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, 49 insertions, 0 deletions

diff --git a/arch/mips/vdso/sigreturn.S b/arch/mips/vdso/sigreturn.S
new file mode 100644
index 000000000000..715bf5993529
--- /dev/null
+++ b/arch/mips/vdso/sigreturn.S
@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2015 Imagination Technologies
+ * Author: Alex Smith <alex.smith@imgtec.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation;  either version 2 of the  License, or (at your
+ * option) any later version.
+ */
+
+#include "vdso.h"
+
+#include <uapi/asm/unistd.h>
+
+#include <asm/regdef.h>
+#include <asm/asm.h>
+
+	.section	.text
+	.cfi_sections	.debug_frame
+
+LEAF(__vdso_rt_sigreturn)
+	.cfi_startproc
+	.frame	sp, 0, ra
+	.mask	0x00000000, 0
+	.fmask	0x00000000, 0
+	.cfi_signal_frame
+
+	li	v0, __NR_rt_sigreturn
+	syscall
+
+	.cfi_endproc
+	END(__vdso_rt_sigreturn)
+
+#if _MIPS_SIM == _MIPS_SIM_ABI32
+
+LEAF(__vdso_sigreturn)
+	.cfi_startproc
+	.frame	sp, 0, ra
+	.mask	0x00000000, 0
+	.fmask	0x00000000, 0
+	.cfi_signal_frame
+
+	li	v0, __NR_sigreturn
+	syscall
+
+	.cfi_endproc
+	END(__vdso_sigreturn)
+
+#endif