterType) {
- // If exists, return.
- for (MCELFStreamer::AttributeSubSection &SubSection : AttributeSubSections) {
- if (VendorName == SubSection.VendorName) {
- activateAttributesSubsection(VendorName);
- return;
- }
+ // If exists, activate and return.
+ if (hasSubsection(VendorName)) {
+ activateAttributesSubsection(VendorName);
+ return;
}
+
// else, add the subsection
MCELFStreamer::AttributeSubSection AttSubSection;
AttSubSection.VendorName = VendorName;
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.h b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.h
index f840058cd759e..4ad80baab9a3a 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.h
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.h
@@ -117,6 +117,7 @@ class AArch64TargetStreamer : public MCTargetStreamer {
MCELFStreamer::AttributeSubSection &AttSubSection);
SmallVector<MCELFStreamer::AttributeSubSection, 64> AttributeSubSections;
+ bool hasSubsection(StringRef SubSectionName);
private:
std::unique_ptr<AssemblerConstantPools> ConstantPools;
diff --git a/llvm/test/MC/AArch64/build-attributes-asm-aeabi-switch_using_name_only.s b/llvm/test/MC/AArch64/build-attributes-asm-aeabi-switch_using_name_only.s
new file mode 100644
index 0000000000000..cf89d3e376f3b
--- /dev/null
+++ b/llvm/test/MC/AArch64/build-attributes-asm-aeabi-switch_using_name_only.s
@@ -0,0 +1,39 @@
+// RUN: llvm-mc -triple=aarch64 %s -o - | FileCheck %s --check-prefix=ASM
+// RUN: llvm-mc -triple=aarch64 -filetype=obj %s -o - | llvm-readelf --hex-dump=.ARM.attributes - | FileCheck %s --check-prefix=ELF
+
+// ASM: .aeabi_subsection aeabi_pauthabi, required, uleb128
+// ASM: .aeabi_subsection aeabi_feature_and_bits, optional, uleb128
+// ASM: .aeabi_attribute 0, 1 // Tag_Feature_BTI
+// ASM: .aeabi_attribute 2, 1 // Tag_PAuth_Schema
+// ASM: .aeabi_attribute 1, 1 // Tag_PAuth_Platform
+// ASM: .aeabi_attribute 2, 1 // Tag_Feature_GCS
+// ASM: .aeabi_attribute 1, 0 // Tag_Feature_PAC
+// ASM: .aeabi_attribute 7, 1
+// ASM: .aeabi_attribute 7, 0
+
+// ELF: Hex dump of section '.ARM.attributes':
+// ELF-NEXT: 0x00000000 411b0000 00616561 62695f70 61757468 A....aeabi_pauth
+// ELF-NEXT: 0x00000010 61626900 00000201 01010700 25000000 abi.........%...
+// ELF-NEXT: 0x00000020 61656162 695f6665 61747572 655f616e aeabi_feature_an
+// ELF-NEXT: 0x00000030 645f6269 74730001 00000102 01010007 d_bits..........
+// ELF-NEXT: 0x00000040 01
+
+
+.aeabi_subsection aeabi_pauthabi, required, uleb128
+.aeabi_subsection aeabi_feature_and_bits, optional, uleb128
+.aeabi_attribute Tag_Feature_BTI, 1
+.aeabi_subsection aeabi_feature_and_bits
+.aeabi_subsection aeabi_pauthabi
+.aeabi_attribute Tag_PAuth_Schema, 1
+.aeabi_subsection aeabi_pauthabi
+.aeabi_attribute Tag_PAuth_Platform, 1
+.aeabi_subsection aeabi_pauthabi
+.aeabi_subsection aeabi_feature_and_bits
+.aeabi_attribute Tag_Feature_GCS, 1
+.aeabi_subsection aeabi_pauthabi
+.aeabi_subsection aeabi_feature_and_bits
+.aeabi_attribute Tag_Feature_PAC, 0
+.aeabi_subsection aeabi_feature_and_bits
+.aeabi_attribute 7, 1
+.aeabi_subsection aeabi_pauthabi
+.aeabi_attribute 7, 0
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