Syntax

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__attribute__((attribute-list))

attribute-list is a comma-separated list of attributes.

Common Attributes

packed

Removes default structure padding and minimizes alignment gaps.

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struct __attribute__((packed)) packed_str {
    uint8_t x;
    uint16_t y;
};

Use with care: unaligned access can reduce performance or cause faults on some architectures.

aligned(n)

Forces object alignment to n bytes.

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int buf[16] __attribute__((aligned(64)));

section("name")

Places variable/function into a custom linker section.

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const char fw_ver[] __attribute__((section(".fwinfo"))) = "1.0.0";

unused

Suppresses unused warnings.

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static void helper(void) __attribute__((unused));

weak

Declares weak symbol (can be overridden by strong definition).

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void board_init(void) __attribute__((weak));

noreturn

Marks function that never returns.

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void fatal_error(void) __attribute__((noreturn));

Notes

• __attribute__ is compiler-specific (GCC/Clang compatible in many cases).
• Prefer macros for portability when targeting multiple compilers.