[PATCH 09/13] riscv: compat: init: Add hw-cap detect in setup_arch

[guoren at kernel.org]

From: Guo Ren <guoren at linux.alibaba.com>

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 at linux.alibaba.com>
---
 arch/riscv/include/asm/elf.h       |  5 ++++-
 arch/riscv/include/asm/processor.h |  1 +
 arch/riscv/kernel/process.c        | 22 ++++++++++++++++++++++
 arch/riscv/kernel/setup.c          |  5 +++++
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
index 37f1cbdaa242..6baa49c4fba1 100644
--- a/arch/riscv/include/asm/elf.h
+++ b/arch/riscv/include/asm/elf.h
@@ -35,7 +35,10 @@
  */
 #define elf_check_arch(x) ((x)->e_machine == EM_RISCV)
 
-#define compat_elf_check_arch(x) ((x)->e_machine == EM_RISCV)
+#ifdef CONFIG_COMPAT
+extern bool compat_elf_check_arch(Elf32_Ehdr *hdr);
+#define compat_elf_check_arch compat_elf_check_arch
+#endif
 
 #define CORE_DUMP_USE_REGSET
 #define ELF_EXEC_PAGESIZE	(PAGE_SIZE)
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 9544c138d9ce..8b288ac0d704 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -64,6 +64,7 @@ extern void start_thread(struct pt_regs *regs,
 #ifdef CONFIG_COMPAT
 extern void compat_start_thread(struct pt_regs *regs,
 				unsigned long pc, unsigned long sp);
+extern void compat_mode_detect(void);
 
 #define DEFAULT_MAP_WINDOW_64 TASK_SIZE_64
 #else
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 9ebf9a95e5ea..496d09c5d384 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -101,6 +101,28 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
 }
 
 #ifdef CONFIG_COMPAT
+static bool compat_mode_support __read_mostly = false;
+
+bool compat_elf_check_arch(Elf32_Ehdr *hdr)
+{
+	if (compat_mode_support && (hdr->e_machine == EM_RISCV))
+		return true;
+
+	return false;
+}
+
+void compat_mode_detect(void)
+{
+	csr_write(CSR_STATUS, (csr_read(CSR_STATUS) & ~SR_UXL) | SR_UXL_32);
+
+	if ((csr_read(CSR_STATUS) & SR_UXL) != SR_UXL_32)
+		return;
+
+	compat_mode_support = true;
+
+	pr_info("riscv: compat: 32bit U-mode applications support\n");
+}
+
 void compat_start_thread(struct pt_regs *regs, unsigned long pc,
 			 unsigned long sp)
 {
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index b42bfdc67482..be131219d549 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -12,6 +12,7 @@
 #include <linux/mm.h>
 #include <linux/memblock.h>
 #include <linux/sched.h>
+#include <linux/compat.h>
 #include <linux/console.h>
 #include <linux/screen_info.h>
 #include <linux/of_fdt.h>
@@ -294,6 +295,10 @@ void __init setup_arch(char **cmdline_p)
 	setup_smp();
 #endif
 
+#ifdef CONFIG_COMPAT
+	compat_mode_detect();
+#endif
+
 	riscv_fill_hwcap();
 }
 
-- 
2.25.1