[LLD][COFF] Do as many passes of resolveRemainingUndefines as necessary for undefined lazy symbols #109082

glandium · 2024-09-18T04:16:55Z

No description provided.

llvmbot · 2024-09-18T04:17:29Z

@llvm/pr-subscribers-platform-windows

@llvm/pr-subscribers-lld

Author: Mike Hommey (glandium)

Changes

Cc: @mstorsjo

This addresses #107365 except for the strdup part.

Full diff: https://github.com/llvm/llvm-project/pull/109082.diff

3 Files Affected:

(modified) lld/COFF/Driver.cpp (+4-1)
(modified) lld/COFF/SymbolTable.cpp (+8-1)
(modified) lld/COFF/SymbolTable.h (+4-1)

diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index 1b94f10acf80e5..38a507cb9752ff 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -2601,7 +2601,10 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
     createECExportThunks();
 
   // Resolve remaining undefined symbols and warn about imported locals.
-  ctx.symtab.resolveRemainingUndefines();
+  if (ctx.symtab.resolveRemainingUndefines()) {
+    run();
+    ctx.symtab.resolveRemainingUndefines();
+  }
   if (errorCount())
     return;
 
diff --git a/lld/COFF/SymbolTable.cpp b/lld/COFF/SymbolTable.cpp
index efea16ccbbfea0..8d69a3966e638f 100644
--- a/lld/COFF/SymbolTable.cpp
+++ b/lld/COFF/SymbolTable.cpp
@@ -479,10 +479,11 @@ void SymbolTable::reportUnresolvable() {
                        /* localImports */ nullptr, true);
 }
 
-void SymbolTable::resolveRemainingUndefines() {
+bool SymbolTable::resolveRemainingUndefines() {
   llvm::TimeTraceScope timeScope("Resolve remaining undefined symbols");
   SmallPtrSet<Symbol *, 8> undefs;
   DenseMap<Symbol *, Symbol *> localImports;
+  bool foundLazy = false;
 
   for (auto &i : symMap) {
     Symbol *sym = i.second;
@@ -502,6 +503,11 @@ void SymbolTable::resolveRemainingUndefines() {
     // This odd rule is for compatibility with MSVC linker.
     if (name.starts_with("__imp_")) {
       Symbol *imp = find(name.substr(strlen("__imp_")));
+      if (imp && imp->isLazy()) {
+        forceLazy(imp);
+        foundLazy = true;
+        continue;
+      }
       if (imp && isa<Defined>(imp)) {
         auto *d = cast<Defined>(imp);
         replaceSymbol<DefinedLocalImport>(sym, ctx, name, d);
@@ -529,6 +535,7 @@ void SymbolTable::resolveRemainingUndefines() {
   reportProblemSymbols(
       ctx, undefs,
       ctx.config.warnLocallyDefinedImported ? &localImports : nullptr, false);
+  return foundLazy;
 }
 
 std::pair<Symbol *, bool> SymbolTable::insert(StringRef name) {
diff --git a/lld/COFF/SymbolTable.h b/lld/COFF/SymbolTable.h
index bf97cf442039e0..1ab35a87cb9fad 100644
--- a/lld/COFF/SymbolTable.h
+++ b/lld/COFF/SymbolTable.h
@@ -57,7 +57,10 @@ class SymbolTable {
   // Try to resolve any undefined symbols and update the symbol table
   // accordingly, then print an error message for any remaining undefined
   // symbols and warn about imported local symbols.
-  void resolveRemainingUndefines();
+  // Returns whether more files might need to be linked in to resolve lazy
+  // symbols, in which case the caller is expected to call the function again
+  // after linking those files.
+  bool resolveRemainingUndefines();
 
   // Load lazy objects that are needed for MinGW automatic import and for
   // doing stdcall fixups.

llvmbot · 2024-09-18T04:17:30Z

@llvm/pr-subscribers-lld-coff

Author: Mike Hommey (glandium)

Changes

Cc: @mstorsjo

This addresses #107365 except for the strdup part.

Full diff: https://github.com/llvm/llvm-project/pull/109082.diff

3 Files Affected:

(modified) lld/COFF/Driver.cpp (+4-1)
(modified) lld/COFF/SymbolTable.cpp (+8-1)
(modified) lld/COFF/SymbolTable.h (+4-1)

diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index 1b94f10acf80e5..38a507cb9752ff 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -2601,7 +2601,10 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
     createECExportThunks();
 
   // Resolve remaining undefined symbols and warn about imported locals.
-  ctx.symtab.resolveRemainingUndefines();
+  if (ctx.symtab.resolveRemainingUndefines()) {
+    run();
+    ctx.symtab.resolveRemainingUndefines();
+  }
   if (errorCount())
     return;
 
diff --git a/lld/COFF/SymbolTable.cpp b/lld/COFF/SymbolTable.cpp
index efea16ccbbfea0..8d69a3966e638f 100644
--- a/lld/COFF/SymbolTable.cpp
+++ b/lld/COFF/SymbolTable.cpp
@@ -479,10 +479,11 @@ void SymbolTable::reportUnresolvable() {
                        /* localImports */ nullptr, true);
 }
 
-void SymbolTable::resolveRemainingUndefines() {
+bool SymbolTable::resolveRemainingUndefines() {
   llvm::TimeTraceScope timeScope("Resolve remaining undefined symbols");
   SmallPtrSet<Symbol *, 8> undefs;
   DenseMap<Symbol *, Symbol *> localImports;
+  bool foundLazy = false;
 
   for (auto &i : symMap) {
     Symbol *sym = i.second;
@@ -502,6 +503,11 @@ void SymbolTable::resolveRemainingUndefines() {
     // This odd rule is for compatibility with MSVC linker.
     if (name.starts_with("__imp_")) {
       Symbol *imp = find(name.substr(strlen("__imp_")));
+      if (imp && imp->isLazy()) {
+        forceLazy(imp);
+        foundLazy = true;
+        continue;
+      }
       if (imp && isa<Defined>(imp)) {
         auto *d = cast<Defined>(imp);
         replaceSymbol<DefinedLocalImport>(sym, ctx, name, d);
@@ -529,6 +535,7 @@ void SymbolTable::resolveRemainingUndefines() {
   reportProblemSymbols(
       ctx, undefs,
       ctx.config.warnLocallyDefinedImported ? &localImports : nullptr, false);
+  return foundLazy;
 }
 
 std::pair<Symbol *, bool> SymbolTable::insert(StringRef name) {
diff --git a/lld/COFF/SymbolTable.h b/lld/COFF/SymbolTable.h
index bf97cf442039e0..1ab35a87cb9fad 100644
--- a/lld/COFF/SymbolTable.h
+++ b/lld/COFF/SymbolTable.h
@@ -57,7 +57,10 @@ class SymbolTable {
   // Try to resolve any undefined symbols and update the symbol table
   // accordingly, then print an error message for any remaining undefined
   // symbols and warn about imported local symbols.
-  void resolveRemainingUndefines();
+  // Returns whether more files might need to be linked in to resolve lazy
+  // symbols, in which case the caller is expected to call the function again
+  // after linking those files.
+  bool resolveRemainingUndefines();
 
   // Load lazy objects that are needed for MinGW automatic import and for
   // doing stdcall fixups.

mstorsjo

The change looks good to me, thanks! But this would need a testcase.

Have a look in lld/test/COFF, some of the more modern testcases using split-file probably serves as the best example. I guess this can be testable with three .s files:
One that contains an undefined reference to __imp_func. Two .s files that are assembled and stored in a static library. One containing a definition of func, and with an undefined reference to other, and the second static library object containing a definition of other.

Then make sure that the testcase does fail on current git main, and succeeds after this change. The third object file containing other might simulate the need for calling run() after forceLazy() - ideally the test should still fail if the run() is removed (but it can also be possible that the test still passes despite that - but we probably still need the run() just to be safe).

lld/COFF/Driver.cpp

mstorsjo · 2024-09-18T07:12:26Z

lld/COFF/SymbolTable.cpp

@@ -502,6 +503,11 @@ void SymbolTable::resolveRemainingUndefines() {
    // This odd rule is for compatibility with MSVC linker.
    if (name.starts_with("__imp_")) {
      Symbol *imp = find(name.substr(strlen("__imp_")));


Side note, I find the variable name imp here kinda misleading, as it's the imp-less symbol! (We can consider changing it in a separate patch later.)

glandium · 2024-09-18T09:11:42Z

One that contains an undefined reference to __imp_func. Two .s files that are assembled and stored in a static library. One containing a definition of func, and with an undefined reference to other, and the second static library object containing a definition of other.

I think there needs to be a DLL involved for the lazy linking?

mstorsjo · 2024-09-18T09:15:18Z

One that contains an undefined reference to __imp_func. Two .s files that are assembled and stored in a static library. One containing a definition of func, and with an undefined reference to other, and the second static library object containing a definition of other.

I think there needs to be a DLL involved for the lazy linking?

Hm, I don't think so? Isn't the lazy symbols just for static libraries, where we've seen symbols and know we can load them if needed, but don't do it unless triggered.

I may very well be wrong though - I guess you'll see what's needed to actually trigger the relevant cases.

glandium · 2024-09-18T09:29:09Z

Ah, I was misremembering and mixing things up with the other lld-link issue I filed with delayload.

glandium · 2024-09-18T11:46:16Z

This new version has the while loop and is rebased on top of current main. I haven't included a test yet.

glandium · 2024-09-18T12:25:58Z

I double checked the test fails without the patch and passes with.

mstorsjo

LGTM overall, thanks! Two minor nits, one inline, and the other about the PR description:

As LLVM uses the "merge and squash" method, the PR subject + description ends up as the commit message (although whoever merges it has a chance to touch it up), so it's good to edit it into the form that is wanted as the final commit message.

In this case, CCs and similar unfortunately is best to do in a separate comment after. It's good to include the issue reference though, but at this point it actually does fix the issue completely AFAIK, so that can be tweaked too.

mstorsjo · 2024-09-18T12:27:21Z

lld/COFF/Driver.cpp

-  ctx.symtab.resolveRemainingUndefines();
+  while (ctx.symtab.resolveRemainingUndefines()) {
+    run();
+  }


I think we stylistically tend to omit the braces for these kinds of single-line statements, see https://llvm.org/docs/CodingStandards.html#don-t-use-braces-on-simple-single-statement-bodies-of-if-else-loop-statements.

…ry for undefined lazy symbols

glandium · 2024-09-19T07:37:47Z

Unfortunately, it seems not to be enough. Further down the line, it seems the import symbols aren't getting a proper relocation.

glandium · 2024-09-19T07:42:35Z

(And the cherry on top: llvm-readobj crashes on the problematic binary)

mstorsjo · 2024-09-19T08:28:43Z

Unfortunately, it seems not to be enough. Further down the line, it seems the import symbols aren't getting a proper relocation.

Hmm, that's tricky :-( I think this patch in itself looks correct in any case, so I think that whatever incorrect relocation you have is related to something else - but I don't mind hold off and waiting for that to be figured out before proceeding with this one.

glandium · 2024-09-19T08:34:14Z

This is the repro that ends up broken because of missing relocations:
https://drive.google.com/file/d/1qh0dWMsg4xftyijorkEMudx4rsi-LVXI/view?usp=sharing
without the patch, it fails with:

lld-link: warning: libwhatsys-6987fe4a7a53db19.rlib(db3b6bfb95261072-windows.o): locally defined symbol imported: strncpy_s (defined in libucrt.lib(strncpy_s.obj)) [LNK4217]
lld-link: warning: libwhatsys-6987fe4a7a53db19.rlib(db3b6bfb95261072-windows.o): locally defined symbol imported: __stdio_common_vsprintf (defined in libucrt.lib(output.obj)) [LNK4217]
lld-link: warning: liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-mdb.o): locally defined symbol imported: __stdio_common_vsprintf (defined in libucrt.lib(output.obj)) [LNK4217]
lld-link: warning: liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-mdb.o): locally defined symbol imported: strerror (defined in libucrt.lib(strerror.obj)) [LNK4217]
lld-link: warning: liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-mdb.o): locally defined symbol imported: calloc (defined in libucrt.lib(calloc.obj)) [LNK4217]
lld-link: warning: liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-mdb.o): locally defined symbol imported: malloc (defined in libucrt.lib(malloc.obj)) [LNK4217]
lld-link: warning: liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-mdb.o): locally defined symbol imported: free (defined in libucrt.lib(free.obj)) [LNK4217]
lld-link: warning: liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-mdb.o): locally defined symbol imported: strncmp (defined in libucrt.lib(strncmp.obj)) [LNK4217]
lld-link: warning: liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-midl.o): locally defined symbol imported: malloc (defined in libucrt.lib(malloc.obj)) [LNK4217]
lld-link: warning: liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-midl.o): locally defined symbol imported: free (defined in libucrt.lib(free.obj)) [LNK4217]
lld-link: warning: liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-midl.o): locally defined symbol imported: realloc (defined in libucrt.lib(realloc.obj)) [LNK4217]
lld-link: warning: oldnames.lib(strdup.obi): locally defined symbol imported: _strdup (defined in libucrt.lib(strdup.obj)) [LNK4217]
lld-link: error: undefined symbol: __declspec(dllimport) wcscpy
>>> referenced by /tmp/gecko/third_party/rust/lmdb-rkv-sys/lmdb/libraries/liblmdb/mdb.c:4238
>>>               liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-mdb.o):(mdb_fopen)

lld-link: error: undefined symbol: __declspec(dllimport) _aligned_malloc
>>> referenced by /tmp/gecko/third_party/rust/lmdb-rkv-sys/lmdb/libraries/liblmdb/mdb.c:9324
>>>               liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-mdb.o):(mdb_env_copyfd1)

lld-link: error: undefined symbol: __declspec(dllimport) _aligned_free
>>> referenced by /tmp/gecko/third_party/rust/lmdb-rkv-sys/lmdb/libraries/liblmdb/mdb.c:9425
>>>               liblmdb_sys-f56ac55de745eb3d.rlib(61d5b3baa82548eb-mdb.o):(mdb_env_copyfd1)

With the patch, executing the binary crashes (to reduce noise from the number of processes spawned, you may run crashreporter-6497c44cdd21c683.exe test::glean_ping_) because __stdio_common_vsprintf doesn't point to the right place (but so do _imp_wcscpy, _imp_aligned_malloc and _imp_aligned_free, and probably the others, but I don't know about that for sure)

glandium · 2024-09-19T08:34:58Z

So indeed, it's probably some preexisting problem that is now exposed because the link goes through now.

glandium · 2024-09-19T10:01:38Z

Boy, this link is actually a mess. link.exe complains about wcscpy, aligned_malloc and aligned_free being missing, and it looks like it's right to do so, because they are in ucrt.lib, but it's not on the command line. But adding it conflicts with libucrt.lib that is pulled in via a /defaultlib directive in libcmt.lib.

glandium · 2024-10-02T22:33:34Z

Let's land this out of caution after all. @mstorsjo can you do that for me?

mstorsjo · 2024-10-03T19:53:21Z

Let's land this out of caution after all. @mstorsjo can you do that for me?

Sure; while the case is a bit contrieved, it's fully possible to hit, so this should be a valid fix for that.

llvmbot added lld lld:COFF platform:windows labels Sep 18, 2024

glandium marked this pull request as draft September 18, 2024 06:41

mstorsjo reviewed Sep 18, 2024

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glandium force-pushed the lld-coff-resolve-remaining-undefines branch from c44939f to 23061e5 Compare September 18, 2024 11:45

glandium force-pushed the lld-coff-resolve-remaining-undefines branch from 23061e5 to 16899d3 Compare September 18, 2024 12:24

glandium marked this pull request as ready for review September 18, 2024 12:25

mstorsjo approved these changes Sep 18, 2024

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glandium changed the title ~~[LLD][COFF] Do another pass of resolveRemainingUndefines for undefined lazy symbols~~ [LLD][COFF] Do as many passes of resolveRemainingUndefines as necessary for undefined lazy symbols Sep 18, 2024

[LLD][COFF] Do as many passes of resolveRemainingUndefines as necessa…

f6a6060

…ry for undefined lazy symbols

glandium force-pushed the lld-coff-resolve-remaining-undefines branch from 16899d3 to f6a6060 Compare September 19, 2024 00:02

glandium marked this pull request as draft September 19, 2024 07:37

glandium mentioned this pull request Sep 20, 2024

[lld][coff] undefined symbols from lazy-loaded archives #107365

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glandium marked this pull request as ready for review October 2, 2024 22:33

mstorsjo merged commit 6a1bdd9 into llvm:main Oct 3, 2024
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[LLD][COFF] Do as many passes of resolveRemainingUndefines as necessary for undefined lazy symbols #109082

[LLD][COFF] Do as many passes of resolveRemainingUndefines as necessary for undefined lazy symbols #109082

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[LLD][COFF] Do as many passes of resolveRemainingUndefines as necessary for undefined lazy symbols #109082

[LLD][COFF] Do as many passes of resolveRemainingUndefines as necessary for undefined lazy symbols #109082

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