RE: [PATCH 1/2] util/getauxval: Ensure setting errno if not found

[Xingtao Yao (Fujitsu)]

> -----Original Message-----
> From: qemu-devel-bounces+yaoxt.fnst=fujitsu.com@nongnu.org
> <qemu-devel-bounces+yaoxt.fnst=fujitsu.com@nongnu.org> On Behalf Of Vivian
> Wang
> Sent: Sunday, July 21, 2024 5:08 PM
> To: qemu-devel@nongnu.org
> Cc: Vivian Wang <uwu@dram.page>; Richard Henderson <rth@twiddle.net>;
> Laurent Vivier <laurent@vivier.eu>
> Subject: [PATCH 1/2] util/getauxval: Ensure setting errno if not found
> 
> Sometimes zero is a valid value for getauxval (e.g. AT_EXECFD). Make
> sure that we can distinguish between a valid zero value and a not found
> entry by setting errno.
> 
> Ignore getauxval from sys/auxv.h on glibc < 2.19 because it does not set
> errno.
> 
> Signed-off-by: Vivian Wang <uwu@dram.page>
> ---
>  util/getauxval.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/util/getauxval.c b/util/getauxval.c
> index b124107d61..f1008bdc59 100644
> --- a/util/getauxval.c
> +++ b/util/getauxval.c
> @@ -24,7 +24,13 @@
> 
>  #include "qemu/osdep.h"
> 
> -#ifdef CONFIG_GETAUXVAL
> +/* If glibc < 2.19, getauxval can't be used because it does not set errno if
> +   entry is not found. */
> +#if defined(CONFIG_GETAUXVAL) && \
> +    (!defined(__GLIBC__) \
> +        || __GLIBC__ > 2 \
> +        || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 19))
you can use GLIB_CHECK_VERSION(2, 19, 0) instead

> +
>  /* 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.  */
> @@ -95,6 +101,7 @@ unsigned long qemu_getauxval(unsigned long type)
>          }
>      }
> 
> +    errno = ENOENT;
>      return 0;
>  }
> 
> @@ -104,7 +111,9 @@ unsigned long qemu_getauxval(unsigned long type)
>  unsigned long qemu_getauxval(unsigned long type)
>  {
>      unsigned long aux = 0;
> -    elf_aux_info(type, &aux, sizeof(aux));
> +    int ret = elf_aux_info(type, &aux, sizeof(aux));
> +    if (ret != 0)
> +        errno = ret;
>      return aux;
>  }
> 
> @@ -112,6 +121,7 @@ unsigned long qemu_getauxval(unsigned long type)
> 
>  unsigned long qemu_getauxval(unsigned long type)
>  {
> +    errno = ENOSYS;
>      return 0;
>  }
> 
> --
> 2.45.1
>