0001369: strange warning "postcondition got status invalid"

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ftest.c (140 bytes) 2013-02-15 11:59

static char *p;

/*@ assigns \nothing;
    ensures \result == p; */
char *foo(void); //{ return p; }

void main(void) { foo(); }

ftest.c (140 bytes) 2013-02-15 11:59

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~0003696 yakobowski (manager) 2013-02-15 13:06	Hello Jochen. Value evaluates functions without a body by looking at their assigns clauses. However, in order (1) to remain sound (2) to keep some precision, it makes a restrictive interpretation of what can be written in the assigned zones. Unlike what happens for WP, you cannot just write "assigns foo, bar; ensures bar = baz". Instead, you must write something like "assigns foo \from \nothing, bar \from baz; ensures bar = baz". In short, you _must_ write 'from' clauses, except in very simple cases. I'm going to refer you to two discussions in the Frama-C list. The first one discusses your exact problem, ie. a function that returns a global pointer (for which you currently need a hack). Do they make things clearer for you? I'm also in the process of improving the relevant section of the manual for Fluorine http://lists.gforge.inria.fr/pipermail/frama-c-discuss/2012-April/003182.html http://lists.gforge.inria.fr/pipermail/frama-c-discuss/2012-November/003445.html

~0003959 Jochen (reporter) 2013-06-13 15:52	Hello Boris, from the April blog article (003182.html), I understand that I should always provide \from in an assigns clause; when I do that on the ftest.c program, the message changes from "... got status invalid" to "... got status unknown", which sounds better. I don't know the interiors of Value good enough to understand your blog explanations involving "post-assigns state" and "alloced_return_..." etc; they seem to explain a difference between pointer- and non-pointer-types. Maybe, an end-user need not understand these details. In any case, it would be useful if the hint "add a \from part to your assigns" (or even "add an assigns clause at all, and equip it with a \from part") would be given by the FRAMA-C output. In the manual, some simple/naive explanation about the meaning of the message "postcondition got status invalid" and "... unknown" would be helpful. Did I understand you right: Value tries to validate an ensures clause even if no code is given for an external function; the only clues it has in that case are the assigns clauses, which better had a \from part. The message "...unknown" means "you user are responsible yourself for validating that function contract, if you don't show me the body code"; while "...invalid" means "although I couldn't check with the body code, the ensures clause must be wrong, as it contradicts (somehow) the assigns clause". Or am I wrong with that?

~0004861 yakobowski (manager) 2014-02-25 14:43	Fix committed to feature/neon-doc-value branch.

~0004862 yakobowski (manager) 2014-02-26 19:57	Fix committed to stable/neon branch.

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Date Modified	Username	Field	Change
Issue History
2013-02-15 11:59	Jochen	New Issue
2013-02-15 11:59	Jochen	Status	new => assigned
2013-02-15 11:59	Jochen	Assigned To	=> yakobowski
2013-02-15 11:59	Jochen	File Added: ftest.c
2013-02-15 13:06	yakobowski	Note Added: 0003696
2013-02-15 13:06	yakobowski	Status	assigned => feedback
2013-05-30 23:21	yakobowski	Target Version	=> Frama-C Neon-20140301
2013-06-13 15:52	Jochen	Note Added: 0003959
2014-02-25 14:43	yakobowski	Source_changeset_attached	=> framac feature/neon-doc-value 19051169
2014-02-25 14:43	yakobowski	Note Added: 0004861
2014-02-25 14:43	yakobowski	Resolution	open => fixed
2014-02-25 17:40	signoles	Status	feedback => resolved
2014-02-26 19:57	yakobowski	Source_changeset_attached	=> framac stable/neon 19051169
2014-02-26 19:57	yakobowski	Note Added: 0004862
2014-03-13 15:56	signoles	Fixed in Version	=> Frama-C Neon-20140301
2014-03-13 15:57	signoles	Status	resolved => closed
2018-01-12 14:26	signoles	Category	Plug-in > value analysis => Plug-in > Eva

Issue History