[PATCH] D64750: [llvm-readelf] - Remove the precompiled binary from gnu-hash-symbols.test.

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added inline comments.


================
Comment at: test/tools/llvm-readobj/elf-hash-symbols.test:48
+      - Tag:   DT_GNU_HASH
+## 0x2C + PT_LOAD's p_offset == offset of .gnu.hash
+        Value: 0x000000000000002C
----------------
grimar wrote:
> grimar wrote:
> > grimar wrote:
> > > MaskRay wrote:
> > > > jhenderson wrote:
> > > > > Perhaps you should explain what 0x2C is (I think it's the size of .hash, right?)
> > > > > PT_LOAD's p_offset
> > > > 
> > > > Nit: I think the usage here is a bit unusual. Normally a `PT_DYNAMIC` is created to contain `.dynamic` and at runtime the rtld decodes `.dynamic` entries by finding the `PT_DYNAMIC` address.
> > > > 
> > > > Maybe you can create a PT_DYNAMIC to make the test look more reasonable?
> > > > 
> > > > If you decide to do that, delete `- Section: .dynamic` from the `PT_LOAD`.
> > > > 
> > > I expanded the comment to reveal the full picture of how the computation happen.
> > > 
> > > Note that in this test case both `.hash` and `.gnu.hash` have section VAs = 0
> > > (yaml2obj doesn't set it). So I tried to explain the underhood without using
> > > a wordings like "address of hash section".
> > >> Nit: I think the usage here is a bit unusual. Normally a PT_DYNAMIC is created to contain .dynamic and at runtime the rtld decodes .dynamic entries by finding the PT_DYNAMIC address.
> > 
> > But we are testing here the logic of `llvm-readelf`. It does not need `PT_DYNAMIC` to dump the hash tables.
> Moreover, I think we could improve dumper to be able to dump these section even without any `.dynamic` section at all.
> They have the unique types: `SHT_HASH` and `SHT_GNU_HASH`. It should be possible do do that.
Not having PT_DYNAMIC should be fine.

One more nit: it made me puzzled because .dynamic is writable and contained in the PT_LOAD but the PT_LOAD is not writable..

You can delete the SHF_WRITE flag from .dynamic (it doesn't include DT_DEBUG so it is not necessarily writable).

> Moreover, I think we could improve dumper to be able to dump these section even without any .dynamic section at all.
> They have the unique types: SHT_HASH and SHT_GNU_HASH. It should be possible do do that.

GNU objcopy just locates the dynamic section with either PT_DYNAMIC or `.dynamic`, then decodes DT_HASH and/or DT_GNU_HASH. It doesn't check `SHT_HASH` or `SHT_GNU_HASH` probably because the section header is optional in ET_DYN/ET_EXEC. However, PT_DYNAMIC must be available for the hash tables to be recognized by ld.so, so objcopy doesn't bother implementing the logic.


================
Comment at: test/tools/llvm-readobj/elf-hash-symbols.test:218
+## doesn't pass due to a mistake in the dynamic section).
+# RUN: llvm-readelf --dyn-symbols %t4.o | FileCheck %s --check-prefix DYNSYMS
+
----------------
`%t4.so`


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D64750/new/

https://reviews.llvm.org/D64750