On 01/15, Song, Yoong Siang wrote:
On Wednesday, January 15, 2025 10:57 PM, Daniel Borkmann daniel@iogearbox.net wrote:
On 1/14/25 4:27 PM, Song Yoong Siang wrote: [...]
- /* Add mqprio qdisc with TC and hardware queue one-to-one mapping */
- char map[256] = {0};
- char queues[256] = {0};
- for (i = 0; i < rxq; i++) {
char buf[8];snprintf(buf, sizeof(buf), "%d ", i);strcat(map, buf);snprintf(buf, sizeof(buf), "1@%d ", i);strcat(queues, buf);- }
- run_command("sudo tc qdisc add dev %s handle 8001: parent root mqprio
num_tc %d map %s queues %s hw 0",
ifname, rxq, map, queues);Fyi, above triggers selftest build errors:
xdp_hw_metadata.c: In function ‘main’: xdp_hw_metadata.c:763:45: error: ‘%d’ directive output may be truncated writing between 1 and 10 bytes into a region of size 8 [-Werror=format- truncation=] 763 | snprintf(buf, sizeof(buf), "%d ", i); | ^~ TEST-OBJ [test_progs] arg_parsing.test.o xdp_hw_metadata.c:763:44: note: directive argument in the range [0, 2147483646] 763 | snprintf(buf, sizeof(buf), "%d ", i); | ^~~~~ xdp_hw_metadata.c:763:17: note: ‘snprintf’ output between 3 and 12 bytes into a destination of size 8 763 | snprintf(buf, sizeof(buf), "%d ", i); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ xdp_hw_metadata.c:766:47: error: ‘%d’ directive output may be truncated writing between 1 and 10 bytes into a region of size 6 [-Werror=format- truncation=] 766 | snprintf(buf, sizeof(buf), "1@%d ", i); | ^~ xdp_hw_metadata.c:766:44: note: directive argument in the range [0, 2147483646] 766 | snprintf(buf, sizeof(buf), "1@%d ", i); | ^~~~~~~ xdp_hw_metadata.c:766:17: note: ‘snprintf’ output between 5 and 14 bytes into a destination of size 8 766 | snprintf(buf, sizeof(buf), "1@%d ", i); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Thanks for pointing this out. Btw, do you know which build command will trigger these errors? I am using "make -C tools/testing/selftests/bpf" but cannot reproduce the build error.
Thanks & Regards Siang
Last time I used the following to reproduce similar issues on my side:
make -C tools/testing/selftests TARGETS="bpf" LLVM=1 USERCFLAGS="-Wformat-truncation"
You can also try to use something like asprintf instead of managing the buffer sizes manually.