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>
diff --git a/arch/mips/vdso/vdso.lds.S b/arch/mips/vdso/vdso.lds.S
new file mode 100644
index 0000000..21655b6
--- /dev/null
+++ b/arch/mips/vdso/vdso.lds.S
@@ -0,0 +1,100 @@
+/*
+ * 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 <asm/sgidefs.h>
+
+#if _MIPS_SIM == _MIPS_SIM_ABI64
+OUTPUT_FORMAT("elf64-tradlittlemips", "elf64-tradbigmips", "elf64-tradlittlemips")
+#elif _MIPS_SIM == _MIPS_SIM_NABI32
+OUTPUT_FORMAT("elf32-ntradlittlemips", "elf32-ntradbigmips", "elf32-ntradlittlemips")
+#else
+OUTPUT_FORMAT("elf32-tradlittlemips", "elf32-tradbigmips", "elf32-tradlittlemips")
+#endif
+
+OUTPUT_ARCH(mips)
+
+SECTIONS
+{
+ PROVIDE(_start = .);
+ . = SIZEOF_HEADERS;
+
+ /*
+ * In order to retain compatibility with older toolchains we provide the
+ * ABI flags section ourself. Newer assemblers will automatically
+ * generate .MIPS.abiflags sections so we discard such input sections,
+ * and then manually define our own section here. genvdso will patch
+ * this section to have the correct name/type.
+ */
+ .mips_abiflags : { *(.mips_abiflags) } :text :abiflags
+
+ .reginfo : { *(.reginfo) } :text :reginfo
+
+ .hash : { *(.hash) } :text
+ .gnu.hash : { *(.gnu.hash) }
+ .dynsym : { *(.dynsym) }
+ .dynstr : { *(.dynstr) }
+ .gnu.version : { *(.gnu.version) }
+ .gnu.version_d : { *(.gnu.version_d) }
+ .gnu.version_r : { *(.gnu.version_r) }
+
+ .note : { *(.note.*) } :text :note
+
+ .text : { *(.text*) } :text
+ PROVIDE (__etext = .);
+ PROVIDE (_etext = .);
+ PROVIDE (etext = .);
+
+ .eh_frame_hdr : { *(.eh_frame_hdr) } :text :eh_frame_hdr
+ .eh_frame : { KEEP (*(.eh_frame)) } :text
+
+ .dynamic : { *(.dynamic) } :text :dynamic
+
+ .rodata : { *(.rodata*) } :text
+
+ _end = .;
+ PROVIDE(end = .);
+
+ /DISCARD/ : {
+ *(.MIPS.abiflags)
+ *(.gnu.attributes)
+ *(.note.GNU-stack)
+ *(.data .data.* .gnu.linkonce.d.* .sdata*)
+ *(.bss .sbss .dynbss .dynsbss)
+ }
+}
+
+PHDRS
+{
+ /*
+ * Provide a PT_MIPS_ABIFLAGS header to assign the ABI flags section
+ * to. We can specify the header type directly here so no modification
+ * is needed later on.
+ */
+ abiflags 0x70000003;
+
+ /*
+ * The ABI flags header must exist directly after the PT_INTERP header,
+ * so we must explicitly place the PT_MIPS_REGINFO header after it to
+ * stop the linker putting one in at the start.
+ */
+ reginfo 0x70000000;
+
+ text PT_LOAD FLAGS(5) FILEHDR PHDRS; /* PF_R|PF_X */
+ dynamic PT_DYNAMIC FLAGS(4); /* PF_R */
+ note PT_NOTE FLAGS(4); /* PF_R */
+ eh_frame_hdr PT_GNU_EH_FRAME;
+}
+
+VERSION
+{
+ LINUX_2.6 {
+ local: *;
+ };
+}