On 6/4/2020 7:26 PM, James Read wrote:
Here is my valgrind output that I don't understand:
==319842== Invalid write of size 1
==319842== at 0x48436E4: mempcpy (in
/usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==319842== by 0x50CD1D8: _IO_default_xsputn (genops.c:386)
==319842== by 0x50CD1D8: _IO_default_xsputn (genops.c:370)
==319842== by 0x50B227B: __vfprintf_internal (vfprintf-internal.c:1688)
==319842== by 0x50C0278: __vsprintf_internal (iovsprintf.c:95)
==319842== by 0x509D047: sprintf (sprintf.c:30)
==319842== by 0x10B88F: html_link_find (crawler.c:452)
==319842== by 0x10BD6F: html_parse (crawler.c:536)
==319842== by 0x10C2CB: check_multi_info (crawler.c:678)
==319842== by 0x10C3DA: event_cb (crawler.c:706)
==319842== by 0x10D828: crawler_init (crawler.c:1154)
==319842== by 0x10DAE8: main (crawler.c:1207)
==319842== Address 0xf107d18 is 0 bytes after a block of size 8,200
alloc'd
==319842== at 0x483B7F3: malloc (in
/usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==319842== by 0x10B736: html_link_find (crawler.c:440)
==319842== by 0x10BD6F: html_parse (crawler.c:536)
==319842== by 0x10C2CB: check_multi_info (crawler.c:678)
==319842== by 0x10C3DA: event_cb (crawler.c:706)
==319842== by 0x10D828: crawler_init (crawler.c:1154)
==319842== by 0x10DAE8: main (crawler.c:1207)
==319842==
valgrind: m_mallocfree.c:305 (get_bszB_as_is): Assertion 'bszB_lo ==
bszB_hi' failed.
valgrind: Heap block lo/hi size mismatch: lo = 8272, hi =
3625731377157460067.
This is probably caused by your program erroneously writing past the
end of a heap block and corrupting heap metadata. If you fix any
invalid writes reported by Memcheck, this assertion failure will
probably go away. Please try that before reporting this as a bug.
The code this pertains to can be found at
https://github.com/JamesRead5737/webcrawler
Any help in understanding what this error means would be greatly
appreciated.
James Read
Line 452 of crawler.c (routine html_link_find()) is calling sprintf(),
which is then writing past the end of an allocated buffer of 8200
bytes. My first guess is that you are not resizing the buffer enough to
fit the text being written by sprintf().
Find out why this is occurring in html_link_find() (it should happen
even when your code is not running under valgrind), fix it, then rerun
valgrind. If your program is writing outside of buffers, it is possible
that valgrind won't catch it and thus the assertion failure later.
--
David Chapman dcchap...@acm.org
Chapman Consulting -- San Jose, CA
EDA Software Developer, Expert Witness
www.chapman-consulting-sj.com
2018-2019 Chair, IEEE Consultants' Network of Silicon Valley
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