On Sat, Sep 15, 2012 at 04:35:59PM +0100, Christoffer Dall wrote:
> When the guest accesses I/O memory this will create data abort
> exceptions and they are handled by decoding the HSR information
> (physical address, read/write, length, register) and forwarding reads
> and writes to QEMU which performs the device emulation.
>
> Certain classes of load/store operations do not support the syndrome
> information provided in the HSR and we therefore must be able to fetch
> the offending instruction from guest memory and decode it manually.
>
> We only support instruction decoding for valid reasonable MMIO operations
> where trapping them do not provide sufficient information in the HSR (no
> 16-bit Thumb instructions provide register writeback that we care about).
>
> The following instruciton types are NOT supported for MMIO operations
> despite the HSR not containing decode info:
> - any Load/Store multiple
> - any load/store exclusive
> - any load/store dual
> - anything with the PC as the dest register
[...]
> +
> +/******************************************************************************
> + * Load-Store instruction emulation
> + *****************************************************************************/
> +
> +/*
> + * Must be ordered with LOADS first and WRITES afterwards
> + * for easy distinction when doing MMIO.
> + */
> +#define NUM_LD_INSTR 9
> +enum INSTR_LS_INDEXES {
> + INSTR_LS_LDRBT, INSTR_LS_LDRT, INSTR_LS_LDR, INSTR_LS_LDRB,
> + INSTR_LS_LDRD, INSTR_LS_LDREX, INSTR_LS_LDRH, INSTR_LS_LDRSB,
> + INSTR_LS_LDRSH,
> + INSTR_LS_STRBT, INSTR_LS_STRT, INSTR_LS_STR, INSTR_LS_STRB,
> + INSTR_LS_STRD, INSTR_LS_STREX, INSTR_LS_STRH,
> + NUM_LS_INSTR
> +};
> +
> +static u32 ls_instr[NUM_LS_INSTR][2] = {
> + {0x04700000, 0x0d700000}, /* LDRBT */
> + {0x04300000, 0x0d700000}, /* LDRT */
> + {0x04100000, 0x0c500000}, /* LDR */
> + {0x04500000, 0x0c500000}, /* LDRB */
> + {0x000000d0, 0x0e1000f0}, /* LDRD */
> + {0x01900090, 0x0ff000f0}, /* LDREX */
> + {0x001000b0, 0x0e1000f0}, /* LDRH */
> + {0x001000d0, 0x0e1000f0}, /* LDRSB */
> + {0x001000f0, 0x0e1000f0}, /* LDRSH */
> + {0x04600000, 0x0d700000}, /* STRBT */
> + {0x04200000, 0x0d700000}, /* STRT */
> + {0x04000000, 0x0c500000}, /* STR */
> + {0x04400000, 0x0c500000}, /* STRB */
> + {0x000000f0, 0x0e1000f0}, /* STRD */
> + {0x01800090, 0x0ff000f0}, /* STREX */
> + {0x000000b0, 0x0e1000f0} /* STRH */
> +};
> +
> +static inline int get_arm_ls_instr_index(u32 instr)
> +{
> + return kvm_instr_index(instr, ls_instr, NUM_LS_INSTR);
> +}
> +
> +/*
> + * Load-Store instruction decoding
> + */
> +#define INSTR_LS_TYPE_BIT 26
> +#define INSTR_LS_RD_MASK 0x0000f000
> +#define INSTR_LS_RD_SHIFT 12
> +#define INSTR_LS_RN_MASK 0x000f0000
> +#define INSTR_LS_RN_SHIFT 16
> +#define INSTR_LS_RM_MASK 0x0000000f
> +#define INSTR_LS_OFFSET12_MASK 0x00000fff
I'm afraid you're not going to thank me much for this, but it's high time we
unified the various instruction decoding functions we have under arch/arm/
and this seems like a good opportunity for that. For example, look at the
following snippets (there is much more in the files I list) in addition to
what you have:
asm/ptrace.h
-------------
#define PSR_T_BIT 0x00000020
#define PSR_F_BIT 0x00000040
#define PSR_I_BIT 0x00000080
#define PSR_A_BIT 0x00000100
#define PSR_E_BIT 0x00000200
#define PSR_J_BIT 0x01000000
#define PSR_Q_BIT 0x08000000
#define PSR_V_BIT 0x10000000
#define PSR_C_BIT 0x20000000
#define PSR_Z_BIT 0x40000000
#define PSR_N_BIT 0x80000000
mm/alignment.c
--------------
#define LDST_I_BIT(i) (i & (1 << 26)) /* Immediate constant */
#define LDST_P_BIT(i) (i & (1 << 24)) /* Preindex */
#define LDST_U_BIT(i) (i & (1 << 23)) /* Add offset */
#define LDST_W_BIT(i) (i & (1 << 21)) /* Writeback */
#define LDST_L_BIT(i) (i & (1 << 20)) /* Load */
kernel/kprobes*.c
-----------------
static void __kprobes
emulate_ldr(struct kprobe *p, struct pt_regs *regs)
{
kprobe_opcode_t insn = p->opcode;
unsigned long pc = (unsigned long)p->addr + 8;
int rt = (insn >> 12) & 0xf;
int rn = (insn >> 16) & 0xf;
int rm = insn & 0xf;
kernel/opcodes.c
----------------
static const unsigned short cc_map[16] = {
0xF0F0, /* EQ == Z set */
0x0F0F, /* NE */
0xCCCC, /* CS == C set */
0x3333, /* CC */
0xFF00, /* MI == N set */
0x00FF, /* PL */
0xAAAA, /* VS == V set */
0x5555, /* VC */
0x0C0C, /* HI == C set && Z clear */
0xF3F3, /* LS == C clear || Z set */
0xAA55, /* GE == (N==V) */
0x55AA, /* LT == (N!=V) */
0x0A05, /* GT == (!Z && (N==V)) */
0xF5FA, /* LE == (Z || (N!=V)) */
0xFFFF, /* AL always */
0 /* NV */
};
kernel/swp_emulate.c
--------------------
#define EXTRACT_REG_NUM(instruction, offset) \
(((instruction) & (0xf << (offset))) >> (offset))
#define RN_OFFSET 16
#define RT_OFFSET 12
#define RT2_OFFSET 0
There are also bits and pieces with the patching frameworks and module
relocations that could benefit from some code sharing. Now, I think Dave had
some ideas about moving a load of this code into a common disassembler under
arch/arm/ so it would be great to tie that in here and implement that for
load/store instructions. Then other users can augment the number of
supported instruction classes as and when it is required.
Will
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