[PATCH] D93362: [llvm-elfabi] Support ELF file that lacks .gnu.hash section

[Haowei Wu via Phabricator via llvm-commits]

haowei marked 3 inline comments as done.
haowei added inline comments.


================
Comment at: llvm/test/tools/llvm-elfabi/read-elf-dynsym.test:10
+# RUN: yaml2obj --docnum=1 %s -o %tw.gnu.hash
+# RUN: llvm-strip --strip-sections %tw.gnu.hash
+# RUN: llvm-elfabi --elf %tw.gnu.hash --emit-tbe=- | FileCheck %s
----------------
jhenderson wrote:
> haowei wrote:
> > grimar wrote:
> > > haowei wrote:
> > > > jhenderson wrote:
> > > > > You don't need to call llvm-strip - yaml2obj can emit an object without the section header table, as pointed out in my earlier comment:
> > > > > 
> > > > > >>! In D93362#2486135, @jhenderson wrote:
> > > > > > For example, yaml2obj has recently gained the ability to not emit the section header table, rather than needing to use llvm-strip to remove it. See llvm\test\tools\yaml2obj\ELF\section-headers.yaml for an example.
> > > > > 
> > > > If I add
> > > > 
> > > > ```
> > > > SectionHeaderTable:
> > > >   Sections:  []
> > > > ```
> > > > it will report errors:
> > > > ```
> > > > yaml2obj: error: section '.text' should be present in the 'Sections' or 'Excluded' lists
> > > > yaml2obj: error: section '.data' should be present in the 'Sections' or 'Excluded' lists
> > > > yaml2obj: error: section '.dynsym' should be present in the 'Sections' or 'Excluded' lists
> > > > yaml2obj: error: section '.hash' should be present in the 'Sections' or 'Excluded' lists
> > > > yaml2obj: error: section '.gnu.hash' should be present in the 'Sections' or 'Excluded' lists
> > > > yaml2obj: error: section '.dynstr' should be present in the 'Sections' or 'Excluded' lists
> > > > yaml2obj: error: section '.dynamic' should be present in the 'Sections' or 'Excluded' lists
> > > > yaml2obj: error: section '.strtab' should be present in the 'Sections' or 'Excluded' lists
> > > > yaml2obj: error: section '.shstrtab' should be present in the 'Sections' or 'Excluded' lists
> > > > ```
> > > > 
> > > > If I try to use:
> > > > 
> > > > ```
> > > > SectionHeaderTable:
> > > >   NoHeaders: true
> > > > ```
> > > > 
> > > > Similar errors will be raised:
> > > > 
> > > > ```
> > > > yaml2obj: error: excluded section referenced: '.text'  by symbol 'foo'
> > > > yaml2obj: error: excluded section referenced: '.data'  by symbol 'bar'
> > > > ```
> > > > 
> > > > That's why I used llvm-strip instead of using this new yaml2obj feature. 
> > > Using of `Sections:  []` is not what you want, it doesn't remove the section headers. It can be used to create a
> > > section headers table with a null section only:
> > > 
> > > ```
> > > SectionHeaderTable:
> > >   Sections: []
> > >   Excluded:
> > >     - Name: .strtab
> > >     - Name: .shstrtab
> > > ```
> > > 
> > > Though, you don`t actually need it, as you can write just the following to achieve the same:
> > > 
> > > ```
> > > SectionHeaderTable:
> > >   Excluded:
> > >     - Name: .strtab
> > >     - Name: .shstrtab
> > > ```
> > > 
> > > So, to exclude the section header table you need to use `NoHeaders: true`.
> > > The errors you see:
> > > 
> > > ```
> > > yaml2obj: error: excluded section referenced: '.text'  by symbol 'foo'
> > > yaml2obj: error: excluded section referenced: '.data'  by symbol 'bar'
> > > ```
> > > 
> > > are because your dynamic symbols specify sections:
> > > 
> > > ```
> > > DynamicSymbols:
> > >   - Name:    foo
> > >     Type:    STT_FUNC
> > >     Section: .text
> > >     Value:   0x100
> > >     Binding: 1
> > >   - Name:    bar
> > >     Type:    STT_OBJECT
> > >     Section: .data
> > >     Value:   0x200
> > >     Binding: 1
> > > ```
> > > 
> > > Can't you just remove `Section: .text` and `Section: .data`?
> > Removing `Section: .text` and `Section: .data` will causing llvm-elfabi's output indicate the symbols are undefined (which is true). I make it pointing something else. 
> > 
> > I think using the llvm-strip here is better. I need to do a lot of macro hacks to make this test to use a single ELF yaml input, while I can use a single one with llvm-strip. It looks cleaner.
> I'm not going to argue this strongly, but it's worth noting that llvm-objcopy and llvm-strip operations can have minor side effects, whereas with yaml2obj you have more precise control over what the output actually is.
Changed to yaml2obj solution.


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