Re: [uml-devel] current_thread_info() returns invalid pointer in early UML boot code

[Thomas M. <th...@m3...>]

Am Sonntag, den 22.05.2016, 17:39 +0200 schrieb Vegard Nossum:
> On 21 May 2016 at 20:18, Thomas Meyer <th...@m3...> wrote:
> > 
> > Am 21.05.2016 um 15:51 schrieb Vegard Nossum <vegard.nossum@gmail.c
> > om>:
> > > 
> > > I'm having some trouble with using current_thread_info() during
> > > UML
> > > early boot. Sometimes it works just fine, but often I get
> > > segfaults
> > > because current_thread_info() is returning an invalid pointer. It
> > > looks random: 0x202118, 0x1003e0003, 0xd33b90b3, 0x6db043, etc.
> > Mhh. Strange. Do you have a stack trace to call to current thread
> > info which ends up with a wrong value. I wonder from were it
> > originates.
> One such trace would be:
> 
> #2  0x000000006026652c in snprintf (buf=<optimized out>,
> size=<optimized out>, fmt=<optimized out>) at lib/vsprintf.c:2181
> #3  0x00000000600046f8 in setup_env_path () at arch/um/os-
> Linux/main.c:109
> #4  main (argc=3, argv=0x7ffc3d8c23e8, envp=<optimized out>) at
> arch/um/os-Linux/main.c:125
> 
> I wonder why setup_env_path() ends up calling the kernel's
> snprintf(),
> I thought that it would be using the glibc snprintf() at this point?

Mhh. Good question!

Doing a make ARCH=um V=1 arch/um/os-Linux/main.o

results in:

gcc -Wp,-MD,arch/um/os-Linux/.main.o.d -Wall -Wundef -Wstrict-
prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Werror-
implicit-function-declaration -Wno-format-security -std=gnu89
-mcmodel=large -fno-builtin -m64 -funit-at-a-time -D__arch_um__
-Dvmap=kernel_vmap -Din6addr_loopback=kernel_in6addr_loopback
-Din6addr_any=kernel_in6addr_any -Dstrrchr=kernel_strrchr
-D_LARGEFILE64_SOURCE  -fno-delete-null-pointer-checks -O2 --
param=allow-store-data-races=0 -fno-reorder-blocks -fno-ipa-cp-clone
-fno-partial-inlining -Wframe-larger-than=1024 -fno-stack-protector
-Wno-unused-but-set-variable -fno-omit-frame-pointer -fno-optimize-
sibling-calls -fno-var-tracking-assignments -g -gdwarf-4 -Wdeclaration-
after-statement -Wno-pointer-sign -fno-strict-overflow -fconserve-stack 
-Werror=implicit-int -Werror=strict-prototypes -Werror=date-time
-Werror=incompatible-pointer-types -DCC_HAVE_ASM_GOTO
-I./arch/um/include/shared -I./arch/x86/um/shared
-I./arch/um/include/shared/skas  -D_FILE_OFFSET_BITS=64 -idirafter
./include -idirafter ./include -D__KERNEL__ -D__UM_HOST__ -D_GNU_SOURCE
-D_LARGEFILE64_SOURCE -include ./include/linux/kern_levels.h -include
user.h  -c -o arch/um/os-Linux/main.o arch/um/os-Linux/main.c

so it includes user.h and is under os-Linux. So I guess it should
actually call the glibc version, I'm not sure why it doesn't.

with kind regards
thomas


> 
> 
> Vegard
>