[XL] Change in coreboot[main]: tests: Add unit tests for CFR

[Angel Pons (Code Review)]

Attention is currently required from: Julius Werner, Patrick Rudolph.

Angel Pons has posted comments on this change by Patrick Rudolph. ( https://review.coreboot.org/c/coreboot/+/78506?usp=email )

Change subject: tests: Add unit tests for CFR
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Patch Set 5:

(5 comments)

File src/commonlib/bsd/cfr_parser.c:

https://review.coreboot.org/c/coreboot/+/78506/comment/fe26dee7_afe3a86f?usp... :
PS5, Line 21: case CFR_TAG_OPTION_ENUM:
            : 		return sizeof(struct lb_cfr_numeric_option);
            : 	case CFR_TAG_OPTION_NUMBER:
            : 		return sizeof(struct lb_cfr_numeric_option);
            : 	case CFR_TAG_OPTION_BOOL:
            : 		return sizeof(struct lb_cfr_numeric_option);
> Is there a reason for these case statements to be separate? They can look like that: […]

I guess it's for visual consistency. For this kind of case-return approach I usually go for one-line:

```
    case CFR_TAG_OPTION_ENUM:       return sizeof(struct lb_cfr_numeric_option);
    case CFR_TAG_OPTION_NUMBER:     return sizeof(struct lb_cfr_numeric_option);
    case CFR_TAG_OPTION_BOOL:       return sizeof(struct lb_cfr_numeric_option);
```
(had to use spaces so that it'd show up nicely on Gerrit)

https://review.coreboot.org/c/coreboot/+/78506/comment/228aeb14_2eaccd8d?usp... :
PS5, Line 31: 	default:
Would it make sense to complain about unknown entries?

https://review.coreboot.org/c/coreboot/+/78506/comment/a3d0a6c5_dd6e2c17?usp... :
PS5, Line 109: ret = cfr_iterate(&child, callback, priv);
> How deep can recursion be here? If someone passes a long enough parent->child->child->... […]

It generally shouldn't be a problem, since the structure must not have loops and won't get too deeply nested.

Still, I think it would be nice to add a recursion guard. Maybe it can be a simple `max_depth` parameter?

```
static int cfr_iterate(const struct region_device *root,
    	       int (*callback)(const struct region_device *root, const struct region_device *child, void *priv),
    	       void *priv, int max_depth)
{
    struct region_device child;
    struct lb_cfr_header hdr;
    int ret, size, offset;

if (max_depth <= 0)
    	return CB_ERR;
```

```suggestion
    	ret = cfr_iterate(&child, callback, priv, max_depth - 1);
```

https://review.coreboot.org/c/coreboot/+/78506/comment/ffb6cd3c_49f15f70?usp... :
PS5, Line 144: // FIXME checksum
> Sorry, but I cannot allow the input parsing code to be submitted w/o checksum checking if there is o […]

+1

File tests/drivers/cfr.c:

https://review.coreboot.org/c/coreboot/+/78506/comment/1bd6bd45_e877ca2b?usp... :
PS5, Line 339: void *head = malloc(0x100000);
             : 	assert(head);
nit: Hmmm, put this inside a helper function?