[PATCH V5 15/21] riscv: compat: Add hw capability check for elf

[guoren@xxxxxxxxxx]

From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>

Detect hardware COMPAT (32bit U-mode) capability in rv64. If not
support COMPAT mode in hw, compat_elf_check_arch would return
false by compat_binfmt_elf.c

Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
---
 arch/riscv/include/asm/elf.h |  3 ++-
 arch/riscv/kernel/process.c  | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
index aee40040917b..3a4293dc7229 100644
--- a/arch/riscv/include/asm/elf.h
+++ b/arch/riscv/include/asm/elf.h
@@ -40,7 +40,8 @@
  * elf64_hdr e_machine's offset are different. The checker is
  * a little bit simple compare to other architectures.
  */
-#define compat_elf_check_arch(x) ((x)->e_machine == EM_RISCV)
+extern bool compat_elf_check_arch(Elf32_Ehdr *hdr);
+#define compat_elf_check_arch	compat_elf_check_arch
 
 #define CORE_DUMP_USE_REGSET
 #define ELF_EXEC_PAGESIZE	(PAGE_SIZE)
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 1a666ad299b4..758847cba391 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -83,6 +83,38 @@ void show_regs(struct pt_regs *regs)
 		dump_backtrace(regs, NULL, KERN_DEFAULT);
 }
 
+#ifdef CONFIG_COMPAT
+static bool compat_mode_support __read_mostly;
+
+bool compat_elf_check_arch(Elf32_Ehdr *hdr)
+{
+	if (compat_mode_support && (hdr->e_machine == EM_RISCV))
+		return true;
+	else
+		return false;
+}
+
+static int compat_mode_detect(void)
+{
+	unsigned long tmp = csr_read(CSR_STATUS);
+
+	csr_write(CSR_STATUS, (tmp & ~SR_UXL) | SR_UXL_32);
+
+	if ((csr_read(CSR_STATUS) & SR_UXL) != SR_UXL_32) {
+		pr_info("riscv: 32bit compat mode detect failed\n");
+		compat_mode_support = false;
+	} else {
+		compat_mode_support = true;
+		pr_info("riscv: 32bit compat mode detected\n");
+	}
+
+	csr_write(CSR_STATUS, tmp);
+
+	return 0;
+}
+arch_initcall(compat_mode_detect);
+#endif
+
 void start_thread(struct pt_regs *regs, unsigned long pc,
 	unsigned long sp)
 {
-- 
2.25.1