Changing the value of the returned pointer after calling the function

Question

Code fragments from two C source files:

Ac

Channel *testChannelGet()
{
    Channel *ch = channelGet (parser,parserCh);
    return ch;
}

Bc

Channel *channelGet(UINT8 parser, UINT16 parserCh)
{
    chnl.player = &solPlayer;
    return((Channel *)&chnl);
}

I compile both files and create a static and shared library. Now I call testChannelGet from the sample program. When I link it to a static library, it works fine. But if I link it to a shared library, its SEGFAULTing. Debugging tells me that the pointer returned from channelGet changes the moment it returns. Gdb below.

174         Channel *ch = channelGet (parser,parserCh);
(gdb) s
channelGet (parser=1 '\001', parserCh=1) at B.c:15174
15174           chnl.player = &solPlayer;
(gdb) n
15175           return((Channel *)&chnl);
(gdb) p ((Channel *)&chnl)
$1 = (Channel *) 0x7ffff7fed1a0
(gdb) n
15176   }
(gdb) n
testChannelGet at A.c:175
175         return ch;
(gdb) p ch
$2 = (Channel *) 0xfffffffff7fed1a0

The address value now seems to indicate a different offset - 0xfffffffff7fed1a0 vs 0x7ffff7fed1a0. The last bytes in both addresses are the same.

Any clues? I tried the -fPIC option to no avail.

Answer 1

channelGet() A.c?

, , , :

• ,
• channelGet() int (- ), 0xf7fed1a0
• 64- , 0xfffffffff7fed1a0

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Answer 2

valgrind. .