For some reason, after invoking an unrelated dlclose() call to unload any .dylib that had previously been loaded via dlopen(..., RTLD_NOW), the subsequent call to task_info(mach_task_self(), TASK_DYLD_INFO, ...) syscall returns unexpected structure in dyld_uuid_info image_infos->uuidArray, that, while it seems to represent an array of struct dyld_uuid_info elements, there is only 1 such element (dyld_all_image_infos *infos->uuidArrayCount == 1) and the app crashes when trying to access dyld_uuid_info image->imageLoadAddress->magic, as image->imageLoadAddress doesn't seem to represent a valid struct mach_header structure address (although it looks like a normal pointer within the process address space. What does it point to?).
This reproduces on macOS 15.4.1 (24E263)
Could you please confirm that this is a bug in the specified OS build, or point to incorrect usage of the task_info() API?
Attaching the C++ file that reproduces the issue to this email message
It needs to be built on macOS 15.4.1 (24E263) via Xcode or just a command line clang++ compiler. It may crash or return garbage, depending on memory layout, but on this macOS build it doesn’t return a correct feedfacf magic number for the struct mach_header structure.
Thank you
Feedback Assistant reference: FB18431345
//On `macOS 15.4.1 (24E263)` create a C++ application (for example, in Xcode), with the following contents. Note, that this application should crash on this macOS build. It will not crash, however, if you either:
//1. Comment out `dlclose()` call
//2. Change the order of the `performDlOpenDlClose()` and `performTaskInfoSyscall()` functions calls (first performTaskInfoSyscall() then performDlOpenDlClose()).
#include <iostream>
#include <dlfcn.h>
#include <mach/mach.h>
#include <mach-o/dyld_images.h>
#include <mach-o/loader.h>
void performDlOpenDlClose() {
printf("dlopen/dlclose function\n");
printf("Note: please adjust the path below to any real dylib on your system, if the path below doesn't exist!\n");
std::string path = "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libswiftDemangle.dylib";
printf("Dylib to open: %s\n", path.c_str());
void* handle = ::dlopen(path.c_str(), RTLD_NOW);
if(handle) {
::dlclose(handle);
} else {
printf("Error: %s\n", dlerror());
}
}
void performTaskInfoSyscall() {
printf("Making a task_info() syscall\n");
printf("\033[34mSource File: %s\033[0m\n", __FILE__);
task_t task = mach_task_self();
struct task_dyld_info dyld_info;
mach_msg_type_number_t size = TASK_DYLD_INFO_COUNT;
kern_return_t kr = task_info(task, TASK_DYLD_INFO, (task_info_t)&dyld_info, &size);
if (kr != KERN_SUCCESS) {
fprintf(stderr, "task_info failed: %s\n", mach_error_string(kr));
}
const struct dyld_all_image_infos* infos =
(const struct dyld_all_image_infos*)dyld_info.all_image_info_addr;
printf("version: %d, infos->infoArrayCount: %d\n", infos->version, infos->infoArrayCount);
for(uint32_t i=0; i<infos->infoArrayCount; i++) {
dyld_image_info image = infos->infoArray[i];
const struct mach_header* header = image.imageLoadAddress;
printf("%d ", i);
printf("%p ", (void*)image.imageLoadAddress);
printf("(%x) ", header->magic);
printf("%s\n", image.imageFilePath);
fflush(stdout);
}
printf("\n\n");
printf("infos->uuidArrayCount: %lu\n", infos->uuidArrayCount);
for(uint32_t i=0; i<infos->uuidArrayCount; i++) {
dyld_uuid_info image = infos->uuidArray[i];
const struct mach_header* header = image.imageLoadAddress;
printf("%d ", i);
printf("%p ", (void*)image.imageLoadAddress);
printf("(%x)\n", header->magic);
fflush(stdout);
}
printf("task_info() syscall result processing is completed\n\n");
}
int main(int argc, const char * argv[]) {
performDlOpenDlClose();
performTaskInfoSyscall();
return 0;
}