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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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References: 
 >vm_protect with VM_PROT_COPY not working on Leopard (From: "Jeremy Todd" <email@hidden>)
 >Re: vm_protect with VM_PROT_COPY not working on Leopard (From: Chris Sarcone <email@hidden>)
 >RE: vm_protect with VM_PROT_COPY not working on Leopard (From: "Jeremy Todd" <email@hidden>)



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