[PATCH V12 20/20] riscv: compat: Add COMPAT Kbuild skeletal support

From: guoren
Date: Tue Apr 05 2022 - 03:17:45 EST


From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>

Adds initial skeletal COMPAT Kbuild (Running 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@xxxxxxxxxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx>
Tested-by: Heiko Stuebner <heiko@xxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
---
arch/riscv/Kconfig | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 00fd9c548f26..def9798e9675 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -76,6 +76,7 @@ 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
@@ -127,12 +128,18 @@ 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
@@ -394,6 +401,18 @@ 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