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Subject[PATCH V2 17/17] riscv: compat: Add COMPAT Kbuild skeletal support
Date
From: Guo Ren <guoren@linux.alibaba.com>

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>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
---
arch/riscv/Kconfig | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 821252b65f89..08f1f3ba3d77 100644
--- 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 +434,18 @@ config CRASH_DUMP

For more details see Documentation/admin-guide/kdump/kdump.rst

+config COMPAT
+ bool "Kernel support for 32-bit U-mode"
+ default 64BIT
+ 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.
+
endmenu

menu "Boot options"
--
2.25.1
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