riscv: Support CONFIG_RELOCATABLE on riscv32

When adjusted to use the correctly-sized ELF types, relocate_kernel()
works on riscv32 as well. The caveat about crossing an intermediate page
table boundary does not apply to riscv32, since for Sv32 the early
kernel mapping uses only PGD entries. Since KASLR is not yet supported
on riscv32, this option is mostly useful for NOMMU.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Link: https://lore.kernel.org/r/20241026171441.3047904-6-samuel.holland@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: SiFiveHolland

arch/riscv/Kconfig

@@ -1075,7 +1075,7 @@ config PARAVIRT_TIME_ACCOUNTING
 
 config RELOCATABLE
 	bool "Build a relocatable kernel"
-	depends on 64BIT && !XIP_KERNEL
+	depends on !XIP_KERNEL
 	select MODULE_SECTIONS if MODULES
 	help
           This builds a kernel as a Position Independent Executable (PIE),

arch/riscv/mm/init.c

@@ -20,15 +20,13 @@
 #include <linux/dma-map-ops.h>
 #include <linux/crash_dump.h>
 #include <linux/hugetlb.h>
-#ifdef CONFIG_RELOCATABLE
-#include <linux/elf.h>
-#endif
 #include <linux/kfence.h>
 #include <linux/execmem.h>
 
 #include <asm/fixmap.h>
 #include <asm/io.h>
 #include <asm/kasan.h>
+#include <asm/module.h>
 #include <asm/numa.h>
 #include <asm/pgtable.h>
 #include <asm/sections.h>
@@ -328,7 +326,7 @@ extern unsigned long __rela_dyn_start, __rela_dyn_end;
 
 static void __init relocate_kernel(void)
 {
-	Elf64_Rela *rela = (Elf64_Rela *)&__rela_dyn_start;
+	Elf_Rela *rela = (Elf_Rela *)&__rela_dyn_start;
 	/*
 	 * This holds the offset between the linked virtual address and the
 	 * relocated virtual address.
@@ -340,9 +338,9 @@ static void __init relocate_kernel(void)
 	 */
 	uintptr_t va_kernel_link_pa_offset = KERNEL_LINK_ADDR - kernel_map.phys_addr;
 
-	for ( ; rela < (Elf64_Rela *)&__rela_dyn_end; rela++) {
-		Elf64_Addr addr = (rela->r_offset - va_kernel_link_pa_offset);
-		Elf64_Addr relocated_addr = rela->r_addend;
+	for ( ; rela < (Elf_Rela *)&__rela_dyn_end; rela++) {
+		Elf_Addr addr = (rela->r_offset - va_kernel_link_pa_offset);
+		Elf_Addr relocated_addr = rela->r_addend;
 
 		if (rela->r_info != R_RISCV_RELATIVE)
 			continue;
@@ -356,7 +354,7 @@ static void __init relocate_kernel(void)
 		if (relocated_addr >= KERNEL_LINK_ADDR)
 			relocated_addr += reloc_offset;
 
-		*(Elf64_Addr *)addr = relocated_addr;
+		*(Elf_Addr *)addr = relocated_addr;
 	}
 }
 #endif /* CONFIG_RELOCATABLE */
@@ -1174,7 +1172,8 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	 * makes the kernel cross over a PUD_SIZE boundary, raise a bug
 	 * since a part of the kernel would not get mapped.
 	 */
-	BUG_ON(PUD_SIZE - (kernel_map.virt_addr & (PUD_SIZE - 1)) < kernel_map.size);
+	if (IS_ENABLED(CONFIG_64BIT))
+		BUG_ON(PUD_SIZE - (kernel_map.virt_addr & (PUD_SIZE - 1)) < kernel_map.size);
 	relocate_kernel();
 #endif