check_add_overflow(9)

💖 check_add_overflow(9) — the kernel API manual, but make it make sense

okay so bestie, welcome to the check_add_overflow page of the Kernel API Manual ✨ this one is short, sweet, and honestly kind of iconic. it does exactly one thing and it does it well. let's get into it 🫶

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🌸 NAME

check_add_overflow — calculate addition with overflow checking 💅

like, it adds two things and it also tells you if the addition went sideways. multitasking queen behavior.

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✨ SYNOPSIS

check_add_overflow (a , b , d );

that's it. three little args. no cap. 🎀

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🦋 ARGUMENTS

• a — first addend 🌸 (the first number going into the addition, bestie)
• b — second addend 💖 (the other number, obviously)
• d — pointer to store sum ✨ (not the sum itself! a pointer to where the sum lives. do not come for me about it)

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🔥 DESCRIPTION

Returns true on wrap-around, false otherwise. literally that's the whole personality 💀

and here's the part you cannot skip, so pay attention:

*d holds the results of the attempted addition, regardless of whether wrap-around occurred.

like. even if the addition wrapped around and everything went to chaos, *d still gets written. so don't go thinking "oh it returned true so *d is garbage" — nope, *d is populated either way, and it's on you to check the return value. main character responsibility 🧚

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👑 SEE ALSO

okay this is the part where the whole friend group shows up. all of these live in the kernel file ./include/linux/overflow.h and honestly the roster is giving family reunion 🌈

• wrapping_add(9)
• wrapping_assign_add(9)
• check_sub_overflow(9)
• wrapping_sub(9)
• wrapping_assign_sub(9)
• check_mul_overflow(9)
• wrapping_mul(9)
• check_shl_overflow(9)
• overflows_type(9)
• range_overflows(9)
• range_overflows_t(9)
• range_end_overflows(9)
• range_end_overflows_t(9)
• castable_to_type(9)
• size_mul(9)
• size_add(9)
• size_sub(9)
• array_size(9)
• array3_size(9)
• flex_array_size(9)
• struct_size(9)
• struct_size_t(9)
• struct_offset(9)
• __DEFINE_FLEX(9)
• _DEFINE_FLEX(9)
• DEFINE_RAW_FLEX(9)
• DEFINE_FLEX(9)
• STACK_FLEX_ARRAY_SIZE(9)
• typeof_flex_counter(9)
• overflows_flex_counter_type(9)
• __set_flex_counter(9)

every single one of them, no skips, no cuts, we support the whole squad 💜

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quick vibe check reminder: this is the checking variant. it tells you about the wrap-around. if you just want the wrap-around with no questions asked, that's what the wrapping_* crew is for. iykyk 😌

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and that's the page, bestie 🎀 this came from the ./include/linux corner of the source tree, dated October 2026, and it's filed under check_add_overflow(9) — go forth and check your overflows, you gorgeous little integer wrangler 🦋💅