riscv: Fix relocatable kernels with early alternatives using -fno-pie

Early alternatives are called with the mmu disabled, and then should not
access any global symbols through the GOT since it requires relocations,
relocations that we do before but *virtually*. So only use medany code
model for this early code.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com> # booted on nezha & unmatched
Fixes: 39b3307 ("riscv: Introduce CONFIG_RELOCATABLE")
Link: https://lore.kernel.org/r/20230526154630.289374-1-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: Alexandre Ghiti

arch/riscv/errata/Makefile

@@ -1,2 +1,6 @@
+ifdef CONFIG_RELOCATABLE
+KBUILD_CFLAGS += -fno-pie
+endif
+
 obj-$(CONFIG_ERRATA_SIFIVE) += sifive/
 obj-$(CONFIG_ERRATA_THEAD) += thead/

arch/riscv/kernel/Makefile

@@ -23,6 +23,10 @@ ifdef CONFIG_FTRACE
 CFLAGS_REMOVE_alternative.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_cpufeature.o = $(CC_FLAGS_FTRACE)
 endif
+ifdef CONFIG_RELOCATABLE
+CFLAGS_alternative.o += -fno-pie
+CFLAGS_cpufeature.o += -fno-pie
+endif
 ifdef CONFIG_KASAN
 KASAN_SANITIZE_alternative.o := n
 KASAN_SANITIZE_cpufeature.o := n