[PATCH] D130668: [libunwind] Use `_dl_find_object` if available

[Adrian Vogelsgesang via Phabricator via llvm-commits]

avogelsgesang added inline comments.


================
Comment at: libunwind/src/AddressSpace.hpp:653
+    }
+    // .eh_frame_hdr records the start of .eh_frame, but not its size.
+    // Rely on a zero terminator to find the end of the section.
----------------
MaskRay wrote:
> > .eh_frame_hdr records the start of .eh_frame
> 
> This sentence is wrong. .eh_frame_hdr is a different section.
`PT_GNU_EH_FRAME` is a bit of a misnormer as it refers to `eh_frame_hdr`, not `eh_frame`. From https://refspecs.linuxbase.org/LSB_3.0.0/LSB-PDA/LSB-PDA/progheader.html

> PT_GNU_EH_FRAME:
> The array element specifies the location and size of the exception handling information as defined by the .eh_frame_hdr section.

The `eh_frame_hdr` is hence the section retrieved by `_dl_find_object`. `EHHeaderParser<LocalAddressSpace>::decodeEHHdr` a couple of lines above decodes the `eh_frame_hdr`.  Parsing the`eh_frame_hdr` gives us the pointer to the start of `eh_frame`, but doesn't give us its size. Hence, we set `dwarf_section_length` to `SIZE_MAX` and thereby rely on the zero terminator to find the end of the section.

Please let me know how to update this comment to make it more understandable.

Also, I shamelessly copied this comment from the `checkForUnwindInfoSegment` function. In case you want me to update also that comment, please let me know


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  https://reviews.llvm.org/D130668/new/

https://reviews.llvm.org/D130668