zig c++ link error when targetting older glibc

[xxxbxxx]

Zig Version

0.12.0-dev.933+b0f031f573

Steps to Reproduce and Observed Behavior

#include <stdlib.h>
int main(int argc, char* argv[]) {
	return strtoul(argv[1], 0, 10);
}

$ zig c++  main.cpp -target x86_64-linux.4.4.0-gnu.2.23
LLD Link... ld.lld: error: undefined symbol: __isoc23_strtoul
>>> referenced by main.cpp:4
>>>               /var/home/xavier/.cache/zig/o/b7dd90f0bc6f5ecf441dda49947e658a/main.o:(main)

also concerns, at least:

error: ld.lld: undefined symbol: __isoc23_strtoll_l
error: ld.lld: undefined symbol: __isoc23_strtoull_l
error: ld.lld: undefined symbol: __isoc23_vsscanf
error: ld.lld: undefined symbol: __isoc23_sscanf
error: ld.lld: undefined symbol: __isoc23_strtol
error: ld.lld: undefined symbol: __isoc23_strtoll
error: ld.lld: undefined symbol: __isoc23_strtoul
error: ld.lld: undefined symbol: __isoc23_strtoull

Expected Behavior

it did work prior to glibc upgrade in zig.

and it still works when targeting native libc (which is 2.38).
$ zig c++ main.cpp

[xxxbxxx]

some investigations:

$ find ~/.cache/zig/ -name libc.so.6
/var/home/xavier/.cache/zig/o/9b3169c14cedda9534a11ca419e2b2e8/libc.so.6
$ ls -l /var/home/xavier/.cache/zig/o/9b3169c14cedda9534a11ca419e2b2e8/libc.so.6
-rwxr-xr-x 1 xavier xavier 195024 Oct 15 18:47 /var/home/xavier/.cache/zig/o/9b3169c14cedda9534a11ca419e2b2e8/libc.so.6
$ cp /usr/lib/libc.so.6 /var/home/xavier/.cache/zig/o/9b3169c14cedda9534a11ca419e2b2e8/libc.so.6
$ ls -l /var/home/xavier/.cache/zig/o/9b3169c14cedda9534a11ca419e2b2e8/libc.so.6
-rwxr-xr-x 1 xavier xavier 1948832 Oct 15 19:02 /var/home/xavier/.cache/zig/o/9b3169c14cedda9534a11ca419e2b2e8/libc.so.6
$ /var/home/xavier/src/zig/zig/build/stage3/bin/zig c++  main.cpp -target x86_64-linux.4.4.0-gnu.2.23

that produces a working binary, but I guess it won't work on actual glibc 2.23 systems...

$eu-strings a.out 
/lib64/ld-linux-x86-64.so.2
__libc_start_main
__gmon_start__
__isoc23_strtoul
libc.so.6
GLIBC_2.34
GLIBC_2.38

[xxxbxxx]

oh and, if converted to c:
zig cc main.c -target x86_64-linux.4.4.0-gnu.2.23 -> ok
zig cc -std=c17 main.c -target x86_64-linux.4.4.0-gnu.2.23 -> ok
zig cc -std=c2x main.c -target x86_64-linux.4.4.0-gnu.2.23 -> error

LLD Link... ld.lld: error: undefined symbol: __isoc23_strtoul
>>> referenced by main.c:5
>>>               /var/home/xavier/.cache/zig/o/febb58e42d8183cf12f3d33fd4052780/main.o:(main)

for the c17 one:

$ eu-strings a.out 
/lib64/ld-linux-x86-64.so.2
__libc_start_main
__gmon_start__
strtoul
libc.so.6
GLIBC_2.2.5

(the c++ one does the error even when built with -std=c++11 )

[rootbeer]

I think the __isoc23_strtoul dependency comes via the glibc stdlib.h header file: https://github.com/ziglang/zig/blob/master/lib/libc/glibc/include/stdlib.h

I'm not entirely sure how this is supposed to work in Zig, but I would expect a set of header files for each supported glibc version because (I believe?) glibc header files can create dependencies on the symbols from the version of glibc the headers are associated with? I think that's what is happening here? (The 2.38 glibc headers depend on a symbol, __isoc23_strtoul, that is only provided by 2.38 glibc versions?).

That said, I'm really not familiar with all the magic in the Zig compat code, so this may be fixed in some other way than duplicating headers. You might dig into exactly which stdlib.h is being linked into your code to see if you can track down the specific source of the dependency?