tequilaOS/platform_bionic
2
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity

Improve the "how to add a system call" doc

Browse source 
Test: None
Bug: None
Change-Id: Ie4212956836ae057009e6985812efcbbb7859dea
This commit is contained in:
zijunzhao 2022-05-10 21:22:00 +00:00
parent c66cb5ba6a
commit e5e1e4e55a
1 changed files with 37 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

37
README.md
View file

@ -211,6 +211,10 @@ Adding a system call usually involves:
implemented in the kernel. For simple syscalls, that's just the
auto-generated argument and return value marshalling.
Add a test in the right file in tests/. We have one file per header, so if
your system call is exposed in <unistd.h>, for example, your test would go
in tests/unistd_test.cpp.
A trivial test that deliberately supplies an invalid argument helps check
that we're generating the right symbol and have the right declaration in
the header file, and that the change to libc.map.txt from step 5 is
@ -237,6 +241,39 @@ feasible to write a working test for the interesting cases -- offsets larger
than 2GiB, say -- so you may end up just writing a "meaningless" program whose
only purpose is to give you patterns to look for when run under strace(1).)
A general example of adding a system call:
https://android-review.googlesource.com/c/platform/bionic/+/2073827
### Debugging tips
1. Key error for a new codename in libc/libc.map.txt
e.g. what you add in libc/libc.map.txt is:
```
LIBC_V { # introduced=Vanilla
global:
xxx; // the new system call you add
} LIBC_U;
```
The error output is:
```
Traceback (most recent call last):
File "/path/tp/out/soong/.temp/Soong.python_qucjwd7g/symbolfile/__init__.py", line 171,
in decode_api_level_tag
decoded = str(decode_api_level(value, api_map))
File "/path/to/out/soong/.temp/Soong.python_qucjwd7g/symbolfile/__init__.py", line 157,
in decode_api_level
return api_map[api]
KeyError: 'Vanilla'
```
Solution: Ask in the team and wait for the update.
2. Use of undeclared identifier of the new system call in the test
Possible Solution: Check everything ready in the files mentioned above first.
Maybe glibc matters. Follow the example and try #if defined(__GLIBC__).
## Updating kernel header files
As mentioned above, this is currently a two-step process: