[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a comment.

LLVM Release Schedule: 10.0.0: Jan 15, 2020: branch, then rc1

It would be nice to get a reply to my mail proposal before the branch.. so we 
could push the code for LLVM 10. (If it was lost, I can resend it) It can 
likely upset both sides, but with the proposal in the end we get a bfd.ld 
drop-in replacement. (One of LLVM goals was to be a drop-in replacement for GNU 
toolchain components, even if some of them are irrelevant on a number of 
platforms.)


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a comment.

Ping?


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a comment.

@MaskRay I will mail you off-list with one question.


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a comment.
Herald added a subscriber: arichardson.

Ping?


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a comment.

Stating it from a different side. If you do not care about GNU ld drop-in 
replacement property for Linux it's not our business, but we do care about this 
in NetBSD and we restrict this to our project only (from ELF targets).  If you 
do not care about NetBSD, you shall not care how and whether we use LLD. We try 
hard to not interfere with Linux looking for a consensus.

You are not forced to use the NetBSD driver neither define it in 
`LLD_SYMLINKS_TO_CREATE`. If you have a strong disrespect to this GNU ld 
drop-in replacement approach, I can patch the `die("")` invocation in `main()` 
to conditionally print `"nb.lld"`. There are around 20 lines patches in the 
generic code and around 1/3 of that is in the code comments. This shall not be 
burden for any of you.


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a comment.

@joerg works on the ELF loader and we just need to wait for him. We wrote our 
temporary patch, but it was not ideal as the long term solution.

compiler-rt is nicely maintained from our perspective and we have almost 
feature parity with Linux.

We maintain and develop around 4000 NetBSD specific LOC in LLDB. That number 
grows, especially with each CPU architecture gaining upstream support.

> it seems NetBSD just needs

This is not everything, but I don't want to derail yet another review into 
offtopic or generic discussion. Getting lld functional standalone is merely a 
starting point for us.

We need a linker that is a GNU ld drop-in replacement. As we have no interest 
in fixing it for Linux, we want this property for NetBSD.


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Fangrui Song via Phabricator via cfe-commits]

MaskRay added a comment.

In D58892#1784119 , @mgorny wrote:

> In D58892#1783042 , @MaskRay wrote:
>
> > In D58892#1783029 , @mgorny wrote:
> >
> > > I know I'm late to the party but this change thoroughly destroyed NetBSD 
> > > support. The NetBSD loader doesn't support having more than two PT_LOAD 
> > > sections. `-z norosegment` helped with that so far but after this change 
> > > practically everything fails to run.
> >
> >
> > This seems to be a very serious limitation. I have difficult to understand 
> > how such limitation could exist at all, but I think this should be 
> > straightforward to fix.
>
>
> Yes, it is a serious limitation, and no, it's not straightforward to fix. The 
> loader has making a lot of assumptions, especially what PT_LOAD segments to 
> expect and in which order. I've previously made a patch that allowed third 
> segment but it was rejected as apparently 'not doing it the right way'. 
> Almost a year has passed, and I am entirely powerless to fix it.


@mgorny told me that NetBSD ld.so has a limitation that it can only handle 2 
PT_LOAD segments.

I think the NetBSD toolchain team's attitude toward certain ELF things should 
probably be made more flexible. For that particular PT_LOAD limitation issue 
(a.out heritage?), if @mgorny don't mind giving me a pointer, I'd like to help 
argue fixing the limitation.

> If 200 LOC for NetBSD is a show stopper, please see e.g. compiler-rt where we 
> maintain 2 orders of magnitude more NetBSD-only LOC.

I am not sure compiler-rt is a good example here. The "2 orders of magnitude 
more" OS specific things make compiler-rt difficult to maintain. Innovations 
can be easily constrained by the numerous OS specific customization. I am glad 
that lld hasn't entered that situation.

I feel that NetBSD's stubborn attitude is adding complexity to many other 
projects.

> I try to avoid forking LLD for downstream and this shall be appreciated.

If you can accept `DT_RUNPATH` and fix the PT_LOAD limitation, then it seems 
NetBSD just needs its own ld wrapper that adds -L, and probably -znognustack 
which saves you 56 bytes. I don't understand why such customization should 
still be upstreamed.


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a comment.

We attempted to patch internally LLD rebasing our code for the buildbot 
purposes but LLD without being used rots quickly, see: 
https://reviews.llvm.org/D58892

We use LD as `ld` and there are no plans neither intentions to break it. It was 
already decided internally in the project.

If you insist, I can rewrite nb.lld from C++ to shell and upstream to the LLD 
repository. We require `-fuse-ld=lld` to be rerouted through this shell script 
and lld invocation call it so we can revert back to the concept from 
https://reviews.llvm.org/D69755. Personally I see no gain in this as I prefer 
to rely on LLVM libs at least for Target Triplet detection.

As I can understand that Linux/GNU behavior is promoted (and enforced to other 
ELF OSs) it does not work for us. I propose a patch that keeps intact the 
GNU/Linux code.

If 200 LOC for NetBSD is a show stopper, please see e.g. compiler-rt where we 
maintain 2 orders of magnitude more NetBSD-only LOC.

I try to avoid forking LLD for downstream and this shall be appreciated.


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Rui Ueyama via Phabricator via cfe-commits]

ruiu added a comment.

lld is not that Linux-centric as you implied in your comment. We have code for 
FreeBSD, OpenBSD, AMDGPU and Fuchsia (which isn't even a POSIX system), and 
adding code for NetBSD is OK and is appreciated. However, the thing we've been 
trying to avoid is to hard-code a platform-specific knowledge such as library 
paths to the linker. Combined with the fact that lld doesn't provide a way to 
enable/disable targets at build-time, all ld.lld executables (sometimes 
installed as /usr/bin/ld) work the same way no matter where they are run on. 
That helps those who do cross compilation a lot. That is a very appreciated 
property of our linker, and I don't think I want make an exception for NetBSD. 
Even on NetBSD, lld should behave the same as running on other kind of hosts.

Also, frankly speaking, having a driver only for NetBSD seems very odd to me. 
We would have 5 drivers for MSVC link.exe, MinGW, ELF-based systems, macOS, and 
NetBSD? That doesn't feel right. If you strongly feel that the linker should 
know the library paths and the like, it shouldn't be too hard to write a shell 
script wrapper to wrap lld.


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Fangrui Song via Phabricator via cfe-commits]

MaskRay added a comment.

> If we could get this patch merged, we could build and link the whole LLVM 
> with lld on NetBSD and it would increase the productivity of the bot (better 
> build times). Right now we need to maintain hacks to link at most with 2/3 
> cores, while 5/6 ones are idling doing nothing due to enormous RAM 
> consumption of GNU ld.

I will be very happy to see the productivity of NetBSD build bot gets improved. 
My comments below are about the approach you choose in this patch.

> FreeBSD/OpenBSD ship with mutations of the behavior of ELF/GNU/Linux in 
> certain nits, we do the same with our driver.

The FreeBSD specific code is just the following 4 lines in ELF/Driver.cpp:

  if (s.endswith("_fbsd")) {
s = s.drop_back(5);
osabi = ELFOSABI_FREEBSD;
  }

`PT_OPENBSD_*` extensions are related to 
https://bugs.llvm.org//show_bug.cgi?id=31288 , which predated my involvement 
into lld.
It was not a good example of issue reports. Neither the bug nor the link it 
referenced provided rationale why such extensions were needed. CC @bradsmith 
here. I will also ask in their IRC channel and/or send an email to their 
mailing list.

The NetBSD extension does much more than FreeBSD (4 lines of code) and OpenBSD 
(7 lines of code modulo comments).
On the contrary, the NetBSD patch introduces another toplevel driver nb.lld, 
and includes ~200 lines of change.
Moreoever, I anticipate you will post another patch with probably than more 
than 200 lines of code that does 
https://blog.netbsd.org/tnf/entry/the_first_report_on_lld#handling-of-indirect-shared-library-dependencies
 , which many people (probably even the GNU maintainers) feel no longer 
appropriate nowadays.

> the linker MUST work in the standalone mode

By standalone mode, do you mean $(LD) or ld? I think for most such use cases, 
we should probably change them to do `gcc/clang -nostdlib` instead. In most 
cases users are not supposed to call ld directly. On FreeBSD (and Google 
servers and Android, if you consider them distributions), it has been proved 
many packages don't need ld customization to function properly.

If you can't migrate off those packages right now, a shell script that gets 
installed at "/usr/bin/ld" will probably work.

> clang NetBSD driver shall not hardcode LLD specific options

Several toolchains in the clang/lib/Driver/ToolChains detect lld and make lld 
specific decisions there. While I hope linker specific options should be kept 
at a minimum, I understand that sometimes it is unavoidable. When we have no 
choice but to add linker specific options, adding such code to clangDriver is 
an established practice followed by almost every toolchain (see Android, 
Fuchsia, MinGW, MSVC, etc). Doing the driver thing in two places will more 
likely to cause conflicts.

> the linker must have support for cross-building

I think this patch will actually harm cross building that targets NetBSD. 
Before, ld.lld is shared by all ELF platforms: Linux, FreeBSD, Fuchsia, 
Android, ChromeOS, etc. If an ELF change works on Linux, it will assuredly work 
on other platforms. This patch will introduce a new driver that naturally gets 
less test coverage.


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a comment.

Ping?


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a reviewer: chandlerc.
krytarowski added a comment.

Ping?

We are in the process of switching our buildbot to newer NetBSD snapshot (-8 to 
-9) and we keep waiting for this patch to land.

If we could get this patch merged, we could build and link the whole LLVM with 
lld on NetBSD and it would increase the productivity of the bot (better build 
times). Right now we need to maintain hacks to link at most with 2/3 cores, 
while 5/6 ones are idling doing nothing due to enormous RAM consumption of GNU 
ld.

We also upgraded LLVM in the current snapshot to a 10git version, and for the 
next snapshot merged (hopefully 10.0 or early 11git) we could ship it together 
with LLD aboard.


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a comment.

ping?


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a comment.

Short summary:

- FreeBSD/OpenBSD ship with mutations of the behavior of ELF/GNU/Linux in 
certain nits, we do the same with our driver.
- MinGW ships with a frontend driver to COFF, we do the same with a driver to 
ELF/GNU/Linux.
- Darwin ships with default search paths, we do the same in our driver.
- NetBSD is not a GNU system, it is a BSD system that differs with 
ELF/GNU/Linux, GNU/Linux is at most an inspiration, none of our project goals 
is about reimplementing Linux. The same applies to MinGW, Darwin etc that do 
not reimplement Linux.

The proposed change does not make anything without prior art.

LLD is practically the last piece of the LLVM toolchain stack without NetBSD 
support. We run the NetBSD buildbot for LLD since 2018 and there are no plans 
to detach it.

We intend to integrate LLD into our distribution, but we first must make it 
work in the upstream version out of the box.


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski updated this revision to Diff 228591.
krytarowski added a comment.

- fix a typo in a comment.


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Files:
  clang/lib/Driver/ToolChain.cpp
  lld/CMakeLists.txt
  lld/NetBSD/CMakeLists.txt
  lld/NetBSD/Driver.cpp
  lld/NetBSD/Options.td
  lld/include/lld/Common/Driver.h
  lld/tools/lld/CMakeLists.txt
  lld/tools/lld/lld.cpp

Index: lld/tools/lld/lld.cpp
===
--- lld/tools/lld/lld.cpp
+++ lld/tools/lld/lld.cpp
@@ -10,12 +10,13 @@
 // function is a thin wrapper which dispatches to the platform specific
 // driver.
 //
-// lld is a single executable that contains four different linkers for ELF,
-// COFF, WebAssembly and Mach-O. The main function dispatches according to
-// argv[0] (i.e. command name). The most common name for each target is shown
+// lld is a single executable that contains five different linkers for ELF,
+// NetBSD, COFF, WebAssembly and Mach-O. The main function dispatches according
+// to argv[0] (i.e. command name). The most common name for each target is shown
 // below:
 //
 //  - ld.lld:ELF (Unix)
+//  - nb.lld:ELF (NetBSD)
 //  - ld64:  Mach-O (macOS)
 //  - lld-link:  COFF (Windows)
 //  - ld-wasm:   WebAssembly
@@ -45,6 +46,7 @@
 enum Flavor {
   Invalid,
   Gnu, // -flavor gnu
+  NetBSD,  // -flavor netbsd
   WinLink, // -flavor link
   Darwin,  // -flavor darwin
   Wasm,// -flavor wasm
@@ -58,6 +60,7 @@
 static Flavor getFlavor(StringRef s) {
   return StringSwitch(s)
   .CasesLower("ld", "ld.lld", "gnu", Gnu)
+  .CasesLower("nb.lld", "netbsd", NetBSD)
   .CasesLower("wasm", "ld-wasm", Wasm)
   .CaseLower("link", WinLink)
   .CasesLower("ld64", "ld64.lld", "darwin", Darwin)
@@ -100,10 +103,15 @@
 #endif
 
 #if LLVM_ON_UNIX
-  // Use GNU driver for "ld" on other Unix-like system.
-  if (progname == "ld")
+  // Use GNU or NetBSD driver for "ld" on other Unix-like system.
+  if (progname == "ld") {
+#if defined(__NetBSD__)
+return NetBSD;
+#else
 return Gnu;
 #endif
+  }
+#endif
 
   // Progname may be something like "lld-gnu". Parse it.
   SmallVector v;
@@ -141,7 +149,7 @@
 // and we use it to detect whether we are running tests or not.
 static bool canExitEarly() { return StringRef(getenv("LLD_IN_TEST")) != "1"; }
 
-/// Universal linker main(). This linker emulates the gnu, darwin, or
+/// Universal linker main(). This linker emulates the gnu, netbsd, darwin, or
 /// windows linker based on the argv[0] or -flavor option.
 int main(int argc, const char **argv) {
   InitLLVM x(argc, argv);
@@ -152,6 +160,8 @@
 if (isPETarget(args))
   return !mingw::link(args);
 return !elf::link(args, canExitEarly());
+  case NetBSD:
+return !netbsd::link(args, canExitEarly());
   case WinLink:
 return !coff::link(args, canExitEarly());
   case Darwin:
@@ -160,7 +170,7 @@
 return !wasm::link(args, canExitEarly());
   default:
 die("lld is a generic driver.\n"
-"Invoke ld.lld (Unix), ld64.lld (macOS), lld-link (Windows), wasm-ld"
-" (WebAssembly) instead");
+"Invoke ld.lld (Unix), nb.lld (NetBSD), ld64.lld (macOS), lld-link "
+"(Windows), wasm-ld (WebAssembly) instead");
   }
 }
Index: lld/tools/lld/CMakeLists.txt
===
--- lld/tools/lld/CMakeLists.txt
+++ lld/tools/lld/CMakeLists.txt
@@ -12,6 +12,7 @@
   lldCOFF
   lldDriver
   lldELF
+  lldNetBSD
   lldMinGW
   lldWasm
   )
@@ -20,7 +21,7 @@
   RUNTIME DESTINATION bin)
 
 if(NOT LLD_SYMLINKS_TO_CREATE)
-  set(LLD_SYMLINKS_TO_CREATE lld-link ld.lld ld64.lld wasm-ld)
+  set(LLD_SYMLINKS_TO_CREATE lld-link ld.lld nb.lld ld64.lld wasm-ld)
 endif()
 
 foreach(link ${LLD_SYMLINKS_TO_CREATE})
Index: lld/include/lld/Common/Driver.h
===
--- lld/include/lld/Common/Driver.h
+++ lld/include/lld/Common/Driver.h
@@ -28,6 +28,11 @@
   llvm::raw_ostream  = llvm::errs());
 }
 
+namespace netbsd {
+bool link(llvm::ArrayRef args, bool canExitEarly,
+  llvm::raw_ostream  = llvm::errs());
+}
+
 namespace mach_o {
 bool link(llvm::ArrayRef args, bool canExitEarly,
   llvm::raw_ostream  = llvm::errs());
Index: lld/NetBSD/Options.td
===
--- /dev/null
+++ lld/NetBSD/Options.td
@@ -0,0 +1,7 @@
+include "llvm/Option/OptParser.td"
+
+class F: Flag<["--", "-"], name>;
+
+def version: F<"version">, HelpText<"Display the version number and exit">;
+def v: Flag<["-"], "v">, HelpText<"Display the version number">;
+def: Flag<["-"], "V">, Alias, HelpText<"Alias for --version">;
Index: lld/NetBSD/Driver.cpp
===
--- /dev/null
+++ lld/NetBSD/Driver.cpp
@@ -0,0 +1,187 @@
+//===- nb.lld.cpp - NetBSD 

[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski added a comment.

Another approach to achieve the same goal as previous attempts. It is already 
better as it avoids two forks.

Does this one look like fine for merging?

The previous one for the reference: https://reviews.llvm.org/D69755


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[PATCH] D70048: [LLD] Add NetBSD support as a new flavor of LLD (nb.lld)

[Kamil Rytarowski via Phabricator via cfe-commits]

krytarowski created this revision.
krytarowski added reviewers: joerg, mgorny, ruiu, MaskRay.
krytarowski added a project: lld.
Herald added subscribers: llvm-commits, cfe-commits, mstorsjo, fedor.sergeev, 
aheejin, emaste, dschuff.
Herald added projects: clang, LLVM.

The NetBSD target wraps the default Linux/ELF target with OS
specific customization. It is implemented as a light netbsd::link()
module wrapper that mutates arguments in argv[] and calls
elf::link().

This flavor detects the native/current and target Triple based on
argv[0] parsing. This is prerequisite for cross-compilation, in
particular the NetBSD distribution is cross-built always.

The default configuration of the ELF target is tuned for Linux and
there is no way to costomize in-place for the NetBSD target in the
same way as FreeBSD/OpenBSD. FreeBSD whenever needed can check
emulation name ("*_fbsd") and OpenBSD calls its extensions
"PT_OPENBSD_*".

This distinct flavor is needed for NetBSD as:

- the linker MUST work in the standalone mode
- it must be useful with gcc/pcc/others out of the box
- clang NetBSD driver shall not hardcode LLD specific options
- the linker must have support for cross-building
- LLD shall be a drop-in replacement for (NetBSD-patched) GNU ld

There is no code-duplication between the NetBSD and ELF modules.
The NetBSD driver for debugging purposes prints the Target string
for the -v|-V|--version command line argument. There is no functional
or code maintenance change for other Operating Systems, especially
the ELF ones.

Equivalent customization is already done for the Darwin mode. For
instance there are hardcoded default search paths such as "/usr/lib"
and "/Library/Frameworks" in DarwinLdDriver.cpp. There is a prior
art with the MinGW target that similarly wraps coff:link().

This change is a starting point for development of NetBSD support
in LLD.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D70048

Files:
  clang/lib/Driver/ToolChain.cpp
  lld/CMakeLists.txt
  lld/NetBSD/CMakeLists.txt
  lld/NetBSD/Driver.cpp
  lld/NetBSD/Options.td
  lld/include/lld/Common/Driver.h
  lld/tools/lld/CMakeLists.txt
  lld/tools/lld/lld.cpp

Index: lld/tools/lld/lld.cpp
===
--- lld/tools/lld/lld.cpp
+++ lld/tools/lld/lld.cpp
@@ -10,12 +10,13 @@
 // function is a thin wrapper which dispatches to the platform specific
 // driver.
 //
-// lld is a single executable that contains four different linkers for ELF,
-// COFF, WebAssembly and Mach-O. The main function dispatches according to
-// argv[0] (i.e. command name). The most common name for each target is shown
+// lld is a single executable that contains five different linkers for ELF,
+// NetBSD, COFF, WebAssembly and Mach-O. The main function dispatches according
+// to argv[0] (i.e. command name). The most common name for each target is shown
 // below:
 //
 //  - ld.lld:ELF (Unix)
+//  - nb.lld:ELF (NetBSD)
 //  - ld64:  Mach-O (macOS)
 //  - lld-link:  COFF (Windows)
 //  - ld-wasm:   WebAssembly
@@ -45,6 +46,7 @@
 enum Flavor {
   Invalid,
   Gnu, // -flavor gnu
+  NetBSD,  // -flavor netbsd
   WinLink, // -flavor link
   Darwin,  // -flavor darwin
   Wasm,// -flavor wasm
@@ -58,6 +60,7 @@
 static Flavor getFlavor(StringRef s) {
   return StringSwitch(s)
   .CasesLower("ld", "ld.lld", "gnu", Gnu)
+  .CasesLower("nb.lld", "netbsd", NetBSD)
   .CasesLower("wasm", "ld-wasm", Wasm)
   .CaseLower("link", WinLink)
   .CasesLower("ld64", "ld64.lld", "darwin", Darwin)
@@ -100,10 +103,15 @@
 #endif
 
 #if LLVM_ON_UNIX
-  // Use GNU driver for "ld" on other Unix-like system.
-  if (progname == "ld")
+  // Use GNU or NetBSD driver for "ld" on other Unix-like system.
+  if (progname == "ld") {
+#if defined(__NetBSD__)
+return NetBSD;
+#else
 return Gnu;
 #endif
+  }
+#endif
 
   // Progname may be something like "lld-gnu". Parse it.
   SmallVector v;
@@ -141,7 +149,7 @@
 // and we use it to detect whether we are running tests or not.
 static bool canExitEarly() { return StringRef(getenv("LLD_IN_TEST")) != "1"; }
 
-/// Universal linker main(). This linker emulates the gnu, darwin, or
+/// Universal linker main(). This linker emulates the gnu, netbsd, darwin, or
 /// windows linker based on the argv[0] or -flavor option.
 int main(int argc, const char **argv) {
   InitLLVM x(argc, argv);
@@ -152,6 +160,8 @@
 if (isPETarget(args))
   return !mingw::link(args);
 return !elf::link(args, canExitEarly());
+  case NetBSD:
+return !netbsd::link(args, canExitEarly());
   case WinLink:
 return !coff::link(args, canExitEarly());
   case Darwin:
@@ -160,7 +170,7 @@
 return !wasm::link(args, canExitEarly());
   default:
 die("lld is a generic driver.\n"
-"Invoke ld.lld (Unix), ld64.lld (macOS), lld-link (Windows), wasm-ld"
-" (WebAssembly) instead");
+"Invoke ld.lld (Unix), nb.lld (NetBSD), ld64.lld (macOS),