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

[Vivian Wang]

On 7/22/24 08:18, Xingtao Yao (Fujitsu) wrote:
>
>> -----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
That wouldn't work. I'm testing for glibc, not glib.
>> +
>>  /* 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
>>