On 11/18/19 8:58 AM, Andrew Jones wrote: > On Sat, Nov 16, 2019 at 12:06:42PM +0100, Richard Henderson wrote: >> Coverity reports, in sve_zcr_get_valid_len, >> >> "Subtract operation overflows on operands >> arm_cpu_vq_map_next_smaller(cpu, start_vq + 1U) and 1U" >> >> First, the aarch32 stub version of arm_cpu_vq_map_next_smaller, >> returning 0, does exactly what Coverity reports. Remove it. >> >> Second, the aarch64 version of arm_cpu_vq_map_next_smaller has >> a set of asserts, but they don't cover the case in question. >> Further, there is a fair amount of extra arithmetic needed to >> convert from the 0-based zcr register, to the 1-base vq form, >> to the 0-based bitmap, and back again. This can be simplified >> by leaving the value in the 0-based form. >> >> Finally, use test_bit to simplify the common case, where the >> length in the zcr registers is in fact a supported length. > > I don't see test_bit() getting used in the changes below.
Argh! It's still uncommitted here in my tree. I guess I forgot the -a on the git commit --append? V3 coming up... r~ > >> >> Reported-by: Coverity (CID 1407217) >> Signed-off-by: Richard Henderson <[email protected]> >> --- >> >> v2: Merge arm_cpu_vq_map_next_smaller into sve_zcr_get_valid_len, >> as suggested by Andrew Jones. >> >> Use test_bit to make the code even more obvious; the >> current_length + 1 thing to let us find current_length in the >> bitmap seemed unnecessarily clever. >> >> --- >> target/arm/cpu.h | 3 --- >> target/arm/cpu64.c | 15 --------------- >> target/arm/helper.c | 8 ++++++-- >> 3 files changed, 6 insertions(+), 20 deletions(-) >> >> diff --git a/target/arm/cpu.h b/target/arm/cpu.h >> index e1a66a2d1c..47d24a5375 100644 >> --- a/target/arm/cpu.h >> +++ b/target/arm/cpu.h >> @@ -185,12 +185,9 @@ typedef struct { >> #ifdef TARGET_AARCH64 >> # define ARM_MAX_VQ 16 >> void arm_cpu_sve_finalize(ARMCPU *cpu, Error **errp); >> -uint32_t arm_cpu_vq_map_next_smaller(ARMCPU *cpu, uint32_t vq); >> #else >> # define ARM_MAX_VQ 1 >> static inline void arm_cpu_sve_finalize(ARMCPU *cpu, Error **errp) { } >> -static inline uint32_t arm_cpu_vq_map_next_smaller(ARMCPU *cpu, uint32_t vq) >> -{ return 0; } >> #endif >> >> typedef struct ARMVectorReg { >> diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c >> index 68baf0482f..a39d6fcea3 100644 >> --- a/target/arm/cpu64.c >> +++ b/target/arm/cpu64.c >> @@ -458,21 +458,6 @@ void arm_cpu_sve_finalize(ARMCPU *cpu, Error **errp) >> cpu->sve_max_vq = max_vq; >> } >> >> -uint32_t arm_cpu_vq_map_next_smaller(ARMCPU *cpu, uint32_t vq) >> -{ >> - uint32_t bitnum; >> - >> - /* >> - * We allow vq == ARM_MAX_VQ + 1 to be input because the caller may want >> - * to find the maximum vq enabled, which may be ARM_MAX_VQ, but this >> - * function always returns the next smaller than the input. >> - */ >> - assert(vq && vq <= ARM_MAX_VQ + 1); >> - >> - bitnum = find_last_bit(cpu->sve_vq_map, vq - 1); >> - return bitnum == vq - 1 ? 0 : bitnum + 1; >> -} >> - >> static void cpu_max_get_sve_max_vq(Object *obj, Visitor *v, const char >> *name, >> void *opaque, Error **errp) >> { >> diff --git a/target/arm/helper.c b/target/arm/helper.c >> index be67e2c66d..b5ee35a174 100644 >> --- a/target/arm/helper.c >> +++ b/target/arm/helper.c >> @@ -5363,9 +5363,13 @@ int sve_exception_el(CPUARMState *env, int el) >> >> static uint32_t sve_zcr_get_valid_len(ARMCPU *cpu, uint32_t start_len) >> { >> - uint32_t start_vq = (start_len & 0xf) + 1; >> + uint32_t end_len; >> >> - return arm_cpu_vq_map_next_smaller(cpu, start_vq + 1) - 1; >> + start_len &= 0xf; >> + end_len = find_last_bit(cpu->sve_vq_map, start_len + 1); >> + >> + assert(end_len <= start_len); >> + return end_len; >> } >> >> /* >> -- >> 2.17.1 >> >> > > Besides the commit message referencing test_bit, but no use of it, this > looks good to me > > Reviewed-by: Andrew Jones <[email protected]> >
