[PowerPC] Default ppc64 linux-gnu/freebsd to -fno-PIC

[MaskRay]

Summary

According to D53384, the default was switched from -fno-PIC to -fPIC to
work around a -fsanitize=leak bug on big-endian.

This gratuitous difference between little-endian and big-endian is
undesired, and not acceptable on powerpc64-unknown-freebsd. If
-fsanitize=leak still has the problem, we should default to -fPIC/-fPIE
only when -fsanitize=leak is specified.

powerpc64-ibm-aix is unaffected: it still defaults to -fPIC.
powerpc64-linux-musl is unaffected: it still defaults to -fPIE.

[Bdragon28]

I am definitely in favor of this change, as the defaulting to PIC has been causing headaches in the FreeBSD kernel.

[merge_guards_bot]

Unit tests: pass. 61304 tests passed, 0 failed and 736 were skipped.

clang-tidy: pass.

clang-format: fail. Please format your changes with clang-format by running git-clang-format HEAD^ or applying this patch.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

[sfertile]

LGTM: I really didn't like setting PIC as the default just to work around some codegen bugs. I believe there are PowerPC codegen tests that will fail with this change though (or perhaps there is a PowerPC leak sanitizer build bot which begins to fail? @stefanp probably knows what exposed the BE issue previously).

A couple minor questions though: Is there a way to emit a warning if the leak sanitizer is used on ELF powerpc64 and PIC/PIE is not also specified? Where should we document that the leak sanitizer needs additional options for a specific target?

[MaskRay]

In D72363#1810036, @sfertile wrote:

LGTM: I really didn't like setting PIC as the default just to work around some codegen bugs. I believe there are PowerPC codegen tests that will fail with this change though (or perhaps there is a PowerPC leak sanitizer build bot which begins to fail? @stefanp probably knows what exposed the BE issue previously).

A couple minor questions though: Is there a way to emit a warning if the leak sanitizer is used on ELF powerpc64 and PIC/PIE is not also specified? Where should we document that the leak sanitizer needs additional options for a specific target?

Some sanitizers default to -fPIE. It -fsanitize=leak still has the bug and there is a desire (imho this is not a very good idea to make BE/LE gratuitously different), getSanitizerArgs().requiresPIE() can be a candidate to patch:

bool Linux::isPIEDefault() const {
  return (getTriple().isAndroid() && !getTriple().isAndroidVersionLT(16)) ||
          getTriple().isMusl() || getSanitizerArgs().requiresPIE();
}

clang/lib/Driver/ToolChains/Gnu.cpp

 bool Generic_GCC::IsUnwindTablesDefault(const ArgList &Args) const {
   return getArch() == llvm::Triple::x86_64;
 }
 
 bool Generic_GCC::isPICDefault() const {
   switch (getArch()) {
   case llvm::Triple::x86_64:
     return getTriple().isOSWindows();
-  case llvm::Triple::ppc64:
-    // Big endian PPC is PIC by default
-    return !getTriple().isOSBinFormatMachO() && !getTriple().isMacOSX();
   case llvm::Triple::mips64:
   case llvm::Triple::mips64el:
     return true;
   default:
     return false;
   }
 }
 

clang/test/Driver/ppc-abi.c

 // RUN:   -mabi=elfv2 | FileCheck -check-prefix=CHECK-ELFv2 %s
 // RUN: %clang -target powerpc64le-unknown-linux-gnu %s -### -o %t.o 2>&1 \
 // RUN:   -mabi=altivec | FileCheck -check-prefix=CHECK-ELFv2 %s
 
 // RUN: %clang -target powerpc64-unknown-freebsd11 %s -### 2>&1 | FileCheck --check-prefix=CHECK-ELFv1 %s
 // RUN: %clang -target powerpc64-unknown-freebsd12 %s -### 2>&1 | FileCheck --check-prefix=CHECK-ELFv1 %s
 // RUN: %clang -target powerpc64-unknown-freebsd13 %s -### 2>&1 | FileCheck --check-prefix=CHECK-ELFv2-BE %s
 // RUN: %clang -target powerpc64-unknown-freebsd14 %s -### 2>&1 | FileCheck --check-prefix=CHECK-ELFv2-BE %s
-// RUN: %clang -target powerpc64-linux-musl %s -### 2>&1 | FileCheck --check-prefix=CHECK-ELFv2-BE %s
+// RUN: %clang -target powerpc64-linux-musl %s -### 2>&1 | FileCheck --check-prefix=CHECK-ELFv2-BE-PIE %s
 
-// CHECK-ELFv1: "-mrelocation-model" "pic" "-pic-level" "2"
+// CHECK-ELFv1: "-mrelocation-model" "static"
 // CHECK-ELFv1: "-target-abi" "elfv1"
 // CHECK-ELFv1-LE: "-mrelocation-model" "static"
 // CHECK-ELFv1-LE: "-target-abi" "elfv1"
-// CHECK-ELFv1-QPX: "-mrelocation-model" "pic" "-pic-level" "2"
+// CHECK-ELFv1-QPX: "-mrelocation-model" "static"
 // CHECK-ELFv1-QPX: "-target-abi" "elfv1-qpx"
 // CHECK-ELFv2: "-mrelocation-model" "static"
 // CHECK-ELFv2: "-target-abi" "elfv2"
-// CHECK-ELFv2-BE: "-mrelocation-model" "pic" "-pic-level" "2"
+// CHECK-ELFv2-BE: "-mrelocation-model" "static"
 // CHECK-ELFv2-BE: "-target-abi" "elfv2"
+// CHECK-ELFv2-BE-PIE: "-mrelocation-model" "pic" "-pic-level" "2" "-pic-is-pie"
+// CHECK-ELFv2-BE-PIE: "-target-abi" "elfv2"
 
 // RUN: %clang -fPIC -target powerpc64-unknown-linux-gnu %s -### -o %t.o 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK-ELFv1-PIC %s
 // RUN: %clang -fPIC -target powerpc64-unknown-linux-gnu %s -### -o %t.o 2>&1 \
 // RUN:   -mabi=elfv1 | FileCheck -check-prefix=CHECK-ELFv1-PIC %s
 // RUN: %clang -fPIC -target powerpc64-unknown-linux-gnu %s -### -o %t.o 2>&1 \
 // RUN:   -mabi=elfv1-qpx | FileCheck -check-prefix=CHECK-ELFv1-QPX-PIC %s
 // RUN: %clang -fPIC -target powerpc64-unknown-linux-gnu %s -### -o %t.o 2>&1 \