gdb/arm: Extend arm_m_addr_is_magic to support FNC_RETURN, add unwind-secure-frames command

This patch makes use of the support for several stack pointers
introduced by the previous patch to switch between them as needed
during unwinding.

It introduces a new 'unwind-secure-frames' arm command to enable/disable
mode switching during unwinding. It is enabled by default.

It has been tested using an STM32L5 board (with cortex-m33) and the
sample applications shipped with the STM32Cube development
environment: GTZC_TZSC_MPCBB_TrustZone in
STM32CubeL5/Projects/NUCLEO-L552ZE-Q/Examples/GTZC.

The test consisted in setting breakpoints in various places and check
that the backtrace is correct: SecureFault_Callback (Non-secure mode),
__gnu_cmse_nonsecure_call (before and after the vpush instruction),
SecureFault_Handler (Secure mode).

This implies that we tested only some parts of this patch (only MSP*
were used), but remaining parts seem reasonable.

Signed-off-by: Torbjörn Svensson <torbjorn.svensson@st.com>
Signed-off-by: Christophe Lyon <christophe.lyon@foss.st.com>
Signed-off-by: Christophe Lyon <christophe.lyon@arm.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index c1e9b09..38ad2ac 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -25133,6 +25133,16 @@ of @samp{set arm fallback-mode}.
 @item show arm force-mode
 Show the current forced instruction mode.
 
+@item set arm unwind-secure-frames
+This command enables unwinding from Non-secure to Secure mode on
+Cortex-M with Security extension.
+This can trigger security exceptions when unwinding the exception
+stack.
+It is enabled by default.
+
+@item show arm unwind-secure-frames
+Show whether unwinding from Non-secure to Secure mode is enabled.
+
 @item set debug arm
 Toggle whether to display ARM-specific debugging messages from the ARM
 target support subsystem.