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stdio: Remove UB on printf_fp

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The __printf_fp_buffer_1 issues count_leading_zeros with 0 argument,
which might leads to call __builtin_ctz depending of the ABI.
Replace with stdbit.h function instead.

Checked on x86_64-linux-gnu and i686-linux-gnu.
Reviewed-by: Paul Eggert <eggert@cs.ucla.edu>
This commit is contained in:
Adhemerval Zanella
2025-04-25 18:06:33 -03:00
parent 77930e0447
commit 2be836fe44
1 changed files with 9 additions and 9 deletions
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18
stdio-common/printf_fp.c
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@@ -29,7 +29,6 @@
#include <gmp.h> #include <gmp.h>
#include <ieee754.h> #include <ieee754.h>
#include <stdlib/gmp-impl.h> #include <stdlib/gmp-impl.h>
#include <stdlib/longlong.h>
#include <stdlib/fpioconst.h> #include <stdlib/fpioconst.h>
#include <locale/localeinfo.h> #include <locale/localeinfo.h>
#include <limits.h> #include <limits.h>
@@ -40,6 +39,7 @@
#include <stdlib.h> #include <stdlib.h>
#include <wchar.h> #include <wchar.h>
#include <stdbool.h> #include <stdbool.h>
#include <stdbit.h>
#include <rounding-mode.h> #include <rounding-mode.h>
#include <printf_buffer.h> #include <printf_buffer.h>
#include <printf_buffer_to_file.h> #include <printf_buffer_to_file.h>
@@ -386,7 +386,7 @@ __printf_fp_buffer_1 (struct __printf_buffer *buf, locale_t loc,
{ {
int cnt; int cnt;
MPN_ASSIGN (p.scale, p.tmp); MPN_ASSIGN (p.scale, p.tmp);
count_leading_zeros (cnt, p.scale[p.scalesize - 1]); cnt = stdc_leading_zeros (p.scale[p.scalesize - 1]);
scaleexpo = (p.scalesize - 2) * BITS_PER_MP_LIMB - cnt - 1; scaleexpo = (p.scalesize - 2) * BITS_PER_MP_LIMB - cnt - 1;
exp10 |= 1 << explog; exp10 |= 1 << explog;
} }
@@ -408,7 +408,7 @@ __printf_fp_buffer_1 (struct __printf_buffer *buf, locale_t loc,
; ;
/* Determine number of bits the scaling factor is misplaced. */ /* Determine number of bits the scaling factor is misplaced. */
count_leading_zeros (cnt_h, p.scale[p.scalesize - 1]); cnt_h = stdc_leading_zeros (p.scale[p.scalesize - 1]);
if (cnt_h == 0) if (cnt_h == 0)
{ {
@@ -426,17 +426,17 @@ __printf_fp_buffer_1 (struct __printf_buffer *buf, locale_t loc,
{ {
if (p.scale[i] != 0) if (p.scale[i] != 0)
{ {
count_trailing_zeros (cnt_l, p.scale[i]); cnt_l = stdc_trailing_zeros (p.scale[i]);
if (p.frac[i] != 0) if (p.frac[i] != 0)
{ {
int cnt_l2; int cnt_l2;
count_trailing_zeros (cnt_l2, p.frac[i]); cnt_l2 = stdc_trailing_zeros (p.frac[i]);
if (cnt_l2 < cnt_l) if (cnt_l2 < cnt_l)
cnt_l = cnt_l2; cnt_l = cnt_l2;
} }
} }
else else
count_trailing_zeros (cnt_l, p.frac[i]); cnt_l = stdc_trailing_zeros (p.frac[i]);
/* Now shift the numbers to their optimal position. */ /* Now shift the numbers to their optimal position. */
if (i == 0 && BITS_PER_MP_LIMB - cnt_h > cnt_l) if (i == 0 && BITS_PER_MP_LIMB - cnt_h > cnt_l)
@@ -528,7 +528,7 @@ __printf_fp_buffer_1 (struct __printf_buffer *buf, locale_t loc,
if (cy == 0) if (cy == 0)
--p.tmpsize; --p.tmpsize;
count_leading_zeros (cnt_h, p.tmp[p.tmpsize - 1]); cnt_h = stdc_leading_zeros (p.tmp[p.tmpsize - 1]);
incr = (p.tmpsize - p.fracsize) * BITS_PER_MP_LIMB incr = (p.tmpsize - p.fracsize) * BITS_PER_MP_LIMB
+ BITS_PER_MP_LIMB - 1 - cnt_h; + BITS_PER_MP_LIMB - 1 - cnt_h;
@@ -584,7 +584,7 @@ __printf_fp_buffer_1 (struct __printf_buffer *buf, locale_t loc,
} }
else else
{ {
count_trailing_zeros (cnt_l, p.tmp[i]); cnt_l = stdc_trailing_zeros (p.tmp[i]);
/* Now shift the numbers to their optimal position. */ /* Now shift the numbers to their optimal position. */
if (i == 0 && BITS_PER_MP_LIMB - 1 - cnt_h > cnt_l) if (i == 0 && BITS_PER_MP_LIMB - 1 - cnt_h > cnt_l)
@@ -630,7 +630,7 @@ __printf_fp_buffer_1 (struct __printf_buffer *buf, locale_t loc,
p.tmpsize = p.fracsize; p.tmpsize = p.fracsize;
assert (cy == 0 || p.tmp[p.tmpsize - 1] < 20); assert (cy == 0 || p.tmp[p.tmpsize - 1] < 20);
count_trailing_zeros (cnt_l, p.tmp[0]); cnt_l = stdc_trailing_zeros (p.tmp[0]);
if (cnt_l < MIN (4, p.exponent)) if (cnt_l < MIN (4, p.exponent))
{ {
cy = __mpn_lshift (p.frac, p.tmp, p.tmpsize, cy = __mpn_lshift (p.frac, p.tmp, p.tmpsize,