• Arun Chandran's avatar
    arm64: convert part of soft_restart() to assembly · 5e051531
    Arun Chandran authored
    
    
    The current soft_restart() and setup_restart implementations incorrectly
    assume that compiler will not spill/fill values to/from stack. However
    this assumption seems to be wrong, revealed by the disassembly of the
    currently existing code (v3.16) built with Linaro GCC 4.9-2014.05.
    
    ffffffc000085224 <soft_restart>:
    ffffffc000085224:  a9be7bfd  stp    x29, x30, [sp,#-32]!
    ffffffc000085228:  910003fd  mov    x29, sp
    ffffffc00008522c:  f9000fa0  str    x0, [x29,#24]
    ffffffc000085230:  94003d21  bl     ffffffc0000946b4 <setup_mm_for_reboot>
    ffffffc000085234:  94003b33  bl     ffffffc000093f00 <flush_cache_all>
    ffffffc000085238:  94003dfa  bl     ffffffc000094a20 <cpu_cache_off>
    ffffffc00008523c:  94003b31  bl     ffffffc000093f00 <flush_cache_all>
    ffffffc000085240:  b0003321  adrp   x1, ffffffc0006ea000 <reset_devices>
    
    ffffffc000085244:  f9400fa0  ldr    x0, [x29,#24] ----> spilled addr
    ffffffc000085248:  f942fc22  ldr    x2, [x1,#1528] ----> global memstart_addr
    
    ffffffc00008524c:  f0000061  adrp   x1, ffffffc000094000 <__inval_cache_range+0x40>
    ffffffc000085250:  91290021  add    x1, x1, #0xa40
    ffffffc000085254:  8b010041  add    x1, x2, x1
    ffffffc000085258:  d2c00802  mov    x2, #0x4000000000           // #274877906944
    ffffffc00008525c:  8b020021  add    x1, x1, x2
    ffffffc000085260:  d63f0020  blr    x1
    ...
    
    Here the compiler generates memory accesses after the cache is disabled,
    loading stale values for the spilled value and global variable. As we cannot
    control when the compiler will access memory we must rewrite the
    functions in assembly to stash values we need in registers prior to
    disabling the cache, avoiding the use of memory.
    Reviewed-by: default avatarMark Rutland <mark.rutland@arm.com>
    Signed-off-by: default avatarArun Chandran <achandran@mvista.com>
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    5e051531
proc.S 5.69 KB