On Tue, Jul 22, 2025 at 12:11:18PM -0700, Nathan Chancellor wrote:
After a recent change in clang to expose uninitialized warnings from const variables [1], there is a warning in cxacru_heavy_init():
drivers/usb/atm/cxacru.c:1104:6: error: variable 'bp' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized] 1104 | if (instance->modem_type->boot_rom_patch) { | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ drivers/usb/atm/cxacru.c:1113:39: note: uninitialized use occurs here 1113 | cxacru_upload_firmware(instance, fw, bp); | ^~ drivers/usb/atm/cxacru.c:1104:2: note: remove the 'if' if its condition is always true 1104 | if (instance->modem_type->boot_rom_patch) { | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ drivers/usb/atm/cxacru.c:1095:32: note: initialize the variable 'bp' to silence this warning 1095 | const struct firmware *fw, *bp; | ^ | = NULL
While the warning is technically correct that bp is conditionally passed uninitialized to cxacru_upload_firmware(), it is ultimately a false positive warning on the uninitialized use of bp because the same condition that initializes bp, instance->modem_type->boot_rom_patch, is the same one that gates the use of bp within cxacru_upload_firmware(). As this warning occurs in clang's frontend before inlining occurs, it cannot know that these conditions are indentical to avoid the warning.
Manually inline cxacru_upload_firmware() into cxacru_heavy_init(), as that is its only callsite, so that clang can see that bp is initialized and used under the same condition, clearing up the warning without any functional changes to the code (LLVM was already doing this inlining later).
Cc: stable@vger.kernel.org Fixes: 1b0e61465234 ("[PATCH] USB ATM: driver for the Conexant AccessRunner chipset cxacru") Closes: https://github.com/ClangBuiltLinux/linux/issues/2102 Link: https://github.com/llvm/llvm-project/commit/2464313eef01c5b1edf0eccf57a32cde... [1] Signed-off-by: Nathan Chancellor nathan@kernel.org
Changes in v2:
- Rather than initialize bp to NULL, manually inline cxacru_upload_firmware() into cxacru_heavy_init() so that clang can see the matching conditions for bp's initialization and use (based on feedback from Greg).
- Drop accessrunner-general@lists.sourceforge.net, as I got bounces when sending to it unsubscribed.
- Link to v1: https://lore.kernel.org/r/20250715-usb-cxacru-fix-clang-21-uninit-warning-v1...
drivers/usb/atm/cxacru.c | 106 ++++++++++++++++++++++------------------------- 1 file changed, 49 insertions(+), 57 deletions(-)
Sorry for the churn, but hey, it's less code now!
Nice work :)
greg k-h