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powerpc: Endian safe trampoline

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Create a trampoline that works in either endian and flips to
the expected endian. Use it for primary and secondary thread
entry as well as RTAS and OF call return.

Credit for finding the magic instruction goes to Paul Mackerras

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Benjamin Herrenschmidt 2013-09-23 12:04:45 +10:00
parent c57a5ce0df
commit 5c0484e25e
3 changed files with 53 additions and 17 deletions
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31
arch/powerpc/include/asm/ppc_asm.h
View File

@ -845,6 +845,35 @@ END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,946)
#define N_SLINE 68
#define N_SO 100
#endif /* __ASSEMBLY__ */
/*
* Create an endian fixup trampoline
*
* This starts with a "tdi 0,0,0x48" instruction which is
* essentially a "trap never", and thus akin to a nop.
*
* The opcode for this instruction read with the wrong endian
* however results in a b . + 8
*
* So essentially we use that trick to execute the following
* trampoline in "reverse endian" if we are running with the
* MSR_LE bit set the "wrong" way for whatever endianness the
* kernel is built for.
*/
#ifdef CONFIG_PPC_BOOK3E
#define FIXUP_ENDIAN
#else
#define FIXUP_ENDIAN \
tdi 0,0,0x48; /* Reverse endian of b . + 8 */ \
b $+36; /* Skip trampoline if endian is good */ \
.long 0x05009f42; /* bcl 20,31,$+4 */ \
.long 0xa602487d; /* mflr r10 */ \
.long 0x1c004a39; /* addi r10,r10,28 */ \
.long 0xa600607d; /* mfmsr r11 */ \
.long 0x01006b69; /* xori r11,r11,1 */ \
.long 0xa6035a7d; /* mtsrr0 r10 */ \
.long 0xa6037b7d; /* mtsrr1 r11 */ \
.long 0x2400004c /* rfid */
#endif /* !CONFIG_PPC_BOOK3E */
#endif /* __ASSEMBLY__ */
#endif /* _ASM_POWERPC_PPC_ASM_H */

32
arch/powerpc/kernel/entry_64.S
View File

@ -1017,7 +1017,7 @@ _GLOBAL(enter_rtas)
li r9,1
rldicr r9,r9,MSR_SF_LG,(63-MSR_SF_LG)
ori r9,r9,MSR_IR|MSR_DR|MSR_FE0|MSR_FE1|MSR_FP|MSR_RI
ori r9,r9,MSR_IR|MSR_DR|MSR_FE0|MSR_FE1|MSR_FP|MSR_RI|MSR_LE
andc r6,r0,r9
sync /* disable interrupts so SRR0/1 */
mtmsrd r0 /* don't get trashed */
@ -1032,6 +1032,8 @@ _GLOBAL(enter_rtas)
b . /* prevent speculative execution */
_STATIC(rtas_return_loc)
FIXUP_ENDIAN
/* relocation is off at this point */
GET_PACA(r4)
clrldi r4,r4,2 /* convert to realmode address */
@ -1103,28 +1105,30 @@ _GLOBAL(enter_prom)
std r10,_CCR(r1)
std r11,_MSR(r1)
/* Get the PROM entrypoint */
/* Put PROM address in SRR0 */
mtsrr0 r4
/* Setup our trampoline return addr in LR */
bcl 20,31,$+4
0: mflr r4
addi r4,r4,(1f - 0b)
mtlr r4
/* Switch MSR to 32 bits mode
/* Prepare a 32-bit mode big endian MSR
*/
#ifdef CONFIG_PPC_BOOK3E
rlwinm r11,r11,0,1,31
mtmsr r11
mtsrr1 r11
rfi
#else /* CONFIG_PPC_BOOK3E */
mfmsr r11
li r12,1
rldicr r12,r12,MSR_SF_LG,(63-MSR_SF_LG)
LOAD_REG_IMMEDIATE(r12, MSR_SF | MSR_ISF | MSR_LE)
andc r11,r11,r12
li r12,1
rldicr r12,r12,MSR_ISF_LG,(63-MSR_ISF_LG)
andc r11,r11,r12
mtmsrd r11
mtsrr1 r11
rfid
#endif /* CONFIG_PPC_BOOK3E */
isync
/* Enter PROM here... */
blrl
1: /* Return from OF */
FIXUP_ENDIAN
/* Just make sure that r1 top 32 bits didn't get
* corrupt by OF

3
arch/powerpc/kernel/head_64.S
View File

@ -68,6 +68,7 @@ _stext:
_GLOBAL(__start)
/* NOP this out unconditionally */
BEGIN_FTR_SECTION
FIXUP_ENDIAN
b .__start_initialization_multiplatform
END_FTR_SECTION(0, 1)
@ -115,6 +116,7 @@ __run_at_load:
*/
.globl __secondary_hold
__secondary_hold:
FIXUP_ENDIAN
#ifndef CONFIG_PPC_BOOK3E
mfmsr r24
ori r24,r24,MSR_RI
@ -205,6 +207,7 @@ _GLOBAL(generic_secondary_thread_init)
* as SCOM before entry).
*/
_GLOBAL(generic_secondary_smp_init)
FIXUP_ENDIAN
mr r24,r3
mr r25,r4