[RISCV] Add GNU note property and CFI support

[jerryzj]

• Based on Add program property and PLT for CFI extension riscv-non-isa/riscv-elf-psabi-doc#417

[sevaa]

Looks like the RISCV people took a page from the ARM people. :) No objections - once the autotest passes.

EDIT: now that I look at that - no new binaries. I take it, one of the existing binaries in the corpus had RISCV notes, and GNU readelf doesn't dump them properly, and neither did pyelftools, but now pyelftools does and there is a discrepancy in readelf output? If that's the case, deal with it how we normally deal with readelf deficiencies: file a bug against binutils (https://sourceware.org/bugzilla/), and exclude the offending file from the relevant readelf test (with a comment mentioning bug no). Like it was done in #563.

[jerryzj]

Looks like the RISCV people took a page from the ARM people. :) No objections - once the autotest passes.

EDIT: now that I look at that - no new binaries. I take it, one of the existing binaries in the corpus had RISCV notes, and GNU readelf doesn't dump them properly, and neither did pyelftools, but now pyelftools does and there is a discrepancy in readelf output? If that's the case, deal with it how we normally deal with readelf deficiencies: file a bug against binutils (sourceware.org/bugzilla), and exclude the offending file from the relevant readelf test (with a comment mentioning bug no). Like it was done in #563.

@sevaa yeap, since CFI is still a new feature for RISC-V, the binutils support is still not upstreamed by us. But my local testing shows the newly added binary test can PASS

• readelf

riscv64-unknown-linux-gnu-readelf -n  ./test/testfiles_for_readelf/riscv-cfi-zicfilp-zicfiss.elf

Displaying notes found in: .note.gnu.property
  Owner                Data size 	Description
  GNU                  0x00000010	NT_GNU_PROPERTY_TYPE_0
      Properties: RISC-V AND feature: ZICFILP, ZICFISS

• pyelftools

python3 ./scripts/readelf.py -n  ./test/testfiles_for_readelf/riscv-cfi-zicfilp-zicfiss.elf

Displaying notes found in: .note.gnu.property
  Owner                Data size        Description
  GNU                  0x00000010	NT_GNU_PROPERTY_TYPE_0 (program properties)
      Properties: RISC-V AND feature: ZICFILP, ZICFISS

Maybe we should keep this as a draft until the binutils are supported.

[sevaa]

If we keep this as a draft until the next release of binutils (and there is no guarantee the fix will make it into their next release), the main branch of pyelftools will get more commits and this PR would need a rebase and maybe even a manual merge. If you ask me, we should exclude the binary/test combination with a comment, merge now, and remove the test exclusion when GNU readelf catches up. @eliben what do you think?

[eliben]

@sevaa yep that sounds reasonable to me

[jerryzj]

@sevaa @eliben okay, I've dropped the test and will have another PR for it.