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/2464313eef01c5b1edf0eccf57a32cdee01472c7 [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-v1-1-de6c652c3079@kernel.org (local)
---
 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