linux/arch/arm/vdso/vdsomunge.c
Nathan Lynch 8512287a81 ARM: 8330/1: add VDSO user-space code
Place VDSO-related user-space code in arch/arm/kernel/vdso/.

It is almost completely written in C with some assembly helpers to
load the data page address, sample the counter, and fall back to
system calls when necessary.

The VDSO can service gettimeofday and clock_gettime when
CONFIG_ARM_ARCH_TIMER is enabled and the architected timer is present
(and correctly configured).  It reads the CP15-based virtual counter
to compute high-resolution timestamps.

Of particular note is that a post-processing step ("vdsomunge") is
necessary to produce a shared object which is architecturally allowed
to be used by both soft- and hard-float EABI programs.

The 2012 edition of the ARM ABI defines Tag_ABI_VFP_args = 3 "Code is
compatible with both the base and VFP variants; the user did not
permit non-variadic functions to pass FP parameters/results."
Unfortunately current toolchains do not support this tag, which is
ideally what we would use.

The best available option is to ensure that both EF_ARM_ABI_FLOAT_SOFT
and EF_ARM_ABI_FLOAT_HARD are unset in the ELF header's e_flags,
indicating that the shared object is "old" and should be accepted for
backward compatibility's sake.  While binutils < 2.24 appear to
produce a vdso.so with both flags clear, 2.24 always sets
EF_ARM_ABI_FLOAT_SOFT, with no way to inhibit this behavior.  So we
have to fix things up with a custom post-processing step.

In fact, the VDSO code in glibc does much less validation (including
checking these flags) than the code for handling conventional
file-backed shared libraries, so this is a bit moot unless glibc's
VDSO code becomes more strict.

Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2015-03-27 22:20:45 +00:00

202 lines
5.3 KiB
C

/*
* Copyright 2015 Mentor Graphics Corporation.
*
* 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; version 2 of the
* License.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*
* vdsomunge - Host program which produces a shared object
* architecturally specified to be usable by both soft- and hard-float
* programs.
*
* The Procedure Call Standard for the ARM Architecture (ARM IHI
* 0042E) says:
*
* 6.4.1 VFP and Base Standard Compatibility
*
* Code compiled for the VFP calling standard is compatible with
* the base standard (and vice-versa) if no floating-point or
* containerized vector arguments or results are used.
*
* And ELF for the ARM Architecture (ARM IHI 0044E) (Table 4-2) says:
*
* If both EF_ARM_ABI_FLOAT_XXXX bits are clear, conformance to the
* base procedure-call standard is implied.
*
* The VDSO is built with -msoft-float, as with the rest of the ARM
* kernel, and uses no floating point arguments or results. The build
* process will produce a shared object that may or may not have the
* EF_ARM_ABI_FLOAT_SOFT flag set (it seems to depend on the binutils
* version; binutils starting with 2.24 appears to set it). The
* EF_ARM_ABI_FLOAT_HARD flag should definitely not be set, and this
* program will error out if it is.
*
* If the soft-float flag is set, this program clears it. That's all
* it does.
*/
#define _GNU_SOURCE
#include <byteswap.h>
#include <elf.h>
#include <errno.h>
#include <error.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#define HOST_ORDER ELFDATA2LSB
#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
#define HOST_ORDER ELFDATA2MSB
#endif
/* Some of the ELF constants we'd like to use were added to <elf.h>
* relatively recently.
*/
#ifndef EF_ARM_EABI_VER5
#define EF_ARM_EABI_VER5 0x05000000
#endif
#ifndef EF_ARM_ABI_FLOAT_SOFT
#define EF_ARM_ABI_FLOAT_SOFT 0x200
#endif
#ifndef EF_ARM_ABI_FLOAT_HARD
#define EF_ARM_ABI_FLOAT_HARD 0x400
#endif
static const char *outfile;
static void cleanup(void)
{
if (error_message_count > 0 && outfile != NULL)
unlink(outfile);
}
static Elf32_Word read_elf_word(Elf32_Word word, bool swap)
{
return swap ? bswap_32(word) : word;
}
static Elf32_Half read_elf_half(Elf32_Half half, bool swap)
{
return swap ? bswap_16(half) : half;
}
static void write_elf_word(Elf32_Word val, Elf32_Word *dst, bool swap)
{
*dst = swap ? bswap_32(val) : val;
}
int main(int argc, char **argv)
{
const Elf32_Ehdr *inhdr;
bool clear_soft_float;
const char *infile;
Elf32_Word e_flags;
const void *inbuf;
struct stat stat;
void *outbuf;
bool swap;
int outfd;
int infd;
atexit(cleanup);
if (argc != 3)
error(EXIT_FAILURE, 0, "Usage: %s [infile] [outfile]", argv[0]);
infile = argv[1];
outfile = argv[2];
infd = open(infile, O_RDONLY);
if (infd < 0)
error(EXIT_FAILURE, errno, "Cannot open %s", infile);
if (fstat(infd, &stat) != 0)
error(EXIT_FAILURE, errno, "Failed stat for %s", infile);
inbuf = mmap(NULL, stat.st_size, PROT_READ, MAP_PRIVATE, infd, 0);
if (inbuf == MAP_FAILED)
error(EXIT_FAILURE, errno, "Failed to map %s", infile);
close(infd);
inhdr = inbuf;
if (memcmp(&inhdr->e_ident, ELFMAG, SELFMAG) != 0)
error(EXIT_FAILURE, 0, "Not an ELF file");
if (inhdr->e_ident[EI_CLASS] != ELFCLASS32)
error(EXIT_FAILURE, 0, "Unsupported ELF class");
swap = inhdr->e_ident[EI_DATA] != HOST_ORDER;
if (read_elf_half(inhdr->e_type, swap) != ET_DYN)
error(EXIT_FAILURE, 0, "Not a shared object");
if (read_elf_half(inhdr->e_machine, swap) != EM_ARM) {
error(EXIT_FAILURE, 0, "Unsupported architecture %#x",
inhdr->e_machine);
}
e_flags = read_elf_word(inhdr->e_flags, swap);
if (EF_ARM_EABI_VERSION(e_flags) != EF_ARM_EABI_VER5) {
error(EXIT_FAILURE, 0, "Unsupported EABI version %#x",
EF_ARM_EABI_VERSION(e_flags));
}
if (e_flags & EF_ARM_ABI_FLOAT_HARD)
error(EXIT_FAILURE, 0,
"Unexpected hard-float flag set in e_flags");
clear_soft_float = !!(e_flags & EF_ARM_ABI_FLOAT_SOFT);
outfd = open(outfile, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
if (outfd < 0)
error(EXIT_FAILURE, errno, "Cannot open %s", outfile);
if (ftruncate(outfd, stat.st_size) != 0)
error(EXIT_FAILURE, errno, "Cannot truncate %s", outfile);
outbuf = mmap(NULL, stat.st_size, PROT_READ | PROT_WRITE, MAP_SHARED,
outfd, 0);
if (outbuf == MAP_FAILED)
error(EXIT_FAILURE, errno, "Failed to map %s", outfile);
close(outfd);
memcpy(outbuf, inbuf, stat.st_size);
if (clear_soft_float) {
Elf32_Ehdr *outhdr;
outhdr = outbuf;
e_flags &= ~EF_ARM_ABI_FLOAT_SOFT;
write_elf_word(e_flags, &outhdr->e_flags, swap);
}
if (msync(outbuf, stat.st_size, MS_SYNC) != 0)
error(EXIT_FAILURE, errno, "Failed to sync %s", outfile);
return EXIT_SUCCESS;
}