tkuchta added inline comments.
================
Comment at: compiler-rt/lib/dfsan/dfsan_custom.cpp:221
+ if (flags().strict_data_dependencies) {
+ *ret_label = res ? dfsan_read_label(base, sizeof(base)) : 0;
+ } else {
----------------
browneee wrote:
> `base, sizeof(base)` does not make sense - the size does not correspond to
> the pointer used.
>
> Either
> ```
> dfsan_read_label(base, sizeof(*base)) // first byte pointed to by base
> dfsan_read_label(base, strlen(base)) // whole string pointed to by base
> dfsan_read_label(&base, sizeof(base)) // the base pointer
> ```
>
> In this case I think we want the base pointer.
>
> `dfsan_read_label(&base, sizeof(base))` // the base pointer
> should be equivalent to doing
> `dfsan_label base_label = dfsan_read_label(s, sizeof(*s))` up at the start
> of the function, just after we declare base then use `base_label` here.
>
> Lets go with the second option to avoid taking the address of a variable.
>
> This is semantically equivalent to my first suggestion:
> `dfsan_get_label(base) == dfsan_read_label(&base, sizeof(base)) ==
> base_label`.
> Sorry I didn't consider the other constraints (no dfsan_get_label in this
> file because the pass is not run on this code; avoid taking address of
> variable) and suggest this in the first place.
Thank you for your comments! Just to clarify:
If we have strict data dependencies we would like *ret_label to be related to
the taints of the contents of the string, is that correct? Should we use the
base_label there too? My understanding is that base_label represents a taint
applied to the pointer, not to the data?
In other words, would that be correct to:
1) use taints of the string data in the first case (strict dependencies) ->
therefore no base_label there as it represents the taint of the pointer
2) use the taints of the string data + the taints of the pointer in the second
case -> therefore using base_label there
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D141389/new/
https://reviews.llvm.org/D141389
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