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    Subject[PATCH 3.14 10/79] ARM: 8429/1: disable GCC SRA optimization
    Date
    3.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Ard Biesheuvel <ard.biesheuvel@linaro.org>

    commit a077224fd35b2f7fbc93f14cf67074fc792fbac2 upstream.

    While working on the 32-bit ARM port of UEFI, I noticed a strange
    corruption in the kernel log. The following snprintf() statement
    (in drivers/firmware/efi/efi.c:efi_md_typeattr_format())

    snprintf(pos, size, "|%3s|%2s|%2s|%2s|%3s|%2s|%2s|%2s|%2s]",

    was producing the following output in the log:

    | | | | | |WB|WT|WC|UC]
    | | | | | |WB|WT|WC|UC]
    | | | | | |WB|WT|WC|UC]
    |RUN| | | | |WB|WT|WC|UC]*
    |RUN| | | | |WB|WT|WC|UC]*
    | | | | | |WB|WT|WC|UC]
    |RUN| | | | |WB|WT|WC|UC]*
    | | | | | |WB|WT|WC|UC]
    |RUN| | | | | | | |UC]
    |RUN| | | | | | | |UC]

    As it turns out, this is caused by incorrect code being emitted for
    the string() function in lib/vsprintf.c. The following code

    if (!(spec.flags & LEFT)) {
    while (len < spec.field_width--) {
    if (buf < end)
    *buf = ' ';
    ++buf;
    }
    }
    for (i = 0; i < len; ++i) {
    if (buf < end)
    *buf = *s;
    ++buf; ++s;
    }
    while (len < spec.field_width--) {
    if (buf < end)
    *buf = ' ';
    ++buf;
    }

    when called with len == 0, triggers an issue in the GCC SRA optimization
    pass (Scalar Replacement of Aggregates), which handles promotion of signed
    struct members incorrectly. This is a known but as yet unresolved issue.
    (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65932). In this particular
    case, it is causing the second while loop to be executed erroneously a
    single time, causing the additional space characters to be printed.

    So disable the optimization by passing -fno-ipa-sra.

    Acked-by: Nicolas Pitre <nico@linaro.org>
    Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/arm/Makefile | 8 ++++++++
    1 file changed, 8 insertions(+)

    --- a/arch/arm/Makefile
    +++ b/arch/arm/Makefile
    @@ -52,6 +52,14 @@ endif

    comma = ,

    +#
    +# The Scalar Replacement of Aggregates (SRA) optimization pass in GCC 4.9 and
    +# later may result in code being generated that handles signed short and signed
    +# char struct members incorrectly. So disable it.
    +# (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65932)
    +#
    +KBUILD_CFLAGS += $(call cc-option,-fno-ipa-sra)
    +
    # This selects which instruction set is used.
    # Note that GCC does not numerically define an architecture version
    # macro, but instead defines a whole series of macros which makes



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