RE: [PATCH 2/3] gdb/arm: Fetch initial sp value prior to compare

[Torbjorn SVENSSON <torbjorn.svensson@st.com>]

Hello,



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> -----Original Message-----
> From: Christophe Lyon <christophe.lyon@arm.com>
> Sent: den 16 maj 2022 16:56
> To: Yvan ROUX - foss <yvan.roux@foss.st.com>; gdb-
> patches@sourceware.org
> Cc: Torbjorn SVENSSON <torbjorn.svensson@st.com>
> Subject: Re: [PATCH 2/3] gdb/arm: Fetch initial sp value prior to compare
> 
> Hi,
> 
> On 5/16/22 15:59, Yvan Roux via Gdb-patches wrote:
> > For Arm Cortex-M33 with security extensions, there are 4 different
> > stacks pointers (msp_s, msp_ns, psp_s, psp_ns).  In order to
> > identify the active one, compare the values of the different
> > stacks. The value of the initla sp register needs to be fetched to
> 
> Typo: "initial"
> 
> > perform this comparison.
> >
> > Signed-off-by: Torbj�rn SVENSSON <torbjorn.svensson@st.com>
> > Signed-off-by: Yvan Roux <yvan.roux@foss.st.com>
> > ---
> >   gdb/arm-tdep.c | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
> > index c37254c2ce1..4aa277f5bc8 100644
> > --- a/gdb/arm-tdep.c
> > +++ b/gdb/arm-tdep.c
> > @@ -341,6 +341,7 @@ arm_cache_init (struct arm_prologue_cache
> *cache, struct frame_info *frame)
> >     arm_gdbarch_tdep *tdep = (arm_gdbarch_tdep *) gdbarch_tdep
> (gdbarch);
> >
> >     arm_cache_init (cache, gdbarch);
> > +  cache->sp = get_frame_register_unsigned (frame, ARM_SP_REGNUM);
> 
> With such simple fixes, I always wonder "how did that somehow worked so
> far?". Can you describe the broken scenario fixed by this patch?

When I  attempted to debug the issues in https://sourceware.org/bugzilla/show_bug.cgi?id=29121, I discovered that the arm_prologue_cache->active_sp_regnum was set to the regnum of psp_ns although psp was not used in the application. After digging a bit further, I noticed that the psp_ns and psp_s registers were both 0x0 and that arm_prologue_cache->sp was also 0x0 even though the sp register was something else.

Kind regards,
Torbjörn