linux-kernel - [PATCH V6 15/20] riscv: compat: Add hw capability check for elf

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Date:   Thu, 24 Feb 2022 16:54:05 +0800
From:   guoren@...nel.org
To:     guoren@...nel.org, palmer@...belt.com, arnd@...db.de,
        anup@...infault.org, gregkh@...uxfoundation.org,
        liush@...winnertech.com, wefu@...hat.com, drew@...gleboard.org,
        wangjunqiang@...as.ac.cn, hch@....de
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-csky@...r.kernel.org,
        linux-s390@...r.kernel.org, sparclinux@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-parisc@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        x86@...nel.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: [PATCH V6 15/20] riscv: compat: Add hw capability check for elf

From: Guo Ren <guoren@...ux.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@...ux.alibaba.com>
Signed-off-by: Guo Ren <guoren@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Christoph Hellwig <hch@....de>
---
 arch/riscv/include/asm/elf.h |  3 ++-
 arch/riscv/kernel/process.c  | 26 ++++++++++++++++++++++++++
 2 files changed, 28 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 54787ca9806a..7bbe4dd95e85 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -83,6 +83,32 @@ void show_regs(struct pt_regs *regs)
 		dump_backtrace(regs, NULL, KERN_DEFAULT);
 }
 
+#ifdef CONFIG_COMPAT
+static bool compat_mode_supported __read_mostly;
+
+bool compat_elf_check_arch(Elf32_Ehdr *hdr)
+{
+	return compat_mode_supported && hdr->e_machine == EM_RISCV;
+}
+
+static int __init compat_mode_detect(void)
+{
+	unsigned long tmp = csr_read(CSR_STATUS);
+
+	csr_write(CSR_STATUS, (tmp & ~SR_UXL) | SR_UXL_32);
+	compat_mode_supported =
+			(csr_read(CSR_STATUS) & SR_UXL) == SR_UXL_32;
+
+	csr_write(CSR_STATUS, tmp);
+
+	pr_info("riscv: ELF compat mode %s",
+			compat_mode_supported ? "supported" : "failed");
+
+	return 0;
+}
+early_initcall(compat_mode_detect);
+#endif
+
 void start_thread(struct pt_regs *regs, unsigned long pc,
 	unsigned long sp)
 {
-- 
2.25.1