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, 68 insertions, 0 deletions

diff --git a/arch/mips/vdso/elf.S b/arch/mips/vdso/elf.S
new file mode 100644
index 000000000000..be37bbb1f061
--- /dev/null
+++ b/arch/mips/vdso/elf.S
@@ -0,0 +1,68 @@
+/*
+ * 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 <linux/elfnote.h>
+#include <linux/version.h>
+
+ELFNOTE_START(Linux, 0, "a")
+	.long LINUX_VERSION_CODE
+ELFNOTE_END
+
+/*
+ * The .MIPS.abiflags section must be defined with the FP ABI flags set
+ * to 'any' to be able to link with both old and new libraries.
+ * Newer toolchains are capable of automatically generating this, but we want
+ * to work with older toolchains as well. Therefore, we define the contents of
+ * this section here (under different names), and then genvdso will patch
+ * it to have the correct name and type.
+ *
+ * We base the .MIPS.abiflags section on preprocessor definitions rather than
+ * CONFIG_* because we need to match the particular ABI we are building the
+ * VDSO for.
+ *
+ * See https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking
+ * for the .MIPS.abiflags section description.
+ */
+
+	.section .mips_abiflags, "a"
+	.align 3
+__mips_abiflags:
+	.hword	0		/* version */
+	.byte	__mips		/* isa_level */
+
+	/* isa_rev */
+#ifdef __mips_isa_rev
+	.byte	__mips_isa_rev
+#else
+	.byte	0
+#endif
+
+	/* gpr_size */
+#ifdef __mips64
+	.byte	2		/* AFL_REG_64 */
+#else
+	.byte	1		/* AFL_REG_32 */
+#endif
+
+	/* cpr1_size */
+#if (defined(__mips_isa_rev) && __mips_isa_rev >= 6) || defined(__mips64)
+	.byte	2		/* AFL_REG_64 */
+#else
+	.byte	1		/* AFL_REG_32 */
+#endif
+
+	.byte	0		/* cpr2_size (AFL_REG_NONE) */
+	.byte	0		/* fp_abi (Val_GNU_MIPS_ABI_FP_ANY) */
+	.word	0		/* isa_ext */
+	.word	0		/* ases */
+	.word	0		/* flags1 */
+	.word	0		/* flags2 */