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Avoid undefined behavior in read_signed_leb128 

-fsanitize=undefined pointed out that read_signed_leb128 had an
undefined left-shift when processing the final byte of a 64-bit leb:

    runtime error: left shift of 127 by 63 places cannot be represented in type 'long int'

and an undefined negation:

    runtime error: negation of -9223372036854775808 cannot be represented in type 'long int'; cast to an unsigned type to negate this value to itself

Both of these problems are readily avoided by havinng
read_signed_leb128 work in an unsigned type, and then casting to the
signed type at the return.

gdb/ChangeLog
2018-10-03  Tom Tromey  <tom@tromey.com>

	* dwarf2read.c (read_signed_leb128): Work in ULONGEST.
This commit is contained in:
Tom Tromey 2018-08-17 20:19:13 -06:00
parent 20562150d8
commit 4dd1b46077
2 changed files with 7 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
gdb/ChangeLog
View File

@ -1,3 +1,7 @@
2018-10-03 Tom Tromey <tom@tromey.com>
* dwarf2read.c (read_signed_leb128): Work in ULONGEST.
2018-10-03 Tom Tromey <tom@tromey.com>
* c-exp.y (parse_number): Work in unsigned. Remove casts.

6
gdb/dwarf2read.c
View File

@ -19627,7 +19627,7 @@ static LONGEST
read_signed_leb128 (bfd *abfd, const gdb_byte *buf,
unsigned int *bytes_read_ptr)
{
LONGEST result;
ULONGEST result;
int shift, num_read;
unsigned char byte;
@ -19639,7 +19639,7 @@ read_signed_leb128 (bfd *abfd, const gdb_byte *buf,
byte = bfd_get_8 (abfd, buf);
buf++;
num_read++;
result |= ((LONGEST) (byte & 127) << shift);
result |= ((ULONGEST) (byte & 127) << shift);
shift += 7;
if ((byte & 128) == 0)
{
@ -19647,7 +19647,7 @@ read_signed_leb128 (bfd *abfd, const gdb_byte *buf,
}
}
if ((shift < 8 * sizeof (result)) && (byte & 0x40))
result |= -(((LONGEST) 1) << shift);
result |= -(((ULONGEST) 1) << shift);
*bytes_read_ptr = num_read;
return result;
}