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Don't use SDL locking functions in our open()/close() hooks

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Other shared library constructors can invoke open()/close() before
SDL2-compat's constructor runs to load SDL3 and populate the SDL3
function table. This causes SDL_AtomicLock()/SDL_AtomicUnlock()
to jump to 0.

See #1707
This commit is contained in:
Cameron Gutman
2025-10-09 20:03:19 -05:00
parent ae1c65805c
commit 490aa5082f
2 changed files with 15 additions and 10 deletions
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2
app/masterhook.c
View File

@@ -9,7 +9,9 @@
// The specific kernel change required to run without root is:
// https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=45bc3d26c95a8fc63a7d8668ca9e57ef0883351c
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
// NOTE: This file MUST NOT include fcntl.h due to open() -> open64()
// redirection that happens when _FILE_OFFSET_BITS=64!

23
app/masterhook_internal.c
View File

@@ -2,7 +2,9 @@
// which must be in a separate compilation unit due to fcntl.h doing
// unwanted redirection of open() to open64().
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include "SDL_compat.h"
#include <dlfcn.h>
@@ -11,6 +13,7 @@
#include <errno.h>
#include <stdbool.h>
#include <sys/stat.h>
#include <pthread.h>
#include <xf86drm.h>
#include <xf86drmMode.h>
@@ -33,7 +36,7 @@ extern struct stat g_DrmMasterStat;
#define MAX_SDL_FD_COUNT 8
int g_SdlDrmMasterFds[MAX_SDL_FD_COUNT];
int g_SdlDrmMasterFdCount = 0;
SDL_SpinLock g_FdTableLock = 0;
pthread_mutex_t g_FdTableLock = PTHREAD_MUTEX_INITIALIZER;
// Caller must hold g_FdTableLock
int getSdlFdEntryIndex(bool unused)
@@ -55,7 +58,7 @@ int getSdlFdEntryIndex(bool unused)
// Returns true if the final SDL FD was removed
bool removeSdlFd(int fd)
{
SDL_AtomicLock(&g_FdTableLock);
pthread_mutex_lock(&g_FdTableLock);
if (g_SdlDrmMasterFdCount != 0) {
// Clear the entry for this fd from the table
for (int i = 0; i < MAX_SDL_FD_COUNT; i++) {
@@ -67,11 +70,11 @@ bool removeSdlFd(int fd)
}
if (g_SdlDrmMasterFdCount == 0) {
SDL_AtomicUnlock(&g_FdTableLock);
pthread_mutex_unlock(&g_FdTableLock);
return true;
}
}
SDL_AtomicUnlock(&g_FdTableLock);
pthread_mutex_unlock(&g_FdTableLock);
return false;
}
@@ -82,12 +85,12 @@ int takeMasterFromSdlFd()
// Since all SDL FDs are actually dups of each other
// we can take master from any one of them.
SDL_AtomicLock(&g_FdTableLock);
pthread_mutex_lock(&g_FdTableLock);
int fdIndex = getSdlFdEntryIndex(false);
if (fdIndex != -1) {
fd = g_SdlDrmMasterFds[fdIndex];
}
SDL_AtomicUnlock(&g_FdTableLock);
pthread_mutex_unlock(&g_FdTableLock);
if (fd >= 0 && drmDropMaster(fd) == 0) {
return fd;
@@ -126,12 +129,12 @@ int openHook(const char *funcname, const char *pathname, int flags, va_list va)
int allocatedFdIndex;
// It is our device. Time to do the magic!
SDL_AtomicLock(&g_FdTableLock);
pthread_mutex_lock(&g_FdTableLock);
// Get a free index for us to put the new entry
freeFdIndex = getSdlFdEntryIndex(true);
if (freeFdIndex < 0) {
SDL_AtomicUnlock(&g_FdTableLock);
pthread_mutex_unlock(&g_FdTableLock);
SDL_assert(freeFdIndex >= 0);
SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
"No unused SDL FD table entries!");
@@ -151,7 +154,7 @@ int openHook(const char *funcname, const char *pathname, int flags, va_list va)
else {
// Drop master on Qt's FD so we can pick it up for SDL.
if (drmDropMaster(g_QtDrmMasterFd) < 0) {
SDL_AtomicUnlock(&g_FdTableLock);
pthread_mutex_unlock(&g_FdTableLock);
SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
"Failed to drop master on Qt DRM FD: %d",
errno);
@@ -182,7 +185,7 @@ int openHook(const char *funcname, const char *pathname, int flags, va_list va)
g_SdlDrmMasterFdCount++;
}
SDL_AtomicUnlock(&g_FdTableLock);
pthread_mutex_unlock(&g_FdTableLock);
}
}
}