makewhatis: segfault in dbadd when using -a

[sternenseemann <sternenseemann@systemli.org>]

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Hi all,

while testing Ingo's latest patch I found a segfault in makewhatis
involving -a and symlinks which I can also reproduce on unpatched CVS.

To reproduce do something like this

mkdir test-manpath
mkdir -p test-manpath/de/man1
ln -sf $(realpath test-manpath/de) test-manpath/DE

So we have a base directory which has one child that is a symlink. This
symlink points to a directory below the base directory which contains
another directory. Running makewhatis -a test-manpath will then segfault
with the following backtrace:

#0  0x000000000041a9e1 in dbadd (dba=dba@entry=0x471050,
mpage=mpage@entry=0x473560) at mandocdb.c:2140
#1  0x000000000041b0ae in mpages_merge (dba=dba@entry=0x471050,
mp=mp@entry=0x46c2b0) at mandocdb.c:1294
#2  0x000000000041ca13 in mandocdb (argc=1, argc@entry=3,
argv=<optimized out>, argv@entry=0x7fffffffd678) at mandocdb.c:513
#3  0x000000000041dffa in main (argc=3, argv=0x7fffffffd678) at main.c:165

Full backtrace is attached as well. I've stared at mpages_merge for a
little bit, but haven't figured out how this is happening so far.

Cheers,

  Lukas

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#0  0x000000000041a9e1 in dbadd (dba=dba@entry=0x471050, mpage=mpage@entry=0x473560) at mandocdb.c:2140
        mlink = 0x472510
        key = <optimized out>
        cp = 0x476460 "DE"
        mask = <optimized out>
        i = 2
        slot = 0
        mustfree = 0
        __PRETTY_FUNCTION__ = "dbadd"
#1  0x000000000041b0ae in mpages_merge (dba=dba@entry=0x471050, mp=mp@entry=0x46c2b0) at mandocdb.c:1294
        mpage = 0x473560
        mpage_dest = <optimized out>
        mlink = 0x0
        mlink_dest = <optimized out>
        meta = 0x46ca00
        cp = 0x437301 <hash_calloc> "H\203\354\b\350\\\374\377\377H\203\304\b\303H\203\354\b\350p\374\377\377H\203\304\b\303H\203\354\070dH\213\004%("
        fd = <optimized out>
        __PRETTY_FUNCTION__ = "mpages_merge"
#2  0x000000000041ca13 in mandocdb (argc=1, argc@entry=3, argv=<optimized out>, argv@entry=0x7fffffffd678) at mandocdb.c:513
        conf = {output = {includes = 0x0, man = 0x0, outfilename = 0x0, paper = 0x0, style = 0x0, tag = 0x0, tagfilename = 0x0, indent = 0, width = 0, fragment = 0, mdoc = 0, noval = 0, synopsisonly = 0, tag_found = 0, toc = 0}, manpath = {paths = 0x46d0c0, sz = 1}}
        mp = 0x46c2b0
        dba = 0x471050
        path_arg = <optimized out>
        progname = <optimized out>
        j = 0
        sz = <optimized out>
        ch = <optimized out>
        i = <optimized out>
#3  0x000000000041dffa in main (argc=3, argv=0x7fffffffd678) at main.c:165
        conf = {output = {includes = 0x100000 <error: Cannot access memory at address 0x100000>, man = 0x0, outfilename = 0xffffffffffffffff <error: Cannot access memory at address 0xffffffffffffffff>, paper = 0x8000 <error: Cannot access memory at address 0x8000>, style = 0x0, 
            tag = 0xffffffffffffffff <error: Cannot access memory at address 0xffffffffffffffff>, tagfilename = 0x0, indent = 140737488347803, width = 140737354082303, fragment = 0, mdoc = 0, noval = 0, synopsisonly = 0, tag_found = 0, toc = 0}, manpath = {paths = 0x0, sz = 140737353989472}}
        outst = {tag_files = 0x1, outdata = 0xffffffffffffffff, use_pager = 4096, wstop = 0, had_output = 256, outtype = OUTT_ASCII}
        ws = {ws_row = 2048, ws_col = 0, ws_xpixel = 0, ws_ypixel = 0}
        search = {arch = 0xffffffffffffffff <error: Cannot access memory at address 0xffffffffffffffff>, sec = 0xc0000 <error: Cannot access memory at address 0xc0000>, outkey = 0x0, argmode = 4294967295, firstmatch = -1}
        res = 0x40
        resn = 0x38000000380
        mp = <optimized out>
        conf_file = <optimized out>
        os_s = <optimized out>
        progname = 0x7fffffffda72 "makewhatis"
        sec = <optimized out>
        defpaths = <optimized out>
        auxpaths = <optimized out>
        oarg = 0x38000000380 <error: Cannot access memory at address 0x38000000380>
        tagarg = <optimized out>
        uc = <optimized out>
        ressz = 17179870080
        resnsz = 1048576
        i = <optimized out>
        ib = <optimized out>
        ssz = <optimized out>
        options = <optimized out>
        show_usage = <optimized out>
        prio = <optimized out>
        best_prio = <optimized out>
        startdir = <optimized out>
        c = <optimized out>
        os_e = MANDOC_OS_OTHER
        outmode = <optimized out>