toolchains: board up broeken window, stub libxml2 to silence ld.lld warning by oharboe · Pull Request #9809 · The-OpenROAD-Project/OpenROAD

oharboe · 2026-03-18T15:36:25Z

avoids sudo ln hacks on Ubuntu, for instance.

ld.lld dynamically links libxml2 but only uses it for Windows manifest merging. Build a versioned stub into @llvm_prebuilt lib/ via patch_cmds so the RUNPATH picks it up instead of the system library, eliminating the "no version information available" warning and the libxml2-dev dependency.

oharboe · 2026-03-18T15:37:26Z

@hzeller 😿 What else can we do?

gemini-code-assist

Code Review

This pull request addresses the issue of ld.lld dynamically linking libxml2 by introducing a stub library. This eliminates the need for the libxml2-dev dependency and resolves the "no version information available" warning. The changes involve modifying the MODULE.bazel file to include the stub and adding new files for the stub's source and documentation. I have identified one area for improvement related to the patch command in MODULE.bazel.

gemini-code-assist · 2026-03-18T15:38:53Z

MODULE.bazel

+        """\
+cat > _stub.c << 'STUB'
+#include <stdlib.h>
+void *xmlFree = 0;
+void *xmlAddChild(void *p, void *c)                           { abort(); }
+void *xmlCopyNamespace(void *n)                                { abort(); }
+void  xmlDocDumpFormatMemoryEnc(void *d,void *b,void *s,
+                                const char *e, int f)          { abort(); }
+void *xmlDocGetRootElement(void *d)                            { abort(); }
+void *xmlDocSetRootElement(void *d, void *r)                   { abort(); }
+void  xmlFreeDoc(void *d)                                      { abort(); }
+void  xmlFreeNode(void *n)                                     { abort(); }
+void  xmlFreeNs(void *n)                                       { abort(); }
+void *xmlNewDoc(const void *v)                                 { abort(); }
+void *xmlNewNs(void *n, const void *h, const void *p)         { abort(); }
+void *xmlNewProp(void *n, const void *a, const void *v)       { abort(); }
+void *xmlReadMemory(const char *b, int sz, const char *u,
+                    const char *e, int o)                      { abort(); }
+void  xmlSetGenericErrorFunc(void *c, void *h)                 { abort(); }
+void *xmlStrdup(const void *s)                                 { abort(); }
+void  xmlUnlinkNode(void *n)                                   { abort(); }
+STUB
+
+cat > _stub.ver << 'VER'
+LIBXML2_2.4.30 {
+    global: xmlAddChild; xmlCopyNamespace; xmlDocDumpFormatMemoryEnc;
+            xmlDocGetRootElement; xmlDocSetRootElement; xmlFree;
+            xmlFreeDoc; xmlFreeNode; xmlFreeNs; xmlNewDoc; xmlNewNs;
+            xmlNewProp; xmlSetGenericErrorFunc; xmlStrdup; xmlUnlinkNode;
+    local: *;
+};
+LIBXML2_2.6.0 {
+    global: xmlReadMemory;
+} LIBXML2_2.4.30;
+VER
+
+cc -shared -o lib/libxml2.so.2 \
+    -Wl,--version-script=_stub.ver \
+    -Wl,-soname,libxml2.so.2 \
+    _stub.c \
+&& rm _stub.c _stub.ver
+""",


The patch_cmds script in MODULE.bazel compiles the stub inline. While functional, this approach tightly couples the stub's compilation details to the MODULE.bazel file. For better maintainability and separation of concerns, consider moving the compilation logic to a separate Bazel rule (e.g., a genrule in bazel/libxml2_stub/BUILD.bazel) and referencing the output of that rule in MODULE.bazel. This would make the stub more modular and easier to update or modify in the future.

Also, the patch_cmds attribute is executed during the repository fetching phase. Any errors in these commands can be difficult to debug, as they occur before the main build process. Moving the compilation to a standard Bazel rule would allow for better error reporting and debugging.

Finally, the canonical source is in bazel/libxml2_stub/, but the actual compilation happens in MODULE.bazel. This is inconsistent and could lead to confusion. Centralizing the logic in bazel/libxml2_stub/ would improve clarity.

github-actions

clang-tidy made some suggestions

github-actions · 2026-03-18T15:39:30Z

bazel/libxml2_stub/libxml2_stub.c

+
+#include <stdlib.h>
+
+void *xmlFree = NULL;


warning: inclusion of deprecated C++ header 'stdlib.h'; consider using 'cstdlib' instead [modernize-deprecated-headers]

Suggested change

void *xmlFree = NULL;

><cstdlib>

github-actions · 2026-03-18T15:39:30Z

bazel/libxml2_stub/libxml2_stub.c

+
+#include <stdlib.h>
+
+void *xmlFree = NULL;


warning: variable 'xmlFree' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void *xmlFree = NULL;

static

github-actions · 2026-03-18T15:39:30Z

bazel/libxml2_stub/libxml2_stub.c

+#include <stdlib.h>
+
+void *xmlFree = NULL;
+


warning: use nullptr [modernize-use-nullptr]

Suggested change

;nullptr

github-actions · 2026-03-18T15:39:30Z

bazel/libxml2_stub/libxml2_stub.c

+
+void *xmlFree = NULL;
+
+void *xmlAddChild(void *p, void *c)                      { abort(); }


warning: function 'xmlAddChild' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void *xmlAddChild(void *p, void *c) { abort(); }

static

github-actions · 2026-03-18T15:39:30Z

bazel/libxml2_stub/libxml2_stub.c

+void *xmlFree = NULL;
+
+void *xmlAddChild(void *p, void *c)                      { abort(); }
+void *xmlCopyNamespace(void *n)                           { abort(); }


warning: function 'xmlCopyNamespace' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void *xmlCopyNamespace(void *n) { abort(); }

}static

github-actions · 2026-03-18T15:39:31Z

bazel/libxml2_stub/libxml2_stub.c

+void  xmlFreeNs(void *n)                                  { abort(); }
+void *xmlNewDoc(const void *v)                            { abort(); }
+void *xmlNewNs(void *n, const void *h, const void *p)    { abort(); }
+void *xmlNewProp(void *n, const void *name, const void *v){ abort(); }


warning: function 'xmlNewProp' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void *xmlNewProp(void *n, const void *name, const void *v){ abort(); }

}static

github-actions · 2026-03-18T15:39:31Z

bazel/libxml2_stub/libxml2_stub.c

+void *xmlNewDoc(const void *v)                            { abort(); }
+void *xmlNewNs(void *n, const void *h, const void *p)    { abort(); }
+void *xmlNewProp(void *n, const void *name, const void *v){ abort(); }
+void *xmlReadMemory(const char *b, int sz, const char *u,


warning: function 'xmlReadMemory' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void *xmlReadMemory(const char *b, int sz, const char *u,

}static

github-actions · 2026-03-18T15:39:31Z

bazel/libxml2_stub/libxml2_stub.c

+void *xmlNewProp(void *n, const void *name, const void *v){ abort(); }
+void *xmlReadMemory(const char *b, int sz, const char *u,
+                    const char *e, int o)                 { abort(); }
+void  xmlSetGenericErrorFunc(void *c, void *h)            { abort(); }


warning: function 'xmlSetGenericErrorFunc' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void xmlSetGenericErrorFunc(void *c, void *h) { abort(); }

}static

github-actions · 2026-03-18T15:39:31Z

bazel/libxml2_stub/libxml2_stub.c

+void *xmlReadMemory(const char *b, int sz, const char *u,
+                    const char *e, int o)                 { abort(); }
+void  xmlSetGenericErrorFunc(void *c, void *h)            { abort(); }
+void *xmlStrdup(const void *s)                            { abort(); }


warning: function 'xmlStrdup' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void *xmlStrdup(const void *s) { abort(); }

}static

github-actions · 2026-03-18T15:39:31Z

bazel/libxml2_stub/libxml2_stub.c

+                    const char *e, int o)                 { abort(); }
+void  xmlSetGenericErrorFunc(void *c, void *h)            { abort(); }
+void *xmlStrdup(const void *s)                            { abort(); }
+void  xmlUnlinkNode(void *n)                              { abort(); }


warning: function 'xmlUnlinkNode' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void xmlUnlinkNode(void *n) { abort(); }

}static

…arning avoids sudo ln hacks on Ubuntu, for instance. ld.lld dynamically links libxml2 but only uses it for Windows manifest merging. Build a versioned stub into @llvm_prebuilt lib/ via patch_cmds so the RUNPATH picks it up instead of the system library, eliminating the "no version information available" warning and the libxml2-dev dependency. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

github-actions

clang-tidy made some suggestions

github-actions · 2026-03-18T15:48:37Z

bazel/libxml2_stub/libxml2_stub.c

+{
+  abort();
+}
+void* xmlCopyNamespace(void* n)


warning: function 'xmlCopyNamespace' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void* xmlCopyNamespace(void* n)

}static

github-actions · 2026-03-18T15:48:37Z

bazel/libxml2_stub/libxml2_stub.c

+{
+  abort();
+}
+void xmlDocDumpFormatMemoryEnc(void* d, void* b, void* s, const char* e, int f)


warning: function 'xmlDocDumpFormatMemoryEnc' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void xmlDocDumpFormatMemoryEnc(void* d, void* b, void* s, const char* e, int f)

}static

github-actions · 2026-03-18T15:48:38Z

bazel/libxml2_stub/libxml2_stub.c

+{
+  abort();
+}
+void* xmlDocGetRootElement(void* d)


warning: function 'xmlDocGetRootElement' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void* xmlDocGetRootElement(void* d)

}static

github-actions · 2026-03-18T15:48:38Z

bazel/libxml2_stub/libxml2_stub.c

+{
+  abort();
+}
+void* xmlDocSetRootElement(void* d, void* r)


warning: function 'xmlDocSetRootElement' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void* xmlDocSetRootElement(void* d, void* r)

}static

github-actions · 2026-03-18T15:48:38Z

bazel/libxml2_stub/libxml2_stub.c

+{
+  abort();
+}
+void xmlFreeDoc(void* d)


warning: function 'xmlFreeDoc' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void xmlFreeDoc(void* d)

}static

github-actions · 2026-03-18T15:48:38Z

bazel/libxml2_stub/libxml2_stub.c

+{
+  abort();
+}
+void* xmlNewProp(void* n, const void* name, const void* v)


warning: function 'xmlNewProp' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void* xmlNewProp(void* n, const void* name, const void* v)

}static

github-actions · 2026-03-18T15:48:38Z

bazel/libxml2_stub/libxml2_stub.c

+{
+  abort();
+}
+void* xmlReadMemory(const char* b, int sz, const char* u, const char* e, int o)


warning: function 'xmlReadMemory' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void* xmlReadMemory(const char* b, int sz, const char* u, const char* e, int o)

}static

github-actions · 2026-03-18T15:48:38Z

bazel/libxml2_stub/libxml2_stub.c

+{
+  abort();
+}
+void xmlSetGenericErrorFunc(void* c, void* h)


warning: function 'xmlSetGenericErrorFunc' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void xmlSetGenericErrorFunc(void* c, void* h)

}static

github-actions · 2026-03-18T15:48:38Z

bazel/libxml2_stub/libxml2_stub.c

+{
+  abort();
+}
+void* xmlStrdup(const void* s)


warning: function 'xmlStrdup' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void* xmlStrdup(const void* s)

}static

github-actions · 2026-03-18T15:48:38Z

bazel/libxml2_stub/libxml2_stub.c

+{
+  abort();
+}
+void xmlUnlinkNode(void* n)


warning: function 'xmlUnlinkNode' can be made static or moved into an anonymous namespace to enforce internal linkage [misc-use-internal-linkage]

Suggested change

void xmlUnlinkNode(void* n)

}static

These functions are exported .so entry points — external linkage is intentional and required for the shared library stub to satisfy ld.lld's dynamic dependency on libxml2.so.2. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

This is a C file — stdlib.h is the correct header, not cstdlib. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

This is a C file — NULL is correct, nullptr is C++ only. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

Address review concern about coupling compilation to MODULE.bazel: patch_cmds runs inside the downloaded archive and cannot reference workspace files, so the stub must be compiled inline. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

github-actions · 2026-03-18T21:43:33Z

clang-tidy review says "All clean, LGTM! 👍"

maliberty · 2026-03-18T22:32:46Z

Yuck. Where does this warning happen?

The stub shared library uses Linux-specific linker flags (--version-script, -soname) that do not exist on macOS ld, causing the Mac CI build to fail. Guard the compilation with a uname check so patch_cmds is a no-op on non-Linux. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

github-actions · 2026-03-18T22:45:43Z

clang-tidy review says "All clean, LGTM! 👍"

oharboe · 2026-03-18T22:48:28Z

Yuck. Where does this warning happen?

Ubuntu 25.10 and who knows where else... this will become better, but for now we don't need Windows xml manifest parsing, so just board up the broken window. It is easier to have Claude board up this broken window than to document it. We never saw it again. 😌

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

github-actions · 2026-03-19T09:00:53Z

clang-tidy review says "All clean, LGTM! 👍"

toolchains_llvm skips auto-download when any toolchain_root is set. Add a separate llvm_prebuilt_macos http_archive for macOS ARM64 and a second toolchain_root entry so macOS CI gets a valid toolchain root. The libxml2 stub is Linux-only, so the macOS archive needs no patching. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

github-actions · 2026-03-19T09:16:37Z

clang-tidy review says "All clean, LGTM! 👍"

maliberty · 2026-03-20T06:03:53Z

I still have no idea what the actual problem is. All this to solve a warning?

oharboe · 2026-03-20T07:29:10Z

I still have no idea what the actual problem is. All this to solve a warning?

Yes: users have to fix mysterious errors on Ubuntu when building with bazel without this. I think this is a shortcoming in the upstream bazel bcr llvm toolchain that will go away as bazel progresses. I'm thinking we should board up the broken window and forget all about it, surely they know upstream and they have a plan to fix it, it just takes time.

As the title says: I'm boarding up a broken window.

Important and useful warnings are drowned out by noise warnings and at some point nobody cares about warnings.

Bad.

@hzeller Thoughts?

oharboe · 2026-03-20T13:21:56Z

I get a ton of these:

INFO: From Linking external/googletest+/libgtest_main.so:
external/toolchains_llvm++llvm+llvm_toolchain/bin/../../toolchains_llvm++llvm+llvm_toolchain_llvm/bin/ld.lld: /lib/x86_64-linux-gnu/libxml2.so.2: no version information available (required by external/toolchains_llvm++llvm+llvm_toolchain/bin/../../toolchains_llvm++llvm+llvm_toolchain_llvm/bin/ld.lld)
external/toolchains_llvm++llvm+llvm_toolchain/bin/../../toolchains_llvm++llvm+llvm_toolchain_llvm/bin/ld.lld: /lib/x86_64-linux-gnu/libxml2.so.2: no version information available (required by external/toolchains_llvm++llvm+llvm_toolchain/bin/../../toolchains_llvm++llvm+llvm_toolchain_llvm/bin/ld.lld)

hzeller · 2026-03-20T19:07:11Z

I think the amount of changes to work around this temporary glitch is not useful. It creates immediate technical debt with a lot of head-scratching of someone trying to understand what is going on.

Not everything that can be hacked around with a massive hack that can be done by Claude ... is something one should be done :)

What I found is, that the builds of llvm are different and sometimes link in libxml, sometimes not, also tinfo is another library that is sometimes linked sometimes not. So I'd try to check a slightly compiler version (not 20.1.8 but something different), also with the newest 1.6.0 toolchains_llvm available on BCR.

If that doesn't work, I think for now it is ok to document that it won't work for certain versions of Ubuntu, and just recommend to comment out the @llvm_toolchain//:all part in register_toolchains to use the local compiler in that case.

oharboe requested a review from maliberty March 18, 2026 15:36

gemini-code-assist bot reviewed Mar 18, 2026

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github-actions bot reviewed Mar 18, 2026

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oharboe force-pushed the libxml-warning-fix branch 2 times, most recently from 36c072d to 96f485a Compare March 18, 2026 15:45

oharboe force-pushed the libxml-warning-fix branch from 96f485a to 32ec425 Compare March 18, 2026 15:45

github-actions bot reviewed Mar 18, 2026

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oharboe and others added 5 commits March 18, 2026 22:23

libxml2 stub: suppress modernize-deprecated-headers clang-tidy warning

f070a19

This is a C file — stdlib.h is the correct header, not cstdlib. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

libxml2 stub: suppress modernize-use-nullptr clang-tidy warning

5dc39ea

This is a C file — NULL is correct, nullptr is C++ only. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

Merge remote-tracking branch 'origin/master' into HEAD

f195140

llvm: fix mac

de8b81e

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

oharboe closed this Mar 20, 2026


		void *xmlFree = NULL;

		void xmlAddChild(void p, void *c) { abort(); }

	void xmlNewProp(void n, const void name, const void v){ abort(); }
	}static

	void xmlReadMemory(const char b, int sz, const char *u,
	}static

	void xmlSetGenericErrorFunc(void c, void h) { abort(); }
	}static

	void xmlDocDumpFormatMemoryEnc(void* d, void* b, void* s, const char* e, int f)
	}static

	void* xmlNewProp(void* n, const void* name, const void* v)
	}static

	void* xmlReadMemory(const char* b, int sz, const char* u, const char* e, int o)
	}static

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oharboe commented Mar 18, 2026

Uh oh!

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oharboe commented Mar 20, 2026 •

edited

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