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Date: Mon, 20 Aug 2012 15:29:19 +0200
From: Borislav Petkov <bp@...64.org>
To: Fenghua Yu <fenghua.yu@...el.com>
Cc: H Peter Anvin <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
Thomas Gleixner <tglx@...utronix.de>,
Asit K Mallick <asit.k.mallick@...el.com>,
Tigran Aivazian <tigran@...azian.fsnet.co.uk>,
Andreas Herrmann <andreas.herrmann3@....com>,
Borislav Petkov <borislav.petkov@....com>,
linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH 02/11] x86/lib/cpio.c: Find cpio data by its file name
On Sat, Aug 18, 2012 at 01:15:20AM -0700, Fenghua Yu wrote:
> From: Fenghua Yu <fenghua.yu@...el.com>
>
> Given a file's name, find its starting point in a cpio formated area. This will
s/file's/file/ cpio-formatted
> be used to find microcode in combined initrd image. But this function is
> generic and could be used in other places.
>
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> ---
> arch/x86/include/asm/cpio.h | 10 +++
> arch/x86/lib/Makefile | 2 +
> arch/x86/lib/cpio.c | 179 +++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 191 insertions(+), 0 deletions(-)
> create mode 100644 arch/x86/include/asm/cpio.h
> create mode 100644 arch/x86/lib/cpio.c
>
> diff --git a/arch/x86/include/asm/cpio.h b/arch/x86/include/asm/cpio.h
> new file mode 100644
> index 0000000..26a4333
> --- /dev/null
> +++ b/arch/x86/include/asm/cpio.h
> @@ -0,0 +1,10 @@
> +#include <stddef.h>
> +#include <stdbool.h>
> +
> +struct cpio_data {
> + void *data;
> + unsigned long size;
> +};
> +
> +extern struct cpio_data
> +find_cpio_data(const char *name, const void *data, size_t len);
> diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
> index b00f678..452a4b5 100644
> --- a/arch/x86/lib/Makefile
> +++ b/arch/x86/lib/Makefile
> @@ -45,3 +45,5 @@ else
> lib-y += copy_user_64.o copy_user_nocache_64.o
> lib-y += cmpxchg16b_emu.o
> endif
> +
> +obj-y += cpio.o
> diff --git a/arch/x86/lib/cpio.c b/arch/x86/lib/cpio.c
> new file mode 100644
> index 0000000..70ac474
> --- /dev/null
> +++ b/arch/x86/lib/cpio.c
> @@ -0,0 +1,179 @@
> +/*
> + * findcpio.c
> + *
> + * Find a specific cpio member; must precede any compressed content.
> + *
> + * Copyright (C) 2012 H Peter Anvin" <hpa@...or.com>
stray "
> + * Fenghua Yu <fenghua.yu@...el.com>
> + */
> +#include <linux/module.h>
> +#include <linux/mm.h>
> +#include <linux/swap.h>
> +#include <linux/slab.h>
> +#include <linux/sysctl.h>
> +#include <linux/bitmap.h>
> +#include <linux/signal.h>
> +#include <linux/printk.h>
> +#include <linux/proc_fs.h>
> +#include <linux/security.h>
> +#include <linux/ctype.h>
> +#include <linux/kmemcheck.h>
> +#include <linux/fs.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/kobject.h>
> +#include <linux/net.h>
> +#include <linux/sysrq.h>
> +#include <linux/highuid.h>
> +#include <linux/writeback.h>
> +#include <linux/ratelimit.h>
> +#include <linux/compaction.h>
> +#include <linux/hugetlb.h>
> +#include <linux/initrd.h>
> +#include <linux/key.h>
> +#include <linux/times.h>
> +#include <linux/limits.h>
> +#include <linux/dcache.h>
> +#include <linux/dnotify.h>
> +#include <linux/syscalls.h>
Why all those includes?
> +#include <asm/cpio.h>
> +
> +enum cpio_fields {
> + C_MAGIC,
> + C_INO,
> + C_MODE,
> + C_UID,
> + C_GID,
> + C_NLINK,
> + C_MTIME,
> + C_FILESIZE,
> + C_MAJ,
> + C_MIN,
> + C_RMAJ,
> + C_RMIN,
> + C_NAMESIZE,
> + C_CHKSUM,
> + C_NFIELDS
> +};
> +
> +#if defined(__i386__) || defined(__x86_64__)
> +static size_t cpio_strlen(const char *name)
> +{
> + size_t n = -1;
> +
> + asm("repne; scasb"
> + : "+D" (name), "+c" (n)
> + : "a" (0));
> +
> + return -2 - n;
> +}
> +
> +static int cpio_memcmp(const void *p1, const void *p2, size_t n)
> +{
> + unsigned char rv;
> +
> + asm("repe; cmpsb; setne %0"
> + : "=r" (rv), "+S" (p1), "+D" (p2), "+c" (n));
> +
> + return rv;
> +}
I guess those are speed optimizations on x86, right? In any
case, can we reuse some of the already present ones like
memcmp in <arch/x86/boot/compressed/string.c> and strlen in
<arch/x86/lib/string_32.c>...
> +#else
> +static size_t cpio_strlen(const char *name)
> +{
> + size_t n = 0;
> +
> + while (*name++)
> + n++;
> +
> + return n;
> +}
> +
> +static int cpio_memcmp(const void *p1, const void *p2, size_t n)
> +{
> + const unsigned char *u1 = p1;
> + const unsigned char *u2 = p2;
> + int d;
> +
> + while (n--) {
> + d = *u2++ - *u1++;
> + if (d)
> + return d;
> + }
> + return 0;
> +}
> +#endif
and, similarly the generic ones in lib/string.c?
> +
> +#define ALIGN4(p) ((void *)(((size_t)p + 3) & ~3))
> +
> +struct cpio_data find_cpio_data(const char *name, const void *data, size_t len)
> +{
> + const size_t cpio_header_len = 8*C_NFIELDS - 2;
> + struct cpio_data cd = { NULL, 0 };
> + const char *p, *dptr, *nptr;
> + unsigned int ch[C_NFIELDS], *chp, v;
> + unsigned char c, x;
> + size_t mynamesize = cpio_strlen(name) + 1;
> + int i, j;
> +
> + p = data;
> +
> + while (len > cpio_header_len) {
> + if (!*p) {
> + /* All cpio headers need to be 4-byte aligned */
> + p += 4;
> + len -= 4;
> + continue;
> + }
> +
> + j = 6; /* The magic field is only 6 characters */
Maybe put all comments above the line they refer to, like above instead
of them trailing?
> + chp = ch;
> + for (i = C_NFIELDS; i; i--) {
> + v = 0;
> + while (j--) {
> + v <<= 4;
> + c = *p++;
> +
> + x = c - '0';
> + if (x < 10) {
> + v += x;
> + continue;
> + }
> +
> + x = (c | 0x20) - 'a';
> + if (x < 6) {
> + v += x + 10;
> + continue;
> + }
> +
> + goto quit; /* Invalid hexadecimal */
> + }
> + *chp++ = v;
> + j = 8; /* All other fields are 8 characters */
> + }
> +
> + if ((ch[C_MAGIC] - 0x070701) > 1)
> + goto quit; /* Invalid magic */
> +
> + len -= cpio_header_len;
> +
> + dptr = ALIGN4(p + ch[C_NAMESIZE]);
> + nptr = ALIGN4(dptr + ch[C_FILESIZE]);
> +
> + if (nptr > p + len || dptr < p || nptr < dptr)
> + goto quit; /* Buffer overrun */
> +
> + if ((ch[C_MODE] & 0170000) == 0100000 &&
> + ch[C_NAMESIZE] == mynamesize &&
> + !cpio_memcmp(p, name, mynamesize)) {
> + cd.data = (void *)dptr;
> + cd.size = ch[C_FILESIZE];
> + return cd; /* Found it! */
> + }
> +
> + len -= (nptr - p);
> + p = nptr;
> + }
> +
> +quit:
> + return cd;
> +}
> --
> 1.7.2
>
>
--
Regards/Gruss,
Boris.
Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach
GM: Alberto Bozzo
Reg: Dornach, Landkreis Muenchen
HRB Nr. 43632 WEEE Registernr: 129 19551
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