MIPS: Initial implementation of a VDSO

Add an initial implementation of a proper (i.e. an ELF shared library)
VDSO. With this commit it does not export any symbols, it only replaces
the current signal return trampoline page. A later commit will add user
implementations of gettimeofday()/clock_gettime().

To support both new toolchains and old ones which don't generate ABI
flags section, we define its content manually and then use a tool
(genvdso) to patch up the section to have the correct name and type.
genvdso also extracts symbol offsets ({,rt_}sigreturn) needed by the
kernel, and generates a C file containing a "struct mips_vdso_image"
containing both the VDSO data and these offsets. This C file is
compiled into the kernel.

On 64-bit kernels we require a different VDSO for each supported ABI,
so we may build up to 3 different VDSOs. The VDSO to use is selected by
the mips_abi structure.

A kernel/user shared data page is created and mapped below the VDSO
image. This is currently empty, but will be used by the user time
function implementations which are added later.

[markos.chandras@imgtec.com:
- Add more comments
- Move abi detection in genvdso.h since it's the get_symbol function
that needs it.
- Add an R6 specific way to calculate the base address of VDSO in order
to avoid the branch instruction which affects performance.
- Do not patch .gnu.attributes since it's not needed for dynamic linking.
- Simplify Makefile a little bit.
- checkpatch fixes
- Restrict VDSO support for binutils < 2.25 for pre-R6
- Include atomic64.h for O32 variant on MIPS64]

Signed-off-by: Alex Smith <alex.smith@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: Matthew Fortune <matthew.fortune@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11337/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 2 insertions, 5 deletions

diff --git a/arch/mips/kernel/signal32.c b/arch/mips/kernel/signal32.c
index f7e89524e316..4909639aa35b 100644
--- a/arch/mips/kernel/signal32.c
+++ b/arch/mips/kernel/signal32.c
@@ -31,7 +31,6 @@
 #include <asm/ucontext.h>
 #include <asm/fpu.h>
 #include <asm/war.h>
-#include <asm/vdso.h>
 #include <asm/dsp.h>
 
 #include "signal-common.h"
@@ -406,14 +405,12 @@ static int setup_rt_frame_32(void *sig_return, struct ksignal *ksig,
  */
 struct mips_abi mips_abi_32 = {
         .setup_frame    = setup_frame_32,
-        .signal_return_offset =
-                offsetof(struct mips_vdso, o32_signal_trampoline),
         .setup_rt_frame = setup_rt_frame_32,
-        .rt_signal_return_offset =
-                offsetof(struct mips_vdso, o32_rt_signal_trampoline),
         .restart        = __NR_O32_restart_syscall,
 
         .off_sc_fpregs = offsetof(struct sigcontext32, sc_fpregs),
         .off_sc_fpc_csr = offsetof(struct sigcontext32, sc_fpc_csr),
         .off_sc_used_math = offsetof(struct sigcontext32, sc_used_math),
+
+        .vdso           = &vdso_image_o32,
 };