[clang][Driver] Fix safestack -u ordering (#98468)

When re-enabling safestack testing on Solaris after the unexplained
b0260c5, all tests `FAIL`ed to link:

```
Undefined			first referenced
 symbol  			    in file
__safestack_unsafe_stack_ptr        buffer-copy-vla.o
__safestack_init                    (command line)
ld: fatal: symbol referencing errors
```

The problem is that `-u __safestack_init` was passed to the linker after
the corresponding version of `libclang_rt.safestack-*.a`. Since the
Solaris linker (like Unix linkers for decades) respects the command line
argument order (unlike e.g. GNU ld which uses GNU getopt), this cannot
work. Fixed by moving the `-u` arg further to the front. Two affected
testcases were fixed accordingly.

Tested on `amd64-pc-solaris2.11`, `sparcv9-sun-solaris2.11`,
`x86_64-pc-linux-gnu`, and `sparc64-unknown-linux-gnu`.

Author: rorth

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -1534,6 +1534,12 @@ bool tools::addSanitizerRuntimes(const ToolChain &TC, const ArgList &Args,
                              RequiredSymbols);
   }
 
+  // -u options must be added before the runtime libs that resolve them.
+  for (auto S : RequiredSymbols) {
+    CmdArgs.push_back("-u");
+    CmdArgs.push_back(Args.MakeArgString(S));
+  }
+
   // Inject libfuzzer dependencies.
   if (SanArgs.needsFuzzer() && SanArgs.linkRuntimes() &&
       !Args.hasArg(options::OPT_shared)) {
@@ -1566,10 +1572,6 @@ bool tools::addSanitizerRuntimes(const ToolChain &TC, const ArgList &Args,
     addSanitizerRuntime(TC, Args, CmdArgs, RT, false, false);
     AddExportDynamic |= !addSanitizerDynamicList(TC, Args, CmdArgs, RT);
   }
-  for (auto S : RequiredSymbols) {
-    CmdArgs.push_back("-u");
-    CmdArgs.push_back(Args.MakeArgString(S));
-  }
   // If there is a static runtime with no dynamic list, force all the symbols
   // to be dynamic to be sure we export sanitizer interface functions.
   if (AddExportDynamic)

clang/test/Driver/ohos.c

@@ -95,8 +95,8 @@
 // RUN:     | FileCheck %s -check-prefix=CHECK-SAFESTACK
 // CHECK-SAFESTACK: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
 // CHECK-SAFESTACK: "-fsanitize=safe-stack"
-// CHECK-SAFESTACK: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}arm-liteos-ohos{{/|\\\\}}libclang_rt.safestack.a"
 // CHECK-SAFESTACK: "__safestack_init"
+// CHECK-SAFESTACK: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}arm-liteos-ohos{{/|\\\\}}libclang_rt.safestack.a"
 
 // RUN: %clang %s -### --target=arm-liteos \
 // RUN:     -fsanitize=address 2>&1 \

clang/test/Driver/sanitizer-ld.c

@@ -753,8 +753,8 @@
 // CHECK-SAFESTACK-LINUX: "{{(.*[^-.0-9A-Z_a-z])?}}ld{{(.exe)?}}"
 // CHECK-SAFESTACK-LINUX-NOT: "-lc"
 // CHECK-SAFESTACK-LINUX-NOT: whole-archive
-// CHECK-SAFESTACK-LINUX: libclang_rt.safestack.a"
 // CHECK-SAFESTACK-LINUX: "-u" "__safestack_init"
+// CHECK-SAFESTACK-LINUX: libclang_rt.safestack.a"
 // CHECK-SAFESTACK-LINUX: "-lpthread"
 // CHECK-SAFESTACK-LINUX: "-ldl"
 // CHECK-SAFESTACK-LINUX: "-lresolv"