Re: [PATCH] Fix exception unwinding for ARM Cortex-M

[Yao Qi <qiyaoltc at gmail dot com>]

"Fredrik Hederstierna" <fredrik.hederstierna@verisure.com> writes:

Hi Fredrik,
Thanks for splitting the patch.

> diff --git a/gdb/ChangeLog b/gdb/ChangeLog
> index 7820302..2c8573c 100644
> --- a/gdb/ChangeLog
> +++ b/gdb/ChangeLog
> @@ -1,3 +1,7 @@
> +2016-08-02  Fredrik Hederstierna  <fredrik.hederstierna@verisure.com>
> +
> +	* arm-tdep.c: Fix EXC_RETURN values for ARMv6-M and ARMv7-M.
> +

ChangeLog entry should cover what do you change on the function level.
Please read https://sourceware.org/gdb/wiki/ContributionChecklist

>  2016-08-01  Joel Brobecker  <brobecker@adacore.com>
>  
>  	* NEWS: Create a new section for the next release branch.
> diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
> index d2661cb..43436df 100644
> --- a/gdb/arm-tdep.c
> +++ b/gdb/arm-tdep.c
> @@ -469,9 +469,11 @@ static CORE_ADDR
>  arm_addr_bits_remove (struct gdbarch *gdbarch, CORE_ADDR val)
>  {
>    /* On M-profile devices, do not strip the low bit from EXC_RETURN
> -     (the magic exception return address).  */
> +     (the magic exception return address).
> +     According to B1.5.8 of both the ARMv6-M and ARMv7-M Reference Manuals
> +     the EXC_RETURN value is 0xF in Bits[31:28].  */
>    if (gdbarch_tdep (gdbarch)->is_m
> -      && (val & 0xfffffff0) == 0xfffffff0)
> +      && (val & 0xf0000000) == 0xf0000000)


Let us do the strict checking.  In ARMv7-M manual, the pseudo code of 
ExceptionReturn(bits(28) EXC_RETURN) has

if HaveFPExt() then
if !IsOnes(EXC_RETURN<27:5>) then UNPREDICTABLE;
else
if !IsOnes(EXC_RETURN<27:4>) then UNPREDICTABLE;

so let's check "val" should be 0xFFFFFF{E,F}{1,9,D}, or use
arm_m_pc_is_magic too, like,

       if (gdbarch_tdep (gdbarch)->is_m
           && arm_m_pc_is_magic (val))
          return val;

Do you have FSF copyright assignment?  I don't find your record.  You
can fill in the form request-assign.future in
https://sourceware.org/gdb/wiki/ContributionChecklist#FSF_copyright_Assignment
then, we can pick up your change.

-- 
Yao (齐尧)