Re: [Valgrind-developers] catch syscall

[Catalin V. <cat...@ke...>]

My issue is in the following way:
I have a mips64 platform and custom ioctl call. Without valgrind the 
scenario works perfectly, with valgrind it does not.

The ioctl handler, as soon as it gets inside the function, it tries to 
make a switch() statement on the "unsigned int cmd" argument. If I print 
the argument it shows the case it should go on. But inside the switch 
statement it goes directly to the default case. I even tried printing 
the value again in the default case, and it shows it should have gone on 
that specific case.
I think the comparison instruction may load the comparable values with 
something that is being initialized differently by valgrind when 
compared to glibc.

I tried running with the trace-syscalls, and the cmd argument seems to 
be set there. I've watched the assembly code in valgrind vs glibc, and 
they seem a bit different.
I've also tried looking at VG_(client_syscall), but this is way upper 
level. I got to this line that I mentioned previously:
dres.jk_StopHere = Ijk_Sys_syscall;

I'm trying to get exactly when valgrind catches the parameters sent by 
the ioctl.

 >Hi Catalin,>


 >> I have a bug which I'm trying to narrow down on a mips64 platform.>

 >Are you seeing a bug in Valgrind or in your application?
 >If it is in Valgrind, can you descibe it (or even better - create a
 >Bugzilla ticket)?>

 >If you believe there is an issue with system calls, you may want to
 >run Valgrind with --trace-syscalls=yes.>

 >Regards,
 >Petar>

 >On Thu, Jun 27, 2019 at 2:58 PM Catalin Vasile via Valgrind-developers
 ><valgrind-developers@...> wrote:
 >>
 >> Hi,
 >>
 >>
 >> I have a bug which I'm trying to narrow down on a mips64 platform.
 >>
 >> For now I'm trying to get to where in valgrind syscall are caught.
 >>
 >> Can you pinpoint me to where in the code that happens?
 >>
 >> The closest I've got to understanding the call chain so far is this 
line:
 >>
 >>    dres.jk_StopHere = Ijk_Sys_syscall;
 >>
 >> Found in the following file:
 >>
 >>    VEX/priv/guest_mips_toIR.c
 >>
 >>
 >> Best regards,
 >>
 >> Catalin Vasile
 >>
 >>
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