Re: [Qemu-devel] [PATCH 1/6] osdep: Create qemu_getauxval and qemu_init_auxval

[Aurelien Jarno <aurelien@aurel32.net>]

On Sat, Aug 17, 2013 at 03:38:03PM -0700, Richard Henderson wrote:
> Abstract away dependence on a system implementation of getauxval.
> 
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
>  include/qemu/osdep.h | 20 ++++++++++++
>  linux-user/main.c    |  1 +
>  util/Makefile.objs   |  1 +
>  util/getauxval.c     | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  vl.c                 |  1 +
>  5 files changed, 114 insertions(+)
>  create mode 100644 util/getauxval.c
> 
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 26136f1..8d1948b 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -215,4 +215,24 @@ bool fips_get_state(void);
>   */
>  char *qemu_get_local_state_pathname(const char *relative_pathname);
>  
> +/* Return a value for an AT_* type in the auxiliary vector.  Return 0 if the
> + * key is not present.  We attempt to emulate AT_HWCAP and AT_PLATFORM as
> + * best we can when real host support is not present.
> + */
> +#ifdef _WIN32
> +static inline unsigned long qemu_getauxval(unsigned long type) { return 0; }
> +#else
> +unsigned long qemu_getauxval(unsigned long type);
> +#endif
> +
> +/* If supported and required, locate the auxiliary vector at program startup.
> + *
> + * @envp must be the third argument to main.
> + */
> +#if defined(CONFIG_GETAUXVAL) || defined(_WIN32)
> +static inline void qemu_init_auxval(char **envp) { }
> +#else
> +void qemu_init_auxval(char **envp);
> +#endif
> +
>  #endif
> diff --git a/linux-user/main.c b/linux-user/main.c
> index 03859bc..fae102a 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -3549,6 +3549,7 @@ int main(int argc, char **argv, char **envp)
>  
>      module_call_init(MODULE_INIT_QOM);
>  
> +    qemu_init_auxval(envp);
>      qemu_cache_utils_init(envp);
>  
>      if ((envlist = envlist_create()) == NULL) {
> diff --git a/util/Makefile.objs b/util/Makefile.objs
> index dc72ab0..8e0c929 100644
> --- a/util/Makefile.objs
> +++ b/util/Makefile.objs
> @@ -11,3 +11,4 @@ util-obj-y += iov.o aes.o qemu-config.o qemu-sockets.o uri.o notify.o
>  util-obj-y += qemu-option.o qemu-progress.o
>  util-obj-y += hexdump.o
>  util-obj-y += crc32c.o
> +util-obj-y += getauxval.o
> diff --git a/util/getauxval.c b/util/getauxval.c
> new file mode 100644
> index 0000000..55b639c
> --- /dev/null
> +++ b/util/getauxval.c
> @@ -0,0 +1,91 @@
> +/*
> + * QEMU access to the auxiliary vector
> + *
> + * Copyright (C) 2013 Red Hat, Inc
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a copy
> + * of this software and associated documentation files (the "Software"), to deal
> + * in the Software without restriction, including without limitation the rights
> + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
> + * copies of the Software, and to permit persons to whom the Software is
> + * furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
> + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
> + * THE SOFTWARE.
> + */
> +
> +#include "qemu-common.h"
> +#include "qemu/osdep.h"
> +
> +#ifdef CONFIG_GETAUXVAL
> +/* Don't inline this in qemu/osdep.h, because pulling in <sys/auxv.h> for
> +   the system declaration of getauxval pulls in the system <elf.h>, which
> +   conflicts with qemu's version.  */
> +
> +#include <sys/auxv.h>
> +
> +unsigned long qemu_getauxval(unsigned long key)
> +{
> +    return getauxval(key);
> +}
> +#elif !defined(_WIN32)
> +#include "elf.h"
> +
> +/* Our elf.h doesn't contain Elf32_auxv_t and Elf64_auxv_t, which is ok because
> +   that just makes it easier to define it properly for the host here.  */
> +typedef struct {
> +    unsigned long a_type;
> +    unsigned long a_val;
> +} ElfW_auxv_t;
> +
> +static const ElfW_auxv_t *auxv;
> +
> +void qemu_init_auxval(char **envp)
> +{
> +#ifdef __linux__
> +    /* The auxiliary vector is located just beyond the initial environment.  */
> +    while (*envp != NULL)
> +        continue;

This is basically an endless loop, so QEMU doesn't start on a system
without getauxval support.

> +    auxv = (const ElfW_auxv_t *)envp;
> +#endif
> +}
> +
> +static const char *default_platform(void)
> +{
> +    return NULL;
> +}
> +
> +static unsigned long default_hwcap(void)
> +{
> +    return 0;
> +}
> +
> +unsigned long qemu_getauxval(unsigned long type)
> +{
> +    /* If we were able to find the auxiliary vector, use it.  */
> +    if (auxv) {
> +        const ElfW_auxv_t *a;
> +        for (a = auxv; a->a_type != 0; a++) {
> +            if (a->a_type == type) {
> +                return a->a_val;
> +            }
> +        }
> +    }
> +
> +    /* Otherwise, guess defaults for the host based on compiler flags.  */
> +    if (type == AT_HWCAP) {
> +        return default_hwcap();
> +    } else if (type == AT_PLATFORM) {
> +        return (unsigned long)default_platform();
> +    }
> +    return 0;
> +}
> +#endif
> diff --git a/vl.c b/vl.c
> index f422a1c..c539fd3 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2967,6 +2967,7 @@ int main(int argc, char **argv, char **envp)
>      init_clocks();
>      rtc_clock = host_clock;
>  
> +    qemu_init_auxval(envp);
>      qemu_cache_utils_init(envp);
>  
>      QLIST_INIT (&vm_change_state_head);
> -- 
> 1.8.1.4
> 
> 
> 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net