riscv: compat: Add COMPAT Kbuild skeletal support

Adds initial skeletal COMPAT Kbuild (Runing 32bit U-mode on 64bit S-mode) support. - Setup kconfig & dummy functions for compiling. - Implement compat_start_thread by the way. Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
c-sky · Dec 21, 2021 · 4fe3cee · 4fe3cee
1 parent a036c4d
commit 4fe3cee
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diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
@@ -72,6 +72,7 @@ config RISCV
 	select HAVE_ARCH_KGDB if !XIP_KERNEL
 	select HAVE_ARCH_KGDB_QXFER_PKT
 	select HAVE_ARCH_MMAP_RND_BITS if MMU
+	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT && MMU
@@ -122,12 +123,18 @@ config ARCH_MMAP_RND_BITS_MIN
 	default 18 if 64BIT
 	default 8
 
+config ARCH_MMAP_RND_COMPAT_BITS_MIN
+	default 8
+
 # max bits determined by the following formula:
 #  VA_BITS - PAGE_SHIFT - 3
 config ARCH_MMAP_RND_BITS_MAX
 	default 24 if 64BIT # SV39 based
 	default 17
 
+config ARCH_MMAP_RND_COMPAT_BITS_MAX
+	default 17
+
 # set if we run in machine mode, cleared if we run in supervisor mode
 config RISCV_M_MODE
 	bool
@@ -427,6 +434,21 @@ config CRASH_DUMP
 
 	  For more details see Documentation/admin-guide/kdump/kdump.rst
 
+config COMPAT
+	bool "Kernel support for 32-bit U-mode"
+	depends on 64BIT && MMU
+	help
+	  This option enables support for a 32-bit U-mode running under a 64-bit
+	  kernel at S-mode. riscv32-specific components such as system calls,
+	  the user helper functions (vdso), signal rt_frame functions and the
+	  ptrace interface are handled appropriately by the kernel.
+
+	  If you want to execute 32-bit userspace applications, say Y.
+
+config SYSVIPC_COMPAT
+	def_bool y
+	depends on COMPAT && SYSVIPC
+
 endmenu
 
 menu "Boot options"

diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
@@ -129,5 +129,13 @@ do {    if ((ex).e_ident[EI_CLASS] == ELFCLASS32)			   \
 typedef compat_ulong_t			compat_elf_greg_t;
 typedef compat_elf_greg_t		compat_elf_gregset_t[ELF_NGREG];
 
+#define compat_start_thread		compat_start_thread
+
+
+extern int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
+					      int uses_interp);
+#define compat_arch_setup_additional_pages \
+				compat_arch_setup_additional_pages
+
 #endif /* CONFIG_COMPAT */
 #endif /* _ASM_RISCV_ELF_H */
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
@@ -62,6 +62,9 @@ extern void start_thread(struct pt_regs *regs,
 			unsigned long pc, unsigned long sp);
 
 #ifdef CONFIG_COMPAT
+extern void compat_start_thread(struct pt_regs *regs,
+				unsigned long pc, unsigned long sp);
+
 #define DEFAULT_MAP_WINDOW_64 TASK_SIZE_64
 #else
 #define DEFAULT_MAP_WINDOW_64 TASK_SIZE

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
@@ -65,3 +65,5 @@ obj-$(CONFIG_CRASH_DUMP)	+= crash_dump.o
 obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
 
 obj-$(CONFIG_EFI)		+= efi.o
+obj-$(CONFIG_COMPAT)		+= compat_syscall_table.o
+obj-$(CONFIG_COMPAT)		+= compat_signal.o
diff --git a/arch/riscv/kernel/compat_signal.c b/arch/riscv/kernel/compat_signal.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/compat.h>
+#include <linux/signal.h>
+#include <linux/uaccess.h>
+#include <linux/syscalls.h>
+#include <linux/tracehook.h>
+#include <linux/linkage.h>
+
+#include <asm/ucontext.h>
+#include <asm/vdso.h>
+#include <asm/switch_to.h>
+#include <asm/csr.h>
+
+COMPAT_SYSCALL_DEFINE0(rt_sigreturn)
+{
+	return 0;
+}
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
@@ -15,6 +15,7 @@
 #include <linux/tick.h>
 #include <linux/ptrace.h>
 #include <linux/uaccess.h>
+#include <uapi/linux/elf.h>
 
 #include <asm/unistd.h>
 #include <asm/processor.h>
@@ -99,6 +100,15 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
 	regs->sp = sp;
 }
 
+#ifdef CONFIG_COMPAT
+void compat_start_thread(struct pt_regs *regs, unsigned long pc,
+			 unsigned long sp)
+{
+	start_thread(regs, pc, sp);
+	regs->status |= SR_UXL_32;
+}
+#endif
+
 void flush_thread(void)
 {
 #ifdef CONFIG_FPU

diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
@@ -12,6 +12,7 @@
 #include <asm/thread_info.h>
 #include <asm/switch_to.h>
 #include <linux/audit.h>
+#include <linux/compat.h>
 #include <linux/ptrace.h>
 #include <linux/elf.h>
 #include <linux/regset.h>
@@ -275,3 +276,11 @@ __visible void do_syscall_trace_exit(struct pt_regs *regs)
 		trace_sys_exit(regs, regs_return_value(regs));
 #endif
 }
+
+#ifdef CONFIG_COMPAT
+long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
+			compat_ulong_t caddr, compat_ulong_t cdata)
+{
+	return 0;
+}
+#endif
diff --git a/arch/riscv/kernel/vdso.c b/arch/riscv/kernel/vdso.c
@@ -253,6 +253,14 @@ static int __setup_additional_pages(struct mm_struct *mm,
 	return PTR_ERR(ret);
 }
 
+#ifdef CONFIG_COMPAT
+int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
+				       int uses_interp)
+{
+	return 0;
+}
+#endif
+
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
 	struct mm_struct *mm = current->mm;