<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/78531>78531</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang]compile fail when declare the snprintf function
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          dongjianqiang2
      </td>
    </tr>
</table>

<pre>
    cat test.c:
`#include <stdio.h>

int snprintf(char* s, size_t n, const char* format, ...);

int main()
{
  char buffer[50];
  char* s = "runoobcom";

  int j = snprintf(buffer, 6, "%s\n", s);

 printf("string:\n%s\ncharacter count = %d\n", buffer, j);
  return 0;
}`
clang test.c -c -o test.o -D_FORTIFY_SOURCE=2 -O2
<source>:3:5: error: expected parameter declarator
    3 | int snprintf(char* s, size_t n, const char* format, ...);
      | ^
Refer to https://godbolt.org/z/3xnbe6E9M
After analysis, I find that this is caused by inconsistent declaration of the __va_arg_pack macro in glibc
https://github.com/bminor/glibc/blob/9ea3686266dca3f004ba874745a4087a89682617/libio/bits/stdio2.h#L62C9-L62C22
This difference is due to the default __GNUC__ macro in clang.
https://github.com/bminor/glibc/blob/9ea3686266dca3f004ba874745a4087a89682617/misc/sys/cdefs.h#L361C1-L361C1
`clang -dM -E - < /dev/null |grep GNUC
#define __GNUC_MINOR__ 2
#define __GNUC_PATCHLEVEL__ 1
#define __GNUC_STDC_INLINE__ 1
#define __GNUC__ 4
`
Do we have any plans to update this version of __GNUC__ in clang?
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJy8VVtv4zYT_TX0y0CGRIq6PPjBka3vC5BLkc0W6JNAkSObqUy6JJXd7K8vKF8SBNgFChT1g0SLnMs5c2YovNc7g7gi_IbwzUJMYW_dSlmze9HC_KWF2dFFb9XbSooAAX1YSsLWJN2QdE2KlFCmjRwnhUBY44PSdrknbHs-MD-1CeDN0WkTBkIruReO0DV4Qhvw-gd2AUxcS2t8gMv2YN1BhPh9uVwSWhN289npQWhDaBU3Tzvl-QjMXqCfhgEd4Tc8JXxzdQDXGB4I2wCh1E3G2l7aA6H0UyCAGOplPvkBxdk3baCIj2hHuSe8MfOyifA-5wxXa0KpD06bXeRytjnZxsSEDOhA2smEc3pcffD7HvjlYwQAh2FyBtL3oOUmVmhey1GY3bl-kEhI7OmPhWTTtY9Pz7ftH92Xx69PzZawDYXkkZ6dsMbbyUmMRWVrRtiaE7YGdM66efH9iDKggqNw4oAxd4VyFE4E6y65ATAgZQP_shRg_kXHhF8kRzPCb_RB7DDWnFb7EI4-0kxbQtudDvupX86Vbsfx9fJKjs6-oAyEtsJ7DJ7Qtq6yPM2qlNAW1ZAyWtKk4KlK8l5VSYVFnXDOByxlnbNSXGX4hAM6CBY-hbaqt2NYWrcjtP1BaMu-mx6LbX1_slsPkTxhxPjm9UzJLQzaKAj72Ht77UF7kGLyqKB_A20iTdoHNOHKubYG7ABhj9B1r6ITbtcdhfwTDkI6C9rAbtS9PEX8BTf9QRvr4tf5OG370faRFBSsqApaFEoKNqRp3ouqzMucizytSlHVRUWLrIy86l7baKlnOufhQJd7QtldQZs6iU96ltlzRKd0lDYaiRGomjCSGJEoHMQ0Bui6_z18bbruHcys6-V_geagfTT0bxGLVDj4ExRWZE2WnF7XsXhqt0TdQ7KFJI5GILRV-Epoa6ZxjJrdOTxCxHMRLlM4aIMXlPe3D49PXQf0J_u_rZ-b_99tf9_edR1kPzn05XnTdLcPd7cP21-c6iB_n-jzYmPhG8JevCII8wbHURgfqzEdlQh4EuMrOn-W29XPpSSEtQu1YqpmtVjgKitTzvOspnyxX2XF0A8oZc16XlapqFk59H0us7oWpcB6oVc0pXmaZVWasSrnS57nqcA0Q6UozQtB8hQPQo_L2LqxoRba-wlXZcVZthhFj6OfrzRKT9lQGm83t5pbvZ92nuTpqH3w7x6CDuN8D54s-Ebaw1GPCIPQI3zbozn3GM6SvEwxGCYjY9ctJjeu_vGwmfOOippT_zsAAP__pl9BLQ">