Bug#994969: jackd2: segfaults after today's upgrade of other Debian testing packages

[Ryan Thoryk]

On 10/3/21 4:59 AM, 小太 wrote:
> On Sun, 3 Oct 2021 at 20:47, Ryan Thoryk <ryan at thoryk.com> wrote:
> "Bad permissions for mapped region at address" can also mean it tried
> to read from unreadable memory. The memory was mapped at some
> point in the past, so it doesn't say unallocated memory
> 
> Also consider the segfault comes from strcmp(). Why would strcmp()
> ever need to write to memory? You can verify with a disassember the
> segfault comes from a read

The strcmp stumped me too.  I assumed it was trying to copy from a null 
pointer, but valgrind shows that the address wasn't null.  I forgot 
about the strcmp detail when writing my comment, strcmp is read-only.

> 
> I suspect this "worked" to fix the issue only due to a memory layout
> change, and luck would have it that after your rebuild it now tries to
> read from readable memory (albeit still not the expected memory)
> 

After looking over the glib docs, the function does a const on the 
string, so it shouldn't be able to do a write.

I don't know enough about handling C-strings (I've mostly done C++ 
strings), but the only difference is the location of stored memory, 
maybe it's getting an access error when trying to access the literal 
(since it's being done from an external library), as opposed to a stack 
allocation.  That's the only thing I can think of.  Valgrind doesn't 
show any warning or error using this method, so it appears to be fine. 
I'll bring this up on the glibmm upstream and see what they say.  I 
think the proper way to to define it is "static const char[]" instead of 
"char[]", but it might not matter that much.

-- 
Ryan Thoryk
ryan at thoryk.com
ryan at tliquest.net