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

[Xingtao Yao (Fujitsu)]

> -----Original Message-----
> From: Vivian Wang <uwu@dram.page>
> Sent: Monday, July 22, 2024 4:24 PM
> To: Yao, Xingtao/姚 幸涛 <yaoxt.fnst@fujitsu.com>; qemu-devel@nongnu.org
> Cc: Richard Henderson <rth@twiddle.net>; Laurent Vivier <laurent@vivier.eu>
> Subject: Re: [PATCH 1/2] util/getauxval: Ensure setting errno if not found
> 
> 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.
sorry, I misunderstood.

> >> +
> >>  /* 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
> >>