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

[Richard Henderson]

On 7/21/24 19:08, Vivian Wang wrote:
> 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))

Version 2.19 is so long ago that all supported OS releases have something newer.  For 
Alpine Linux using musl, the first commit of getauxval had the errno setting.

Therefore we don't need this check.

> @@ -95,6 +101,7 @@ unsigned long qemu_getauxval(unsigned long type)
>           }
>       }
>   
> +    errno = ENOENT;
>       return 0;
>   }

Ok.

> @@ -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;

Braces required.

>       return aux;
>   }
>   
> @@ -112,6 +121,7 @@ unsigned long qemu_getauxval(unsigned long type)
>   
>   unsigned long qemu_getauxval(unsigned long type)
>   {
> +    errno = ENOSYS;
>       return 0;
>   }

Ok.


r~