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GC_init segfaults if called from asm code on Linux/x86_64 #654

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gyps opened this issue Aug 13, 2024 · 2 comments
Open

GC_init segfaults if called from asm code on Linux/x86_64 #654

gyps opened this issue Aug 13, 2024 · 2 comments

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@gyps
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gyps commented Aug 13, 2024

Dear all,
Since I'm currently writing a compiler for a functional language I thought about using bdwgc as a garbage collector.
Since the compiler generates code for the x86_64 plattform (using nasm as assembler) I wanted to use the GC in assembler code directly, avoiding parts written in C/C++. So far it worked well but today I dicovered a strange phenomenon: the following code works fine:

extern  GC_malloc, GC_init, exit

section .text
	global main

main:
	push rbp
	call GC_init
	pop rbp
	mov edi, 0 
	call exit

while

extern  GC_malloc, GC_init, exit

section .text
	global main

main:
	push rbp
	push rbp
	call GC_init
	pop rbp
	pop rbp
	mov edi, 0 
	call exit

segfaults. How can pushing and popping rbp to/from the stack twice can influence the behavior of GC_init? Or am I calling it completely wrong?

The commands used to assemble the program are:

$ nasm -o test_gc.o -f elf64 test_gc.asm
$ gcc -o test_gc test_gc.o -lgc
$ ./test_gc
@ivmai ivmai changed the title Usage of GC in assmbler code Aug 13, 2024
@ivmai
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ivmai commented Aug 13, 2024

Sorry, I cannot compile/test your sample at this moment. Would be nice if you dig into the crash details and provide more information - e.g. does it segfaults during initial collection or when detecting stack bottom? (I am assuming you are using fresh bdwgc master.)
@gyps
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gyps commented Aug 14, 2024 •
edited
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I have a guix-Linux distribution with libgc version 8.2.2 installed.
I just checked out the current code, compiled it via autogen/configure and rebuild my test using gcc -L./bdwgc/.libs -o test2_gc test2_gc.o -lgc. This should have used the newly build library but the effect is still the same. I debuged this version using gdb and the error appears in the function GC_get_main_stack_base() where something goes wrong in if (pthread_getattr_np(pthread_self(), &attr) == 0). I attached the (Sorry) very long trace of a gdb session until it actually breaks.

(gdb) start
Temporary breakpoint 1 at 0x401140
Starting program: /home/aster/src/test2_gc 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/gnu/store/ln6hxqjvz6m9gdd9s97pivlqck7hzs99-glibc-2.35/lib/libthread_db.so.1".

Temporary breakpoint 1, 0x0000000000401140 in main ()
(gdb) step
Single stepping until exit from function main,
which has no line number information.
GC_init () at extra/../misc.c:995
995         if (EXPECT(GC_is_initialized, TRUE)) return;
(gdb) 
989     GC_API void GC_CALL GC_init(void)
(gdb) 
GC_init () at extra/../misc.c:1011
1011        DISABLE_CANCEL(cancel_state);
(gdb) 
1072        GC_setpagesize();
(gdb) 
GC_setpagesize () at extra/../os_dep.c:814
814           GC_page_size = (size_t)GETPAGESIZE();
(gdb) 
816             if (0 == GC_page_size)
(gdb) 
827             if (((GC_page_size-1) & GC_page_size) != 0)
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
831             log_pgsize++;
(gdb) 
830           for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
(gdb) 
832           GC_log_pagesize = log_pgsize;
(gdb) 
GC_init () at extra/../misc.c:1085
1085            if (0 != GETENV("GC_PRINT_VERBOSE_STATS")) {
(gdb) 
1087            } else if (0 != GETENV("GC_PRINT_STATS")) {
(gdb) 
1096              const char *fname = TRUSTED_STRING(GETENV("GC_LOG_FILE"));
(gdb) 
1101                if (0 != fname)
(gdb) 
1134          if (0 != GETENV("GC_DUMP_REGULARLY")) {
(gdb) 
1148        if (0 != GETENV("GC_FIND_LEAK")) {
(gdb) 
1152          if (0 != GETENV("GC_FINDLEAK_DELAY_FREE")) {
(gdb) 
1156        if (0 != GETENV("GC_ALL_INTERIOR_POINTERS")) {
(gdb) 
1159        if (0 != GETENV("GC_DONT_GC")) {
(gdb) 
1167        if (0 != GETENV("GC_PRINT_BACK_HEIGHT")) {
(gdb) 
1170        if (0 != GETENV("GC_NO_BLACKLIST_WARNING")) {
(gdb) 
1174          const char *str = GETENV("GC_TRACE");
(gdb) 
1176          if (str != NULL) {
(gdb) 
1202            const char *str = GETENV("GC_PAUSE_TIME_TARGET");
(gdb) 
1204            if (str != NULL) {
(gdb) 
1215            const char *str = GETENV("GC_FULL_FREQUENCY");
(gdb) 
1217            if (str != NULL) {
(gdb) 
1226          char const *str = GETENV("GC_LARGE_ALLOC_WARN_INTERVAL");
(gdb) 
1228          if (str != NULL) {
(gdb) 
1240            const char *str = GETENV("GC_FREE_SPACE_DIVISOR");
(gdb) 
1242            if (str != NULL) {
(gdb) 
1251            const char *str = GETENV("GC_UNMAP_THRESHOLD");
(gdb) 
1253            if (str != NULL) {
(gdb) 
1266            const char *str = GETENV("GC_FORCE_UNMAP_ON_GCOLLECT");
(gdb) 
1268            if (str != NULL) {
(gdb) 
1278            const char *str = GETENV("GC_USE_ENTIRE_HEAP");
(gdb) 
1280            if (str != NULL) {
(gdb) 
1291          GET_TIME(GC_init_time);
(gdb) 
1293        maybe_install_looping_handler();
(gdb) 
maybe_install_looping_handler () at extra/../misc.c:822
822         if (!installed_looping_handler && 0 != GETENV("GC_LOOP_ON_ABORT")) {
(gdb) 
824           installed_looping_handler = TRUE;
(gdb) 
GC_init () at extra/../misc.c:1296
1296          if (EXTRA_BYTES != 0)
(gdb) 
1297            GC_obj_kinds[NORMAL].ok_descriptor
(gdb) 
1300        GC_exclude_static_roots_inner(beginGC_arrays, endGC_arrays);
(gdb) 
GC_exclude_static_roots_inner (start=start@entry=0x7ffff7f80aa0 <GC_arrays> "", finish=finish@entry=0x7ffff7fad4b0 <GC_no_dls> "")
    at extra/../mark_rts.c:609
609         next = GC_next_exclusion(start);
(gdb) 
GC_next_exclusion (start_addr=start_addr@entry=0x7ffff7f80aa0 <GC_arrays> "") at extra/../mark_rts.c:582
582         if (EXPECT(0 == GC_excl_table_entries, FALSE)) return NULL;
(gdb) 
GC_exclude_static_roots_inner (start=start@entry=0x7ffff7f80aa0 <GC_arrays> "", finish=finish@entry=0x7ffff7fad4b0 <GC_no_dls> "")
    at extra/../mark_rts.c:610
610         if (next != NULL) {
(gdb) 
626         next_index = GC_excl_table_entries;
(gdb) 
627         if (next_index >= MAX_EXCLUSIONS) ABORT("Too many exclusions");
(gdb) 
640         GC_excl_table[next_index].e_start = start;
(gdb) 
641         GC_excl_table[next_index].e_end = finish;
(gdb) 
642         ++GC_excl_table_entries;
(gdb) 
GC_init () at extra/../misc.c:1301
1301        GC_exclude_static_roots_inner(beginGC_obj_kinds, endGC_obj_kinds);
(gdb) 
GC_exclude_static_roots_inner (start=start@entry=0x7ffff7f805c0 <GC_obj_kinds> "\200\024\370\367\377\177", finish=finish@entry=0x7ffff7f80a40 "")
    at extra/../mark_rts.c:609
609         next = GC_next_exclusion(start);
(gdb) 
GC_next_exclusion (start_addr=start_addr@entry=0x7ffff7f805c0 <GC_obj_kinds> "\200\024\370\367\377\177") at extra/../mark_rts.c:582
582         if (EXPECT(0 == GC_excl_table_entries, FALSE)) return NULL;
(gdb) 
583         high = GC_excl_table_entries - 1;
(gdb) 
584         while (high > low) {
(gdb) 
594         if (ADDR_GE(start_addr, GC_excl_table[low].e_end)) return NULL;
(gdb) 
596         return GC_excl_table + low;
(gdb) 
GC_exclude_static_roots_inner (start=start@entry=0x7ffff7f805c0 <GC_obj_kinds> "\200\024\370\367\377\177", finish=finish@entry=0x7ffff7f80a40 "")
    at extra/../mark_rts.c:610
610         if (next != NULL) {
(gdb) 
611           if (ADDR_LT(next -> e_start, finish)) {
(gdb) 
615           if (ADDR(next -> e_start) == ADDR(finish)) {
(gdb) 
626         next_index = GC_excl_table_entries;
(gdb) 
627         if (next_index >= MAX_EXCLUSIONS) ABORT("Too many exclusions");
(gdb) 
631           next_index = (size_t)(next - GC_excl_table);
(gdb) 
632           for (i = GC_excl_table_entries; i > next_index; --i) {
(gdb) 
640         GC_excl_table[next_index].e_start = start;
(gdb) 
641         GC_excl_table[next_index].e_end = finish;
(gdb) 
642         ++GC_excl_table_entries;
(gdb) 
GC_init () at extra/../misc.c:1315
1315          if (GC_stackbottom == 0) {
(gdb) 
1316            GC_stackbottom = GC_get_main_stack_base();
(gdb) 
GC_get_main_stack_base () at extra/../os_dep.c:1310
1310            if (pthread_getattr_np(pthread_self(), &attr) == 0)
(gdb) 

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7d939b6 in __vfscanf_internal () from /gnu/store/ln6hxqjvz6m9gdd9s97pivlqck7hzs99-glibc-2.35/lib/libc.so.6
(gdb)
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@ivmai @gyps