[ppc64le] runtime fails to build on clang 20

[mateusrodrigues]

Describe the Bug

Building the VMR on ppc64le and clang 20 fails during the runtime build for both .NET 8 and .NET 9 with:

[ 81%] Building ASM object pal/src/CMakeFiles/coreclrpal.dir/arch/ppc64le/debugbreak.S.o
             cd /<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/coreclr/linux.ppc64le.Release/pal/src && /usr/bin/clang -DCOMPILER_SUPPORTS_W_RESERVED_IDENTIFIER -DCORECLR -DDISABLE_CONTRACTS -DHOST_64BIT -DHOST_POWERPC64 -DHOST_UNIX -DLP64COMPATIBLE -DNDEBUG -DPIC -DTARGET_64BIT -DTARGET_LINUX -DTARGET_POWERPC64 -DTARGET_UNIX -DURTBLDENV_FRIENDLY=Retail -DUSE_STL -D_FILE_OFFSET_BITS=64 -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/coreclr/linux.ppc64le.Release/pal/src -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native/inc -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/inc -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/../inc -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native/external/libunwind/include -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native/external/libunwind/include/tdep -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/external/libunwind/include -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/external/libunwind/include/tdep -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src/include -isystem /usr/local/include -O3 -DNDEBUG -fPIC -O3 -g -Wall -Wno-null-conversion -Wa,--noexecstack -fno-omit-frame-pointer -fms-extensions -fwrapv -fstack-protector-strong -Wno-unused-variable -Wno-unused-value -Wno-unused-function -Wno-tautological-compare -Wno-unknown-pragmas -Wimplicit-fallthrough -Wno-unused-but-set-variable -ffp-contract=off -Wno-unknown-warning-option -ferror-limit=4096 -Wno-unused-private-field -Wno-constant-logical-operand -Wno-pragma-pack -Wno-incompatible-ms-struct -Wno-reserved-identifier -Wno-unsafe-buffer-usage -Wno-single-bit-bitfield-constant-conversion -Wno-cast-function-type-strict -Wno-switch-default -fsigned-char -fvisibility=hidden -ffunction-sections -fexceptions -o CMakeFiles/coreclrpal.dir/arch/ppc64le/debugbreak.S.o -c /<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src/arch/ppc64le/debugbreak.S
             /<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src/arch/ppc64le/context2.S:140:15: error: invalid register name
              ld %r0, 0 +8(%R3)
                           ^
             make[5]: *** [pal/src/CMakeFiles/coreclrpal.dir/build.make:1240: pal/src/CMakeFiles/coreclrpal.dir/arch/ppc64le/context2.S.o] Error 1
             make[5]: *** Waiting for unfinished jobs....

Other Information

Logs for the .NET 8 build: https://launchpad.net/~canonical-toolchains-squad/+archive/ubuntu/llvm-20-transition/+build/30262768/+files/buildlog_ubuntu-plucky-ppc64el.dotnet8_8.0.113-8.0.13-0ubuntu1_BUILDING.txt.gz

Logs for the .NET 9 build: https://launchpad.net/~canonical-toolchains-squad/+archive/ubuntu/llvm-20-transition/+build/30262772/+files/buildlog_ubuntu-plucky-ppc64el.dotnet9_9.0.103-9.0.2-0ubuntu1_BUILDING.txt.gz

cc @dotnet/distro-maintainers

[omajid]

cc @alhad-deshpande

[alhad-deshpande]

@omajid
We are checking this issue.

[tuliom]

FYI: this has been reported as a regression in LLVM: llvm/llvm-project#126786

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[mateusrodrigues]

After reading through llvm/llvm-project#126786, I tested building .NET 8 and .NET 9 with the change below and it works.

--- a/src/runtime/src/coreclr/pal/src/arch/ppc64le/context2.S	2025-02-10 16:14:03.000000000 -0300
+++ b/src/runtime/src/coreclr/pal/src/arch/ppc64le/context2.S	2025-02-20 10:39:37.979727228 -0300
@@ -137,7 +137,7 @@
 	lfd %f31, CONTEXT_F31(%r3)
 
 	// Restore all general purpose registers
-	ld %r0, CONTEXT_R0(%R3)
+	ld %r0, CONTEXT_R0(%r3)
 	ld %r1, CONTEXT_R1(%r3)
 	ld %r2, CONTEXT_R2(%r3)
 	ld %r4, CONTEXT_R4(%r3)

This does seem to be a typo, considering all other register references have a lowecase r.

[alhad-deshpande]

@mateusrodrigues
Yes it is a typo. Raising PR soon to fix this upstream. Will keep you posted.