[coreboot-gerrit] [XL] Change in coreboot[main]: lib/device_tree: Add some FDT helper functions

[Jakub Czapiga (Code Review)]

Attention is currently required from: Julius Werner, Martin L Roth, Maximilian Brune.

Jakub Czapiga has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/81081?usp=email )

Change subject: lib/device_tree: Add some FDT helper functions
......................................................................

Patch Set 6:

(3 comments)

Patchset:

PS6:
> > Test failed with exception: Segmentation fault(11) […]

I tested it on my machine and it fails too. There is incorrect memory access in `tests_lib_device_tree-test(tests).test_fdt_find_node_by_path`

1. You should align arrays:
> The devicetree blob shall be located at an 8-byte-aligned address. To maintain backwards compatibilty for 32-bit machines, 4-byte alignment is supported by some software, but this is not DTSpec-compliant.

```
uint8_ dtb[] __attribute__((aligned(8))) = ...
```

2. Code segfaults at:

```log
[==========] tests_lib_device_tree-test(tests): Running 4 test(s).
[ RUN      ] test_fdt_find_node_by_path

Program received signal SIGSEGV, Segmentation fault.
0x0000000000401ac0 in fdt_find_multiple_nodes_by_path (blob=blob@entry=0x41d980 <dtb>, path=<optimized out>, path@entry=0x4020ad "/cpus/cpu@*", addrcp=addrcp@entry=0x7fffffffce50, sizecp=sizecp@entry=0x7fffffffce54, 
    results=results@entry=0x7fffffffce58, count_results=count_results@entry=0x7fffffffce4e) at src/lib/device_tree.c:272
272                     node_offset = results[(*count_results)++] = off; // save occurrence
(gdb) where
#0  0x0000000000401ac0 in fdt_find_multiple_nodes_by_path (blob=blob@entry=0x41d980 <dtb>, path=<optimized out>, path@entry=0x4020ad "/cpus/cpu@*", addrcp=addrcp@entry=0x7fffffffce50, sizecp=sizecp@entry=0x7fffffffce54, 
    results=results@entry=0x7fffffffce58, count_results=count_results@entry=0x7fffffffce4e) at src/lib/device_tree.c:272
#1  0x00000000004015a3 in test_fdt_find_node_by_path (state=<optimized out>) at tests/lib/device_tree-test.c:50
#2  0x00007ffff7fbb75d in cmocka_run_one_test_or_fixture () from build/tests/util/cmocka/src/libcmocka.so.0
#3  0x00007ffff7fbba2b in cmocka_run_one_tests () from build/tests/util/cmocka/src/libcmocka.so.0
#4  0x00007ffff7fbbfb1 in _cmocka_run_group_tests () from build/tests/util/cmocka/src/libcmocka.so.0
#5  0x00000000004010ab in main () at tests/lib/device_tree-test.c:97

```

`count_results` reaches absurd numbers in thousands, because you use it without initialization, as was passed from caller.

ALSO please fix checkpatch issues wherever possible. xxd files can be omited.

File src/lib/device_tree.c:

https://review.coreboot.org/c/coreboot/+/81081/comment/4d305d44_016460a1 :
PS6, Line 67: size = fdt_next_node_name(blob, offset, &name);
`int size = ...`. Let's not multiply code without need.

https://review.coreboot.org/c/coreboot/+/81081/comment/38d9202f_d945ef0d :
PS6, Line 272: node_offset = results[(*count_results)++] = off; // save occurrence
`count_results` is left uninitialized. More info in another comment.