Commit 84a0bd5b2830722cf80ff6ad33ef98101a947e14
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a9fa20a7af
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gdbstub: Optimize kgdb's "thread:" response for the gdb serial protocol
The gdb debugger understands how to parse short versions of the thread
reference string as long as the bytes are paired in sets of two
characters. The kgdb implementation was always sending 8 leading
zeros which could be omitted, and further optimized in the case of
non-negative thread numbers. The negative numbers are used to
reference a specific cpu in the case of kgdb.
An example of the previous i386 stop packet looks like:
T05thread:00000000000003bb;
New stop packet response:
T05thread:03bb;
The previous ThreadInfo response looks like:
m00000000fffffffe,0000000000000001,0000000000000002,0000000000000003,0000000000000004,0000000000000005,0000000000000006,0000000000000007,000000000000000c,0000000000000088,000000000000008a,000000000000008b,000000000000008c,000000000000008d,000000000000008e,00000000000000d4,00000000000000d5,00000000000000dd
New ThreadInfo response:
mfffffffe,01,02,03,04,05,06,07,0c,88,8a,8b,8c,8d,8e,d4,d5,dd
A few bytes saved means better response time when using kgdb over a
serial line.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Showing 1 changed file with 19 additions and 18 deletions Side-by-side Diff
kernel/debug/gdbstub.c
| ... | ... | @@ -367,28 +367,31 @@ |
| 367 | 367 | * remapped to negative TIDs. |
| 368 | 368 | */ |
| 369 | 369 | |
| 370 | -#define BUF_THREAD_ID_SIZE 16 | |
| 370 | +#define BUF_THREAD_ID_SIZE 8 | |
| 371 | 371 | |
| 372 | 372 | static char *pack_threadid(char *pkt, unsigned char *id) |
| 373 | 373 | { |
| 374 | - char *limit; | |
| 374 | + unsigned char *limit; | |
| 375 | + int lzero = 1; | |
| 375 | 376 | |
| 376 | - limit = pkt + BUF_THREAD_ID_SIZE; | |
| 377 | - while (pkt < limit) | |
| 378 | - pkt = pack_hex_byte(pkt, *id++); | |
| 377 | + limit = id + (BUF_THREAD_ID_SIZE / 2); | |
| 378 | + while (id < limit) { | |
| 379 | + if (!lzero || *id != 0) { | |
| 380 | + pkt = pack_hex_byte(pkt, *id); | |
| 381 | + lzero = 0; | |
| 382 | + } | |
| 383 | + id++; | |
| 384 | + } | |
| 379 | 385 | |
| 386 | + if (lzero) | |
| 387 | + pkt = pack_hex_byte(pkt, 0); | |
| 388 | + | |
| 380 | 389 | return pkt; |
| 381 | 390 | } |
| 382 | 391 | |
| 383 | 392 | static void int_to_threadref(unsigned char *id, int value) |
| 384 | 393 | { |
| 385 | - unsigned char *scan; | |
| 386 | - int i = 4; | |
| 387 | - | |
| 388 | - scan = (unsigned char *)id; | |
| 389 | - while (i--) | |
| 390 | - *scan++ = 0; | |
| 391 | - put_unaligned_be32(value, scan); | |
| 394 | + put_unaligned_be32(value, id); | |
| 392 | 395 | } |
| 393 | 396 | |
| 394 | 397 | static struct task_struct *getthread(struct pt_regs *regs, int tid) |
| ... | ... | @@ -601,7 +604,7 @@ |
| 601 | 604 | { |
| 602 | 605 | struct task_struct *g; |
| 603 | 606 | struct task_struct *p; |
| 604 | - unsigned char thref[8]; | |
| 607 | + unsigned char thref[BUF_THREAD_ID_SIZE]; | |
| 605 | 608 | char *ptr; |
| 606 | 609 | int i; |
| 607 | 610 | int cpu; |
| ... | ... | @@ -621,8 +624,7 @@ |
| 621 | 624 | for_each_online_cpu(cpu) { |
| 622 | 625 | ks->thr_query = 0; |
| 623 | 626 | int_to_threadref(thref, -cpu - 2); |
| 624 | - pack_threadid(ptr, thref); | |
| 625 | - ptr += BUF_THREAD_ID_SIZE; | |
| 627 | + ptr = pack_threadid(ptr, thref); | |
| 626 | 628 | *(ptr++) = ','; |
| 627 | 629 | i++; |
| 628 | 630 | } |
| ... | ... | @@ -631,8 +633,7 @@ |
| 631 | 633 | do_each_thread(g, p) { |
| 632 | 634 | if (i >= ks->thr_query && !finished) { |
| 633 | 635 | int_to_threadref(thref, p->pid); |
| 634 | - pack_threadid(ptr, thref); | |
| 635 | - ptr += BUF_THREAD_ID_SIZE; | |
| 636 | + ptr = pack_threadid(ptr, thref); | |
| 636 | 637 | *(ptr++) = ','; |
| 637 | 638 | ks->thr_query++; |
| 638 | 639 | if (ks->thr_query % KGDB_MAX_THREAD_QUERY == 0) |
| ... | ... | @@ -851,7 +852,7 @@ |
| 851 | 852 | memset(remcom_out_buffer, 0, sizeof(remcom_out_buffer)); |
| 852 | 853 | |
| 853 | 854 | if (kgdb_connected) { |
| 854 | - unsigned char thref[8]; | |
| 855 | + unsigned char thref[BUF_THREAD_ID_SIZE]; | |
| 855 | 856 | char *ptr; |
| 856 | 857 | |
| 857 | 858 | /* Reply to host that an exception has occurred */ |