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

[Bin Meng]

On Sun, Sep 27, 2020 at 4:24 PM Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> 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);
>

Reviewed-by: Bin Meng <bin.meng at windriver.com>

Does other arch suffer the same issue?