ld silently generates bad DLL when there are more than 65536 exports

[Max Bolingbroke]

Windows DLLs use 16-bit ordinals to name exports, but when ld is told
to export more than 65536 exports from a DLL it does not fail.
Instead, it generates a broken DLL which correctly exports the
alphabetically-first 65k exports but also contains bogus "junk"
exports for the remaining exports.

At the very least, ld should error out rather than silently generating
a bad DLL.

Proposed patch:

"""
--- ld-old/pe-dll.c     2011-07-04 15:16:56.050491400 +0100
+++ ld/pe-dll.c 2011-07-04 15:05:27.497120800 +0100
@@ -1095,6 +1095,12 @@
        pe_def_file->exports[i].ordinal = next_ordinal;
       }

+  if (max_ordinal > 65535 || next_ordinal > 65535) {
+    /* xgettext:c-format */
+    einfo(_("%XError, export ordinal too large: %d\n"),
+          max_ordinal > next_ordinal ? max_ordinal : next_ordinal);
+  }
+
   /* OK, now we can allocate some memory.  */
   edata_sz = (40                               /* directory */
              + 4 * export_table_size           /* addresses */
"""

Test case:

"""
$ cat generate.c
#include <stdio.h>

int main(int argc, char **argv) {
    FILE *file = fopen("too_big.c", "w");
    int i;

    for (i = 0; i < (1 << 16); i++) {
        fprintf(file, "__declspec(dllexport) int
export%05d(void);\nint export%05d(void) { return %d; }\n\n", i, i, i);
    }

    fclose(file);

    return 0;
}

$ gcc generate.c -o generate && ./generate
$ gcc -shared too_big.c -o too_big.dll
"""

Inspect the generated too_big.dll in e.g. Dependency Walker.
Dependency Walker shows two exports with the same ordinal (this a
result of integer overflow). This is wrong.

Cheers,
Max