MT: Improved multithreading support.

[ This is ancient code, but the bug is straight forward -- dan ]

Hello Ralf Baechle,

The patch 41c594ab65fc: "[MIPS] MT: Improved multithreading support." from Apr 5, 2006, leads to the following static checker warning:

	arch/mips/kernel/smp-mt.c:168 vsmp_boot_secondary()
	warn: potential pointer math issue

arch/mips/kernel/smp-mt.c
142 static int vsmp_boot_secondary(int cpu, struct task_struct *idle) 143 {

   144          struct thread_info *gp = task_thread_info(idle);
                ^^^^^^^^^^^^^^^^^^^^^^

gp is a thread_info struct pointer.

145 dvpe();
146 set_c0_mvpcontrol(MVPCONTROL_VPC);
147
148 settc(cpu);
149
150 /* restart */
151 write_tc_c0_tcrestart((unsigned long)&smp_bootstrap);
152
153 /* enable the tc this vpe/cpu will be running */
154 write_tc_c0_tcstatus((read_tc_c0_tcstatus() & ~TCSTATUS_IXMT) | TCSTATUS_A);
155
156 write_tc_c0_tchalt(0);
157
158 /* enable the VPE */
159 write_vpe_c0_vpeconf0(read_vpe_c0_vpeconf0() | VPECONF0_VPA);
160
161 /* stack pointer */
162 write_tc_gpr_sp( __KSTK_TOS(idle));
163
164 /* global pointer */
165 write_tc_gpr_gp((unsigned long)gp);
166
167 flush_icache_range((unsigned long)gp,

   168                             (unsigned long)(gp + sizeof(struct thread_info)));
                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This should almost certainly be "gp + 1" because of pointer math.

   169  
   170          /* finally out of configuration and into chaos */
   171          clear_c0_mvpcontrol(MVPCONTROL_VPC);
   172  
   173          evpe(EVPE_ENABLE);
   174  
   175          return 0;
   176  }

regards,
dan carpenter