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Wed, 16 Apr 2025 09:45:00 +0000 (UTC) Date: Wed, 16 Apr 2025 17:44:50 +0800 Subject: [PATCH RFC v2 4/5] tpm: add __always_inline for tpm_is_hwrng_enabled Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20250416-noautoinline-v2-4-e69a2717530f@uniontech.com> References: <20250416-noautoinline-v2-0-e69a2717530f@uniontech.com> In-Reply-To: <20250416-noautoinline-v2-0-e69a2717530f@uniontech.com> To: Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg , Andrew Morton , Yishai Hadas , Jason Gunthorpe , Shameer Kolothum , Kevin Tian , Alex Williamson , Peter Huewe , Jarkko Sakkinen , Masahiro Yamada , Nathan Chancellor , Nicolas Schier , Nick Desaulniers , Bill Wendling , Justin Stitt Cc: linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, virtualization@lists.linux.dev, linux-integrity@vger.kernel.org, linux-kbuild@vger.kernel.org, llvm@lists.linux.dev, Winston Wen , Chen Linxuan , Changbin Du X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; 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a=openpgp; fpr=D818ACDD385CAE92D4BAC01A6269794D24791D21 X-Endpoint-Received: by B4 Relay for chenlinxuan@uniontech.com/default with auth_id=380 X-Original-From: Chen Linxuan Reply-To: chenlinxuan@uniontech.com From: Chen Linxuan From: Winston Wen Presume that kernel is compiled for x86_64 with gcc version 13.3.0: make defconfig ./scripts/kconfig/merge_config.sh .config <( echo CONFIG_TCG_TPM=y echo CONFIG_HW_RANDOM=m ) make KCFLAGS="-fno-inline-small-functions -fno-inline-functions-called-once" This results a link error: ld: vmlinux.o: in function `tpm_add_hwrng': tpm-chip.c:(.text+0x6c5924): undefined reference to `hwrng_register' ld: vmlinux.o: in function `tpm_chip_unregister': (.text+0x6c5bc9): undefined reference to `hwrng_unregister' ld: vmlinux.o: in function `tpm_chip_register': (.text+0x6c5c9b): undefined reference to `hwrng_unregister' With `CONFIG_TCG_TPM=y` and `CONFIG_HW_RANDOM=m`, the functions `tpm_add_hwrng`, `tpm_chip_unregister`, and `tpm_chip_register` are compiled into `vmlinux.o` and reference the symbols `hwrng_register` and `hwrng_unregister`. These symbols, however, are compiled into `rng-core.ko`, which results in the linking error. I am not sure but I think this weird linking error only arises when auto inlining is disabled because of some dead code elimination. `CONFIG_TCG_TPM=y` and `CONFIG_HW_RANDOM=m` set `CONFIG_HW_RANDOM_TPM=n`. This causes the function `tpm_is_hwrng_enabled` to always return `false`, as shown below: static bool tpm_is_hwrng_enabled(struct tpm_chip *chip) { if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM)) return false; if (tpm_is_firmware_upgrade(chip)) return false; if (chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED) return false; return true; } When `tpm_is_hwrng_enabled` is inlined, dead code elimination optimizations are applied and the reference to the `hwrng_*` functions will been removed. For instance, in the `tpm_chip_unregister` function: void tpm_chip_unregister(struct tpm_chip *chip) { #ifdef CONFIG_TCG_TPM2_HMAC int rc; rc = tpm_try_get_ops(chip); if (!rc) { tpm2_end_auth_session(chip); tpm_put_ops(chip); } #endif tpm_del_legacy_sysfs(chip); if (tpm_is_hwrng_enabled(chip)) hwrng_unregister(&chip->hwrng); tpm_bios_log_teardown(chip); if (chip->flags & TPM_CHIP_FLAG_TPM2 && !tpm_is_firmware_upgrade(chip)) tpm_devs_remove(chip); tpm_del_char_device(chip); } When `tpm_is_hwrng_enabled` is inlined and always returns `false`, the call to `hwrng_unregister` is effectively part of a `if (false)` block, which I guess that will be then optimized out. However, when the `-fno-inline-small-functions` and `-fno-inline-functions-called-once` flags are used, tpm_is_hwrng_enabled is not inline. And this optimization some how cannot occur, leading to the undefined reference errors during linking. Adding the `__always_inline` attribute ensures that `tpm_is_hwrng_enabled` is inlined regardless of the compiler flags. This allows the dead code elimination to proceed as expected, resolving the linking issue. Co-developed-by: Chen Linxuan Signed-off-by: Chen Linxuan Signed-off-by: Winston Wen Reviewed-by: Jarkko Sakkinen --- drivers/char/tpm/tpm-chip.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c index e25daf2396d37bcaeae8a96267764df0861ad1be..48cc74d84247e258a39f2118e03aa10d0cbb066a 100644 --- a/drivers/char/tpm/tpm-chip.c +++ b/drivers/char/tpm/tpm-chip.c @@ -534,7 +534,7 @@ static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait) return tpm_get_random(chip, data, max); } -static bool tpm_is_hwrng_enabled(struct tpm_chip *chip) +static __always_inline bool tpm_is_hwrng_enabled(struct tpm_chip *chip) { if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM)) return false;