target/xtensa: Make use of 'segment' in pptlb helper less confusing

Coverity gets confused about the use of the 'segment' variable in the
pptlb helper function: it thinks that we can take a code path where
we first initialize it:
  unsigned segment = XTENSA_MPU_PROBE_B;  // 0x40000000
and then use that value as a shift count:
  } else if (nhits == 1 && (env->sregs[MPUENB] & (1u << segment))) {

In fact this isn't possible, beacuse xtensa_mpu_lookup() is passed
'&segment', and it uses that as an output value, which it will always
set if it returns nonzero.  But the way the code is currently written
is confusing to a human reader as well as to Coverity.

Instead of initializing 'segment' at the top of the function with a
value that's only used in the "nhits == 0" code path, use the
constant value directly in that code path, and don't initialize
segment.  This matches the way we use xtensa_mpu_lookup() in its
other callsites in get_physical_addr_mpu().

Resolves: Coverity CID 1547589

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Max Filippov <jcmvbkbc@gmail.com>
Message-id: 20240723151454.1396826-1-peter.maydell@linaro.org

diff --git a/target/xtensa/mmu_helper.c b/target/xtensa/mmu_helper.c
index 997b21d3890f56babb60fbe266ec1849f4df20c8..29b84d5dbf66e0a21e6e3424f76130d4f80dc3d1 100644 (file)
--- a/target/xtensa/mmu_helper.c
+++ b/target/xtensa/mmu_helper.c
@@ -991,7 +991,7 @@ uint32_t HELPER(rptlb1)(CPUXtensaState *env, uint32_t s)
 uint32_t HELPER(pptlb)(CPUXtensaState *env, uint32_t v)
 {
     unsigned nhits;
-    unsigned segment = XTENSA_MPU_PROBE_B;
+    unsigned segment;
     unsigned bg_segment;
 
     nhits = xtensa_mpu_lookup(env->mpu_fg, env->config->n_mpu_fg_segments,
@@ -1005,7 +1005,7 @@ uint32_t HELPER(pptlb)(CPUXtensaState *env, uint32_t v)
         xtensa_mpu_lookup(env->config->mpu_bg,
                           env->config->n_mpu_bg_segments,
                           v, &bg_segment);
-        return env->config->mpu_bg[bg_segment].attr | segment;
+        return env->config->mpu_bg[bg_segment].attr | XTENSA_MPU_PROBE_B;
     }
 }