Hi Rui,
I have finished my tool to generate short import libs for mingw-w64.
It works fine with lld for actual symbols.
But it seems lld segfaults when I try to use and an alias as we discussed before.
I have attached 3 import libraries.
They all only have 1 import function.
libuser32orig.a → Works fine and only has MessageBoxA
libuser32b.a → the symbol table has MessageBoxB and __imp_MessageBoxB but the Import object has MessageBoxA.user32.dll.
This causes a segfault in lld but should link correctly right ?
Additionally I have attached libuser32.a
This is the same as libuser32b.a but the symbol table has MessageBoxA and __imp_MessageBoxB rather then MessageBoxB and __imp_MessageBoxB
This also segfaults I assume due to the same bug.
The reason I created this iteration is because we should be able to in the import library just add extra _imp{alias} to the symbol tables that point to the original import of MessageBoxA.
Other then alias support the only difference between my new tool and lib.exe is that I don’t bother to create .debug sections as we don’t need them.
Kind Regards
Martell
libuser32orig.a (1.36 KB)
libuser32b.a (1.36 KB)
libuser32.a (1.36 KB)
The header of libuser32b.a says that it defines MessageBoxB and __imp_MessageBoxB, but the import library file in the archive actually defines MessageBoxA (not B). So the archive file is broken. You may want to fix the header and try again.
The header of libuser32b.a says that it defines MessageBoxB and __imp_MessageBoxB, but the import library file in the archive actually defines MessageBoxA (not B). So the archive file is broken. You may want to fix the header and try again.
Yes this is how I done the alias.
If you consider this invalid then look at libuser32.a
The header defines MessageBoxA and __imp_MessageBoxB.
This should be valid yes ?
Hmm, that’s not correct too. All symbols listed in the archive header must be defined by some member in the archive. In other words, the header is created just by extracting all external symbols from members. It’s not doable to rename symbol A to B by writing B to the archive file header.
By aliasing, I was suggesting adding an extra object file to an archive file containing a short import file. The extra object file is to define aliases to symbols defined by the import library.
Say, you are creating a DLL which defines a function symbol “foo”. You need to create an import library that defines “foo” and “__imp_foo”. This is what normal linkers do.
If you want to define an alias symbol “bar” to “foo” (which is an extension you want to provide), one way is to create an object file that defines “bar” and “__imp_bar” as aliases to “foo” and “__imp_foo”, respectively, and add that object file to the import library. As a result, the import library file defines four symbols, {,_imp}{foo,bar}.
Do you know how to define symbol aliases in COFF? If you don’t, take a look a member of oldnames.lib (which comes with MSVC). That library file defines bunch of aliases, and you can do the same thing.
If you want to define an alias symbol “bar” to “foo” (which is an extension you want to provide), one way is to create an object file that defines “bar” and “__imp_bar” as aliases to “foo” and “__imp_foo”, respectively, and add that object file to the import library. As a result, the import library file defines four symbols, {,_imp}{foo,bar}.
Do you know how to define symbol aliases in COFF? If you don’t, take a look a member of oldnames.lib (which comes with MSVC). That library file defines bunch of aliases, and you can do the same thing.
Thanks for pointing me in the right direction 
After looking at oldnames.lib I done a little more reading and I assume I do it like this then for the alias.
The import table points to the functions like this.
__imp_oldfu → newfun.obi
oldfu → newfun.obj
I have attached the 2 files named here.
I assume this is what you meant by Weak Externals ?
(Attachment newfun.obi is missing)
newfun.obj (214 Bytes)
newfun.obj seems broken – dumpbin couldn’t read.
newfun.obj seems broken – dumpbin couldn’t read.
Dunno how it got malformed.
This one should be valid
(Attachment newfun.obj is missing)