[lld][ELF]Emit warning when both scripts are specified #163497

mingmingl-llvm · 2025-10-15T05:03:11Z

For lld ELF, there are two ways of specifying linker script, -Wl,--script and -Wl,--default-script. The latter one is used if the former one is absent, and the former one takes precedence.

This patch proposes to emit warning for compiler user awareness when both are specified.

The motivating use case is elaborated below:

For a binary whose build configuration is managed by bazel, --script and --default-script specification might be scattered in more than one file, and it's obscure for compiler user to tell which one is used.

llvmbot · 2025-10-15T05:03:43Z

@llvm/pr-subscribers-lld-elf

Author: Mingming Liu (mingmingl-llvm)

Changes

For lld ELF, there are two ways of specifying linker script, -Wl,--script and -Wl,--default-script. The latter one is used if the former one is absent, and the former one takes precedence.

This patch proposes to emit warning for compiler user information when both are specified.

Full diff: https://github.com/llvm/llvm-project/pull/163497.diff

2 Files Affected:

(modified) lld/ELF/Driver.cpp (+9)
(modified) lld/test/ELF/linkerscript/default-script.s (+12)

diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 62f7fffce7dbe..c8cce0810ef9a 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -2091,6 +2091,7 @@ void LinkerDriver::createFiles(opt::InputArgList &args) {
   nextGroupId = 0;
   isInGroup = false;
   bool hasInput = false, hasScript = false;
+  StringRef scriptFilePath, defaultScriptFilePath;
   for (auto *arg : args) {
     switch (arg->getOption().getID()) {
     case OPT_library:
@@ -2106,7 +2107,11 @@ void LinkerDriver::createFiles(opt::InputArgList &args) {
       break;
     }
     case OPT_script:
+      scriptFilePath = arg->getValue();
+      [[fallthrough]];
     case OPT_default_script:
+      if (arg->getOption().matches(OPT_default_script))
+        defaultScriptFilePath = arg->getValue();
       if (std::optional<std::string> path =
               searchScript(ctx, arg->getValue())) {
         if (std::optional<MemoryBufferRef> mb = readFile(ctx, *path)) {
@@ -2201,6 +2206,10 @@ void LinkerDriver::createFiles(opt::InputArgList &args) {
 
   if (defaultScript && !hasScript)
     readLinkerScript(ctx, *defaultScript);
+  if (defaultScript && hasScript)
+    Warn(ctx) << "--script at path " << scriptFilePath
+              << " will override --default-script at path "
+              << defaultScriptFilePath;
   if (files.empty() && !hasInput && errCount(ctx) == 0)
     ErrAlways(ctx) << "no input files";
 }
diff --git a/lld/test/ELF/linkerscript/default-script.s b/lld/test/ELF/linkerscript/default-script.s
index bb716a5fe0cdd..a06f96b7165d4 100644
--- a/lld/test/ELF/linkerscript/default-script.s
+++ b/lld/test/ELF/linkerscript/default-script.s
@@ -32,6 +32,17 @@
 # CHECK1-NEXT: 3: 000000000000002a     0 NOTYPE  GLOBAL DEFAULT   ABS def
 # CHECK1-EMPTY:
 
+## When both --script and --default-script are specified, --script overrides
+## --default-script.
+# RUN: ld.lld --default-script def.t --script b.t a.o -o out2 2>warn.txt
+# RUN: llvm-readelf -Ss out2 | FileCheck %s --check-prefix=OVERRIDE
+# OVERRIDE:      .foo0
+# OVERRIDE-NEXT: foo1
+# OVERRIDE-NEXT: foo2
+# RUN: cat warn.txt | FileCheck %s --check-prefix=WARNING
+# WARNING: --script at path b.t will override --default-script at path def.t
+
+
 # RUN: not ld.lld --default-script not-exist.t b.t -T a.t a.o 2>&1 | FileCheck %s --check-prefix=ERR
 # ERR: error: cannot find linker script not-exist.t
 
@@ -61,3 +72,4 @@ SECTIONS {
   .foo1 : {}
   .foo0 : {}
 }
+

llvmbot · 2025-10-15T05:03:44Z

@llvm/pr-subscribers-lld

Author: Mingming Liu (mingmingl-llvm)

Changes

For lld ELF, there are two ways of specifying linker script, -Wl,--script and -Wl,--default-script. The latter one is used if the former one is absent, and the former one takes precedence.

This patch proposes to emit warning for compiler user information when both are specified.

Full diff: https://github.com/llvm/llvm-project/pull/163497.diff

2 Files Affected:

(modified) lld/ELF/Driver.cpp (+9)
(modified) lld/test/ELF/linkerscript/default-script.s (+12)

diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 62f7fffce7dbe..c8cce0810ef9a 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -2091,6 +2091,7 @@ void LinkerDriver::createFiles(opt::InputArgList &args) {
   nextGroupId = 0;
   isInGroup = false;
   bool hasInput = false, hasScript = false;
+  StringRef scriptFilePath, defaultScriptFilePath;
   for (auto *arg : args) {
     switch (arg->getOption().getID()) {
     case OPT_library:
@@ -2106,7 +2107,11 @@ void LinkerDriver::createFiles(opt::InputArgList &args) {
       break;
     }
     case OPT_script:
+      scriptFilePath = arg->getValue();
+      [[fallthrough]];
     case OPT_default_script:
+      if (arg->getOption().matches(OPT_default_script))
+        defaultScriptFilePath = arg->getValue();
       if (std::optional<std::string> path =
               searchScript(ctx, arg->getValue())) {
         if (std::optional<MemoryBufferRef> mb = readFile(ctx, *path)) {
@@ -2201,6 +2206,10 @@ void LinkerDriver::createFiles(opt::InputArgList &args) {
 
   if (defaultScript && !hasScript)
     readLinkerScript(ctx, *defaultScript);
+  if (defaultScript && hasScript)
+    Warn(ctx) << "--script at path " << scriptFilePath
+              << " will override --default-script at path "
+              << defaultScriptFilePath;
   if (files.empty() && !hasInput && errCount(ctx) == 0)
     ErrAlways(ctx) << "no input files";
 }
diff --git a/lld/test/ELF/linkerscript/default-script.s b/lld/test/ELF/linkerscript/default-script.s
index bb716a5fe0cdd..a06f96b7165d4 100644
--- a/lld/test/ELF/linkerscript/default-script.s
+++ b/lld/test/ELF/linkerscript/default-script.s
@@ -32,6 +32,17 @@
 # CHECK1-NEXT: 3: 000000000000002a     0 NOTYPE  GLOBAL DEFAULT   ABS def
 # CHECK1-EMPTY:
 
+## When both --script and --default-script are specified, --script overrides
+## --default-script.
+# RUN: ld.lld --default-script def.t --script b.t a.o -o out2 2>warn.txt
+# RUN: llvm-readelf -Ss out2 | FileCheck %s --check-prefix=OVERRIDE
+# OVERRIDE:      .foo0
+# OVERRIDE-NEXT: foo1
+# OVERRIDE-NEXT: foo2
+# RUN: cat warn.txt | FileCheck %s --check-prefix=WARNING
+# WARNING: --script at path b.t will override --default-script at path def.t
+
+
 # RUN: not ld.lld --default-script not-exist.t b.t -T a.t a.o 2>&1 | FileCheck %s --check-prefix=ERR
 # ERR: error: cannot find linker script not-exist.t
 
@@ -61,3 +72,4 @@ SECTIONS {
   .foo1 : {}
   .foo0 : {}
 }
+

lenary · 2025-10-15T05:13:28Z

I believe the intention of --default-script is to be used by e.g. toolchain configs, so that users can override the script if they have one of their own. In this usecase a warning would not be wanted, because the options are working as expected.

My understanding could be wrong, I'll defer to MaskRay if he has other opinions.

MaskRay

I agree with lenary's analysis. The design intent of --default-script is to allow it to be overridden by linker scripts without generating a warning (or an error if --fatal-warnings is used). A lint could be added to a linker wrapper to report the warning, but this functionality should not be part of LLD itself.

mingmingl-llvm · 2025-10-15T05:21:48Z

Thanks for sharing the thoughts folks!

I believe the intention of --default-script is to be used by e.g. toolchain configs, so that users can override the script if they have one of their own.

Exactly. This matches how --default-script is used on the motivating use cases.

A lint could be added to a linker wrapper to report the warning, but this functionality should not be part of LLD itself.

This is not unreasonable. I'll close this patch then.

lenary · 2025-10-16T00:58:50Z

One thought is whether we should be documenting --default-script for users at all, if it's effectively a hidden option for toolchains to use. Maybe not making it visible to users might reduce confusion?

mingmingl-llvm · 2025-10-18T06:03:06Z

One thought is whether we should be documenting --default-script for users at all, if it's effectively a hidden option for toolchains to use. Maybe not making it visible to users might reduce confusion?

I'm in favor of the idea to make --default-script more visible to toolchain users. Is there a canonical (.rst) file to make this change? Or is it more conventional to start a new .rst for linker script support, like https://lld.llvm.org/ELF/start-stop-gc.html does for 'start-stop-gc'?

MaskRay · 2025-10-18T18:52:18Z

This option is relatively obscure but offers value when necessary.
The description of its supported linker script syntax is in docs/ELF/linker_script.rst

[lld][ELF]Emit warning when both scripts are specified

b0f593a

mingmingl-llvm requested a review from MaskRay October 15, 2025 05:03

llvmbot added lld lld:ELF labels Oct 15, 2025

trim blank lines

a96588d

MaskRay requested changes Oct 15, 2025

View reviewed changes

mingmingl-llvm closed this Oct 15, 2025

mingmingl-llvm deleted the users/mingmingl-llvm/lld-linker-script branch October 18, 2025 06:03

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[lld][ELF]Emit warning when both scripts are specified #163497

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