• Will Deacon's avatar
    ARM: 6668/1: ptrace: remove single-step emulation code · 425fc47a
    Will Deacon authored
    PTRACE_SINGLESTEP is a ptrace request designed to offer single-stepping
    support to userspace when the underlying architecture has hardware
    support for this operation.
    
    On ARM, we set arch_has_single_step() to 1 and attempt to emulate hardware
    single-stepping by disassembling the current instruction to determine the
    next pc and placing a software breakpoint on that location.
    
    Unfortunately this has the following problems:
    
    1.) Only a subset of ARMv7 instructions are supported
    2.) Thumb-2 is unsupported
    3.) The code is not SMP safe
    
    We could try to fix this code, but it turns out that because of the above
    issues it is rarely used in practice.  GDB, for example, uses PTRACE_POKETEXT
    and PTRACE_PEEKTEXT to manage breakpoints itself and does not require any
    kernel assistance.
    
    This patch removes the single-step emulation code from ptrace meaning that
    the PTRACE_SINGLESTEP request will return -EIO on ARM. Portable code must
    check the return value from a ptrace call and handle the failure gracefully.
    Acked-by: default avatarNicolas Pitre <nicolas.pitre@linaro.org>
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
    425fc47a
traps.c 19.5 KB