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https://github.com/cirosantilli/linux-kernel-module-cheat.git
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61 lines
1.5 KiB
ArmAsm
61 lines
1.5 KiB
ArmAsm
/* https://github.com/cirosantilli/linux-kernel-module-cheat#arm-str-instruction */
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#include <lkmc.h>
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.data;
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/* Must be in the .data section, since we want to modify it. */
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myvar:
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.word 0x12345678
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LKMC_PROLOGUE
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/* Sanity check. */
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ldr r0, =myvar
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ldr r1, [r0]
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movw r2, 0x5678
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movt r2, 0x1234
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LKMC_ASSERT_EQ_REG(r1, r2)
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/* Modify the value. */
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ldr r0, =myvar
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movw r1, 0xDEF0
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movt r1, 0x9ABC
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str r1, [r0]
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/* Check that it changed. */
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ldr r0, =myvar
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ldr r1, [r0]
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movw r2, 0xDEF0
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movt r2, 0x9ABC
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LKMC_ASSERT_EQ_REG(r1, r2)
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/* Cannot use PC relative addressing to a different segment,
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* or else it fails with:
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*
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* ....
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* Error: internal_relocation (type: OFFSET_IMM) not fixed up
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* ....
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*
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* https://stackoverflow.com/questions/10094282/internal-relocation-not-fixed-up
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*/
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/*ldr r0, myvar*/
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#if 0
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/* We could in theory write this to set the address of myvar,
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* but it will always segfault under Linux because the text segment is read-only.
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* This is however useful in baremetal programming.
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* This construct is not possible in ARMv8 for str:
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* https://github.com/cirosantilli/linux-kernel-module-cheat#armv8-aarch64-str-instruction
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*/
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str r1, var_in_same_section
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var_in_same_section:
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#endif
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/* = sign just doesn't make sense for str, you can't set the
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* address of a variable.
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*/
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#if 0
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str r1, =myvar
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#endif
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LKMC_EPILOGUE
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