Unable to use memfd_create method

[Aitha Tarun]

Hi, I am unable to use the memfd_create method while building the C script to emscripten.

Below I have given my references to reproduce the error.

Code :

#include <stdio.h>
#include <sys/mman.h>
#include <unistd.h>
#include <stdlib.h>
#define _GNU_SOURCE

int memfd_create(const char *name, unsigned int flags);

int main()
{
    int fd = memfd_create("temp", 0);

    printf("Fd : %d\n", fd);

    int wrote = write(fd, "Hello", 5);

    printf("Wrote : %d\n", wrote);

    char * buf = malloc(5);

    int red = pread(fd, buf, 5, 0);

    printf("Read : %d\n", red);
    printf("Content %s\n", buf);
}

Error :

[Sam Clegg]

Emscripten doesn't yet support the memfd_create API.  If you need to use it you could look into adding support for it (or file a bug to get it added).   I imagine that most codebased that use that API have some kind of cross-platform fallback.  Perhaps you could use that instead?

cheers,

sam

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[Aitha Tarun]

Thanks for the reply, I will raise a bug to get this added.

[Floh]

Hmm... does it really make sense to add such Linux specific functions to Emscripten? From looking at the MUSL source, it does have an memfd_create entry point, but that just jumps into the Linux SYS_memfd_create syscall, so it doesn't work anywhere but on Linux. Suppporting a random collection of Linux-specific syscalls might be more confusing to Emscripten users than having a clear definition of what's supposed to work (for instance: only CRT functions, only POSIX functions up to version X, etc...).

For instance, OP's code doesn't compile on macOS either:

Undefined symbols for architecture arm64:
  "_memfd_create", referenced from:
      _main in test-26b3ed.o
ld: symbol(s) not found for architecture arm64

Cheers,

-Floh.