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example/ssh2: replace GCC silencer pragma with a simpler workaround

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As of gcc-16, this still causes a false positive:
```
example/ssh2.c: In function 'main':
example/ssh2.c:215:34: error: '__builtin_snprintf' output may be truncated before the last format character [-Werror=format-truncation=]
  215 |             snprintf(fn1, fn1sz, "%s/%s", h, pubkey);
      |                                  ^~~~~~~
example/ssh2.c:215:40: note: format string is defined here
  215 |             snprintf(fn1, fn1sz, "%s/%s", h, pubkey);
      |                                        ^
example/ssh2.c:215:13: note: '__builtin_snprintf' output 17 or more bytes (assuming 18) into a destination of size 17
  215 |             snprintf(fn1, fn1sz, "%s/%s", h, pubkey);
      |             ^~~~~~~~
example/ssh2.c:216:34: error: '__builtin_snprintf' output may be truncated before the last format character [-Werror=format-truncation=]
  216 |             snprintf(fn2, fn2sz, "%s/%s", h, privkey);
      |                                  ^~~~~~~
example/ssh2.c:216:40: note: format string is defined here
  216 |             snprintf(fn2, fn2sz, "%s/%s", h, privkey);
      |                                        ^
example/ssh2.c:216:13: note: '__builtin_snprintf' output 13 or more bytes (assuming 14) into a destination of size 13
  216 |             snprintf(fn2, fn2sz, "%s/%s", h, privkey);
      |             ^~~~~~~~
```

By bumping the allocated buffers by one byte, the above disappears, but
remains in gcc-13. Fix by bumping buffer by one more byte.
```
example/ssh2.c: In function ‘main’:
example/ssh2.c:228:40: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
  228 |             snprintf(fn1, fn1sz, "%s/%s", h, pubkey);
      |                                        ^
example/ssh2.c:228:13: note: ‘snprintf’ output 3 or more bytes (assuming 4) into a destination of size 3
  228 |             snprintf(fn1, fn1sz, "%s/%s", h, pubkey);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
example/ssh2.c:229:40: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
  229 |             snprintf(fn2, fn2sz, "%s/%s", h, privkey);
      |                                        ^
example/ssh2.c:229:13: note: ‘snprintf’ output 3 or more bytes (assuming 4) into a destination of size 3
  229 |             snprintf(fn2, fn2sz, "%s/%s", h, privkey);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```
Ref: https://github.com/libssh2/libssh2/actions/runs/27890978881/job/82534253967#step:24:67

Closes #2100
This commit is contained in:
Viktor Szakats
2026-06-21 04:28:27 +02:00
parent 33f6508a58
commit 165a9c3bee
1 changed files with 4 additions and 10 deletions
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14
example/ssh2.c
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@@ -199,8 +199,10 @@ int main(int argc, char *argv[])
char const *h = getenv("HOME");
if(!h || !*h)
h = ".";
fn1sz = strlen(h) + strlen(pubkey) + 2;
fn2sz = strlen(h) + strlen(privkey) + 2;
/* Silence GCC -Wformat-truncation false positives by allocating
2 extra bytes for each buffer. */
fn1sz = strlen(h) + strlen(pubkey) + 2 + 2;
fn2sz = strlen(h) + strlen(privkey) + 2 + 2;
fn1 = malloc(fn1sz);
fn2 = malloc(fn2sz);
if(!fn1 || !fn2) {
@@ -210,18 +212,10 @@ int main(int argc, char *argv[])
goto shutdown;
}
/* Avoid false positives */
#if defined(__GNUC__) && __GNUC__ >= 7
#pragma GCC diagnostic push
#pragma GCC diagnostic warning "-Wformat-truncation=1"
#endif
/* Using asprintf() here would be much cleaner,
but less portable */
snprintf(fn1, fn1sz, "%s/%s", h, pubkey);
snprintf(fn2, fn2sz, "%s/%s", h, privkey);
#if defined(__GNUC__) && __GNUC__ >= 7
#pragma GCC diagnostic pop
#endif
if(libssh2_userauth_publickey_fromfile(session, username,
fn1, fn2,
password)) {