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riscv: show code leading to exception

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To make analyzing exceptions easier output the code that leads to it.
We already do the same on the ARM platform.

Here is an example:

    => exception ebreak
    Unhandled exception: Breakpoint
    EPC: 000000008ff5d50e RA: 000000008ff5d62c TVAL: 0000000000000000
    EPC: 000000008020b50e RA: 000000008020b62c reloc adjusted

    Code: 2785 0693 07a0 dce3 fef6 47a5 d563 00e7 (9002)

To disassemble the code we can use the decodecode script:

    $ echo 'Code: 2785 0693 07a0 dce3 fef6 47a5 d563 00e7 (9002)' | \
      CROSS_COMPILE=riscv64-linux-gnu- scripts/decodecode

    Code: 2785 0693 07a0 dce3 fef6 47a5 d563 00e7 (9002)
    All code
    ========
       0:   2785                    addiw   a5,a5,1
       2:   07a00693                li      a3,122
       6:   fef6dce3                bge     a3,a5,0xfffffffffffffffe
       a:   47a5                    li      a5,9
       c:   00e7d563                bge     a5,a4,0x16
      10:*  9002                    ebreak         <-- trapping instruction
            ...

    Code starting with the faulting instruction
    ===========================================
       0:   9002                    ebreak
            ...

As it is not always clear if the first 16 bits are at the start or in the
middle of a 32bit instruction it may become necessary to strip the first
u16 from the output before calling decodecode to get the correct
disassembled code.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
This commit is contained in:
Heinrich Schuchardt 2021-09-04 10:36:49 +02:00 committed by Leo Yu-Chi Liang
parent 5b2d359d9a
commit f6431e8fb3
1 changed files with 33 additions and 0 deletions
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33
arch/riscv/lib/interrupts.c
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@ -51,6 +51,38 @@ static void show_regs(struct pt_regs *regs)
#endif
}
/**
* instr_len() - get instruction length
*
* @i: low 16 bits of the instruction
* Return: number of u16 in instruction
*/
static int instr_len(u16 i)
{
if ((i & 0x03) != 0x03)
return 1;
/* Instructions with more than 32 bits are not yet specified */
return 2;
}
/**
* show_code() - display code leading to exception
*
* @epc: program counter
*/
static void show_code(ulong epc)
{
u16 *pos = (u16 *)(epc & ~1UL);
int i, len = instr_len(*pos);
printf("\nCode: ");
for (i = -8; i; ++i)
printf("%04x ", pos[i]);
printf("(");
for (i = 0; i < len; ++i)
printf("%04x%s", pos[i], i + 1 == len ? ")\n" : " ");
}
static void _exit_trap(ulong code, ulong epc, ulong tval, struct pt_regs *regs)
{
static const char * const exception_code[] = {
@ -85,6 +117,7 @@ static void _exit_trap(ulong code, ulong epc, ulong tval, struct pt_regs *regs)
epc - gd->reloc_off, regs->ra - gd->reloc_off);
show_regs(regs);
show_code(epc);
show_efi_loaded_images(epc);
panic("\n");
}