[v5,2/3] ACPI: Add APEI GHES Table Generation support

This implements APEI GHES Table by passing the error CPER info
to the guest via a fw_cfg_blob. After a CPER info is recorded, an
SEA(Synchronous External Abort)/SEI(SError Interrupt) exception
will be injected into the guest OS.

Below is the table layout, the max number of error soure is 11,
which is classified by notification type.

etc/acpi/tables                 etc/hardware_errors

On Wed, Jul 12, 2017 at 10:08:16AM +0800, Dongjiu Geng wrote:
> This implements APEI GHES Table by passing the error CPER info
> to the guest via a fw_cfg_blob. After a CPER info is recorded, an
> SEA(Synchronous External Abort)/SEI(SError Interrupt) exception
> will be injected into the guest OS.
> 
> Below is the table layout, the max number of error soure is 11,
> which is classified by notification type.
> 
> etc/acpi/tables                 etc/hardware_errors
> ================     ==========================================
>                      +-----------+
> +--------------+     | address   |         +-> +--------------+
> |    HEST      +     | registers |         |   | Error Status |
> + +------------+     | +---------+         |   | Data Block 0 |
> | | GHES0      | --> | |address0 | --------+   | +------------+
> | | GHES1      | --> | |address1 | ------+     | |  CPER      |
> | | GHES2      | --> | |address2 | ----+ |     | |  CPER      |
> | |  ....      | --> | | ....... |     | |     | |  CPER      |
> | | GHES10     | --> | |address10| -+  | |     | |  CPER      |
> +-+------------+     +-+---------+  |  | |     +-+------------+
>                                     |  | |
>                                     |  | +---> +--------------+
>                                     |  |       | Error Status |
>                                     |  |       | Data Block 1 |
>                                     |  |       | +------------+
>                                     |  |       | |  CPER      |
>                                     |  |       | |  CPER      |
>                                     |  |       +-+------------+
>                                     |  |
>                                     |  +-----> +--------------+
>                                     |          | Error Status |
>                                     |          | Data Block 2 |
>                                     |          | +------------+
>                                     |          | |  CPER      |
>                                     |          +-+------------+
>                                     |            ...........
>                                     +--------> +--------------+
>                                                | Error Status |
>                                                | Data Block 10|
>                                                | +------------+
>                                                | |  CPER      |
>                                                | |  CPER      |
>                                                | |  CPER      |
>                                                +-+------------+
> Signed-off-by: Dongjiu Geng <gengdongjiu@huawei.com>
> ---
> thanks a lot Laszlo's review and comments: 
> 
> change since v4:
> 1. fix email threading in this series is incorrect issue
> 
> change since v3:
> 1. remove the unnecessary include for "hw/acpi/vmgenid.h" in 
>    hw/arm/virt-acpi-build.c
> 2. add conversion between LE and host-endian for the CPER record
> 3. handle the case that run out of the preallocated memory for the CPER record
> 4. change to use g_malloc0 instead of g_malloc 
> 5. change block_reqr_size name to block_rer_size
> 6. change QEMU coding style, that is, the operator is at the end of the line.
> 7. drop the ERROR_STATUS_ADDRESS_OFFSET and GAS_ADDRESS_OFFSET macros (from
>    the header file as well), and use the offsetof to replace it.
> 8. remove the init_aml_allocator() / free_aml_allocator(), calculate the
>    needed size, and push that many bytes directly to "table_data".
> 9. take an "OVMF header probe suppressor" into account
> 10.corrct HEST and CPER value assigment, for example, correct the source_id
>    for every error source, this identifier of source_id should be unique among
>    all error sources; 
> 11. create only one WRITE_POINTER command, for the base address of "etc/hardware_errors".
>    This should be done outside of the loop.The base addresses of the individual error
>    status data blocks should be calculated in ghes_update_guest(), based on the error
>    source / notification type
> 12.correct the commit message lists error sources / notification types 0 through 10 (count=11 in total). 
> 13.correct the size calculation for GHES_DATA_ADDR_FW_CFG_FILE 
> 14.range-checked the value of "notify" before using it as an array subscript
> ---
>  hw/acpi/aml-build.c      |   2 +
>  hw/acpi/hest_ghes.c      | 219 +++++++++++++++++++++++++++++++++++++++++++++++
>  hw/arm/virt-acpi-build.c |   6 ++
>  3 files changed, 227 insertions(+)
>  create mode 100644 hw/acpi/hest_ghes.c
> 
> diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
> index c6f2032..802b98d 100644
> --- a/hw/acpi/aml-build.c
> +++ b/hw/acpi/aml-build.c
> @@ -1560,6 +1560,7 @@ void acpi_build_tables_init(AcpiBuildTables *tables)
>      tables->table_data = g_array_new(false, true /* clear */, 1);
>      tables->tcpalog = g_array_new(false, true /* clear */, 1);
>      tables->vmgenid = g_array_new(false, true /* clear */, 1);
> +    tables->hardware_errors = g_array_new(false, true /* clear */, 1);
>      tables->linker = bios_linker_loader_init();
>  }
>  
> @@ -1570,6 +1571,7 @@ void acpi_build_tables_cleanup(AcpiBuildTables *tables, bool mfre)
>      g_array_free(tables->table_data, true);
>      g_array_free(tables->tcpalog, mfre);
>      g_array_free(tables->vmgenid, mfre);
> +    g_array_free(tables->hardware_errors, mfre);
>  }
>  
>  /* Build rsdt table */
> diff --git a/hw/acpi/hest_ghes.c b/hw/acpi/hest_ghes.c
> new file mode 100644
> index 0000000..c9442b6
> --- /dev/null
> +++ b/hw/acpi/hest_ghes.c
> @@ -0,0 +1,219 @@
> +/*
> + *  APEI GHES table Generation
> + *
> + *  Copyright (C) 2017 huawei.
> + *
> + *  Author: Dongjiu Geng <gengdongjiu@huawei.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + *
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qmp-commands.h"
> +#include "hw/acpi/acpi.h"
> +#include "hw/acpi/aml-build.h"
> +#include "hw/acpi/hest_ghes.h"
> +#include "hw/nvram/fw_cfg.h"
> +#include "sysemu/sysemu.h"
> +
> +static int ghes_record_cper(uint64_t error_block_address,
> +                                    uint64_t error_physical_addr)
> +{
> +    AcpiGenericErrorStatus block;
> +    AcpiGenericErrorData *gdata;
> +    UefiCperSecMemErr *mem_err;
> +    uint64_t current_block_length;
> +    unsigned char *buffer;
> +    QemuUUID section_id_le = UEFI_CPER_SEC_PLATFORM_MEM;
> +
> +
> +    cpu_physical_memory_read(error_block_address, &block,
> +                                sizeof(AcpiGenericErrorStatus));
> +
> +    /* Get the current generic error status block length */
> +    current_block_length = sizeof(AcpiGenericErrorStatus) +
> +        le32_to_cpu(block.data_length);
> +
> +    /* If the Generic Error Status Block is NULL, update
> +     * the block header
> +     */
> +    if (!block.block_status) {
> +        block.block_status = ACPI_GEBS_UNCORRECTABLE;
> +        block.error_severity = ACPI_CPER_SEV_FATAL;
> +    }
> +
> +    block.data_length += cpu_to_le32(sizeof(AcpiGenericErrorData));
> +    block.data_length += cpu_to_le32(sizeof(UefiCperSecMemErr));
> +
> +    /* check whether it runs out of the preallocated memory */
> +    if ((le32_to_cpu(block.data_length) + sizeof(AcpiGenericErrorStatus)) >
> +       GHES_MAX_RAW_DATA_LENGTH) {
> +        return GHES_CPER_FAIL;
> +    }
> +    /* Write back the Generic Error Status Block to guest memory */
> +    cpu_physical_memory_write(error_block_address, &block,
> +                        sizeof(AcpiGenericErrorStatus));
> +
> +    /* Fill in Generic Error Data Entry */
> +    buffer = g_malloc0(sizeof(AcpiGenericErrorData) +
> +                       sizeof(UefiCperSecMemErr));
> +    memset(buffer, 0, sizeof(AcpiGenericErrorData) + sizeof(UefiCperSecMemErr));
> +    gdata = (AcpiGenericErrorData *)buffer;
> +
> +    qemu_uuid_bswap(&section_id_le);
> +    memcpy(&(gdata->section_type_le), &section_id_le,
> +                sizeof(QemuUUID));
> +    gdata->error_data_length = cpu_to_le32(sizeof(UefiCperSecMemErr));
> +
> +    mem_err = (UefiCperSecMemErr *) (gdata + 1);
> +
> +    /* In order to simplify simulation, hard code the CPER section to memory
> +     * section.
> +     */
> +
> +    /* Hard code to Multi-bit ECC error */
> +    mem_err->validation_bits |= cpu_to_le32(UEFI_CPER_MEM_VALID_ERROR_TYPE);
> +    mem_err->error_type = cpu_to_le32(UEFI_CPER_MEM_ERROR_TYPE_MULTI_ECC);
> +
> +    /* Record the physical address at which the memory error occurred */
> +    mem_err->validation_bits |= cpu_to_le32(UEFI_CPER_MEM_VALID_PA);
> +    mem_err->physical_addr = cpu_to_le32(error_physical_addr);
> +
> +    /* Write back the Generic Error Data Entry to guest memory */
> +    cpu_physical_memory_write(error_block_address + current_block_length,
> +        buffer, sizeof(AcpiGenericErrorData) + sizeof(UefiCperSecMemErr));
> +
> +    g_free(buffer);
> +    return GHES_CPER_OK;
> +}
> +
> +void ghes_build_acpi(GArray *table_data, GArray *hardware_error,
> +                                            BIOSLinker *linker)
> +{
> +    GArray *buffer;
> +    uint32_t address_registers_offset;
> +    AcpiHardwareErrorSourceTable *error_source_table;
> +    AcpiGenericHardwareErrorSource *error_source;
> +    int i;
> +    /*
> +     * The block_req_size stands for one address and one
> +     * generic error status block
> +      +---------+
> +      | address | --------+-> +---------+
> +      +---------+             |  CPER   |
> +                              |  CPER   |
> +                              |  CPER   |
> +                              |  CPER   |
> +                              |  ....   |
> +                              +---------+
> +     */
> +    int block_req_size = sizeof(uint64_t) + GHES_MAX_RAW_DATA_LENGTH;
> +
> +    /* The total size for address of data structure and
> +     * error status data block

Pls start multiple comments with /* by itself

> +     */
> +    g_array_set_size(hardware_error, GHES_ACPI_HEST_NOTIFY_RESERVED *
> +                                                block_req_size);
> +
> +    buffer = g_array_new(false, true /* clear */, 1);
> +    address_registers_offset = table_data->len +
> +        sizeof(AcpiHardwareErrorSourceTable) +
> +        offsetof(AcpiGenericHardwareErrorSource, error_status_address) +
> +        offsetof(struct AcpiGenericAddress, address);
> +
> +    /* Reserve space for HEST table size */
> +    acpi_data_push(buffer, sizeof(AcpiHardwareErrorSourceTable) +
> +                                GHES_ACPI_HEST_NOTIFY_RESERVED *
> +                                sizeof(AcpiGenericHardwareErrorSource));
> +
> +    g_array_append_vals(table_data, buffer->data, buffer->len);
> +    /* Allocate guest memory for the Data fw_cfg blob */
> +    bios_linker_loader_alloc(linker, GHES_ERRORS_FW_CFG_FILE, hardware_error,
> +                            4096, false /* page boundary, high memory */);

page boundary refers to 4096? Pls move it there, or put
before bios_linker_loader_alloc.

> +
> +    error_source_table = (AcpiHardwareErrorSourceTable *)(table_data->data
> +                        + table_data->len - buffer->len);
> +    error_source_table->error_source_count = GHES_ACPI_HEST_NOTIFY_RESERVED;
> +    error_source = (AcpiGenericHardwareErrorSource *)
> +        ((AcpiHardwareErrorSourceTable *)error_source_table + 1);

Concern with all these casts and pointer math is that it is barely readable.
We can easily overflow the array and get hard to debug heap corruption
errors.

What can I suggest?  Just add this to the array in steps. Then you will
not need all the math.

Or again, you can just add things as you init them using build_append_int_noprefix.


> +
> +    bios_linker_loader_write_pointer(linker, GHES_DATA_ADDR_FW_CFG_FILE,
> +        0, sizeof(uint64_t), GHES_ERRORS_FW_CFG_FILE,
> +        GHES_ACPI_HEST_NOTIFY_RESERVED * sizeof(uint64_t));

What does this uint64_t refer to? It's repeated everywhere.

> +
> +    for (i = 0; i < GHES_ACPI_HEST_NOTIFY_RESERVED; i++) {
> +        error_source->type = ACPI_HEST_SOURCE_GENERIC_ERROR;
> +        error_source->source_id = cpu_to_le16(i);
> +        error_source->related_source_id = 0xffff;
> +        error_source->flags = 0;
> +        error_source->enabled = 1;
> +        /* The number of error status block per Generic Hardware Error Source */

number of ... blocks ?

> +        error_source->number_of_records = 1;
> +        error_source->max_sections_per_record = 1;
> +        error_source->max_raw_data_length = GHES_MAX_RAW_DATA_LENGTH;
> +        error_source->error_status_address.space_id =
> +                                    AML_SYSTEM_MEMORY;
> +        error_source->error_status_address.bit_width = 64;
> +        error_source->error_status_address.bit_offset = 0;
> +        error_source->error_status_address.access_width = 4;
> +        error_source->notify.type = i;
> +        error_source->notify.length = sizeof(AcpiHestNotify);
> +
> +        error_source->error_status_block_length = GHES_MAX_RAW_DATA_LENGTH;
> +
> +        bios_linker_loader_add_pointer(linker,
> +            ACPI_BUILD_TABLE_FILE, address_registers_offset + i *
> +            sizeof(AcpiGenericHardwareErrorSource), sizeof(uint64_t),
> +            GHES_ERRORS_FW_CFG_FILE, i * sizeof(uint64_t));

and what's this math for?

> +
> +        error_source++;
> +    }
> +
> +    for (i = 0; i < GHES_ACPI_HEST_NOTIFY_RESERVED; i++) {
> +        bios_linker_loader_add_pointer(linker,
> +            GHES_ERRORS_FW_CFG_FILE, sizeof(uint64_t) * i, sizeof(uint64_t),
> +            GHES_ERRORS_FW_CFG_FILE, GHES_ACPI_HEST_NOTIFY_RESERVED *
> +            sizeof(uint64_t) + i * GHES_MAX_RAW_DATA_LENGTH);
> +    }
> +
> +    build_header(linker, table_data,
> +        (void *)error_source_table, "HEST", buffer->len, 1, NULL, "GHES");

Pls indent so continuation lines are ro the right of (.

> +
> +    g_array_free(buffer, true);
> +}
> +
> +static GhesState ges;
> +void ghes_add_fw_cfg(FWCfgState *s, GArray *hardware_error)
> +{
> +
> +    size_t request_block_size = sizeof(uint64_t) + GHES_MAX_RAW_DATA_LENGTH;
> +    size_t size = GHES_ACPI_HEST_NOTIFY_RESERVED * request_block_size;
> +
> +    /* Create a read-only fw_cfg file for GHES */
> +    fw_cfg_add_file(s, GHES_ERRORS_FW_CFG_FILE, hardware_error->data,
> +                    size);
> +    /* Create a read-write fw_cfg file for Address */
> +    fw_cfg_add_file_callback(s, GHES_DATA_ADDR_FW_CFG_FILE, NULL, NULL,
> +        &ges.ghes_addr_le, sizeof(ges.ghes_addr_le), false);
> +}
> +
> +bool ghes_update_guest(uint32_t notify, uint64_t physical_address)
> +{
> +    uint64_t error_block_addr;
> +
> +    if (physical_address && notify < GHES_ACPI_HEST_NOTIFY_RESERVED) {
> +        error_block_addr = ges.ghes_addr_le + notify * GHES_MAX_RAW_DATA_LENGTH;
> +        error_block_addr = le32_to_cpu(error_block_addr);
> +
> +        /* A zero value in ghes_addr means that BIOS has not yet written
> +         * the address
> +         */
> +        if (error_block_addr) {
> +            return ghes_record_cper(error_block_addr, physical_address);
> +        }
> +    }
> +
> +    return GHES_CPER_FAIL;
> +}
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index 0835e59..5c97016 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -45,6 +45,7 @@
>  #include "hw/arm/virt.h"
>  #include "sysemu/numa.h"
>  #include "kvm_arm.h"
> +#include "hw/acpi/hest_ghes.h"
>  
>  #define ARM_SPI_BASE 32
>  #define ACPI_POWER_BUTTON_DEVICE "PWRB"
> @@ -778,6 +779,9 @@ void virt_acpi_build(VirtMachineState *vms, AcpiBuildTables *tables)
>      acpi_add_table(table_offsets, tables_blob);
>      build_spcr(tables_blob, tables->linker, vms);
>  
> +    acpi_add_table(table_offsets, tables_blob);
> +    ghes_build_acpi(tables_blob, tables->hardware_errors, tables->linker);
> +
>      if (nb_numa_nodes > 0) {
>          acpi_add_table(table_offsets, tables_blob);
>          build_srat(tables_blob, tables->linker, vms);
> @@ -890,6 +894,8 @@ void virt_acpi_setup(VirtMachineState *vms)
>      fw_cfg_add_file(vms->fw_cfg, ACPI_BUILD_TPMLOG_FILE, tables.tcpalog->data,
>                      acpi_data_len(tables.tcpalog));
>  
> +    ghes_add_fw_cfg(vms->fw_cfg, tables.hardware_errors);
> +
>      build_state->rsdp_mr = acpi_add_rom_blob(build_state, tables.rsdp,
>                                                ACPI_BUILD_RSDP_FILE, 0);
>  
> -- 
> 2.10.1

On 07/13/17 19:32, Michael S. Tsirkin wrote:
> On Wed, Jul 12, 2017 at 10:08:16AM +0800, Dongjiu Geng wrote:

snip

>> etc/acpi/tables                 etc/hardware_errors
>> ================     ==========================================
>>                      +-----------+
>> +--------------+     | address   |         +-> +--------------+
>> |    HEST      +     | registers |         |   | Error Status |
>> + +------------+     | +---------+         |   | Data Block 0 |
>> | | GHES0      | --> | |address0 | --------+   | +------------+
>> | | GHES1      | --> | |address1 | ------+     | |  CPER      |
>> | | GHES2      | --> | |address2 | ----+ |     | |  CPER      |
>> | |  ....      | --> | | ....... |     | |     | |  CPER      |
>> | | GHES10     | --> | |address10| -+  | |     | |  CPER      |
>> +-+------------+     +-+---------+  |  | |     +-+------------+
>>                                     |  | |
>>                                     |  | +---> +--------------+
>>                                     |  |       | Error Status |
>>                                     |  |       | Data Block 1 |
>>                                     |  |       | +------------+
>>                                     |  |       | |  CPER      |
>>                                     |  |       | |  CPER      |
>>                                     |  |       +-+------------+
>>                                     |  |
>>                                     |  +-----> +--------------+
>>                                     |          | Error Status |
>>                                     |          | Data Block 2 |
>>                                     |          | +------------+
>>                                     |          | |  CPER      |
>>                                     |          +-+------------+
>>                                     |            ...........
>>                                     +--------> +--------------+
>>                                                | Error Status |
>>                                                | Data Block 10|
>>                                                | +------------+
>>                                                | |  CPER      |
>>                                                | |  CPER      |
>>                                                | |  CPER      |
>>                                                +-+------------+

snip

>> +
>> +    error_source_table = (AcpiHardwareErrorSourceTable *)(table_data->data
>> +                        + table_data->len - buffer->len);
>> +    error_source_table->error_source_count = GHES_ACPI_HEST_NOTIFY_RESERVED;
>> +    error_source = (AcpiGenericHardwareErrorSource *)
>> +        ((AcpiHardwareErrorSourceTable *)error_source_table + 1);
> 
> Concern with all these casts and pointer math is that it is barely readable.
> We can easily overflow the array and get hard to debug heap corruption
> errors.
> 
> What can I suggest?  Just add this to the array in steps. Then you will
> not need all the math.
> 
> Or again, you can just add things as you init them using build_append_int_noprefix.
> 
> 
>> +
>> +    bios_linker_loader_write_pointer(linker, GHES_DATA_ADDR_FW_CFG_FILE,
>> +        0, sizeof(uint64_t), GHES_ERRORS_FW_CFG_FILE,
>> +        GHES_ACPI_HEST_NOTIFY_RESERVED * sizeof(uint64_t));
> 
> What does this uint64_t refer to? It's repeated everywhere.
> 
>> +
>> +    for (i = 0; i < GHES_ACPI_HEST_NOTIFY_RESERVED; i++) {
>> +        error_source->type = ACPI_HEST_SOURCE_GENERIC_ERROR;
>> +        error_source->source_id = cpu_to_le16(i);
>> +        error_source->related_source_id = 0xffff;
>> +        error_source->flags = 0;
>> +        error_source->enabled = 1;
>> +        /* The number of error status block per Generic Hardware Error Source */
> 
> number of ... blocks ?
> 
>> +        error_source->number_of_records = 1;
>> +        error_source->max_sections_per_record = 1;
>> +        error_source->max_raw_data_length = GHES_MAX_RAW_DATA_LENGTH;
>> +        error_source->error_status_address.space_id =
>> +                                    AML_SYSTEM_MEMORY;
>> +        error_source->error_status_address.bit_width = 64;
>> +        error_source->error_status_address.bit_offset = 0;
>> +        error_source->error_status_address.access_width = 4;
>> +        error_source->notify.type = i;
>> +        error_source->notify.length = sizeof(AcpiHestNotify);
>> +
>> +        error_source->error_status_block_length = GHES_MAX_RAW_DATA_LENGTH;
>> +
>> +        bios_linker_loader_add_pointer(linker,
>> +            ACPI_BUILD_TABLE_FILE, address_registers_offset + i *
>> +            sizeof(AcpiGenericHardwareErrorSource), sizeof(uint64_t),
>> +            GHES_ERRORS_FW_CFG_FILE, i * sizeof(uint64_t));
> 
> and what's this math for?
> 
>> +
>> +        error_source++;
>> +    }
>> +
>> +    for (i = 0; i < GHES_ACPI_HEST_NOTIFY_RESERVED; i++) {
>> +        bios_linker_loader_add_pointer(linker,
>> +            GHES_ERRORS_FW_CFG_FILE, sizeof(uint64_t) * i, sizeof(uint64_t),
>> +            GHES_ERRORS_FW_CFG_FILE, GHES_ACPI_HEST_NOTIFY_RESERVED *
>> +            sizeof(uint64_t) + i * GHES_MAX_RAW_DATA_LENGTH);
>> +    }

So basically all this math exists to set up the pointers that are shown
in the diagram in the commit message. It is a bit tricky because most of
those pointer fields (all 8-bytes wide) are individually embedded into
their own containing structures. In the previous version of this patch
set, I painstakingly verified the math, and pointed out wherever I
thought updates were necessary.

I agree the math is hard to read, the code is very "dense". My
suggestion (supporting yours) would be to calculate the fw_cfg blob
offsets that should be patched in more fine-grained steps, possibly with
multiple separate increments, using:
- structure type names,
- sizeof operators,
- offsetof macros,
- and possibly a separate comment for each offset increment.

Thanks,
Laszlo

On Thu, Jul 13, 2017 at 09:41:03PM +0200, Laszlo Ersek wrote:
> >> +
> >> +        error_source++;
> >> +    }
> >> +
> >> +    for (i = 0; i < GHES_ACPI_HEST_NOTIFY_RESERVED; i++) {
> >> +        bios_linker_loader_add_pointer(linker,
> >> +            GHES_ERRORS_FW_CFG_FILE, sizeof(uint64_t) * i, sizeof(uint64_t),
> >> +            GHES_ERRORS_FW_CFG_FILE, GHES_ACPI_HEST_NOTIFY_RESERVED *
> >> +            sizeof(uint64_t) + i * GHES_MAX_RAW_DATA_LENGTH);
> >> +    }
> 
> So basically all this math exists to set up the pointers that are shown
> in the diagram in the commit message. It is a bit tricky because most of
> those pointer fields (all 8-bytes wide) are individually embedded into
> their own containing structures. In the previous version of this patch
> set, I painstakingly verified the math, and pointed out wherever I
> thought updates were necessary.
> 
> I agree the math is hard to read, the code is very "dense". My
> suggestion (supporting yours) would be to calculate the fw_cfg blob
> offsets that should be patched in more fine-grained steps, possibly with
> multiple separate increments, using:
> - structure type names,
> - sizeof operators,
> - offsetof macros,
> - and possibly a separate comment for each offset increment.
> 
> Thanks,
> Laszlo

Right. That's not what rest of ACPI does though. What we do there
is one of:

1. Use GArray to gradually build up the structure.

Struct *s = acpi_data_push(table, sizeof (*s));
s->foo = bar;

2. Even simpler: use build_append_int_noprefix:

build_append_int_noprefix(table, 2, bar); /* Foo field */

this removes the need to declare Struct in a header,
just add comments to match the spec exactly.

We might gradually move more code to (2) but (1) is an
OK style too, it makes it obvious the sizes are fine.

Laszlo,
  Thanks for the comments.

On 2017/7/14 3:41, Laszlo Ersek wrote:
snip

> 
> snip
> 
>>> +
>>> +    error_source_table = (AcpiHardwareErrorSourceTable *)(table_data->data
>>> +                        + table_data->len - buffer->len);
>>> +    error_source_table->error_source_count = GHES_ACPI_HEST_NOTIFY_RESERVED;
>>> +    error_source = (AcpiGenericHardwareErrorSource *)
>>> +        ((AcpiHardwareErrorSourceTable *)error_source_table + 1);
>>
>> Concern with all these casts and pointer math is that it is barely readable.
>> We can easily overflow the array and get hard to debug heap corruption
>> errors.
>>
>> What can I suggest?  Just add this to the array in steps. Then you will
>> not need all the math.
>>
>> Or again, you can just add things as you init them using build_append_int_noprefix.
>>
>>
>>> +
>>> +    bios_linker_loader_write_pointer(linker, GHES_DATA_ADDR_FW_CFG_FILE,
>>> +        0, sizeof(uint64_t), GHES_ERRORS_FW_CFG_FILE,
>>> +        GHES_ACPI_HEST_NOTIFY_RESERVED * sizeof(uint64_t));
>>
>> What does this uint64_t refer to? It's repeated everywhere.
>>
>>> +
>>> +    for (i = 0; i < GHES_ACPI_HEST_NOTIFY_RESERVED; i++) {
>>> +        error_source->type = ACPI_HEST_SOURCE_GENERIC_ERROR;
>>> +        error_source->source_id = cpu_to_le16(i);
>>> +        error_source->related_source_id = 0xffff;
>>> +        error_source->flags = 0;
>>> +        error_source->enabled = 1;
>>> +        /* The number of error status block per Generic Hardware Error Source */
>>
>> number of ... blocks ?
>>
>>> +        error_source->number_of_records = 1;
>>> +        error_source->max_sections_per_record = 1;
>>> +        error_source->max_raw_data_length = GHES_MAX_RAW_DATA_LENGTH;
>>> +        error_source->error_status_address.space_id =
>>> +                                    AML_SYSTEM_MEMORY;
>>> +        error_source->error_status_address.bit_width = 64;
>>> +        error_source->error_status_address.bit_offset = 0;
>>> +        error_source->error_status_address.access_width = 4;
>>> +        error_source->notify.type = i;
>>> +        error_source->notify.length = sizeof(AcpiHestNotify);
>>> +
>>> +        error_source->error_status_block_length = GHES_MAX_RAW_DATA_LENGTH;
>>> +
>>> +        bios_linker_loader_add_pointer(linker,
>>> +            ACPI_BUILD_TABLE_FILE, address_registers_offset + i *
>>> +            sizeof(AcpiGenericHardwareErrorSource), sizeof(uint64_t),
>>> +            GHES_ERRORS_FW_CFG_FILE, i * sizeof(uint64_t));
>>
>> and what's this math for?
>>
>>> +
>>> +        error_source++;
>>> +    }
>>> +
>>> +    for (i = 0; i < GHES_ACPI_HEST_NOTIFY_RESERVED; i++) {
>>> +        bios_linker_loader_add_pointer(linker,
>>> +            GHES_ERRORS_FW_CFG_FILE, sizeof(uint64_t) * i, sizeof(uint64_t),
>>> +            GHES_ERRORS_FW_CFG_FILE, GHES_ACPI_HEST_NOTIFY_RESERVED *
>>> +            sizeof(uint64_t) + i * GHES_MAX_RAW_DATA_LENGTH);
>>> +    }
> 
> So basically all this math exists to set up the pointers that are shown
> in the diagram in the commit message. It is a bit tricky because most of
> those pointer fields (all 8-bytes wide) are individually embedded into
> their own containing structures. In the previous version of this patch
> set, I painstakingly verified the math, and pointed out wherever I
> thought updates were necessary.
Laszlo, you are right. it is indeed a bit tricky. Michael also has a concern
about it. I am changing to make it clear

> 
> I agree the math is hard to read, the code is very "dense". My
> suggestion (supporting yours) would be to calculate the fw_cfg blob
> offsets that should be patched in more fine-grained steps, possibly with
> multiple separate increments, using:
> - structure type names,
> - sizeof operators,
> - offsetof macros,
> - and possibly a separate comment for each offset increment.
good suggestion. I will follow that.

> 
> Thanks,
> Laszlo
> 
> .
>