I found a significant difference in my failing vs. working
armv7 contexts as installed: Presence vs. Lack of a .symtab
entry for the symbol _rtld_get_stack_prot in
/libexec/ld-elf.so.1 .
gdb inspection of operation shows distinctions based on
the difference.
This is related to the code:
(gdb) list 140
135 void
136 _thr_stack_fix_protection(struct pthread *thrd)
137 {
138
139 mprotect((char *)thrd->attr.stackaddr_attr +
140 round_up(thrd->attr.guardsize_attr),
141 round_up(thrd->attr.stacksize_attr),
142 _rtld_get_stack_prot());
143 }
Working context (Personal build):
NOTE THE .symtab ENTRY BELOW. It allows the gdb run to work:
# readelf -a /libexec/ld-elf.so.1 | grep -E "(^[^ 0-9]|.*_rtld_get_stack_prot)"
| less
ELF Header:
Elf file type is DYN (Shared object file)
Entry point 0x14548
There are 10 program headers, starting at offset 52
Program Headers:
There are 24 section headers, starting at offset 0x1f2b8:
Section Headers:
Key to Flags:
Dynamic section at offset 0x199f8 contains 15 entries:
Relocation section (.rel.dyn):
r_offset r_info r_type st_value st_name
Symbol table '.dynsym' contains 27 entries:
5: 000000000001b9ac 16 FUNC GLOBAL DEFAULT 11
_rtld_get_stack_prot@@FBSDprivate_1.0 (11)
Symbol table '.symtab' contains 911 entries:
903: 000000000001b9ac 16 FUNC GLOBAL DEFAULT 11 _rtld_get_stack_prot
Notes at offset 0x00000174 with length 0x00000018:
Histogram for bucket list length (total of 6 buckets):
Histogram for bucket list length (total of 27 buckets):
Version symbol section (.gnu.version):
Version definition section (.gnu.version_d):
Attribute Section: aeabi
File Attributes
Breakpoint 8.3, _thr_stack_fix_protection (thrd=0x2006f000) at
/usr/main-src/lib/libthr/thread/thr_stack.c:139
139 mprotect((char *)thrd->attr.stackaddr_attr +
(gdb) si
141 round_up(thrd->attr.stacksize_attr),
(gdb)
140 round_up(thrd->attr.guardsize_attr),
(gdb)
round_up (size=4096) at /usr/main-src/lib/libthr/thread/thr_stack.c:129
129 if (size % _thr_page_size != 0)
(gdb)
0x201110b8 129 if (size % _thr_page_size != 0)
130 size = ((size / _thr_page_size) + 1) *
(gdb)
0x201110c0 130 size = ((size / _thr_page_size) + 1) *
(gdb)
0x201110c4 in round_up (size=4096) at
/usr/main-src/lib/libthr/thread/thr_stack.c:130
130 size = ((size / _thr_page_size) + 1) *
(gdb)
0x201110c8 130 size = ((size / _thr_page_size) + 1) *
(gdb)
round_up (size=67108864) at /usr/main-src/lib/libthr/thread/thr_stack.c:129
129 if (size % _thr_page_size != 0)
(gdb)
0x201110d0 in round_up (size=4096) at
/usr/main-src/lib/libthr/thread/thr_stack.c:129
129 if (size % _thr_page_size != 0)
(gdb)
0x201110d4 in round_up (size=67108864) at
/usr/main-src/lib/libthr/thread/thr_stack.c:129
129 if (size % _thr_page_size != 0)
(gdb)
0x201110d8 129 if (size % _thr_page_size != 0)
(gdb)
0x201110dc in round_up (size=4096) at
/usr/main-src/lib/libthr/thread/thr_stack.c:129
129 if (size % _thr_page_size != 0)
(gdb)
0x201110e0 129 if (size % _thr_page_size != 0)
(gdb)
_thr_stack_fix_protection (thrd=0x2006f000) at
/usr/main-src/lib/libthr/thread/thr_stack.c:139
139 mprotect((char *)thrd->attr.stackaddr_attr +
(gdb)
142 _rtld_get_stack_prot());
(gdb)
0x20114880 in ?? () from /lib/libthr.so.3
(gdb)
0x20114884 in ?? () from /lib/libthr.so.3
(gdb)
0x20114888 in ?? () from /lib/libthr.so.3
(gdb)
Breakpoint 9.1, _rtld_get_stack_prot () at
/usr/main-src/libexec/rtld-elf/rtld.c:5884
5884 return (stack_prot);
(gdb)
0x2005b9b0 5884 return (stack_prot);
(gdb)
0x2005b9b4 5884 return (stack_prot);
Failing context (Official PkgBase build):
NOTE THE *LACK OF* THE .symtab ENTRY ABOVE. _rtld_bind_start ends
up in use instead, which looks to lead to the gdb run not working.
IN FACT, NOTE THE LACK OF ANY "Symbol table '.symtab' contains"
TEXT AT ALL!
# readelf -a /libexec/ld-elf.so.1 | grep -E "(^[^ 0-9]|.*_rtld_get_stack_prot)"
| less
ELF Header:
Elf file type is DYN (Shared object file)
Entry point 0x147b0
There are 10 program headers, starting at offset 52
Program Headers:
There are 22 section headers, starting at offset 0x1a960:
Section Headers:
Key to Flags:
Dynamic section at offset 0x1a4cc contains 15 entries:
Relocation section (.rel.dyn):
r_offset r_info r_type st_value st_name
Symbol table '.dynsym' contains 27 entries:
5: 000000000001bcd8 16 FUNC GLOBAL DEFAULT 11
_rtld_get_stack_prot@@FBSDprivate_1.0 (11)
Notes at offset 0x00000174 with length 0x00000018:
Histogram for bucket list length (total of 6 buckets):
Histogram for bucket list length (total of 27 buckets):
Version symbol section (.gnu.version):
Version definition section (.gnu.version_d):
Attribute Section: aeabi
File Attributes
Breakpoint 2.3, _thr_stack_fix_protection (thrd=0x20070000) at
/home/pkgbuild/worktrees/main/lib/libthr/thread/thr_stack.c:140
140 round_up(thrd->attr.guardsize_attr),
(gdb) si
139 mprotect((char *)thrd->attr.stackaddr_attr +
(gdb)
141 round_up(thrd->attr.stacksize_attr),
(gdb)
round_up (size=4096) at
/home/pkgbuild/worktrees/main/lib/libthr/thread/thr_stack.c:129
129 if (size % _thr_page_size != 0)
(gdb)
130 size = ((size / _thr_page_size) + 1) *
(gdb)
129 if (size % _thr_page_size != 0)
(gdb)
130 size = ((size / _thr_page_size) + 1) *
(gdb)
0x20112ef8 130 size = ((size / _thr_page_size) + 1) *
(gdb)
0x20116b60 in ?? () from /lib/libthr.so.3
(gdb)
0x20116b64 in ?? () from /lib/libthr.so.3
(gdb)
0x20116b68 in ?? () from /lib/libthr.so.3
(gdb)
0x20116760 in ?? () from /lib/libthr.so.3
(gdb)
0x20116764 in ?? () from /lib/libthr.so.3
(gdb)
0x20116768 in ?? () from /lib/libthr.so.3
(gdb)
0x2011676c in ?? () from /lib/libthr.so.3
(gdb)
_rtld_bind_start () at
/home/pkgbuild/worktrees/main/libexec/rtld-elf/arm/rtld_start.S:78
78 stmdb sp!,{r0-r5,sl,fp}
(gdb) si
80 sub r1, ip, lr /* r1 = 4 * (n + 1) */
(gdb)
81 sub r1, r1, #4 /* r1 = 4 * n */
(gdb)
82 add r1, r1, r1 /* r1 = 8 * n */
(gdb)
84 ldr r0, [lr, #-4] /* get obj ptr from GOT[1] */
(gdb)
85 mov r4, ip /* save GOT location */
(gdb)
87 mov r5, sp /* Save the stack pointer */
(gdb)
88 bic sp, sp, #7 /* Align the stack pointer */
(gdb)
_rtld_bind_start () at
/home/pkgbuild/worktrees/main/libexec/rtld-elf/arm/rtld_start.S:89
89 bl _rtld_bind /* Call the binder */
I have not checked for other .symtab entry problems.
Nor have I figured out why the installed materials are
different for Symbol table '.symtab' . So this is not
yet root-cause information.
===
Mark Millard
marklmi at yahoo.com
