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

[Heinrich Schuchardt]

On 9/27/20 10:40 AM, Bin Meng wrote:
> 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?
>

Hello Bin,

x86 does not use a register of gd.
arm has this statement already.
No further architectures support UEFI.

Best regards

Heinrich