[XS] Change in coreboot[master]: commonlib/bsd/tpm_log_defs.h: Use C99 flexible arrays

[Martin L Roth (Code Review)]

Attention is currently required from: Arthur Heymans, Elyes Haouas, Sergii Dmytruk.

Martin L Roth has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/76787?usp=email )

Change subject: commonlib/bsd/tpm_log_defs.h: Use C99 flexible arrays
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Patch Set 3:

(1 comment)

Patchset:

PS2:
> `&tcpa_spec_entry. […]

The problem isn't with the tcpa_log_entry itself, it's the inclusion of that into tcpa_spec_entry.

To fix this without changing anything else, we can create an additional structure:

```
#define TCPA_LOG_DIGEST_LENGTH 20
struct tcpa_log_entry_header {
    uint32_t pcr;
    uint32_t event_type;
    uint8_t digest[TCPA_LOG_DIGEST_LENGTH];
    uint32_t event_data_size;
} __packed;

struct tcpa_log_entry {
    uint32_t pcr;
    uint32_t event_type;
    uint8_t digest[TCPA_LOG_DIGEST_LENGTH];
    uint32_t event_data_size;
    uint8_t event[0];
} __packed;

struct tcpa_spec_entry {
    struct tcpa_log_entry_header entry;
    uint8_t signature[16];
    uint32_t platform_class;
    uint8_t spec_version_minor;
    uint8_t spec_version_major;
    uint8_t spec_errata;
    uint8_t reserved;
    uint8_t vendor_info_size;
    uint8_t vendor_info[0];
} __packed;
```

I'm not crazy about the duplicated code here, but unless we want to do the ugly conversion in the one location in util/cbmem that `->event` is used the duplicated code is probably the next best alternative to get rid of that array. Using the ugly conversion means that this:

```
    	if (len != 0) {
    		current += len;
    		printf("\tEvent data: ");
    		if (can_print(log_entry->event, len))
    			printf("%.*s\n", len, log_entry->event);
    		else
    			print_hex_line(log_entry->event, len);
    	} else {
    		printf("\tEvent data not provided\n");
    	}
```
Becomes this:

```
    	if (len != 0) {
    		uint8_t *ptr = (uint8_t *)log_entry + sizeof(*log_entry);
    		current += len;
    		printf("\tEvent data: ");
    		if (can_print(ptr, len))
    			printf("%.*s\n", len, ptr);
    		else
    			print_hex_line(ptr, len);
    	} else {
    		printf("\tEvent data not provided\n");
    	}
```

Personally, I could live with that ugly change.