Ref:
https://best.openssf.org/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C++.html
(2023-11-29)
Enable new warnings:
- replace `-Wno-sign-conversion` with `-Wsign-conversion`.
Fix them in example, tests and wincng. There remain about 360 of these
warnings in `src`. Add a TODO item for those and disable `-Werror` for
this particular warning.
- enable `-Wformat=2` for clang (in both cmake and autotools).
- enable `__attribute__((format))` for `_libssh2_debug()`,
`_libssh2_snprintf()` and in tests for `run_command()`.
`LIBSSH2_PRINTF()` copied from `CURL_TEMP_PRINTF()` in curl.
- enable `-Wimplicit-fallthrough`.
- enable `-Wtrampolines`.
Fix them:
- src: replace obsolete fall-through-comments with
`__attribute__((fallthrough))`.
- wincng: fix `-Wsign-conversion` warnings.
- tests: fix `-Wsign-conversion` warnings.
- example: fix `-Wsign-conversion` warnings.
- src: fix `-Wformat` issues in trace calls.
Also, where necessary fix `int` and `unsigned char` casts to
`unsigned int` and adjust printf format strings. These were not
causing compiler warnings.
Cast large types to `long` to avoid dealing with printf masks for
`size_t` and other C99 types. Existing code often used `int` for this.
I'll update them to `long` in an upcoming commit.
- tests: fix `-Wformat` warning.
- silence `-Wformat-nonliteral` warnings.
- mbedtls: silence `-Wsign-conversion`/`-Warith-conversion`
in external header.
Closes#1257
Then sync this warning option with curl.
Seems like a false positive and/or couldn't figure how to fix it, so silence:
```
example/ssh2.c:227:38: error: '%s' directive output may be truncated writing likely 1 or more bytes into a region of size 0 [-Werror=format-truncation=]
227 | snprintf(fn1, fn1sz, "%s/%s", h, pubkey);
| ^~
example/ssh2.c:227:34: note: assuming directive output of 1 byte
227 | snprintf(fn1, fn1sz, "%s/%s", h, pubkey);
| ^~~~~~~
example/ssh2.c:227:13: note: 'snprintf' output 3 or more bytes (assuming 4) into a destination of size 2
227 | snprintf(fn1, fn1sz, "%s/%s", h, pubkey);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
example/ssh2.c:228:38: error: '%s' directive output may be truncated writing likely 1 or more bytes into a region of size 0 [-Werror=format-truncation=]
228 | snprintf(fn2, fn2sz, "%s/%s", h, privkey);
| ^~
example/ssh2.c:228:34: note: assuming directive output of 1 byte
228 | snprintf(fn2, fn2sz, "%s/%s", h, privkey);
| ^~~~~~~
example/ssh2.c:228:13: note: 'snprintf' output 3 or more bytes (assuming 4) into a destination of size 2
228 | snprintf(fn2, fn2sz, "%s/%s", h, privkey);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```
Ref: https://github.com/libssh2/libssh2/actions/runs/7055480458/job/19205970397#step:10:98
Fix:
```
tests/openssh_fixture.c:116:38: error: ' 2>&1' directive output may be truncated writing 5 bytes into a region of size between 1 and 1024 [-Werror=format-truncation=]
tests/openssh_fixture.c:116:11: note: 'snprintf' output between 6 and 1029 bytes into a destination of size 1024
```
Ref: https://github.com/libssh2/libssh2/actions/runs/7055480458/job/19205969221#step:10:51
Tested via #1257
