Frank Ch. Eigler - Re: Question about mudflap (original) (raw)

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• From: "Frank Ch. Eigler"
• To: Doug Graham
• Cc: gcc at gcc dot gnu dot org
• Date: Wed, 16 Nov 2005 08:48:43 -0500
• Subject: Re: Question about mudflap
• References: 20040629203155.GN10148@redhat.com 20050407172217.GH3512@nortelnetworks.com 20050407173914.GA15740@redhat.com 20050407202356.GI3512@nortelnetworks.com 20050408005509.GD5923@redhat.com 20050408022625.GL3512@nortelnetworks.com 20050408114112.GH5923@redhat.com 20050409213942.GP3512@nortelnetworks.com 20050410101136.GA9265@redhat.com 20051116082054.GY3483@nortelnetworks.com

Hi -

What I'm wondering is whether or not mudflap should instrument accesses to globals that it doesn't know the size of. In the following code: [...] printf("%d\n", global[3]); [...] Mudflap does not emit any __mf_check calls.

It is probably kicking in an optimization that says that if the indexes are literals and thus statically checkable against array bounds, then there is no need for a runtime check. The problem here is of course that we can't do the static check after all because of the extern[]. There is also another complication (unhelpful TREE_ADDRESSABLE flag setting for this and a few other cases).

[...] I'd much prefer if it did go on and check all accesses to the array because in my case, global[] will always be registered by the compilation unit in which it is defined. [...]

On the other hand, mudflap can't know that this extern[] will be registered by that other compilation unit, since that might be compiled without -fmudflap. An mf_check against it would then fail.

• FChE

• Follow-Ups:
  • Re: Question about mudflap
    * From: Richard Guenther
  • Re: Question about mudflap
    * From: Doug Graham