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Avoid undefined behavior in parse_number

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-fsanitize=undefined pointed out that c-exp.y relied on undefined
behavior here:

      if (c != 'l' && c != 'u')
	n *= base;

...when a large hex constant "just fit" into a LONGEST, causing the
high bit to be set.

This fixes the problem by having the function work in an unsigned
type.

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

	* c-exp.y (parse_number): Work in unsigned.  Remove casts.
This commit is contained in:
Tom Tromey 2018-07-29 20:23:33 -06:00
parent d359392f97
commit 20562150d8
2 changed files with 8 additions and 6 deletions
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4
gdb/ChangeLog
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@ -1,3 +1,7 @@
2018-10-03 Tom Tromey <tom@tromey.com>
* c-exp.y (parse_number): Work in unsigned. Remove casts.
2018-10-03 Tom Tromey <tom@tromey.com>
* dwarf2read.c (read_subrange_type): Make "negative_mask"

10
gdb/c-exp.y
View File

@ -1760,10 +1760,8 @@ static int
parse_number (struct parser_state *par_state,
const char *buf, int len, int parsed_float, YYSTYPE *putithere)
{
/* FIXME: Shouldn't these be unsigned? We don't deal with negative values
here, and we do kind of silly things like cast to unsigned. */
LONGEST n = 0;
LONGEST prevn = 0;
ULONGEST n = 0;
ULONGEST prevn = 0;
ULONGEST un;
int i = 0;
@ -1922,7 +1920,7 @@ parse_number (struct parser_state *par_state,
on 0x123456789 when LONGEST is 32 bits. */
if (c != 'l' && c != 'u' && n != 0)
{
if ((unsigned_p && (ULONGEST) prevn >= (ULONGEST) n))
if (unsigned_p && prevn >= n)
error (_("Numeric constant too large."));
}
prevn = n;
@ -1940,7 +1938,7 @@ parse_number (struct parser_state *par_state,
the case where it is we just always shift the value more than
once, with fewer bits each time. */
un = (ULONGEST)n >> 2;
un = n >> 2;
if (long_p == 0
&& (un >> (gdbarch_int_bit (parse_gdbarch (par_state)) - 2)) == 0)
{