Re: [uml-devel] [PATCH] um: v3: Fix FP register size for XSTATE/XSAVE

[Richard W. <ri...@no...>]

Thomas,

Am 12.07.2017 um 17:11 schrieb Thomas Meyer:
> Am 10.07.2017 9:06 nachm. schrieb Richard Weinberger <ri...@no...>:
> 
>     Thomas,
> 
>     Am 10.07.2017 um 00:33 schrieb Thomas Meyer:
>     > Hard code max size. Taken from
>     > https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=gdb/common/x86-xstate.h
>     >
>     > v3: use static fp_regs for get_skas_faultinfo
>     >
>     > Signed-off-by: Thomas Meyer <th...@m3...>
>     > ---
>     >  arch/um/os-Linux/skas/process.c  |  7 ++++---
>     >  arch/x86/um/os-Linux/registers.c | 18 ++++++++++++------
>     >  arch/x86/um/user-offsets.c       |  2 +-
>     >  3 files changed, 17 insertions(+), 10 deletions(-)
>     >
>     > diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
>     > index 03b3c4cc7735..b5fdef795985 100644
>     > --- a/arch/um/os-Linux/skas/process.c
>     > +++ b/arch/um/os-Linux/skas/process.c
>     > @@ -88,12 +88,13 @@ void wait_stub_done(int pid)
>     > 
>     >  extern unsigned long current_stub_stack(void);
>     > 
>     > +static unsigned long skas_faultinfo_fpregs[FP_SIZE];
>     > +
> 
>     Uhmm, are you sure that this does not race with other userspace() instances?
> 
> Oh, is it really possible that a task gets schedule while we are in userspace signal handling from ptrace?

I hoped that you'd double check. ;)
>From my knowledge it is not possible, but this code was not written by me and UML internal
semantics are more than tricky.
Let's postpone this patch for -rc2 and check again.

> Another question: when malloc a memory area in userspace: when does a userspace process end in userspace function!? Where would you free the malloced memory?

It ends via handle_trap() when userspac does an exit syscall.
I agree this is tricky to catch and needs more effort.

Thanks,
//richard