riscv: compat: Add elf.h implementation

Implement necessary type and macro for compat elf. See the code
comment for detail.
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20220405071314.3225832-15-guoren@kernel.orgSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/elf.h

@@ -8,6 +8,8 @@
 #ifndef _ASM_RISCV_ELF_H
 #define _ASM_RISCV_ELF_H
 
+#include <uapi/linux/elf.h>
+#include <linux/compat.h>
 #include <uapi/asm/elf.h>
 #include <asm/auxvec.h>
 #include <asm/byteorder.h>
@@ -18,11 +20,13 @@
  */
 #define ELF_ARCH	EM_RISCV
 
+#ifndef ELF_CLASS
 #ifdef CONFIG_64BIT
 #define ELF_CLASS	ELFCLASS64
 #else
 #define ELF_CLASS	ELFCLASS32
 #endif
+#endif
 
 #define ELF_DATA	ELFDATA2LSB
 
@@ -31,6 +35,8 @@
  */
 #define elf_check_arch(x) ((x)->e_machine == EM_RISCV)
 
+#define compat_elf_check_arch(x) ((x)->e_machine == EM_RISCV)
+
 #define CORE_DUMP_USE_REGSET
 #define ELF_EXEC_PAGESIZE	(PAGE_SIZE)
 
@@ -43,8 +49,14 @@
 #define ELF_ET_DYN_BASE		((TASK_SIZE / 3) * 2)
 
 #ifdef CONFIG_64BIT
+#ifdef CONFIG_COMPAT
+#define STACK_RND_MASK		(test_thread_flag(TIF_32BIT) ? \
+				 0x7ff >> (PAGE_SHIFT - 12) : \
+				 0x3ffff >> (PAGE_SHIFT - 12))
+#else
 #define STACK_RND_MASK		(0x3ffff >> (PAGE_SHIFT - 12))
 #endif
+#endif
 /*
  * This yields a mask that user programs can use to figure out what
  * instruction set this CPU supports.  This could be done in user space,
@@ -60,11 +72,19 @@ extern unsigned long elf_hwcap;
  */
 #define ELF_PLATFORM	(NULL)
 
+#define COMPAT_ELF_PLATFORM	(NULL)
+
 #ifdef CONFIG_MMU
 #define ARCH_DLINFO						\
 do {								\
+	/*							\
+	 * Note that we add ulong after elf_addr_t because	\
+	 * casting current->mm->context.vdso triggers a cast	\
+	 * warning of cast from pointer to integer for		\
+	 * COMPAT ELFCLASS32.					\
+	 */							\
 	NEW_AUX_ENT(AT_SYSINFO_EHDR,				\
-		(elf_addr_t)current->mm->context.vdso);		\
+		(elf_addr_t)(ulong)current->mm->context.vdso);	\
 	NEW_AUX_ENT(AT_L1I_CACHESIZE,				\
 		get_cache_size(1, CACHE_TYPE_INST));		\
 	NEW_AUX_ENT(AT_L1I_CACHEGEOMETRY,			\
@@ -90,4 +110,23 @@ do {							\
 		*(struct user_regs_struct *)regs;	\
 } while (0);
 
+#ifdef CONFIG_COMPAT
+
+#define SET_PERSONALITY(ex)					\
+do {    if ((ex).e_ident[EI_CLASS] == ELFCLASS32)		\
+		set_thread_flag(TIF_32BIT);			\
+	else							\
+		clear_thread_flag(TIF_32BIT);			\
+	if (personality(current->personality) != PER_LINUX32)	\
+		set_personality(PER_LINUX |			\
+			(current->personality & (~PER_MASK)));	\
+} while (0)
+
+#define COMPAT_ELF_ET_DYN_BASE		((TASK_SIZE_32 / 3) * 2)
+
+/* rv32 registers */
+typedef compat_ulong_t			compat_elf_greg_t;
+typedef compat_elf_greg_t		compat_elf_gregset_t[ELF_NGREG];
+
+#endif /* CONFIG_COMPAT */
 #endif /* _ASM_RISCV_ELF_H */