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s390: Fix MEMCHR_Z900_G5 ifunc-variant if n>=0x80000000 [BZ #28024]

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On s390 (31bit), the pointer to the first byte after s always wraps
around with n >= 0x80000000 and can lead to stop searching before
end of s.

Thus this patch just use NULL as byte after s in this case and
the srst instruction stops searching with "not found" when wrapping
around from top address to zero.

This is observable with testcase string/test-memchr
starting with commit "String: Add overflow tests for strnlen, memchr,
and strncat [BZ #27974]"
https://sourceware.org/git/?p=glibc.git;a=commit;h=da5a6fba0febbfc90896ce1b2eb75c6d8a88a72d
This commit is contained in:
Stefan Liebler 2021-06-29 11:37:28 +02:00
parent ba436665b1
commit 7c45df18e1
1 changed files with 13 additions and 0 deletions
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13
sysdeps/s390/memchr-z900.S
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@ -44,12 +44,25 @@ ENTRY(MEMCHR_Z900_G5)
LGHI %r0,0xff
NGR %r0,%r3
LGR %r1,%r2
# if ! defined __s390x__
tmlh %r4,32768
jo 3f /* Jump away if n >= 0x80000000 */
# endif
la %r2,0(%r4,%r1)
0: srst %r2,%r1
jo 0b
brc 13,1f
SLGR %r2,%r2
1: br %r14
# if ! defined __s390x__
/* On s390 (31bit), the pointer to the first byte after s (stored in
r2) always wraps around with n >= 0x80000000 and can lead to stop
searching before end of s. Thus just use r2=0 in this case.
If r2 < r1, the srst instruction stops searching with cc=2 "not
found" when wrapping around from top address to zero. */
3: SLGR %r2,%r2
j 0b
# endif
END(MEMCHR_Z900_G5)
# if ! HAVE_MEMCHR_IFUNC