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Change os_unfair_lock calls to use a dispatch queue instead. #837

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Oct 12, 2020
Merged

Change os_unfair_lock calls to use a dispatch queue instead. #837

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94 changes: 10 additions & 84 deletions Bugsnag/KSCrash/Source/KSCrash/Recording/Tools/BSG_KSMachHeaders.m
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Original file line number Diff line number Diff line change
Expand Up @@ -11,82 +11,12 @@
#import <Foundation/Foundation.h>
#import "BSG_KSDynamicLinker.h"
#import "BSG_KSMachHeaders.h"
#import "BugsnagPlatformConditional.h"

// MARK: - Locking

static const NSOperatingSystemVersion minSdkForUnfairLock =
#if BSG_PLATFORM_IOS
{10,0,0};
#elif BSG_PLATFORM_OSX
{10,12,0};
#elif BSG_PLATFORM_TVOS
{10,0,0};
#elif BSG_PLATFORM_WATCHOS
{3,0,0}
#endif

// Pragma's hide unavoidable (and expected) deprecation/unavailable warnings
_Pragma("clang diagnostic push")
_Pragma("clang diagnostic ignored \"-Wunguarded-availability\"")
static os_unfair_lock bsg_mach_binary_images_access_lock_unfair = OS_UNFAIR_LOCK_INIT;
_Pragma("clang diagnostic pop")

_Pragma("clang diagnostic push")
_Pragma("clang diagnostic ignored \"-Wdeprecated-declarations\"")
static OSSpinLock bsg_mach_binary_images_access_lock_spin = OS_SPINLOCK_INIT;
_Pragma("clang diagnostic pop")

// Lock helpers. These use bulky Pragmas to hide warnings so are in their own functions for clarity.

void bsg_spin_lock() {
_Pragma("clang diagnostic push")
_Pragma("clang diagnostic ignored \"-Wdeprecated-declarations\"")
OSSpinLockLock(&bsg_mach_binary_images_access_lock_spin);
_Pragma("clang diagnostic pop")
}

void bsg_spin_unlock() {
_Pragma("clang diagnostic push")
_Pragma("clang diagnostic ignored \"-Wdeprecated-declarations\"")
OSSpinLockUnlock(&bsg_mach_binary_images_access_lock_spin);
_Pragma("clang diagnostic pop")
}

void bsg_unfair_lock() {
_Pragma("clang diagnostic push")
_Pragma("clang diagnostic ignored \"-Wunguarded-availability\"")
os_unfair_lock_lock(&bsg_mach_binary_images_access_lock_unfair);
_Pragma("clang diagnostic pop")
}

void bsg_unfair_unlock() {
_Pragma("clang diagnostic push")
_Pragma("clang diagnostic ignored \"-Wunguarded-availability\"")
os_unfair_lock_unlock(&bsg_mach_binary_images_access_lock_unfair);
_Pragma("clang diagnostic pop")
}

void bsg_mach_headers_cache_lock() {
if ([[NSProcessInfo processInfo] isOperatingSystemAtLeastVersion:minSdkForUnfairLock]) {
bsg_unfair_lock();
} else {
bsg_spin_lock();
}
}

void bsg_mach_headers_cache_unlock() {
if ([[NSProcessInfo processInfo] isOperatingSystemAtLeastVersion:minSdkForUnfairLock]) {
bsg_unfair_unlock();
} else {
bsg_spin_unlock();
}
}

// MARK: - Mach Header Linked List

static BSG_Mach_Header_Info *bsg_g_mach_headers_images_head;
static BSG_Mach_Header_Info *bsg_g_mach_headers_images_tail;
static dispatch_queue_t bsg_g_serial_queue;

BSG_Mach_Header_Info *bsg_mach_headers_get_images() {
return bsg_g_mach_headers_images_head;
Expand All @@ -103,6 +33,7 @@ void bsg_mach_headers_initialize() {

bsg_g_mach_headers_images_head = NULL;
bsg_g_mach_headers_images_tail = NULL;
bsg_g_serial_queue = dispatch_queue_create("com.bugsnag.mach-headers", DISPATCH_QUEUE_SERIAL);
}

void bsg_mach_headers_register_for_changes() {
Expand Down Expand Up @@ -190,24 +121,19 @@ bool bsg_mach_headers_populate_info(const struct mach_header *header, intptr_t s
}

void bsg_mach_headers_add_image(const struct mach_header *header, intptr_t slide) {

BSG_Mach_Header_Info *newImage = malloc(sizeof(BSG_Mach_Header_Info));
if (newImage != NULL) {
if (bsg_mach_headers_populate_info(header, slide, newImage)) {

bsg_mach_headers_cache_lock();

if (bsg_g_mach_headers_images_head == NULL) {
bsg_g_mach_headers_images_head = newImage;
} else {
bsg_g_mach_headers_images_tail->next = newImage;
}
bsg_g_mach_headers_images_tail = newImage;

bsg_mach_headers_cache_unlock();
dispatch_sync(bsg_g_serial_queue, ^{
if (bsg_g_mach_headers_images_head == NULL) {
bsg_g_mach_headers_images_head = newImage;
} else {
bsg_g_mach_headers_images_tail->next = newImage;
}
bsg_g_mach_headers_images_tail = newImage;
});
}
}

}

/**
Expand Down
8 changes: 8 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,6 +1,14 @@
Changelog
=========

## TBD

## Bug fixes

* Changed synchronization method when responding to dynamic library image events
to a dispatch queue, which is a more bulletproof and battle-hardened approach.
[837](https://github.com/bugsnag/bugsnag-cocoa/pull/837)

## 6.2.0 (2020-10-07)

### Enhancements
Expand Down