tpm_pcr_extend(9)

💅 tpm_pcr_extend(9) — the Kernel API Manual, bestie edition 🎀

okay so welcome to tpm_pcr_extend(9), straight out of the Kernel API Manual, and no because we are literally about to extend a PCR value in the SHA1 bank and it's giving very much main character energy ✨

🌸 NAME 🌸

tpm_pcr_extend — extend a PCR value in SHA1 bank. periodt. that's the whole vibe 💖

🦋 SYNOPSIS 🦋

int tpm_pcr_extend (struct tpm_chip *chip , u32 pcr_idx , struct
tpm_digest *digests );

like, look at her. she returns an int, she takes a chip, a pcr_idx, and some digests. iconic. 🔥

🎀 ARGUMENTS 🎀

• chip — a struct tpm_chip instance, or NULL for the default chip. yes bestie, NULL is valid here and it just means "give me the default one" 🫶
• pcr_idx — the PCR to be retrieved. that's the one you're pointing at 💅
• digests — array of tpm_digest structures used to extend PCRs. plural, babes, it's an array 🌈

⭐ NOTE ⭐

okay this is the part where you actually have to pay attention, no cap:

callers must pass a digest for every allocated PCR bank, in the same order of the banks in chip->allocated_banks.

so like... one digest per allocated bank, same order as chip->allocated_banks. don't get cute with the ordering. the kernel will simply not be slayed by that 😭

💜 RETURN 💜

same as with tpm_transmit_cmd. so whatever that gives you back is what you get back here, fr fr. ⭐

🧚 SEE ALSO 🧚

• Kernel file ./drivers/char/tpm/tpm-interface.c
• tpm_calc_ordinal_duration(9)
• tpm_transmit(9)
• tpm_transmit_cmd(9)
• tpm_is_tpm2(9)
• tpm_pcr_read(9)
• tpm_get_random(9)

like a little reading list, go off 👑

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and that's the page! huge shoutout to ./drivers/char/tpm for being the source/version home of all this, dated October 2026 — mwah, see you in the group chat, bestie 💖🦋💅