When debugging the JIT on an embedded platform or cross build
environment, libbfd may not be available, making it impossible to run
bpf_jit_disasm natively.
Add an option to emit a binary image of the JIT code to a file. This
file can then be disassembled off line. Typical usage in this case
might be (pasting mips64 dmesg output to cat command):
$ cat > jit.raw
$ bpf_jit_disasm -f jit.raw -O jit.bin
$ mips64-linux-gnu-objdump -D -b binary -m mips:isa64r2 -EB jit.bin
Signed-off-by: David Daney <[email protected]>
---
tools/net/bpf_jit_disasm.c | 40 ++++++++++++++++++++++++++++++++++++----
1 file changed, 36 insertions(+), 4 deletions(-)
diff --git a/tools/net/bpf_jit_disasm.c b/tools/net/bpf_jit_disasm.c
index 544b05a..ad572e6 100644
--- a/tools/net/bpf_jit_disasm.c
+++ b/tools/net/bpf_jit_disasm.c
@@ -229,6 +229,7 @@ static void usage(void)
{
printf("Usage: bpf_jit_disasm [...]\n");
printf(" -o Also display related opcodes (default: off).\n");
+ printf(" -O <file> Write binary image of code to file, don't disassemble to stdout.\n");
printf(" -f <file> Read last image dump from file or stdin (default: klog).\n");
printf(" -h Display this help.\n");
}
@@ -238,12 +239,19 @@ int main(int argc, char **argv)
unsigned int len, klen, opt, opcodes = 0;
static uint8_t image[32768];
char *kbuff, *file = NULL;
+ char *ofile = NULL;
+ int ofd;
+ ssize_t nr;
+ uint8_t *pos;
- while ((opt = getopt(argc, argv, "of:")) != -1) {
+ while ((opt = getopt(argc, argv, "of:O:")) != -1) {
switch (opt) {
case 'o':
opcodes = 1;
break;
+ case 'O':
+ ofile = optarg;
+ break;
case 'f':
file = optarg;
break;
@@ -263,11 +271,35 @@ int main(int argc, char **argv)
}
len = get_last_jit_image(kbuff, klen, image, sizeof(image));
- if (len > 0)
- get_asm_insns(image, len, opcodes);
- else
+ if (len <= 0) {
fprintf(stderr, "No JIT image found!\n");
+ goto done;
+ }
+ if (!ofile) {
+ get_asm_insns(image, len, opcodes);
+ goto done;
+ }
+
+ ofd = open(ofile, O_WRONLY | O_CREAT | O_TRUNC, DEFFILEMODE);
+ if (ofd < 0) {
+ fprintf(stderr, "Could not open file %s for writing: ", ofile);
+ perror(NULL);
+ goto done;
+ }
+ pos = image;
+ do {
+ nr = write(ofd, pos, len);
+ if (nr < 0) {
+ fprintf(stderr, "Could not write data to %s: ", ofile);
+ perror(NULL);
+ goto done;
+ }
+ len -= nr;
+ pos += nr;
+ } while (len);
+ close(ofd);
+done:
put_log_buff(kbuff);
return 0;
}
--
2.9.3
On 04/11/2017 11:30 PM, David Daney wrote:
> When debugging the JIT on an embedded platform or cross build
> environment, libbfd may not be available, making it impossible to run
> bpf_jit_disasm natively.
>
> Add an option to emit a binary image of the JIT code to a file. This
> file can then be disassembled off line. Typical usage in this case
> might be (pasting mips64 dmesg output to cat command):
>
> $ cat > jit.raw
> $ bpf_jit_disasm -f jit.raw -O jit.bin
> $ mips64-linux-gnu-objdump -D -b binary -m mips:isa64r2 -EB jit.bin
>
> Signed-off-by: David Daney <[email protected]>
Seems good, we could at some point also add an -I jit.bin option
if needed for offline analysis/comparison instead of using -f
plain text.
Thanks!
Acked-by: Daniel Borkmann <[email protected]>
On 04/11/2017 02:54 PM, Daniel Borkmann wrote:
> On 04/11/2017 11:30 PM, David Daney wrote:
>> When debugging the JIT on an embedded platform or cross build
>> environment, libbfd may not be available, making it impossible to run
>> bpf_jit_disasm natively.
>>
>> Add an option to emit a binary image of the JIT code to a file. This
>> file can then be disassembled off line. Typical usage in this case
>> might be (pasting mips64 dmesg output to cat command):
>>
>> $ cat > jit.raw
>> $ bpf_jit_disasm -f jit.raw -O jit.bin
>> $ mips64-linux-gnu-objdump -D -b binary -m mips:isa64r2 -EB jit.bin
>>
>> Signed-off-by: David Daney <[email protected]>
>
> Seems good, we could at some point also add an -I jit.bin option
> if needed for offline analysis/comparison instead of using -f
> plain text.
>
FWIW: The objdump incantation in the changelog does just about the same
disassembly as the bpf_jit_disasm internal implementation.
> Thanks!
>
> Acked-by: Daniel Borkmann <[email protected]>
From: David Daney <[email protected]>
Date: Tue, 11 Apr 2017 14:30:52 -0700
> When debugging the JIT on an embedded platform or cross build
> environment, libbfd may not be available, making it impossible to run
> bpf_jit_disasm natively.
>
> Add an option to emit a binary image of the JIT code to a file. This
> file can then be disassembled off line. Typical usage in this case
> might be (pasting mips64 dmesg output to cat command):
>
> $ cat > jit.raw
> $ bpf_jit_disasm -f jit.raw -O jit.bin
> $ mips64-linux-gnu-objdump -D -b binary -m mips:isa64r2 -EB jit.bin
>
> Signed-off-by: David Daney <[email protected]>
Applied, thanks.