Debugging an efivar test failure (bug #1863475) leads to the discovery that variadic functions are missing the last variadic argument from their prototype definition in debgging data.

Without -lfto option, foo() is decribe by GDB correctly:

$ cat test.c
#include <stdarg.h>
void foo(int args, ...) {
    va_list ap;
    va_start(ap, args);
    va_end(ap);
}
$ gcc -fPIC -shared -o libtest.so -O0 -g test.c
$ gdb libtest.so
[...]
Reading symbols from libtest.so...
(gdb) info functions foo
All functions matching regular expression "foo":

File test.c:
2:      void foo(int, ...);
(gdb) quit

But when compiling with -flto:

$ gcc -fPIC -shared -o libtest.so -O0 -g -flto test.c
$ gdb libtest.so
[...]
Reading symbols from libtest.so...
(gdb) info functions foo
All functions matching regular expression "foo":

File <artificial>:
2:      void foo(int);
(gdb) quit

The printed prototype is missing the last "..." argument.

I believe this is only a problem in the debugging data, not in the generated code, as processing the variadic arguments in the foo() works as expected. Dissassembly also confirms it. This is probably not a bug in GDB, because abidw tool from libabigail package, which processs the debugging sections of ELF, also suffer from the same issue (as spotted in the efivar bug #1863475).

My toolchain:

$ rpm -q gcc binutils elfutils
gcc-10.2.1-5.fc33.x86_64
binutils-2.35-11.fc33.x86_64
elfutils-0.181-1.fc33.x86_64