On Fri, 2020-01-17 at 13:15 +0100, Daniel Schwierzeck wrote: > > Am 17.01.20 um 08:45 schrieb Weijie Gao: > > In U-Boot the exception vector base will be moved to top of memory, to be > > used to display register dump when exception occurs. > > > > But some old linux kernel does not honor the base set in CP0_EBASE. A > > modified exception vector base will cause kernel crash. > > > > This patch adds an option to enable reset exception vector base to its > > previous value, or a user configured value before booting linux kernel. > > > > Signed-off-by: Weijie Gao <weijie....@mediatek.com> > > --- > > Changes since v1: > > Moved core operations to trap_restore() in arch/mips/lib/traps.c. > > Save previous ebase instead of using 0x80000000 directly. > > Add options to use customized ebase. > > --- > > arch/mips/Kconfig | 30 +++++++++++++++++++++++++++++ > > arch/mips/include/asm/u-boot-mips.h | 2 ++ > > arch/mips/lib/bootm.c | 3 +++ > > arch/mips/lib/traps.c | 19 ++++++++++++++++++ > > 4 files changed, 54 insertions(+) > > > > diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig > > index a3ae603044..5e20feeefb 100644 > > --- a/arch/mips/Kconfig > > +++ b/arch/mips/Kconfig > > @@ -287,6 +287,36 @@ config MIPS_RELOCATION_TABLE_SIZE > > > > If unsure, leave at the default value. > > > > +config RESTORE_EXCEPTION_VECTOR_BASE > > + bool "Restore exception vector base before booting linux kernel" > > + default n > > + help > > + In U-Boot the exception vector base will be moved to top of memory, > > + to be used to display register dump when exception occurs. > > + But some old linux kernel does not honor the base set in CP0_EBASE. > > + A modified exception vector base will cause kernel crash. > > + > > + This option will restore the exception vector base to its previous > > + value. > > + > > + If unsure, say N. > > + > > +config OVERRIDE_EXCEPTION_VECTOR_BASE > > + bool "Override the exception vector base to be restored" > > + depends on RESTORE_EXCEPTION_VECTOR_BASE > > + default n > > + help > > + Enable this option if you want to use a different exception vector > > + base rather than the previously saved one. > > + > > +config NEW_EXCEPTION_VECTOR_BASE > > + hex "New exception vector base" > > + depends on OVERRIDE_EXCEPTION_VECTOR_BASE > > + range 0x80000000 0xbffff000 > > + default 0x80000000 > > + help > > + The exception vector base to be restored before booting linux kernel > > + > > endmenu > > > > menu "OS boot interface" > > diff --git a/arch/mips/include/asm/u-boot-mips.h > > b/arch/mips/include/asm/u-boot-mips.h > > index 88438b9576..8b37cc4029 100644 > > --- a/arch/mips/include/asm/u-boot-mips.h > > +++ b/arch/mips/include/asm/u-boot-mips.h > > @@ -9,4 +9,6 @@ void except_vec_ejtag_debug(void); > > > > int arch_misc_init(void); > > > > +void trap_restore(void); > > + > > #endif /* _U_BOOT_MIPS_H_ */ > > diff --git a/arch/mips/lib/bootm.c b/arch/mips/lib/bootm.c > > index 8c0d7672f2..f1db6d23b8 100644 > > --- a/arch/mips/lib/bootm.c > > +++ b/arch/mips/lib/bootm.c > > @@ -294,6 +294,9 @@ static void boot_jump_linux(bootm_headers_t *images) > > bootstage_report(); > > #endif > > > > + if (CONFIG_IS_ENABLED(RESTORE_EXCEPTION_VECTOR_BASE)) > > + trap_restore(); > > + > > if (images->ft_len) > > kernel(-2, (ulong)images->ft_addr, 0, 0); > > else > > diff --git a/arch/mips/lib/traps.c b/arch/mips/lib/traps.c > > index 6fe8ebd16b..20f45fc4ed 100644 > > --- a/arch/mips/lib/traps.c > > +++ b/arch/mips/lib/traps.c > > @@ -19,6 +19,8 @@ > > > > DECLARE_GLOBAL_DATA_PTR; > > > > +static unsigned long saved_ebase; > > + > > static void show_regs(const struct pt_regs *regs) > > { > > const int field = 2 * sizeof(unsigned long); > > @@ -101,7 +103,24 @@ void trap_init(ulong reloc_addr) > > set_handler(0x180, &except_vec3_generic, 0x80); > > set_handler(0x280, &except_vec_ejtag_debug, 0x80); > > > > + saved_ebase = read_c0_ebase() & 0xfffff000; > > + > > write_c0_ebase(ebase); > > clear_c0_status(ST0_BEV); > > execution_hazard_barrier(); > > } > > + > > +void trap_restore(void) > > +{ > > + set_c0_status(ST0_BEV); > > + execution_hazard_barrier(); > > + > > +#ifdef CONFIG_OVERRIDE_EXCEPTION_VECTOR_BASE > > + write_c0_ebase(CONFIG_NEW_EXCEPTION_VECTOR_BASE & 0xfffff000); > > +#else > > + write_c0_ebase(saved_ebase); > > +#endif > > + > > + clear_c0_status(ST0_BEV); > > + execution_hazard_barrier(); > > +} > > > > looks actually good now, thanks. But now I'm thinking that it should be > enough to simply set ST0_BEV to use the CPU's default EBase. Restoring > the original EBase and clearing ST0_BEV again seems redundant. How about > this? > > void trap_restore(void) > { > set_c0_status(ST0_BEV); > execution_hazard_barrier(); > > #ifdef CONFIG_OVERRIDE_EXCEPTION_VECTOR_BASE > write_c0_ebase(CONFIG_NEW_EXCEPTION_VECTOR_BASE & 0xfffff000); > clear_c0_status(ST0_BEV); > execution_hazard_barrier(); > #endif > } >
Actually it's a little bit redundant. saved_ebase is reserved for the case that u-boot acts as a secondary bootloader, and the first stage bootloader changes the ebase. Currently it seems there is no such case. I'll simplify this patch.