Re: [Qemu-devel] [PATCH v3] linux-user: rename gettid() to sys_gettid() to avoid clash with glibc

[Laurent Vivier]

Le 20/03/2019 à 13:36, Daniel P. Berrangé a écrit :
> The glibc-2.29.9000-6.fc31.x86_64 package finally includes the gettid()
> function as part of unistd.h when __USE_GNU is defined. This clashes
> with linux-user code which unconditionally defines this function name
> itself.
> 
> /home/berrange/src/virt/qemu/linux-user/syscall.c:253:16: error: static 
> declaration of ‘gettid’ follows non-static declaration
>   253 | _syscall0(int, gettid)
>       |                ^~~~~~
> /home/berrange/src/virt/qemu/linux-user/syscall.c:184:13: note: in definition 
> of macro ‘_syscall0’
>   184 | static type name (void)   \
>       |             ^~~~
> In file included from /usr/include/unistd.h:1170,
>                  from /home/berrange/src/virt/qemu/include/qemu/osdep.h:107,
>                  from /home/berrange/src/virt/qemu/linux-user/syscall.c:20:
> /usr/include/bits/unistd_ext.h:34:16: note: previous declaration of ‘gettid’ 
> was here
>    34 | extern __pid_t gettid (void) __THROW;
>       |                ^~~~~~
>   CC      aarch64-linux-user/linux-user/signal.o
> make[1]: *** [/home/berrange/src/virt/qemu/rules.mak:69: 
> linux-user/syscall.o] Error 1
> make[1]: *** Waiting for unfinished jobs....
> make: *** [Makefile:449: subdir-aarch64-linux-user] Error 2
> 
> While we could make our definition conditional and rely on glibc's impl,
> this patch simply renames our definition to sys_gettid() which is a
> common pattern in this file.
> 
> Signed-off-by: Daniel P. Berrangé <address@hidden>
> ---
> 
> Changed in v3:
>  - put { on separate line to please checkpatch
> 
> Changed in v2:
>  - Rename to sys_gettid instead of using conditional compilation
> 
>  linux-user/syscall.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 208fd1813d..804695411f 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -250,11 +250,15 @@ static type name (type1 arg1,type2 arg2,type3 
> arg3,type4 arg4,type5 arg5,       \
>  #endif
>  
>  #ifdef __NR_gettid
> -_syscall0(int, gettid)
> +static int sys_gettid(void)
> +{
> +    return syscall(__NR_gettid);
> +}

For other sys_ syscall we have something like

#define __NR_sys_gettid __NR_gettid

#ifdef __NR_gettid
syscall0(int, sys_gettid)
...


>  #else
>  /* This is a replacement for the host gettid() and must return a host
>     errno. */
> -static int gettid(void) {
> +static int sys_gettid(void)
> +{
>      return -ENOSYS;
>  }

Perhaps we can avoid the "#else" as it will put a -ENOSYS in the ->tid
of the structures.

According to manpage, gettid appeared with linux 2.4.11
I don't think we support a kernel as old as this.

Thanks,
Laurent