[RFC PATCH u-boot 02/12] sandbox: errno: avoid conflict with libc's errno

[Marek Behun]

On Fri, 5 Mar 2021 09:58:34 -0700
Simon Glass <sjg at chromium.org> wrote:

> Hi Marek,
> 
> On Fri, 5 Mar 2021 at 09:50, Marek Behun <marek.behun at nic.cz> wrote:
> >
> > On Fri, 5 Mar 2021 09:39:53 -0700
> > Simon Glass <sjg at chromium.org> wrote:
> >  
> > > Hi Marek,
> > >
> > > On Fri, 5 Mar 2021 at 08:37, Marek Behun <marek.behun at nic.cz> wrote:  
> > > >
> > > > On Fri, 5 Mar 2021 11:00:45 +0800
> > > > Bin Meng <bmeng.cn at gmail.com> wrote:
> > > >  
> > > > > On Wed, Mar 3, 2021 at 12:13 PM Marek Behún <marek.behun at nic.cz> wrote:  
> > > > > >
> > > > > > When building with LTO, the system libc's `errno` variable used in
> > > > > > arch/sandbox/cpu/os.c conflicts with U-Boot's `errno` (defined in
> > > > > > lib/errno.c) with the following error:
> > > > > >  .../ld: errno@@GLIBC_PRIVATE: TLS definition in /lib64/libc.so.6
> > > > > >          section .tbss mismatches non-TLS reference in
> > > > > >          /tmp/u-boot.EQlEXz.ltrans0.ltrans.o  
> > > > >
> > > > > Do you know if this is the expected behavior when enabling LTO on the compiler?  
> > > >
> > > > I don't, but this is a bug anyway. The symbol clashes with the symbol
> > > > from glibc. Does somebody know whether the usage of this symbol in os.c
> > > > does really use glibc's version or U-Boot's one?  
> > >
> > > It is intended to use glibc's version. In fact I don't think U-Boot
> > > should have an errno. We return errors in each case, as does Linux.  
> >
> > The problem is that libc defines errno as a thread-local variable or,
> > in older version, as a macro expading to a function dereference, i.e.
> >   #define errno (*__get_threads_errno())
> > But U-Boot usis the errno symbol defined in include/errno.h as a symbol.
> >
> > So in order for these two symbols not to clash (in case libc is using
> > thread-local symbol with name errno), we need to rename the U-Boot
> > errno variable's symbol name.  
> 
> Rename is OK, but can we delete it instead? I really don't think it
> should be there.

We can't simply delete it. The whole u-boot is using the errno symbol
from include/errno.h and if we want the whole u-boot to use libc's
symbol we need to code include/errno.h to declare it in the same way as
libc, which may be different for different libcs.