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tsan: fix latent bug in shadow computation 

We use kShadowCnt (number of shadow cells per application granule)
when computing shadow, but it's wrong. We need the ratio
between shadow and app memory (how much shadow is larger than app memory),
which is kShadowMultiplier.
Currently both are equal to 4, so it works fine.
Use the correct constant.

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D108033
This commit is contained in:
Dmitry Vyukov 2021-08-13 15:24:23 +02:00
parent 027c5a6adc
commit ef2ff556a2
1 changed files with 3 additions and 2 deletions
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5
compiler-rt/lib/tsan/rtl/tsan_platform.h
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@ -840,7 +840,7 @@ struct MemToShadowImpl {
DCHECK(IsAppMemImpl::Apply<Mapping>(x));
return (((x) & ~(Mapping::kShadowMsk | (kShadowCell - 1))) ^
Mapping::kShadowXor) *
kShadowCnt +
kShadowMultiplier +
Mapping::kShadowAdd;
}
};
@ -873,7 +873,8 @@ struct ShadowToMemImpl {
// a bijection, so we try to restore the address as belonging to
// low/mid/high range consecutively and see if shadow->app->shadow mapping
// gives us the same address.
uptr p = ((sp - Mapping::kShadowAdd) / kShadowCnt) ^ Mapping::kShadowXor;
uptr p =
((sp - Mapping::kShadowAdd) / kShadowMultiplier) ^ Mapping::kShadowXor;
if (p >= Mapping::kLoAppMemBeg && p < Mapping::kLoAppMemEnd &&
MemToShadowImpl::Apply<Mapping>(p) == sp)
return p;