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[libunwind] Fix getSLEB128 on large values 

Previously, for large-enough values, getSLEB128 would attempt to shift
a signed int in the range [0..0x7f] by 28, 35, 42... bits, which is
undefined behavior and likely to fail.

Avoid shifting (-1ULL) by 70 for large values. e.g. For INT64_MAX, the
last two bytes will be:
 - 0x7f [bit==56]
 - 0x00 [bit==63]

Differential Revision: https://reviews.llvm.org/D83742
This commit is contained in:
Ryan Prichard 2020-07-13 22:06:47 -07:00
parent 52d0a78b83
commit fd802cc4de
1 changed files with 2 additions and 2 deletions
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4
libunwind/src/AddressSpace.hpp
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@ -290,11 +290,11 @@ inline int64_t LocalAddressSpace::getSLEB128(pint_t &addr, pint_t end) {
if (p == pend)
_LIBUNWIND_ABORT("truncated sleb128 expression");
byte = *p++;
result |= ((byte & 0x7f) << bit);
result |= (uint64_t)(byte & 0x7f) << bit;
bit += 7;
} while (byte & 0x80);
// sign extend negative numbers
if ((byte & 0x40) != 0)
if ((byte & 0x40) != 0 && bit < 64)
result |= (-1ULL) << bit;
addr = (pint_t) p;
return result;