[bug report] Linux-2.6.12-rc2

[Dan Carpenter <dan.carpenter@linaro.org>]

Hello Alpha Maintainers,

Commit 1da177e4c3f4 ("Linux-2.6.12-rc2") from Apr 16, 2005
(linux-next), leads to the following Smatch static checker warning:

arch/alpha/kernel/err_marvel.c:884 marvel_find_io7_with_error() warn: statement has no effect 'csrs->POx_ERR_SUM.csr'
arch/alpha/kernel/err_marvel.c:892 marvel_find_io7_with_error() warn: statement has no effect 'io7->csrs->PO7_ERROR_SUM.csr'

arch/alpha/kernel/err_marvel.c
    797 static struct ev7_pal_io_subpacket *
    798 marvel_find_io7_with_error(struct ev7_lf_subpackets *lf_subpackets)
    799 {
    800         struct ev7_pal_io_subpacket *io = lf_subpackets->io;
    801         struct io7 *io7;
    802         int i;
    803 
    804         /*
    805          * Caller must provide the packet to fill
    806          */
    807         if (!io)
    808                 return NULL;
    809 
    810         /*
    811          * Fill the subpacket with the console's standard fill pattern
    812          */
    813         memset(io, 0x55, sizeof(*io));
    814 
    815         for (io7 = NULL; NULL != (io7 = marvel_next_io7(io7)); ) {
    816                 unsigned long err_sum = 0;
    817 
    818                 err_sum |= io7->csrs->PO7_ERROR_SUM.csr;
    819                 for (i = 0; i < IO7_NUM_PORTS; i++) {
    820                         if (!io7->ports[i].enabled)
    821                                 continue;
    822                         err_sum |= io7->ports[i].csrs->POx_ERR_SUM.csr;
    823                 }
    824 
    825                 /*
    826                  * Is there at least one error? 
    827                  */
    828                 if (err_sum & (1UL << 63))
    829                         break;
    830         }
    831 
    832         /*
    833          * Did we find an IO7 with an error?
    834          */
    835         if (!io7)
    836                 return NULL;
    837 
    838         /*
    839          * We have an IO7 with an error. 
    840          *
    841          * Fill in the IO subpacket.
    842          */
    843         io->io_asic_rev   = io7->csrs->IO_ASIC_REV.csr;
    844         io->io_sys_rev    = io7->csrs->IO_SYS_REV.csr;
    845         io->io7_uph       = io7->csrs->IO7_UPH.csr;
    846         io->hpi_ctl       = io7->csrs->HPI_CTL.csr;
    847         io->crd_ctl       = io7->csrs->CRD_CTL.csr;
    848         io->hei_ctl       = io7->csrs->HEI_CTL.csr;
    849         io->po7_error_sum = io7->csrs->PO7_ERROR_SUM.csr;
    850         io->po7_uncrr_sym = io7->csrs->PO7_UNCRR_SYM.csr;
    851         io->po7_crrct_sym = io7->csrs->PO7_CRRCT_SYM.csr;
    852         io->po7_ugbge_sym = io7->csrs->PO7_UGBGE_SYM.csr;
    853         io->po7_err_pkt0  = io7->csrs->PO7_ERR_PKT[0].csr;
    854         io->po7_err_pkt1  = io7->csrs->PO7_ERR_PKT[1].csr;
    855         
    856         for (i = 0; i < IO7_NUM_PORTS; i++) {
    857                 io7_ioport_csrs *csrs = io7->ports[i].csrs;
    858 
    859                 if (!io7->ports[i].enabled)
    860                         continue;
    861 
    862                 io->ports[i].pox_err_sum   = csrs->POx_ERR_SUM.csr;
    863                 io->ports[i].pox_tlb_err   = csrs->POx_TLB_ERR.csr;
    864                 io->ports[i].pox_spl_cmplt = csrs->POx_SPL_COMPLT.csr;
    865                 io->ports[i].pox_trans_sum = csrs->POx_TRANS_SUM.csr;
    866                 io->ports[i].pox_first_err = csrs->POx_FIRST_ERR.csr;
    867                 io->ports[i].pox_mult_err  = csrs->POx_MULT_ERR.csr;
    868                 io->ports[i].pox_dm_source = csrs->POx_DM_SOURCE.csr;
    869                 io->ports[i].pox_dm_dest   = csrs->POx_DM_DEST.csr;
    870                 io->ports[i].pox_dm_size   = csrs->POx_DM_SIZE.csr;
    871                 io->ports[i].pox_dm_ctrl   = csrs->POx_DM_CTRL.csr;
    872 
    873                 /*
    874                  * Ack this port's errors, if any. POx_ERR_SUM must be last.
    875                  *
    876                  * Most of the error registers get cleared and unlocked when
    877                  * the associated bits in POx_ERR_SUM are cleared (by writing
    878                  * 1). POx_TLB_ERR is an exception and must be explicitly 
    879                  * cleared.
    880                  */
    881                 csrs->POx_TLB_ERR.csr = io->ports[i].pox_tlb_err;
    882                 csrs->POx_ERR_SUM.csr =        io->ports[i].pox_err_sum;
    883                 mb();
--> 884                 csrs->POx_ERR_SUM.csr;                
                        ^^^^^^^^^^^^^^^^^^^^^^
I occasionally try to run Smatch against code that I can't actually
compile and it found this code from before the git era.  These days
we build with -Wall and so this kind of code doesn't normally compile
on x86 or Arm.  We would get a warning like:

test.c:18:9: warning: statement with no effect [-Wunused-value]
   18 |         x;
      |         ^

So it makes me wonder if this code can actually build?

    885         }
    886 
    887         /*
    888          * Ack any port 7 error(s).
    889          */
    890         io7->csrs->PO7_ERROR_SUM.csr = io->po7_error_sum;
    91         mb();
--> 892         io7->csrs->PO7_ERROR_SUM.csr;
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    893         
    894         /*
    895          * Correct the io7_pid.
    896          */
    897         lf_subpackets->io_pid = io7->pe;
    898 
    899         return io;
    900 }

regards,
dan carpenter