[uclibc-ng-devel] Using thread local storage on aarch64

Hi, I was trying to compile a buildroot-2019.02.4 system for an aarch64 platform using gcc 8.3.0 and uClibc-ng-1.0.31. Everything seemed to boot fine, but when I added the ntpd daemon, the daemon kept segfaulting. Some debugging showed, that the segfault happened inside the res_init function, so i made the following test program: ----test_res_init.c---- #include <resolv.h> void main(void) { res_init(); } ----------------------- This program always segfaults as soon as res_init tries to access the _res structure. Some more debugging revealed, that there seems to be a general problem with accessing thread local storage from a dynamicly linked library, so I wrote the following test code: ----test_lib.c---- #include <stdio.h> int ii; __thread int *iip = &ii; void print_ptrs(void) { printf("print_ptrs:\n"); printf("&iip = %p\n", &iip); printf("&ii = %p\n", &ii); printf("iip = %p\n", iip); } ----test_tls.c---- #include <stdio.h> void print_ptrs(void); extern int ii; extern __thread int *iip; void main(void) { printf("main:\n"); printf("&iip = %p\n", &iip); printf("&ii = %p\n", &ii); printf("iip = %p\n", iip); print_ptrs(); } ------------------ When compiling the source linke this: # aarch64-linux-gcc -g -fPIC -c -o test_lib.o test_lib.c # aarch64-linux-gcc -shared -o test_lib.so test_lib.o # aarch64-linux-gcc -g test_tls.c test_lib.so -o test_tls the result looks like this: ------------------------------- # LD_LIBRARY_PATH=/root /root/test_tls main: &iip = 0x7fa0d756d0 &ii = 0x411048 iip = 0x411048 print_ptrs: &iip = 0xff41ac4d90 &ii = 0x411048 [ 7654.009770] test_tls[1942]: unhandled level 0 translation fault (11) at 0xff41ac4d90, esr 0x92000004 [ 7654.018844] pgd = ffffffc07d48c000 [ 7654.027775] [ff41ac4d90] *pgd=0000000000000000 [ 7654.036007] , *pud=0000000000000000 [ 7654.039488] [ 7654.040951] [ 7654.042441] CPU: 2 PID: 1942 Comm: test_tls Not tainted 4.9.0-g196f33d0-dirty #6 [ 7654.049820] Hardware name: xlnx,zynqmp (DT) [ 7654.053981] task: ffffffc05e71ad00 task.stack: ffffffc05d9d4000 [ 7654.059884] PC is at 0x7fa0d4f8f4 [ 7654.063186] LR is at 0x7fa0d4f8ec [ 7654.066478] pc : [<0000007fa0d4f8f4>] lr : [<0000007fa0d4f8ec>] pstate: 60000000 [ 7654.073864] sp : 0000007fe5405170 [ 7654.077148] x29: 0000007fe5405170 x28: 0000000000000000 [ 7654.082442] x27: 0000000000000000 x26: 0000000000000000 [ 7654.087736] x25: 0000000000000000 x24: 0000000000000000 [ 7654.093031] x23: 0000000000000000 x22: 0000000000000000 [ 7654.098326] x21: 0000000000400740 x20: 0000000000000000 [ 7654.103620] x19: 0000000000000000 x18: 0000000000000000 [ 7654.108915] x17: 0000007fa0c8f698 x16: 0000007fa0d60000 [ 7654.114210] x15: 0000000000000001 x14: 0000000000000000 [ 7654.119505] x13: 0000007fa0d77a18 x12: 0000000000000018 [ 7654.124800] x11: 0000000000000001 x10: 0000007fa0d4f517 [ 7654.130095] x9 : 0000007fa0d77a08 x8 : 0000000000000040 [ 7654.135389] x7 : 000000000000000a x6 : 000000000000000a [ 7654.140684] x5 : 0000007fa0d36b6f x4 : 0000007fa0d4f951 [ 7654.145979] x3 : 0000000000000000 x2 : 36bc912578986b49 [ 7654.151274] x1 : 0000007fa0d756c0 x0 : 000000ff41ac4d90 [ 7654.156568] Segmentation fault ------------------------------- Note that the program shows two different addresses for &iip with the latter pointing outside the normal memory map. However the test_tls program works as expected, if you set the LD_BIND_NOW environment variable: ------------------------------- # LD_BIND_NOW=1 LD_LIBRARY_PATH=/root /root/test_tls main: &iip = 0x7f99b606d0 &ii = 0x411048 iip = 0x411048 print_ptrs: &iip = 0x7f99b606d0 &ii = 0x411048 iip = 0x411048 ------------------------------- Unfortunately this trick does not seem to work for either the test_res_init program or the ntpd. Regards, Christoph Mammitzsch