Hi; Coverity points out a possible issue in booke206_get_tlbm() (this is CID 1421942):
static inline ppcmas_tlb_t *booke206_get_tlbm(CPUPPCState *env, const int tlbn, target_ulong ea, int way) { int r; uint32_t ways = booke206_tlb_ways(env, tlbn); int ways_bits = ctz32(ways); int tlb_bits = ctz32(booke206_tlb_size(env, tlbn)); int i; way &= ways - 1; ea >>= MAS2_EPN_SHIFT; ea &= (1 << (tlb_bits - ways_bits)) - 1; r = (ea << ways_bits) | way; Here if booke206_tlb_ways() returns zero, then ways_bits() will be 32 and the shift left 'ea << ways_bits' is undefined behaviour. My first assumption was that booke206_tlb_ways() is not supposed to ever return 0 (it's looking at what I think are read-only system registers, and it doesn't make much sense to have a zero-way TLB). So I tried adding an assert: diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h index 88d94495554..aedb6bcb265 100644 --- a/target/ppc/cpu.h +++ b/target/ppc/cpu.h @@ -2403,6 +2403,7 @@ static inline int booke206_tlb_ways(CPUPPCState *env, int tlbn) { uint32_t tlbncfg = env->spr[SPR_BOOKE_TLB0CFG + tlbn]; int r = tlbncfg >> TLBnCFG_ASSOC_SHIFT; + assert(r > 0); return r; } However, this isn't right, because it causes one of the check-acceptance tests to fail, with this backtrace: #3 0x00007ffff074d412 in __GI___assert_fail (assertion=0x5555560a0d7d "r > 0", file=0x5555560a0d40 "/home/petmay01/linaro/qemu-from-laptop/qemu/target/ppc/cpu.h", line=2406, function=0x5555560a1720 <__PRETTY_FUNCTION__.20811> "booke206_tlb_ways") at assert.c:101 #4 0x0000555555a9939b in booke206_tlb_ways (env=0x555556e52a30, tlbn=2) at /home/petmay01/linaro/qemu-from-laptop/qemu/target/ppc/cpu.h:2406 #5 0x0000555555a9b3ac in mmubooke206_get_physical_address (env=0x555556e52a30, ctx=0x7fffd77008a0, address=9223380835095282947, rw=0, access_type=0, mmu_idx=1) at /home/petmay01/linaro/qemu-from-laptop/qemu/target/ppc/mmu_helper.c:1093 #6 0x0000555555a9c25d in get_physical_address_wtlb (env=0x555556e52a30, ctx=0x7fffd77008a0, eaddr=9223380835095282947, rw=0, access_type=0, mmu_idx=1) at /home/petmay01/linaro/qemu-from-laptop/qemu/target/ppc/mmu_helper.c:1455 #7 0x0000555555a9c82b in cpu_ppc_handle_mmu_fault (env=0x555556e52a30, address=9223380835095282947, rw=0, mmu_idx=1) at /home/petmay01/linaro/qemu-from-laptop/qemu/target/ppc/mmu_helper.c:1597 #8 0x0000555555a9f975 in ppc_cpu_tlb_fill (cs=0x555556e49560, addr=9223380835095282947, size=1, access_type=MMU_DATA_LOAD, mmu_idx=1, probe=false, retaddr=140735610345781) at /home/petmay01/linaro/qemu-from-laptop/qemu/target/ppc/mmu_helper.c:3053 #9 0x00005555558e1422 in tlb_fill (cpu=0x555556e49560, addr=9223380835095282947, size=1, access_type=MMU_DATA_LOAD, mmu_idx=1, retaddr=140735610345781) at /home/petmay01/linaro/qemu-from-laptop/qemu/accel/tcg/cputlb.c:1017 #10 0x00005555558e279b in load_helper (env=0x555556e52a30, addr=9223380835095282947, oi=1, retaddr=140735610345781, op=MO_8, code_read=false, full_load=0x5555558e2b3a <full_ldub_mmu>) at /home/petmay01/linaro/qemu-from-laptop/qemu/accel/tcg/cputlb.c:1534 #11 0x00005555558e2b80 in full_ldub_mmu (env=0x555556e52a30, addr=9223380835095282947, oi=1, retaddr=140735610345781) at /home/petmay01/linaro/qemu-from-laptop/qemu/accel/tcg/cputlb.c:1624 #12 0x00005555558e2bb4 in helper_ret_ldub_mmu (env=0x555556e52a30, addr=9223380835095282947, oi=1, retaddr=140735610345781) at /home/petmay01/linaro/qemu-from-laptop/qemu/accel/tcg/cputlb.c:1630 #13 0x00007fff900fd9c6 in code_gen_buffer () #14 0x00005555558f9915 in cpu_tb_exec (cpu=0x555556e49560, itb=0x7fff900fd780 <code_gen_buffer+1038163>) at /home/petmay01/linaro/qemu-from-laptop/qemu/accel/tcg/cpu-exec.c:172 #15 0x00005555558fa732 in cpu_loop_exec_tb (cpu=0x555556e49560, tb=0x7fff900fd780 <code_gen_buffer+1038163>, last_tb=0x7fffd7701078, tb_exit=0x7fffd7701070) at /home/petmay01/linaro/qemu-from-laptop/qemu/accel/tcg/cpu-exec.c:619 #16 0x00005555558faa4c in cpu_exec (cpu=0x555556e49560) at /home/petmay01/linaro/qemu-from-laptop/qemu/accel/tcg/cpu-exec.c:732 #17 0x00005555558bcf29 in tcg_cpu_exec (cpu=0x555556e49560) at /home/petmay01/linaro/qemu-from-laptop/qemu/cpus.c:1405 #18 0x00005555558bd77f in qemu_tcg_cpu_thread_fn (arg=0x555556e49560) at /home/petmay01/linaro/qemu-from-laptop/qemu/cpus.c:1713 #19 0x0000555555f2ff3f in qemu_thread_start (args=0x555556e8dd10) at /home/petmay01/linaro/qemu-from-laptop/qemu/util/qemu-thread-posix.c:519 #20 0x00007ffff0b156db in start_thread (arg=0x7fffd7704700) at pthread_create.c:463 #21 0x00007ffff083e88f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95 So under what circumstances can booke206_tlb_ways() validly return 0? Should booke206_get_tlbm() cope with a zero return, or can it assert() that it will never call booke206_tlb_ways() in a way that will cause one? thanks -- PMM