[PATCH 9/9] powerpc/64s: Work around llvm-as not recognising pla

[Nicholas Piggin]

llvm-as does not recognise the pla mnemonic, which is used for pcrel
address generation. Use the equivalent paddi opcode instead. Clang
can not build working pcrel kernels yet, but this patch does allow it
to build a non-working pcrel kernel with llvm-as.

This could be unconditional or use a raw encoding, but this gives a
placeholder to track the issue.

Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
 arch/powerpc/Kconfig               | 5 +++++
 arch/powerpc/include/asm/ppc_asm.h | 5 +++++
 arch/powerpc/kernel/vector.S       | 6 ++++++
 3 files changed, 16 insertions(+)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 39cd8d3ff846..2f7840577f7f 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -22,6 +22,11 @@ config CC_HAS_PCREL
        # do pcrel yet.
        def_bool PPC64 && CC_IS_GCC &&  $(cc-option, -mcpu=power10 -mpcrel)
 
+config AS_HAS_MISSING_PLA_INSN
+       # llvm-as is missing some extended mnemonics including pla
+       # (https://github.com/llvm/llvm-project/issues/62373).
+       def_bool AS_IS_LLVM
+
 config 32BIT
        bool
        default y if PPC32
diff --git a/arch/powerpc/include/asm/ppc_asm.h 
b/arch/powerpc/include/asm/ppc_asm.h
index 5f05a984b103..736202ebc1be 100644
--- a/arch/powerpc/include/asm/ppc_asm.h
+++ b/arch/powerpc/include/asm/ppc_asm.h
@@ -380,8 +380,13 @@ GLUE(.,name):
        rldimi  reg, tmp, 32, 0
 
 #ifdef CONFIG_PPC_KERNEL_PCREL
+#ifdef CONFIG_AS_HAS_MISSING_PLA_INSN
+#define LOAD_REG_ADDR(reg,name)                        \
+       paddi   reg,0,name@pcrel,1
+#else
 #define LOAD_REG_ADDR(reg,name)                        \
        pla     reg,name@pcrel
+#endif
 
 #else
 #define LOAD_REG_ADDR(reg,name)                        \
diff --git a/arch/powerpc/kernel/vector.S b/arch/powerpc/kernel/vector.S
index fcc0ad6d9c7b..c2feaea5e673 100644
--- a/arch/powerpc/kernel/vector.S
+++ b/arch/powerpc/kernel/vector.S
@@ -178,9 +178,15 @@ fphalf:
        .quad   0x3fe0000000000000      /* 0.5 */
 
 #ifdef CONFIG_PPC_KERNEL_PCREL
+#ifdef CONFIG_AS_HAS_MISSING_PLA_INSN
+#define LDCONST(fr, name)              \
+       paddi   r11,0,name@pcrel,1;     \
+       lfd     fr,0(r11)
+#else
 #define LDCONST(fr, name)              \
        pla     r11,name@pcrel;         \
        lfd     fr,0(r11)
+#endif
 #else
 #define LDCONST(fr, name)              \
        addis   r11,r2,name@toc@ha;     \
-- 
2.40.0