SDL3 : SIGSEGV: address not mapped to object (fault address: 0x0)

SDL Development
1

Hi,
I am porting shadps4 to FreeBSD, and i have a problem with SIGSEGV on FreeBSD.
The problem is NULL with environ variable.
This is an official bug. I think the problem is inside SDL3. Do you have any idea?

[[APP BUG]: SIGSEGV: address not mapped to object (fault address: 0x0) · Issue #2765 · shadps4-emu/shadPS4 · GitHub](Ps4 emulator)

2

It looks like the application initializes SDL in a separate thread.

The FreeBSD getenv manual calls out that combining getenv and putenv can results in undefined behavior:

SDL assumes SDL_Init is run very early in the lifetime of a process, when multithreading is not an issue.
Environment variables are notoriously tricky to use in multithreaded environments.
This is also why you see SDL_CreateEnvironment_REAL in the stacktrace: SDL is copying the environmment to avoid multithreading issues.

3

so SDL getenv uses wrong. How to fix this problem ?

5

Where do you see getenv ?

6 
frame #3: 0x00001f3449e01cdc shadps4`SDL_CreateEnvironment_REAL(populated=true) at SDL_getenv.c:129:34
   126 	        char **strings = (char **)dlsym(RTLD_DEFAULT, "environ");
   127 	        if (strings) {
   128 	            for (int i = 0; strings[i]; ++i) {
-> 129 	                char *variable = SDL_strdup(strings[i]);
   130 	                if (!variable) {
   131 	                    continue;
   132 	                }
(lldb) print strings[0]
(char *) 0x0000365a3fabfe00 "`\xae\xa2?Z6"
(lldb) print strings[1]
(char *) 0x0000365a3fa10500 "\xb8bPJ4\U0000001f"
(lldb) print *(strings)
(char *) 0x0000365a3fabfe00 "`\xae\xa2?Z6"
7

I stand corrected. SDL does not call getenv, but uses the environ symbol.

SDL wants to clone the environment, and thus needs to iterate all keys.
SDL does this here.

8

Yes, but in environ variable is garbage

9

The small program below prints all environment variables. (It works fine on Linux)

#include <SDL3/SDL.h>
int main(int argc, char *argv[]) {
    SDL_Environment *env = SDL_CreateEnvironment(true);
    char **env_vars = SDL_GetEnvironmentVariables(env);
    for (size_t i = 0; env_vars[i] != NULL; i++) {
        SDL_Log("[%d] %s", i, env_vars[i]);
    }
    SDL_free(env_vars);
    SDL_DestroyEnvironment(env);
    return 0;
}

I’ve got a few questions:

  1. Does the program work on your system?
  2. When copying and adapting into shadps4 (running it in the thread that calls SDL_Init), does it print sensible thins?
10

I have FreeBSD RELEASE 14.2 amd64.
I tried this, but without output.


#include <SDL3/SDL.h>
#include <SDL3/SDL_stdinc.h>
#include <iostream>
#include <thread>

void sdl_worker() {
    if (!SDL_SetHint(SDL_HINT_APP_NAME, "Test")) {
        std::cerr << "Failed to set SDL window hint: " << SDL_GetError() << std::endl;
    }

    if (!SDL_Init(SDL_INIT_VIDEO)) {
        std::cerr << "SDL_Init failed: " << SDL_GetError() << std::endl;
        return;
    }

    SDL_Environment *env = SDL_CreateEnvironment(true);
    if (!env) {
        std::cerr << "SDL_CreateEnvironment failed: " << SDL_GetError() << std::endl;
        SDL_Quit();
        return;
    }

    char **env_vars = SDL_GetEnvironmentVariables(env);
    if (env_vars) {
        for (size_t i = 0; env_vars[i] != NULL; ++i) {
            std::cout << "[" << i << "] " << env_vars[i] << std::endl;
        }
        SDL_free(env_vars);
    }

    SDL_DestroyEnvironment(env);
    SDL_Quit();
}

int main(int argc, char* argv[]) {
    std::thread worker(sdl_worker);;
    worker.join();

    return 0;
}

when i tried your code add to shadps4 after SDL_Init() so crash is inside SDL_Init()

11

No output at all? Not even an error message from your added error checking?

when i tried your code add to shadps4 after SDL_Init() so crash is inside SDL_Init()

We already established it crashes inside SDL_Init (from your stack trace in the GitHub issue), so you have to run the code first (before SDL_Init).
But since it even fails to print anything when running on the main thread, don’t bother running it.

Can you please create a GitHub issue with:

  • links to the GitHub issue and this conservation
  • Result of running the last SDL_Environment c++ test code, with a complete copy-paste of stdout+stderr (don’t forget to censor PII)?

I remember there being an issue with environ on FreeBSD, but I cannot find it right now.

Add SDL_Process subsystem by Semphriss · Pull Request #10618 · libsdl-org/SDL · GitHub contains:

I asked on a #freebsd-devel why we can t access environ, and they say it s because our use of version scripts. We d need to explicitly add environ (and __progname) to the global section.

12

Just a note - SDL3/SDL.h includes SDL3/SDL_stdinc.h, so you don’t really need it there

13

Also I find myself SDL3 working weird with other thread libraries. Maybe SDL Threads will work better?

I mean, is this really related to SDL_Environment? Does not SDL3 create it also internally at initialization?

14

The problem is inside SDL_SetHint() this is first call SDL, but i commented this code, and
the second call is SDL_Init() (shadps4). I forget for this changes. I am sorry.
I will to create github issue with this problem.

15

I tried with SDL_Threads and the result is the same.