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authorAlex Smith <alex.smith@imgtec.com>2015-10-21 11:54:38 +0300
committerRalf Baechle <ralf@linux-mips.org>2015-11-11 10:36:36 +0300
commitebb5e78cc63417a35254a791de66e1cc84f963cc (patch)
tree49814946abe594cb8e7a11ce8d0a5fdaabb49d31 /arch/mips/vdso/genvdso.h
parent22773aa9b95657f0adc2b5342428d9da7a6d5d02 (diff)
downloadlinux-ebb5e78cc63417a35254a791de66e1cc84f963cc.tar.xz
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>
Diffstat (limited to 'arch/mips/vdso/genvdso.h')
-rw-r--r--arch/mips/vdso/genvdso.h187
1 files changed, 187 insertions, 0 deletions
diff --git a/arch/mips/vdso/genvdso.h b/arch/mips/vdso/genvdso.h
new file mode 100644
index 000000000000..94334727059a
--- /dev/null
+++ b/arch/mips/vdso/genvdso.h
@@ -0,0 +1,187 @@
+/*
+ * 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.
+ */
+
+static inline bool FUNC(patch_vdso)(const char *path, void *vdso)
+{
+ const ELF(Ehdr) *ehdr = vdso;
+ void *shdrs;
+ ELF(Shdr) *shdr;
+ char *shstrtab, *name;
+ uint16_t sh_count, sh_entsize, i;
+ unsigned int local_gotno, symtabno, gotsym;
+ ELF(Dyn) *dyn = NULL;
+
+ shdrs = vdso + FUNC(swap_uint)(ehdr->e_shoff);
+ sh_count = swap_uint16(ehdr->e_shnum);
+ sh_entsize = swap_uint16(ehdr->e_shentsize);
+
+ shdr = shdrs + (sh_entsize * swap_uint16(ehdr->e_shstrndx));
+ shstrtab = vdso + FUNC(swap_uint)(shdr->sh_offset);
+
+ for (i = 0; i < sh_count; i++) {
+ shdr = shdrs + (i * sh_entsize);
+ name = shstrtab + swap_uint32(shdr->sh_name);
+
+ /*
+ * Ensure there are no relocation sections - ld.so does not
+ * relocate the VDSO so if there are relocations things will
+ * break.
+ */
+ switch (swap_uint32(shdr->sh_type)) {
+ case SHT_REL:
+ case SHT_RELA:
+ fprintf(stderr,
+ "%s: '%s' contains relocation sections\n",
+ program_name, path);
+ return false;
+ case SHT_DYNAMIC:
+ dyn = vdso + FUNC(swap_uint)(shdr->sh_offset);
+ break;
+ }
+
+ /* Check for existing sections. */
+ if (strcmp(name, ".MIPS.abiflags") == 0) {
+ fprintf(stderr,
+ "%s: '%s' already contains a '.MIPS.abiflags' section\n",
+ program_name, path);
+ return false;
+ }
+
+ if (strcmp(name, ".mips_abiflags") == 0) {
+ strcpy(name, ".MIPS.abiflags");
+ shdr->sh_type = swap_uint32(SHT_MIPS_ABIFLAGS);
+ shdr->sh_entsize = shdr->sh_size;
+ }
+ }
+
+ /*
+ * Ensure the GOT has no entries other than the standard 2, for the same
+ * reason we check that there's no relocation sections above.
+ * The standard two entries are:
+ * - Lazy resolver
+ * - Module pointer
+ */
+ if (dyn) {
+ local_gotno = symtabno = gotsym = 0;
+
+ while (FUNC(swap_uint)(dyn->d_tag) != DT_NULL) {
+ switch (FUNC(swap_uint)(dyn->d_tag)) {
+ /*
+ * This member holds the number of local GOT entries.
+ */
+ case DT_MIPS_LOCAL_GOTNO:
+ local_gotno = FUNC(swap_uint)(dyn->d_un.d_val);
+ break;
+ /*
+ * This member holds the number of entries in the
+ * .dynsym section.
+ */
+ case DT_MIPS_SYMTABNO:
+ symtabno = FUNC(swap_uint)(dyn->d_un.d_val);
+ break;
+ /*
+ * This member holds the index of the first dynamic
+ * symbol table entry that corresponds to an entry in
+ * the GOT.
+ */
+ case DT_MIPS_GOTSYM:
+ gotsym = FUNC(swap_uint)(dyn->d_un.d_val);
+ break;
+ }
+
+ dyn++;
+ }
+
+ if (local_gotno > 2 || symtabno - gotsym) {
+ fprintf(stderr,
+ "%s: '%s' contains unexpected GOT entries\n",
+ program_name, path);
+ return false;
+ }
+ }
+
+ return true;
+}
+
+static inline bool FUNC(get_symbols)(const char *path, void *vdso)
+{
+ const ELF(Ehdr) *ehdr = vdso;
+ void *shdrs, *symtab;
+ ELF(Shdr) *shdr;
+ const ELF(Sym) *sym;
+ char *strtab, *name;
+ uint16_t sh_count, sh_entsize, st_count, st_entsize, i, j;
+ uint64_t offset;
+ uint32_t flags;
+
+ shdrs = vdso + FUNC(swap_uint)(ehdr->e_shoff);
+ sh_count = swap_uint16(ehdr->e_shnum);
+ sh_entsize = swap_uint16(ehdr->e_shentsize);
+
+ for (i = 0; i < sh_count; i++) {
+ shdr = shdrs + (i * sh_entsize);
+
+ if (swap_uint32(shdr->sh_type) == SHT_SYMTAB)
+ break;
+ }
+
+ if (i == sh_count) {
+ fprintf(stderr, "%s: '%s' has no symbol table\n", program_name,
+ path);
+ return false;
+ }
+
+ /* Get flags */
+ flags = swap_uint32(ehdr->e_flags);
+ if (elf_class == ELFCLASS64)
+ elf_abi = ABI_N64;
+ else if (flags & EF_MIPS_ABI2)
+ elf_abi = ABI_N32;
+ else
+ elf_abi = ABI_O32;
+
+ /* Get symbol table. */
+ symtab = vdso + FUNC(swap_uint)(shdr->sh_offset);
+ st_entsize = FUNC(swap_uint)(shdr->sh_entsize);
+ st_count = FUNC(swap_uint)(shdr->sh_size) / st_entsize;
+
+ /* Get string table. */
+ shdr = shdrs + (swap_uint32(shdr->sh_link) * sh_entsize);
+ strtab = vdso + FUNC(swap_uint)(shdr->sh_offset);
+
+ /* Write offsets for symbols needed by the kernel. */
+ for (i = 0; vdso_symbols[i].name; i++) {
+ if (!(vdso_symbols[i].abis & elf_abi))
+ continue;
+
+ for (j = 0; j < st_count; j++) {
+ sym = symtab + (j * st_entsize);
+ name = strtab + swap_uint32(sym->st_name);
+
+ if (!strcmp(name, vdso_symbols[i].name)) {
+ offset = FUNC(swap_uint)(sym->st_value);
+
+ fprintf(out_file,
+ "\t.%s = 0x%" PRIx64 ",\n",
+ vdso_symbols[i].offset_name, offset);
+ break;
+ }
+ }
+
+ if (j == st_count) {
+ fprintf(stderr,
+ "%s: '%s' is missing required symbol '%s'\n",
+ program_name, path, vdso_symbols[i].name);
+ return false;
+ }
+ }
+
+ return true;
+}