Comments (2)
jpoimboe
commented on August 19, 2024
This is very similar to the .smp_locks issue, except these relocations are 8 bytes:
Relocation section [73] '.rela__jump_table' for section [72] '__jump_table' at offset 0x11bb0 contains 36 entries:
Offset Type Value Addend Name
000000000000000000 X86_64_64 000000000000000000 +43 .text.call_timer_fn
0x0000000000000008 X86_64_64 000000000000000000 +160 .text.call_timer_fn
0x0000000000000010 X86_64_64 0x0000000000000280 +8 __tracepoint_timer_expire_entry
0x0000000000000018 X86_64_64 000000000000000000 +54 .text.call_timer_fn
0x0000000000000020 X86_64_64 000000000000000000 +112 .text.call_timer_fn
0x0000000000000028 X86_64_64 0x0000000000000240 +8 __tracepoint_timer_expire_exit
0x0000000000000030 X86_64_64 000000000000000000 +257 .text.run_timer_softirq
0x0000000000000038 X86_64_64 000000000000000000 +416 .text.run_timer_softirq
0x0000000000000040 X86_64_64 0x0000000000000200 +8 __tracepoint_timer_cancel
0x0000000000000048 X86_64_64 000000000000000000 +20 .text.init_timer_key
0x0000000000000050 X86_64_64 000000000000000000 +112 .text.init_timer_key
0x0000000000000058 X86_64_64 0x0000000000000300 +8 __tracepoint_timer_init
0x0000000000000060 X86_64_64 000000000000000000 +35 .text.detach_if_pending
0x0000000000000068 X86_64_64 000000000000000000 +128 .text.detach_if_pending
0x0000000000000070 X86_64_64 0x0000000000000200 +8 __tracepoint_timer_cancel
0x0000000000000078 X86_64_64 000000000000000000 +32 .text.migrate_timer_list
0x0000000000000080 X86_64_64 000000000000000000 +120 .text.migrate_timer_list
0x0000000000000088 X86_64_64 0x0000000000000200 +8 __tracepoint_timer_cancel
0x0000000000000090 X86_64_64 000000000000000000 +80 .sched.text
0x0000000000000098 X86_64_64 000000000000000000 +440 .sched.text
0x00000000000000a0 X86_64_64 0x0000000000000300 +8 __tracepoint_timer_init
0x00000000000000a8 X86_64_64 000000000000000000 +237 .sched.text
0x00000000000000b0 X86_64_64 000000000000000000 +504 .sched.text
0x00000000000000b8 X86_64_64 0x00000000000002c0 +8 __tracepoint_timer_start
0x00000000000000c0 X86_64_64 000000000000000000 +115 .text.add_timer_on
0x00000000000000c8 X86_64_64 000000000000000000 +176 .text.add_timer_on
0x00000000000000d0 X86_64_64 0x00000000000002c0 +8 __tracepoint_timer_start
0x00000000000000d8 X86_64_64 000000000000000000 +95 .text.mod_timer_pinned
0x00000000000000e0 X86_64_64 000000000000000000 +232 .text.mod_timer_pinned
0x00000000000000e8 X86_64_64 0x00000000000002c0 +8 __tracepoint_timer_start
0x00000000000000f0 X86_64_64 000000000000000000 +128 .text.mod_timer_pending
0x00000000000000f8 X86_64_64 000000000000000000 +256 .text.mod_timer_pending
0x0000000000000100 X86_64_64 0x00000000000002c0 +8 __tracepoint_timer_start
0x0000000000000108 X86_64_64 000000000000000000 +136 .text.mod_timer
0x0000000000000110 X86_64_64 000000000000000000 +144 .text.mod_timer
0x0000000000000118 X86_64_64 0x00000000000002c0 +8 __tracepoint_timer_start
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sjenning
commented on August 19, 2024
Revised analysis:
__jump_table is a table of struct jump_entry, 24 bytes in size on x86_64, init'ed to 0. All three fields are reloc'ed.
from arch/x86/include/asm/jump_label.h
#ifdef CONFIG_X86_64
typedef u64 jump_label_t;
#else
typedef u32 jump_label_t;
#endif
struct jump_entry {
jump_label_t code;
jump_label_t target;
jump_label_t key;
};
.rela__jump_table looks like this:
Relocation section [73] '.rela__jump_table' for section [72] '__jump_table' at offset 0x11bb0 contains 36 entries:
Offset Type Value Addend Name
000000000000000000 X86_64_64 000000000000000000 +43 .text.call_timer_fn
0x0000000000000008 X86_64_64 000000000000000000 +160 .text.call_timer_fn
0x0000000000000010 X86_64_64 0x0000000000000280 +8 __tracepoint_timer_expire_entry
The "code" and "target" fields point to locations within the function with the tracepoint. The "key" field points to a symbol "__tracepoint_timer_expire_entry" which references the __tracepoints section. There is a _tracepoint* symbol for each tracepoint in the __tracepoints section.
The __tracepoints section, in turn, is a table of struct tracepoints, 64 bytes in size on x86_64, init'ed to 0.
from include/linux/tracepoint.h
struct tracepoint {
const char *name; /* Tracepoint name */
struct static_key key;
void (*regfunc)(void);
void (*unregfunc)(void);
struct tracepoint_func __rcu *funcs;
};
The "name" field is reloc'ed, referencing an offset in a string table contained in the __tracepoints_strings section:
Relocation section [288] '.rela__tracepoints' for section [287] '__tracepoints' at offset 0x14f88 contains 13 entries:
Offset Type Value Addend Name
000000000000000000 X86_64_64 000000000000000000 +0 __tracepoints_strings
0x0000000000000040 X86_64_64 000000000000000000 +10 __tracepoints_strings
0x0000000000000080 X86_64_64 000000000000000000 +24 __tracepoints_strings
...
There are _tpstrtab* symbols pointing to each string in the string in the table.
Additionally there is a __tracepoints_ptrs section that is a table of pointers that reference the struct tracepoints in the __tracepoints section. There are also _tracepoint_ptr* symbols that reference the pointers in __tracepoint_ptrs.
So... this rabbit hole goes much deeper than originally thought.
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