• Ard Biesheuvel's avatar
    ARM: 8515/2: move .vectors and .stubs sections back into the kernel VMA · 31b96cae
    Ard Biesheuvel authored
    Commit b9b32bf7 ("ARM: use linker magic for vectors and vector stubs")
    updated the linker script to emit the .vectors and .stubs sections into a
    VMA range that is zero based and disjoint from the normal static kernel
    region. The reason for that was that this way, the sections can be placed
    exactly 4 KB apart, while the payload of the .vectors section is only 32
    bytes.
    
    Since the symbols that are part of the .stubs section are emitted into the
    kallsyms table, they appear with zero based addresses as well, e.g.,
    
      00001004 t vector_rst
      00001020 t vector_irq
      000010a0 t vector_dabt
      00001120 t vector_pabt
      000011a0 t vector_und
      00001220 t vector_addrexcptn
      00001240 t vector_fiq
      00001240 T vector_fiq_offset
    
    As this confuses perf when it accesses the kallsyms tables, commit
    7122c3e9
    
     ("scripts/link-vmlinux.sh: only filter kernel symbols for
    arm") implemented a somewhat ugly special case for ARM, where the value
    of CONFIG_PAGE_OFFSET is passed to scripts/kallsyms, and symbols whose
    addresses are below it are filtered out. Note that this special case only
    applies to CONFIG_XIP_KERNEL=n, not because the issue the patch addresses
    exists only in that case, but because finding a limit below which to apply
    the filtering is not entirely straightforward.
    
    Since the .vectors and .stubs sections contain position independent code
    that is never executed in place, we can emit it at its most likely runtime
    VMA (for more recent CPUs), which is 0xffff0000 for the vector table and
    0xffff1000 for the stubs. Not only does this fix the perf issue with
    kallsyms, allowing us to drop the special case in scripts/kallsyms
    entirely, it also gives debuggers a more realistic view of the address
    space, and setting breakpoints or single stepping through code in the
    vector table or the stubs is more likely to work as expected on CPUs that
    use a high vector address. E.g.,
    
      00001240 A vector_fiq_offset
      ...
      c0c35000 T __init_begin
      c0c35000 T __vectors_start
      c0c35020 T __stubs_start
      c0c35020 T __vectors_end
      c0c352e0 T _sinittext
      c0c352e0 T __stubs_end
      ...
      ffff1004 t vector_rst
      ffff1020 t vector_irq
      ffff10a0 t vector_dabt
      ffff1120 t vector_pabt
      ffff11a0 t vector_und
      ffff1220 t vector_addrexcptn
      ffff1240 T vector_fiq
    
    (Note that vector_fiq_offset is now an absolute symbol, which kallsyms
    already ignores by default)
    
    The LMA footprint is identical with or without this change, only the VMAs
    are different:
    
      Before:
      Idx Name          Size      VMA       LMA       File off  Algn
       ...
       14 .notes        00000024  c0c34020  c0c34020  00a34020  2**2
                        CONTENTS, ALLOC, LOAD, READONLY, CODE
       15 .vectors      00000020  00000000  c0c35000  00a40000  2**1
                        CONTENTS, ALLOC, LOAD, READONLY, CODE
       16 .stubs        000002c0  00001000  c0c35020  00a41000  2**5
                        CONTENTS, ALLOC, LOAD, READONLY, CODE
       17 .init.text    0006b1b8  c0c352e0  c0c352e0  00a452e0  2**5
                        CONTENTS, ALLOC, LOAD, READONLY, CODE
       ...
    
      After:
      Idx Name          Size      VMA       LMA       File off  Algn
       ...
       14 .notes        00000024  c0c34020  c0c34020  00a34020  2**2
                        CONTENTS, ALLOC, LOAD, READONLY, CODE
       15 .vectors      00000020  ffff0000  c0c35000  00a40000  2**1
                        CONTENTS, ALLOC, LOAD, READONLY, CODE
       16 .stubs        000002c0  ffff1000  c0c35020  00a41000  2**5
                        CONTENTS, ALLOC, LOAD, READONLY, CODE
       17 .init.text    0006b1b8  c0c352e0  c0c352e0  00a452e0  2**5
                        CONTENTS, ALLOC, LOAD, READONLY, CODE
       ...
    Acked-by: default avatarNicolas Pitre <nico@linaro.org>
    Acked-by: default avatarChris Brandt <chris.brandt@renesas.com>
    Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
    Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
    31b96cae
vmlinux-xip.lds.S 6.63 KB