RE: vm_protect with VM_PROT_COPY not working on Leopard
RE: vm_protect with VM_PROT_COPY not working on Leopard
- Subject: RE: vm_protect with VM_PROT_COPY not working on Leopard
- From: "Jeremy Todd" <email@hidden>
- Date: Thu, 6 Mar 2008 10:53:29 -0500
That's good news - the one remaining problem is that it would be nice if I could enable this at runtime. Is it true that interposing must be done by the linker at link-time?
I'm also still wondering why the vm_protect() VM_PROT_COPY mechanism described below is failing under Leopard. Surely it must be possible to get write access to the malloc() implementation somehow. For example doesn't gdb need this sort of access?
Regards,
Jeremy
> -----Original Message-----
> From: Eric Gouriou [mailto:email@hidden]
> Sent: Thursday, March 06, 2008 1:06 AM
> To: Jeremy Todd
> Cc: Darwin Dev
> Subject: Re: vm_protect with VM_PROT_COPY not working on Leopard
>
>
> On Mar 5, 2008, at 9:07 PM, Jeremy Todd wrote:
> > This looks interesting, but I'm curious whether it will allow me to
> > replace all invocations of malloc. For example if my code calls a
> > function defined in some system library, and that function in turn
> > calls malloc(), will it call my interposed malloc?
>
> Yes, even calls to malloc() from within libc / libsystem
> (e.g., strdup()).
>
> malloc (and friends) is one of those entry points for which
> interposing is part of the ABI contract. Direct calls to its
> default implementation are not allowed, everything must go
> through the dynamic symbol resolution.
>
> Such guarantees do not exist in general for other library
> entry points.
> Intra-library calls are frequently done directly, bypassing
> the dyld logic.
>
> Eric
>
> > Jeremy
> >
> >
> >> -----Original Message-----
> >> From: Chris Sarcone [mailto:email@hidden]
> >> Sent: Wednesday, March 05, 2008 6:03 PM
> >> To: Jeremy Todd
> >> Cc: email@hidden
> >> Subject: Re: vm_protect with VM_PROT_COPY not working on Leopard
> >>
> >> Jeremy --
> >>
> >> You might find this helpful:
> >>
> >> http://developer.apple.com/documentation/DeveloperTools/Concep
> >> tual/DynamicLibraries/DynamicLibraries.pdf
> >>
> >> Search for "interposing".
> >>
> >>
> >> -- Chris
> >>
> >> On Mar 5, 2008, at 2:44 PM, Jeremy Todd wrote:
> >>
> >>
> >> Hi,
> >>
> >> I'm trying to patch the malloc function
> [...]
> >> In case anyone is wondering, I need to do this as part of our
> >> development process for audio plug-ins. These plug-ins should not
> >> call certain functions (including malloc) from the high-priority
> >> processing thread to avoid priority inversion and related
> problems.
> >> We have special debug builds which patch the malloc
> function, and if
> >> a malloc is detected in the processing thread, we get a very nice
> >> call stack in the debugger which makes it trivial to find
> the source
> >> of these problems.
> >>
>
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