What does SEGV_ACCERR mean?

Question

I am examining a few crashes that all have the signal SIGSEGV with the reason SEGV_ACCERR. After searching for SEGV_ACCERR, the closest thing I have found to a human readable explanation is: Invalid Permissions for object

What does this mean in a more general sense? When would a SEGV_ACCERR arise? Is there more specific documentation on this reason?

Answer 1

This is an error that I have mostly seen on 64 bit iOS devices and can happen if multiple threads read and change a variable under ARC. For example, I fixed a crash today where multiple background threads were reading and using a static NSDate and NSString variable and updating them without doing any kind of locking or queueing.

Using core data objects on multiple threads can also cause this crash, as I have seen many times in my crash logs.

I also use Crittercism, and this particular crash was a SEGV_ACCERR that only affected 64 bit devices.

Answer 2

As stated in the man page of sigaction, SEGV_ACCERR is a signal code for SIGSEGV that specifies Invalid permissions for mapped object. Contrary to SEGV_MAPERR which means that the address is not mapped to a valid object, SEGV_ACCERR means the address matches an object, but for sure it is neither the good one, nor one the process is allowed to access.

Answer 3

I've seen this in cases where code tries to execute from places other than "text".

For eg, if your pointer is pointing to a function in heap or stack and you try to execute that code (from heap or stack), the CPU throws this exception.

Answer 4

It's possible to get a SEGV_ACCERR because of a stack overflow. Specifically, this happened to me on Android ARM64 with the following:

VeryLargeStruct s;
s = {}; // SEGV_ACCERR

It seems that the zero-initialization created a temporary that caused a stack overflow. This only happened with -O0; presumably the temporary was optimized away at higher optimization levels.

Answer 5

On android arm64 if stack.cpp contains:

struct VeryLargeStruct  {
    int array[4096*4096];
    };
int main() {
    struct VeryLargeStruct s;
    s = {}; 
    }

and typing:

aarch64-linux-android26-clang++  -std=c++20 -g -DANDROID_STL=c++_static -static-libstdc++ stack.cpp -o stack
adb push stack /data/local/tmp
adb shell  /data/local/tmp/stack

/data/tombstones/tombstone_01 contains a SEGV_MAPERR, not SEGV_ACCERR:

id: 11363, tid: 11363, name: stack  >>> /data/local/tmp/stack <<<
signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x7ff2d02dd8

I get SEGV_ACCERR, when const.c contains:

int main() {
    char *str="hello";
    str[0]='H';
    }

Then /data/tombstones/tombstone_00 contains:

pid: 9844, tid: 9844, name: consts  >>> /data/local/tmp/consts <<<
Signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 0x55d10674e8