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libdrgn: binary_buffer: add binary_buffer_next_sleb128()

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Revive it from all the way back in commit 90fbec02fc ("dwarfindex:
delete unused read_sleb128() and read_strlen()") and add an _into_u64
variant. These will be used for parsing .debug_frame, .eh_frame, and
DWARF expressions.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
This commit is contained in:
Omar Sandoval 2020-11-12 16:30:31 -08:00
parent 7eab40aaeb
commit e5219b13e3
1 changed files with 49 additions and 0 deletions
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49
libdrgn/binary_buffer.h
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@ -246,6 +246,55 @@ binary_buffer_next_uleb128(struct binary_buffer *bb, uint64_t *ret)
return binary_buffer_error_at(bb, bb->pos, "expected ULEB128 number");
}
/**
* Decode a Signed Little-Endian Base 128 (SLEB128) number at the current buffer
* position and advance the position.
*
* If the number does not fit in a @c int64_t, an error is returned.
*
* @param[out] ret Returned value.
*/
static inline struct drgn_error *
binary_buffer_next_sleb128(struct binary_buffer *bb, int64_t *ret)
{
int shift = 0;
int64_t value = 0;
const char *pos = bb->pos;
while (likely(pos < bb->end)) {
uint8_t byte = *(uint8_t *)(pos++);
if (unlikely(shift == 63 && byte != 0 && byte != 0x7f)) {
return binary_buffer_error_at(bb, bb->pos,
"SLEB128 number overflows signed 64-bit integer");
}
value |= (uint64_t)(byte & 0x7f) << shift;
shift += 7;
if (!(byte & 0x80)) {
bb->prev = bb->pos;
bb->pos = pos;
if (shift < 64 && (byte & 0x40))
value |= ~(UINT64_C(1) << shift) + 1;
*ret = value;
return NULL;
}
}
return binary_buffer_error_at(bb, bb->pos, "expected SLEB128 number");
}
/**
* Like @ref binary_buffer_next_sleb128(), but return the value as a @c
* uint64_t. Negative values are sign extended.
*/
static inline struct drgn_error *
binary_buffer_next_sleb128_into_u64(struct binary_buffer *bb, uint64_t *ret)
{
struct drgn_error *err;
int64_t tmp;
if ((err = binary_buffer_next_sleb128(bb, &tmp)))
return err;
*ret = tmp;
return NULL;
}
/** Skip past a LEB128 number at the current buffer position. */
static inline struct drgn_error *
binary_buffer_skip_leb128(struct binary_buffer *bb)