https://llvm.org/bugs/show_bug.cgi?id=27436
Bug ID: 27436
Summary: lld-link writes import .lib files with the wrong byte
order in the second header
Product: lld
Version: unspecified
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: unassignedb...@nondot.org
Reporter: nicolaswe...@gmx.de
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
To learn more about the .lib format, I wrote a simple dumper
(https://github.com/nico/hack/blob/master/libdump.c). While doing this, I
noticed that the .lib files written by lld-link always write big-ending
numbers.
The PE spec section 7 explicitly says that the entries in the first linker
member should be big-endian. It is silent about endianness for the second
linker member, but the .lib files written by link.exe have little-endian files
there.
Now, link.exe can use the .lib files produces by lld-link:
C:\src\llvm-build-new>type test.cc
__declspec(dllexport) void f() {}
C:\src\llvm-build-new>type main.cc
__declspec(dllimport) void f();
int main() { f(); };
C:\src\llvm-build-new>cl /c test.cc
Microsoft (R) C/C++ Optimizing Compiler Version 18.00.31101 for x64
Copyright (C) Microsoft Corporation. All rights reserved.
test.cc
C:\src\llvm-build-new>cl /c main.cc
Microsoft (R) C/C++ Optimizing Compiler Version 18.00.31101 for x64
Copyright (C) Microsoft Corporation. All rights reserved.
main.cc
C:\src\llvm-build-new>bin\lld-link /dll test.obj
Creating library test.lib and object test.exp
C:\src\llvm-build-new>link main.obj test.lib
Microsoft (R) Incremental Linker Version 12.00.31101.0
Copyright (C) Microsoft Corporation. All rights reserved.
I guess this works because link.exe falls back to the first linker member if it
can't decode the second linker member? One way to test this theory would be to
create a large import lib and see if using the dll is faster when the import
library for it is created by link or lld-link (since using the second linker
member should make linking a bit faster, since it has a sorted symbol list --
but maybe the difference is too small to measure).
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