clang: Always pass PowerPC endian information to GNU as

[nathanchance]

Summary

When building a 64-bit big endian PowerPC Linux kernel with a 64-bit
little endian PowerPC target, the 32-bit vDSO errors:

$ make ARCH=powerpc CC=clang CROSS_COMPILE=powerpc64le-linux-gnu- \
       pseries_defconfig arch/powerpc/kernel/vdso32/
ld.lld: error: arch/powerpc/kernel/vdso32/sigtramp.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/gettimeofday.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/datapage.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/cacheflush.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/note.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/getcpu.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/vgettimeofday.o is incompatible with elf32-powerpc
...

This happens because the endian information is missing from the call to
the assembler, even though it was explicitly passed to clang. See the
below example.

$ echo | clang --target=powerpc64le-linux-gnu \
               --prefix=/usr/bin/powerpc64le-linux-gnu- \
               -no-integrated-as -m32 -mbig-endian -### -x c -c -
 ".../clang-12" "-cc1" "-triple" "powerpc-unknown-linux-gnu" ...
...
  "/usr/bin/powerpc64le-linux-gnu-as" "-a32" "-mppc" "-many" "-o" "-.o" "/tmp/--e69e28.s"

clang sets the right target with -m32 and -mbig-endian but -mbig-endian
does not make it to the assembler, resulting in a 32-bit little endian
binary. This differs from the little endian targets, which always pass
-mlittle-endian.

$ echo | clang --target=powerpc64-linux-gnu \
               --prefix=/usr/bin/powerpc64-linux-gnu- \
               -no-integrated-as -m32 -mlittle-endian -### -x c -c -
 ".../clang-12" "-cc1" "-triple" "powerpcle-unknown-linux-gnu" ...
...
 "/usr/bin/powerpc64-linux-gnu-as" "-a32" "-mppc" "-mlittle-endian" "-many" "-o" "-.o" "/tmp/--405dbd.s"

Do the same thing for the big endian targets so that there is no more
error. This matches GCC's behavior, where -mbig and -mlittle are always
passed along to GNU as.

$ echo | powerpc64-linux-gcc -### -x c -c -
...
.../powerpc64-linux/bin/as -a64 -mpower4 -many -mbig -o -.o /tmp/ccVn7NAm.s
...

$ echo | powerpc64le-linux-gcc -### -x c -c -
...
.../powerpc64le-linux/bin/as -a64 -mpower8 -many -mlittle -o -.o /tmp/ccPN9ato.s
...

[nickdesaulniers]

This differs from the little endian targets, which always pass
-mbig-endian.

I think you meant -mlittle-endian here?

[nathanchance]

Indeed, updated!

[MaskRay]

LGTM.

Context not available.

https://llvm.org/docs/GettingStarted.html#sending-patches arc diff HEAD~1 is convenient as it automatically sends the context lines.

clang/test/Driver/ppc-features.cpp

161

CHECK_32_BE_AS_ARGS-SAME: is slightly better (checking the the content is on the same line).

[nathanchance]

Addressed Fangrui's comments. If this looks good, please commit it on my behalf: Nathan Chancellor <[e-mail]>

[nathanchance]

clang/test/Driver/ppc-features.cpp

161

Thanks, I will remember that for the future :)

[nickdesaulniers]

Sure. I'll commit it.

clang/lib/Driver/ToolChains/Gnu.cpp

case llvm::Triple::x86_64:
     if (getToolChain().getTriple().getEnvironment() == llvm::Triple::GNUX32)
       CmdArgs.push_back("--x32");
     else
       CmdArgs.push_back("--64");
     break;
   case llvm::Triple::ppc: {
     CmdArgs.push_back("-a32");
     CmdArgs.push_back("-mppc");
+    CmdArgs.push_back("-mbig-endian");
     CmdArgs.push_back(
       ppc::getPPCAsmModeForCPU(getCPUName(Args, getToolChain().getTriple())));
     break;
   }
   case llvm::Triple::ppcle: {
     CmdArgs.push_back("-a32");
     CmdArgs.push_back("-mppc");
     CmdArgs.push_back("-mlittle-endian");
     CmdArgs.push_back(
         ppc::getPPCAsmModeForCPU(getCPUName(Args, getToolChain().getTriple())));
     break;
   }
   case llvm::Triple::ppc64: {
     CmdArgs.push_back("-a64");
     CmdArgs.push_back("-mppc64");
+    CmdArgs.push_back("-mbig-endian");
     CmdArgs.push_back(
       ppc::getPPCAsmModeForCPU(getCPUName(Args, getToolChain().getTriple())));
     break;
   }
   case llvm::Triple::ppc64le: {
     CmdArgs.push_back("-a64");
     CmdArgs.push_back("-mppc64");
     CmdArgs.push_back("-mlittle-endian");

clang/test/Driver/ppc-features.cpp

 
 // RUN: %clang -target powerpc %s -mno-spe -mspe -c -### 2>&1 | FileCheck -check-prefix=CHECK-SPE %s
 // RUN: %clang -target powerpcspe %s -c -### 2>&1 | FileCheck -check-prefix=CHECK-SPE %s
 // RUN: %clang -target powerpcspe %s -mno-spe -c -### 2>&1 | FileCheck -check-prefix=CHECK-NOSPE %s
 // CHECK-SPE: "-target-feature" "+spe"
 // CHECK-NOSPE: "-target-feature" "-spe"
 
 // Assembler features
-// RUN: %clang -target powerpc64-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_BE_AS_ARGS %s
-// CHECK_BE_AS_ARGS: "-mppc64"
-// CHECK_BE_AS_ARGS: "-many"
-
-// RUN: %clang -target powerpc64le-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_LE_AS_ARGS %s
-// CHECK_LE_AS_ARGS: "-mppc64"
-// CHECK_LE_AS_ARGS: "-mlittle-endian"
-// CHECK_LE_AS_ARGS: "-mpower8"
+// RUN: %clang -target powerpc-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_32_BE_AS_ARGS %s
+// CHECK_32_BE_AS_ARGS: "-mppc"
+// CHECK_32_BE_AS_ARGS-SAME: "-mbig-endian"
+// CHECK_32_BE_AS_ARGS-SAME: "-many"
+
+// RUN: %clang -target powerpcle-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_32_LE_AS_ARGS %s
+// CHECK_32_LE_AS_ARGS: "-mppc"
+// CHECK_32_LE_AS_ARGS-SAME: "-mlittle-endian"
+// CHECK_32_LE_AS_ARGS-SAME: "-many"
+
+// RUN: %clang -target powerpc64-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_64_BE_AS_ARGS %s
+// CHECK_64_BE_AS_ARGS: "-mppc64"
+// CHECK_64_BE_AS_ARGS-SAME: "-mbig-endian"
+// CHECK_64_BE_AS_ARGS-SAME: "-many"
+
+// RUN: %clang -target powerpc64le-unknown-linux-gnu %s -### -o %t.o -no-integrated-as 2>&1 | FileCheck -check-prefix=CHECK_64_LE_AS_ARGS %s
+// CHECK_64_LE_AS_ARGS: "-mppc64"
+// CHECK_64_LE_AS_ARGS-SAME: "-mlittle-endian"
+// CHECK_64_LE_AS_ARGS-SAME: "-mpower8"
 
 // OpenMP features
 // RUN: %clang -target powerpc-unknown-linux-gnu %s -### -fopenmp=libomp -o %t.o 2>&1 | FileCheck -check-prefix=CHECK_OPENMP_TLS %s
 // RUN: %clang -target powerpcle-unknown-linux-gnu %s -### -fopenmp=libomp -o %t.o 2>&1 | FileCheck -check-prefix=CHECK_OPENMP_TLS %s
 // RUN: %clang -target powerpc64-unknown-linux-gnu %s -### -fopenmp=libomp -o %t.o 2>&1 | FileCheck -check-prefix=CHECK_OPENMP_TLS %s
 // RUN: %clang -target powerpc64le-unknown-linux-gnu %s -### -fopenmp=libomp -o %t.o 2>&1 | FileCheck -check-prefix=CHECK_OPENMP_TLS %s
 // CHECK_OPENMP_TLS-NOT: "-fnoopenmp-use-tls"