[PATCH v2 1/1] riscv: restore global data pointer in trap handler

[Heinrich Schuchardt]

The gp register is used to store U-Boot's global data pointer. We should
not assume that an UEFI application leaves the gp register unchanged as
the UEFI specifications does not define who is the owner of the gp and tp
registers.

So the following sequence should be followed in the trap handler:

* save the caller's gp register
* restore the global data pointer
* serve interrupts or print crash dump and reset
* restore the caller's gp register

Cc: Abner Chang <abner.chang at hpe.com>
Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
---
v2:
	Saving and restoring the caller's x3 is already handled in mtrap.S.
	efi_loader.h provides an empty fallback efi_restore_gd() function
	if CONFIG_EFI_LOADER=n.
---
 arch/riscv/lib/interrupts.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/riscv/lib/interrupts.c b/arch/riscv/lib/interrupts.c
index cd47e64487..8ff40f0f36 100644
--- a/arch/riscv/lib/interrupts.c
+++ b/arch/riscv/lib/interrupts.c
@@ -111,6 +111,9 @@ ulong handle_trap(ulong cause, ulong epc, ulong tval, struct pt_regs *regs)
 {
 	ulong is_irq, irq;

+	/* An UEFI application may have changed gd. Restore U-Boot's gd. */
+	efi_restore_gd();
+
 	is_irq = (cause & MCAUSE_INT);
 	irq = (cause & ~MCAUSE_INT);

--
2.28.0