[Lldb-commits] [PATCH] D71487: [LLDB] Fix address computation for inline function

Tue Jan 14 10:51:32 PST 2020

clayborg added a comment.

In D71487#1820074 <https://reviews.llvm.org/D71487#1820074>, @probinson wrote:

> In D71487#1791824 <https://reviews.llvm.org/D71487#1791824>, @clayborg wrote:
>
> > BTW: is used to be that both DW_AT_low_pc and DW_AT_high_pc would be set to zero when a function was dead stripped. This was back when both the low and high pc used DW_FORM_addr (a file address). But then DWARF changed such that DW_AT_high_pc could be encoded as a data form: DW_FORM_data1, DW_FORM_data2, DW_FORM_data4, or DW_FORM_data8. This is used to mean it is an offset from the low PC. Seems the linkers now didn't have a relocation for the DW_AT_high_pc so they couldn't zero it out. This is sad because we can end up with many functions at address zero that didn't get linked, and if zero is a valid address, then our DWARF contains a bunch of useless info that only hides which function is the real function for address zero.
>
>
> One solution, which we do in Sony, is to make the linker fix up undefined references to be -1 instead of 0 (at least, in the .debug_* sections).  That's more obviously an invalid address.  Doesn't help with existing objects in the wild but I'd like to keep that idea in the air as a forward evolutionary step.

I second this motion and would love to see this in more linkers.

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https://reviews.llvm.org/D71487