FROMLIST: BACKPORT: [PATCH 6/6] arm64: Wire up and expose the new compat vDSO

(cherry pick from url https://patchwork.kernel.org/patch/10060447/)

Expose the new compat vDSO via the COMPAT_VDSO config option.

The option is not enabled in defconfig because we really need a 32-bit
compiler this time, and we rely on the user to provide it themselves
by setting CROSS_COMPILE_ARM32. Therefore enabling the option by
default would make little sense, since the user must explicitly set a
non-standard environment variable anyway.

CONFIG_COMPAT_VDSO is not directly used in the code, because we want
to ignore it (build as if it were not set) if the user didn't set
CROSS_COMPILE_ARM32. If the variable has been set to a valid prefix,
CONFIG_VDSO32 will be set; this is the option that the code and
Makefiles test.

For more flexibility, like CROSS_COMPILE, CROSS_COMPILE_ARM32 can also
be set via CONFIG_CROSS_COMPILE_ARM32 (the environment variable
overrides the config option, as expected).

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Dave Martin <Dave.Martin@arm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Bug: 63737556
Bug: 20045882
Change-Id: Ie8a7d6c2b5ba3edca591a9a953ce99ec792da882

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index cbaf63be02bbc2d931f6f8ed52895e2b42012d29..c7efdb5e5934f1f72914d1cfa60da9a597d23fe7 100644 (file)
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1216,6 +1216,30 @@ config KEYS_COMPAT
        def_bool y
        depends on COMPAT && KEYS
 
+config COMPAT_VDSO
+       bool "32-bit vDSO"
+       depends on COMPAT
+       default n
+       help
+         Warning: a 32-bit toolchain is necessary to build the vDSO. You
+         must explicitly define which toolchain should be used by setting
+         CROSS_COMPILE_ARM32 to the prefix of the 32-bit toolchain (same format
+         as CROSS_COMPILE). If CROSS_COMPILE_ARM32 is empty, a warning will be
+         printed and the kernel will be built as if COMPAT_VDSO had not been
+         set. If CROSS_COMPILE_ARM32 is set to an invalid prefix, compilation
+         will be aborted.
+
+         Provide a vDSO to 32-bit processes. It includes the symbols provided
+         by the vDSO from the 32-bit kernel, so that a 32-bit libc can use
+         the compat vDSO without modification. It also provides sigreturn
+         trampolines, replacing the sigreturn page.
+
+config CROSS_COMPILE_ARM32
+       string "32-bit toolchain prefix"
+       help
+         Same as setting CROSS_COMPILE_ARM32 in the environment, but saved for
+         future builds. The environment variable overrides this config option.
+
 endmenu
 
 menu "Power management options"

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 9bc4663f0c8d1063b590b505b1cb4a8db772ece6..e572a16ee6b52191d03cdb37b6cc2d9ad2ecf120 100644 (file)
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -58,10 +58,40 @@ else
 KBUILD_CFLAGS  += -mgeneral-regs-only
 endif
 KBUILD_CFLAGS  += $(lseinstr)
+
+ifeq ($(CONFIG_COMPAT_VDSO), y)
+  CROSS_COMPILE_ARM32 ?= $(CONFIG_CROSS_COMPILE_ARM32:"%"=%)
+   # Check that the user has provided a valid prefix for the 32-bit toolchain.
+  # To prevent selecting the system $(cc-name) by default, the prefix is not
+  # allowed to be empty, unlike CROSS_COMPILE. In the unlikely event that the
+  # system $(cc-name) is actually the 32-bit ARM compiler to be used, the
+  # variable can be set to the dirname (e.g. CROSS_COMPILE_ARM32=/usr/bin/).
+  # Note: this Makefile is read both before and after regenerating the config
+  # (if needed). Any warning appearing before the config has been regenerated
+  # should be ignored. If the error is triggered and you set
+  # CONFIG_CROSS_COMPILE_ARM32, set CROSS_COMPILE_ARM32 to an appropriate value
+  # when invoking make and fix CONFIG_CROSS_COMPILE_ARM32.
+  ifeq ($(CROSS_COMPILE_ARM32),)
+    $(warning CROSS_COMPILE_ARM32 not defined or empty, the compat vDSO will not be built)
+  else ifeq ($(cc-name),clang)
+    export CLANG_TRIPLE_ARM32 ?= $(CROSS_COMPILE_ARM32)
+    export CLANG_TARGET_ARM32 := --target=$(notdir $(CLANG_TRIPLE_ARM32:%-=%))
+    export CONFIG_VDSO32 := y
+    vdso32 := -DCONFIG_VDSO32=1
+  else ifeq ($(shell which $(CROSS_COMPILE_ARM32)$(cc-name) 2> /dev/null),)
+    $(error $(CROSS_COMPILE_ARM32)$(cc-name) not found, check CROSS_COMPILE_ARM32)
+  else
+    export CROSS_COMPILE_ARM32
+    export CONFIG_VDSO32 := y
+    vdso32 := -DCONFIG_VDSO32=1
+  endif
+endif
+
+KBUILD_CFLAGS  += $(vdso32)
 KBUILD_CFLAGS  += -fno-asynchronous-unwind-tables
 KBUILD_CFLAGS  += $(call cc-option, -mpc-relative-literal-loads)
 KBUILD_CFLAGS  += -fno-pic
-KBUILD_AFLAGS  += $(lseinstr)
+KBUILD_AFLAGS  += $(lseinstr) $(vdso32)
 
 ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
 KBUILD_CPPFLAGS        += -mbig-endian
@@ -184,6 +214,8 @@ ifeq ($(KBUILD_EXTMOD),)
 prepare: vdso_prepare
 vdso_prepare: prepare0
        $(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso include/generated/vdso-offsets.h
+       $(if $(CONFIG_VDSO32),$(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso32 \
+                                         include/generated/vdso32-offsets.h)
 endif
 
 define archhelp

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 37b4ac147fd1249422bad01868d951d45ddd3ee5..3b575ffb6b1344d6008ec022a4c4876fb8eb2a90 100644 (file)
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -29,7 +29,9 @@ $(obj)/%.stub.o: $(obj)/%.o FORCE
 
 arm64-obj-$(CONFIG_COMPAT)             += sys32.o signal32.o   \
                                           sys_compat.o entry32.o
+ifneq ($(CONFIG_VDSO32),y)
 arm64-obj-$(CONFIG_COMPAT)             += sigreturn32.o
+endif
 arm64-obj-$(CONFIG_KUSER_HELPERS)      += kuser32.o
 arm64-obj-$(CONFIG_FUNCTION_TRACER)    += ftrace.o entry-ftrace.o
 arm64-obj-$(CONFIG_MODULES)            += arm64ksyms.o module.o
@@ -59,6 +61,7 @@ arm64-obj-$(CONFIG_HARDEN_BRANCH_PREDICTOR)   += bpi.o
 endif
 
 obj-y                                  += $(arm64-obj-y) vdso/ probes/
+obj-$(CONFIG_VDSO32)                   += vdso32/
 obj-m                                  += $(arm64-obj-m)
 head-y                                 := head.o
 extra-y                                        += $(head-y) vmlinux.lds