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LINKER_SCRIPT_SUPPORT.md

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Linker Script Support

This page documents which linker script features Wild supports, which are partially implemented, and which are planned for the future. Each feature is marked with one of four statuses: ✅ (supported), 🧪 (partial), 📅 (planned), or ❌ (not planned). A dedicated section at the end lists the features required to link the Linux kernel.

Top-Level Commands

Feature Status Notes
GROUP(files...) ✅
INPUT(files...) ✅
AS_NEEDED(files...) ✅
INCLUDE(file) 📅
OUTPUT_FORMAT(...) ✅ Parsed and ignored
OUTPUT_ARCH(arch) ❌
OUTPUT(filename) ❌
SECTIONS { ... } ✅
ENTRY(symbol) ✅
VERSION { ... } ✅
PROVIDE(sym = expr) ✅
PROVIDE_HIDDEN(sym = expr) ✅
ASSERT(expr, "msg") ✅
MEMORY { ... } 🧪 Region parsing supported; attribute flags and >region placement not yet implemented
REGION_ALIAS(alias, region) ❌
SEARCH_DIR(path) ❌
STARTUP(filename) ❌
TARGET(bfdname) ❌
NOCROSSREFS(sections...) ❌
INSERT [AFTER|BEFORE] section ❌
Top-level symbol assignment (sym = expr) ✅
Compound assignment operators (+=, -=, etc.) ❌

SECTIONS Block

Feature Status Notes
Output section definitions (name : { ... }) ✅
Input section matchers (*(pattern), file(pattern)) ✅
Glob patterns in section and file names ✅
KEEP(...) to prevent garbage collection ✅
PROVIDE(sym = expr) inside sections ✅
PROVIDE_HIDDEN(sym = expr) inside sections ✅
Symbol assignment inside sections (sym = .) 🧪 Only assignment of the location counter (sym = .) is supported; arbitrary expressions on the right-hand side are not
Location counter assignment (. = expr) 🧪 Hex address literals (e.g. . = 0x1000) supported between output sections only; not inside section contents
ALIGN(n) on the location counter (. = ALIGN(n)) ✅
Per-section ALIGN(n) specifier ✅
ASSERT(expr, "msg") inside SECTIONS ✅
OVERLAY { ... } ❌
Output section type specifiers ((NOLOAD), (COPY), etc.) 📅
FILL(value) and =fillexp 📅
AT(addr) load-address specifier on output sections 📅
Numeric address between section name and : (e.g. name 0 : { ... }) 🧪 Only numeric literals are currently supported
SORT_BY_NAME(...), SORT_BY_ALIGNMENT(...), SORT_BY_INIT_PRIORITY(...) 📅
EXCLUDE_FILE(...) inside input section matchers 📅
BYTE(expr), SHORT(expr), LONG(expr), QUAD(expr) output data ❌
SUBALIGN(n) forced input alignment ❌
ONLY_IF_RO / ONLY_IF_RW output section constraints ❌

Expressions and Functions

Feature Status Notes
Arithmetic operators: +, -, *, / ✅
Comparison operators: <, >, <=, >=, ==, != ✅
Bitwise operators: &, |, ^, ~, <<, >> ✅
Logical operators: &&, || ✅
Unary operators: -, !, ~ ✅
Numeric literals: decimal and hexadecimal ✅
Numeric literal K/M suffixes (e.g. 64K, 2M) ✅
Symbol references and location counter (.) ✅
Parenthesised sub-expressions ✅
SIZEOF(section) ✅
ALIGNOF(section) ✅
ADDR(section) ✅
LOADADDR(section) 🧪 Implemented as alias for ADDR (returns VMA); full LMA requires AT(addr) support
ALIGN(expr) ✅
LENGTH(region) ✅
ORIGIN(region) ✅
MIN(a, b) ✅
MAX(a, b) ✅
Ternary operator (condition ? a : b) 📅
DEFINED(sym) 📅
SIZEOF_HEADERS 📅
SEGMENT_START(segment, default) ✅ Supports "text", "data", "bss", "rodata"; returns -Ttext/-Tdata/-Tbss override if provided, otherwise default; unknown segment names always return default

MEMORY Command

The MEMORY command defines named memory regions with an origin address and a length. Wild parses MEMORY blocks including the ORIGIN/org/o and LENGTH/len/l attribute keywords and their expressions. Attribute flags such as (rwx) are not yet parsed. Placement directives that assign an output section to a named region (>region, AT>region) are not yet implemented.

Feature Status Notes
MEMORY { ... } block parsing ✅
Region name ✅
ORIGIN/org/o attribute ✅
LENGTH/len/l attribute ✅
Attribute flags ((rwx), (rx), etc.) 📅
>region output section placement 📅
AT>region load-region placement 📅

Linux Kernel Requirements

The Linux kernel's build system uses a rich set of linker script features across vmlinux.lds and related architecture-specific scripts. Several of these features are not yet fully supported by Wild. The table below lists each such feature along with its current status, so contributors can see at a glance what remains before Wild can link the kernel.

Feature Status Notes
OVERLAY { ... } sections ❌
Output section type specifiers ((NOLOAD), (COPY)) 📅
FILL(value) and =fillexp 📅
AT(addr) load-address specifier on output sections 📅
>region and AT>region memory region placement 📅
SORT_BY_NAME(...), SORT_BY_ALIGNMENT(...), SORT_BY_INIT_PRIORITY(...) 📅
EXCLUDE_FILE(...) inside input section matchers 📅
CONSTRUCTORS command 📅
PHDRS command for explicit program header definition 📅
Ternary operator (condition ? a : b) 📅
DEFINED(sym) function 📅
SIZEOF_HEADERS built-in symbol 📅