Support parsing and enforcing struct alignment and packed attributes in C header import

• Type: feature
• Status: done
• Track: C (C frontend)
• Owner: —
• Opened: 2026-06-28

Motivation

Currently, the C lexer (compiler/clexer.inc) extracts structural layout attribute modifiers such as __attribute__((packed)) and __attribute__((aligned)) and sets simple binary flags CAttrPacked and CAttrAligned. However:

1. The compiler does not parse the exact alignment values (such as aligned(16) or aligned(32)).
2. It does not apply these modifiers during layout calculations for structures whose fields are read or written directly in Pascal.
3. This creates a risk of structural field drift and memory corruption when interoping with C structures that have custom byte alignments or are packed.

Scope

1. Attribute Value Parsing:
   • Update compiler/clexer.inc to extract the alignment byte boundary integer $N$ from aligned(N).
   • Store $N$ in the parsed symbol metadata or structural definition in compiler/symtab.inc.
2. Structure Layout Enforcer:
   • Update structure layout calculations (compiler/parser.inc or related struct offset generators) to respect packed (offset alignment = 1) and aligned(N) (pad fields or struct size to multiples of $N$).
   • Ensure these alignments match the host platform's C compiler layout conventions.

Acceptance

• A structure defined with __attribute__((packed)) or __attribute__((aligned(16))) has identical field offsets and total size in Pascal and C.
• Tests (e.g. test/test_c_packed_aligned.pas) verify that field offsets and total sizes match the compiled C counterparts.

Log

• 2026-06-28 — ticket opened.
• 2026-06-29 — implemented aligned(N) value capture in the C lexer and applied packed / aligned(N) in C struct layout. test/test_c_packed_aligned.pas now verifies concrete field offsets and sizes for normal, packed, field-aligned, and type-aligned C structs. Self-host fixedpoint passes via make compiler/pascal26.