Re: [PULL 26/45] ACPI: Record Generic Error Status Block(GESB) table

[Peter Maydell <peter.maydell@linaro.org>]

On Thu, 14 May 2020 at 15:22, Peter Maydell <peter.maydell@linaro.org> wrote:
>
> From: Dongjiu Geng <gengdongjiu@huawei.com>
>
> kvm_arch_on_sigbus_vcpu() error injection uses source_id as
> index in etc/hardware_errors to find out Error Status Data
> Block entry corresponding to error source. So supported source_id
> values should be assigned here and not be changed afterwards to
> make sure that guest will write error into expected Error Status
> Data Block.
>
> Before QEMU writes a new error to ACPI table, it will check whether
> previous error has been acknowledged. If not acknowledged, the new
> errors will be ignored and not be recorded. For the errors section
> type, QEMU simulate it to memory section error.

Hi; Coverity points out (CID 1428962) that there is
unreachable code in this function:

> +static int acpi_ghes_record_mem_error(uint64_t error_block_address,
> +                                      uint64_t error_physical_addr)
> +{
> +    GArray *block;
> +
> +    /* Memory Error Section Type */
> +    const uint8_t uefi_cper_mem_sec[] =
> +          UUID_LE(0xA5BC1114, 0x6F64, 0x4EDE, 0xB8, 0x63, 0x3E, 0x83, \
> +                  0xED, 0x7C, 0x83, 0xB1);
> +
> +    /* invalid fru id: ACPI 4.0: 17.3.2.6.1 Generic Error Data,
> +     * Table 17-13 Generic Error Data Entry
> +     */
> +    QemuUUID fru_id = {};
> +    uint32_t data_length;
> +
> +    block = g_array_new(false, true /* clear */, 1);
> +
> +    /* This is the length if adding a new generic error data entry*/
> +    data_length = ACPI_GHES_DATA_LENGTH + ACPI_GHES_MEM_CPER_LENGTH;

Here data_length has a constant value...

> +
> +    /*
> +     * Check whether it will run out of the preallocated memory if adding a new
> +     * generic error data entry
> +     */
> +    if ((data_length + ACPI_GHES_GESB_SIZE) > ACPI_GHES_MAX_RAW_DATA_LENGTH) {

...but here we immediately have a runtime check which can't possibly
fail because of the values of the constants involved, so this
if() block is dead code.

> +        error_report("Not enough memory to record new CPER!!!");
> +        g_array_free(block, true);
> +        return -1;
> +    }

What was this code trying to do? Is the initial value of
data_length incorrect, or is the if() condition wrong, or
should this simply have been an assert() ?

thanks
-- PMM