diff options
Diffstat (limited to 'libdw/memory-access.h')
| -rw-r--r-- | libdw/memory-access.h | 44 |
1 files changed, 38 insertions, 6 deletions
diff --git a/libdw/memory-access.h b/libdw/memory-access.h index a39ad6d2..8b2386ee 100644 --- a/libdw/memory-access.h +++ b/libdw/memory-access.h @@ -113,19 +113,22 @@ __libdw_get_uleb128_unchecked (const unsigned char **addrp) #define get_sleb128_step(var, addr, nth) \ do { \ unsigned char __b = *(addr)++; \ + (var) |= (typeof (var)) (__b & 0x7f) << ((nth) * 7); \ if (likely ((__b & 0x80) == 0)) \ { \ - struct { signed int i:7; } __s = { .i = __b }; \ - (var) |= (typeof (var)) __s.i * ((typeof (var)) 1 << ((nth) * 7)); \ + if ((__b & 0x40) != 0) \ + (var) |= - ((typeof (var)) 1 << (((nth) + 1) * 7)); \ return (var); \ } \ - (var) |= (typeof (var)) (__b & 0x7f) << ((nth) * 7); \ } while (0) static inline int64_t __libdw_get_sleb128 (const unsigned char **addrp, const unsigned char *end) { - int64_t acc = 0; + /* Do the work in an unsigned type, but use implementation-defined + behavior to cast to signed on return. This avoids some undefined + behavior when shifting. */ + uint64_t acc = 0; /* Unroll the first step to help the compiler optimize for the common single-byte case. */ @@ -134,6 +137,20 @@ __libdw_get_sleb128 (const unsigned char **addrp, const unsigned char *end) const size_t max = __libdw_max_len_sleb128 (*addrp - 1, end); for (size_t i = 1; i < max; ++i) get_sleb128_step (acc, *addrp, i); + if (*addrp == end) + return INT64_MAX; + + /* There might be one extra byte. */ + unsigned char b = **addrp; + ++*addrp; + if (likely ((b & 0x80) == 0)) + { + /* We only need the low bit of the final byte, and as it is the + sign bit, we don't need to do anything else here. */ + acc |= ((typeof (acc)) b) << 7 * max; + return acc; + } + /* Other implementations set VALUE to INT_MAX in this case. So we better do this as well. */ return INT64_MAX; @@ -142,7 +159,10 @@ __libdw_get_sleb128 (const unsigned char **addrp, const unsigned char *end) static inline int64_t __libdw_get_sleb128_unchecked (const unsigned char **addrp) { - int64_t acc = 0; + /* Do the work in an unsigned type, but use implementation-defined + behavior to cast to signed on return. This avoids some undefined + behavior when shifting. */ + uint64_t acc = 0; /* Unroll the first step to help the compiler optimize for the common single-byte case. */ @@ -152,6 +172,18 @@ __libdw_get_sleb128_unchecked (const unsigned char **addrp) const size_t max = len_leb128 (int64_t) - 1; for (size_t i = 1; i < max; ++i) get_sleb128_step (acc, *addrp, i); + + /* There might be one extra byte. */ + unsigned char b = **addrp; + ++*addrp; + if (likely ((b & 0x80) == 0)) + { + /* We only need the low bit of the final byte, and as it is the + sign bit, we don't need to do anything else here. */ + acc |= ((typeof (acc)) b) << 7 * max; + return acc; + } + /* Other implementations set VALUE to INT_MAX in this case. So we better do this as well. */ return INT64_MAX; @@ -363,7 +395,7 @@ read_3ubyte_unaligned (Dwarf *dbg, const unsigned char *p) #define read_3ubyte_unaligned_inc(Dbg, Addr) \ - ({ uint32_t t_ = read_2ubyte_unaligned (Dbg, Addr); \ + ({ uint32_t t_ = read_3ubyte_unaligned (Dbg, Addr); \ Addr = (__typeof (Addr)) (((uintptr_t) (Addr)) + 3); \ t_; }) |