[Driver] specify -stack-protector 0 for -fno-stack-protector

[nickdesaulniers]

Summary

-fno-stack-protector now explicitly sets -stack-protector 0 for the
invocation of cc1. In turn, -stack-protector 0 will set nossp IR fn attr
on all functions defined in the translation unit.

Fixes pr/47479.

[nickdesaulniers]

Might be nice to add an integration test where -fno-stack-protector results in nossp function attributes (so -fno-stack-protector -> -stack-protector 0 -> nossp fn attrs).

[nickdesaulniers]

In D90348#2360621, @nickdesaulniers wrote:

Might be nice to add an integration test where -fno-stack-protector results in nossp function attributes (so -fno-stack-protector -> -stack-protector 0 -> nossp fn attrs).

Oh, this is covered somewhat by clang/test/CodeGen/stack-protector.c which was updated in parent commit D90194.

[nickdesaulniers]

Bumping for review

[nickdesaulniers]

Prefer: https://reviews.llvm.org/D91816

clang/lib/CodeGen/CodeGenModule.cpp

if (CodeGenOpts.UnwindTables)
     B.addAttribute(llvm::Attribute::UWTable);
 
   if (CodeGenOpts.StackClashProtector)
     B.addAttribute("probe-stack", "inline-asm");
 
   if (!hasUnwindExceptions(LangOpts))
     B.addAttribute(llvm::Attribute::NoUnwind);
 
-  if (D && D->hasAttr<NoStackProtectorAttr>())
+  if (LangOpts.getStackProtector() == LangOptions::SSPOff ||
+      (D && D->hasAttr<NoStackProtectorAttr>()))
     B.addAttribute(llvm::Attribute::NoStackProtect);
   else if (LangOpts.getStackProtector() == LangOptions::SSPOn)
     B.addAttribute(llvm::Attribute::StackProtect);
   else if (LangOpts.getStackProtector() == LangOptions::SSPStrong)
     B.addAttribute(llvm::Attribute::StackProtectStrong);
   else if (LangOpts.getStackProtector() == LangOptions::SSPReq)
     B.addAttribute(llvm::Attribute::StackProtectReq);
 

clang/lib/Driver/ToolChains/Clang.cpp

if (A->getOption().matches(options::OPT_fstack_protector))
         StackProtectorLevel = LangOptions::SSPOn;
       else
         StackProtectorLevel =
             std::max<>(LangOptions::SSPOn, DefaultStackProtectorLevel);
     else if (A->getOption().matches(options::OPT_fstack_protector_strong))
       StackProtectorLevel = LangOptions::SSPStrong;
     else if (A->getOption().matches(options::OPT_fstack_protector_all))
       StackProtectorLevel = LangOptions::SSPReq;
+    else if (A->getOption().matches(options::OPT_fno_stack_protector))
+      StackProtectorLevel = LangOptions::SSPOff;
   } else {
     StackProtectorLevel = DefaultStackProtectorLevel;
   }
 
   if (StackProtectorLevel != LangOptions::SSPUnspecified) {
     CmdArgs.push_back("-stack-protector");
     CmdArgs.push_back(Args.MakeArgString(Twine(StackProtectorLevel)));
   }

clang/test/Driver/stack-protector.c

 // RUN: %clang -fno-stack-protector -### %s 2>&1 | FileCheck %s -check-prefix=NOSSP
-// NOSSP-NOT: "-stack-protector"
-// NOSSP-NOT: "-stack-protector-buffer-size" 
+// NOSSP: "-stack-protector" "0"
+// NOSSP-NOT: "-stack-protector-buffer-size"
 
 // RUN: %clang -target i386-unknown-linux -fstack-protector -### %s 2>&1 | FileCheck %s -check-prefix=SSP
 // SSP: "-stack-protector" "1"
 // SSP-NOT: "-stack-protector-buffer-size" 
 
 // RUN: %clang -target i386-unknown-linux -fstack-protector --param ssp-buffer-size=16 -### %s 2>&1 | FileCheck %s -check-prefix=SSP-BUF
 // SSP-BUF: "-stack-protector" "1"
 // SSP-BUF: "-stack-protector-buffer-size" "16"