[lld] [LLD] Add CLASS syntax to SECTIONS (PR #95323)

[Fangrui Song via llvm-commits]

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+# REQUIRES: x86
+
+# RUN: rm -rf %t && split-file %s %t && cd %t
+
+# RUN: llvm-mc -n -filetype=obj -triple=x86_64 matching.s -o matching.o
+
+## CLASS definitions match sections in linker script order. The sections may be
+## placed in a different order. Classes may derive from one another, and class
+## references may be restricted by INPUT_SECTION_FLAGS.
+
+# RUN: ld.lld -T matching.ld matching.o -o matching
+# RUN: llvm-readobj -x .rodata -x .rodata.d matching | FileCheck %s --check-prefix=MATCHING
+
+# MATCHING:      .rodata
+# MATCHING-NEXT: 020301cc 0605
+# MATCHING:      .rodata.d
+# MATCHING-NEXT: 04
+
+
+## An error is reported when a section class has more than one description.
+
+# RUN: not ld.lld -T already-defined.ld matching.o 2>&1 | \
+# RUN:   FileCheck %s --check-prefix=ALREADY-DEFINED --implicit-check-not=error:
+
+# ALREADY-DEFINED: error: already-defined.ld:3: section class 'a' already defined
+
+
+## An error is reported when a filename pattern is missing in a section class
+## description.
+
+# RUN: not ld.lld -T missing-filename-pattern.ld matching.o 2>&1 | \
+# RUN:   FileCheck %s --check-prefix=MISSING-FILENAME-PATTERN --implicit-check-not=error:
+
+# MISSING-FILENAME-PATTERN: error: missing-filename-pattern.ld:2: expected filename pattern
+
+
+## An error is reported when more than one class is mentioned in a reference.
+
+# RUN: not ld.lld -T multiple-class-names.ld matching.o 2>&1 | \
+# RUN:   FileCheck %s --check-prefix=MULTIPLE-CLASS-NAMES --implicit-check-not=error:
+
+# MULTIPLE-CLASS-NAMES: error: multiple-class-names.ld:4: ) expected, but got b
+
+
+## An error is reported when the content of section classes is demanded before
+## its definition is processed.
+
+# RUN: not ld.lld -T referenced-before-defined.ld matching.o 2>&1 | \
+# RUN:   FileCheck %s --check-prefix=REFERENCED-BEFORE-DEFINED
+
+# REFERENCED-BEFORE-DEFINED: error: section class 'a' referenced by '.rodata' before class definition
+
+## An error is reported when an input section is bound to a section class but
+## is not referenced by at least one output section.
+
+# RUN: not ld.lld -T unreferenced.ld matching.o 2>&1 | \
+# RUN:   FileCheck %s --check-prefix=UNREFERENCED
+
+# UNREFERENCED: error: section '.rodata.a' assigned to class 'a' but unreferenced by any output section
+
+
+## An error is reported when one section class references another.
+
+# RUN: not ld.lld -T class-references-class.ld matching.o 2>&1 | \
+# RUN:   FileCheck %s --check-prefix=CLASS-REFERENCES-CLASS --implicit-check-not=error:
+
+# CLASS-REFERENCES-CLASS: error: class-references-class.ld:3: section class 'b' references class 'a'
+
+
+# RUN: llvm-mc -n -filetype=obj -triple=x86_64 spill.s -o spill.o
+
+
+## An input section in a class spills to a later class ref when the region of
+## its first ref would overflow. The spill uses the alignment of the later ref.
+
+# RUN: ld.lld -T spill.ld spill.o -o spill
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MaskRay wrote:

We usually place positive tests first, then negative tests.

https://github.com/llvm/llvm-project/pull/95323