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    SubjectRe: linux-next: build failure after merge of the kspp tree
    On Wed, Mar 09, 2022 at 09:10:29PM +1100, Stephen Rothwell wrote:
    > Hi all,
    >
    > After merging the kspp tree, today's linux-next build (x86_64
    > allmodconfig) failed like this:
    >
    > In file included from include/linux/bitops.h:33,
    > from include/linux/kernel.h:22,
    > from drivers/platform/x86/thinkpad_acpi.c:37:
    > drivers/platform/x86/thinkpad_acpi.c: In function 'tpacpi_dytc_profile_init':
    > arch/x86/include/asm/bitops.h:207:22: error: array subscript 'long unsigned int[0]' is partly outside array bounds of 'int[1]' [-Werror=array-bounds]
    > 207 | (addr[nr >> _BITOPS_LONG_SHIFT])) != 0;
    > | ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
    > drivers/platform/x86/thinkpad_acpi.c:10385:18: note: while referencing 'output'
    > 10385 | int err, output;
    > | ^~~~~~
    >
    > Actually the test_bit() in line 10409.
    >
    > Caused by commit
    >
    > e1c21608e3cf ("platform/x86: thinkpad_acpi: Add PSC mode support")
    >
    > from the drivers-x86 tree interacting with the enablement of
    > -Werror=array-bounds.
    >
    > I have reverted that commit for today.

    Looking at https://lore.kernel.org/all/20220225182505.7234-1-markpearson@lenovo.com/

    The problem is with the cast of "int output" to "unsigned long". Past
    fixes have either made the variable unsigned long, or adding a new
    variable and removal of casts. e.g. this pseudo-patch:

    + unsigned long bits;

    ...
    + bits = output;
    - if (test_bit(DYTC_FC_MMC, (void *)&output)) { /* MMC MODE */
    + if (test_bit(DYTC_FC_MMC, &bits)) { /* MMC MODE */

    ...

    - } else if (test_bit(DYTC_FC_PSC, (void *)&output)) { /*PSC MODE */
    + } else if (test_bit(DYTC_FC_PSC, &bits)) { /*PSC MODE */



    --
    Kees Cook

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