[Valgrind-users] "Invalid read" error but offset is not out-of-bounds?

[Chris F. <cf...@gm...>]

Hi all,

I'm getting a perplexing error message with Valgrind. I get an
"invalid read of size 8", but the address is inside an allocated block
(and the access size doesn't go out-of-bounds). The access goes
through fine but I'm debugging a segfault much later in execution (the
reason I started using Valgrind just now and saw a bunch of these
errors). I'm wondering if maybe there's some other reason I would see
this message:


==16432== Invalid read of size 8
==16432==    at 0x43319E: trampoline() (thread.cc:134)
==16432==  Address 0x646b5d8 is 56 bytes inside a block of size 72 alloc'd
==16432==    at 0x4C285A4: operator new(unsigned long) (vg_replace_malloc.c:298)
==16432==    by 0x432EFF: thread_new(void (*)(void*, void*, void*),
void*, void*, void*, unsigned long, int) (thread.cc:142)
[ snip internal stuff ]
==16432==    by 0x4083AF: main (main.cc:210)

If it's relevant, this is inside a little
userspace-cooperative-threads package I wrote and the code is running
on a malloc()'d stack.

Any suggestions?

Thanks!
Chris Fallin