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Ian Jackson authored
In 25182:6c3345d7e9d9 the practice of passing NULL to gc-using memory allocation functions was introduced. However, the arrangements there were not correct as committed, because the error handling and logging depends on getting a ctx from the gc - so an allocation error would in fact result in libxl dereferencing NULL. Instead, provide a special dummy gc in the ctx, called `nogc_gc'. It is marked out specially by having alloc_maxsize==-1, which is otherwise invalid. Functions which need to actually look into the gc use the new test function gc_is_real (whose purpose is mainly clarity of the code) to check whether the gc is the dummy one, and do nothing if it is. And we provide a helper macro NOGC which uses the in-scope real gc to find the ctx and hence the dummy gc (and which replaces the previous #define NOGC NULL). Change all callers which pass 0 or NULL to an allocation function to use NOGC or &ctx->nogc_gc, as applicable in the context. We add a comment near the definition of LIBXL_INIT_GC pointing out that it isn't any more the only place a libxl__gc struct is initialised, for the benefit of anyone changing the contents of gc's in the future. Also, actually document that libxl__ptr_add is legal with ptr==NULL, and change a couple of calls not to check for NULL argument. Reported-by: Bamvor Jian Zhang <bjzhang@suse.com> Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com> Cc: Bamvor Jian Zhang <bjzhang@suse.com> Acked-by: Ian Campbell <Ian.Campbell@citrix.com> Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
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