From 4a1e885c6d143ff1b557ec7f3fc6ddf39c51502f Mon Sep 17 00:00:00 2001 From: Rong Tao Date: Wed, 12 Apr 2023 16:16:24 +0800 Subject: samples/bpf: sampleip: Replace PAGE_OFFSET with _text address Macro PAGE_OFFSET(0xffff880000000000) in sampleip_user.c is inaccurate, for example, in aarch64 architecture, this value depends on the CONFIG_ARM64_VA_BITS compilation configuration, this value defaults to 48, the corresponding PAGE_OFFSET is 0xffff800000000000, if we use the value defined in sampleip_user.c, then all KSYMs obtained by sampleip are (user) Symbol error due to PAGE_OFFSET error: $ sudo ./sampleip 1 Sampling at 99 Hertz for 1 seconds. Ctrl-C also ends. ADDR KSYM COUNT 0xffff80000810ceb8 (user) 1 0xffffb28ec880 (user) 1 0xffff8000080c82b8 (user) 1 0xffffb23fed24 (user) 1 0xffffb28944fc (user) 1 0xffff8000084628bc (user) 1 0xffffb2a935c0 (user) 1 0xffff80000844677c (user) 1 0xffff80000857a3a4 (user) 1 ... A few examples of addresses in the CONFIG_ARM64_VA_BITS=48 environment in the aarch64 environment: $ sudo head /proc/kallsyms ffff8000080a0000 T _text ffff8000080b0000 t gic_handle_irq ffff8000080b0000 T _stext ffff8000080b0000 T __irqentry_text_start ffff8000080b00b0 t gic_handle_irq ffff8000080b0230 t gic_handle_irq ffff8000080b03b4 T __irqentry_text_end ffff8000080b03b8 T __softirqentry_text_start ffff8000080b03c0 T __do_softirq ffff8000080b0718 T __entry_text_start We just need to replace the PAGE_OFFSET with the address _text in /proc/kallsyms to solve this problem: $ sudo ./sampleip 1 Sampling at 99 Hertz for 1 seconds. Ctrl-C also ends. ADDR KSYM COUNT 0xffffb2892ab0 (user) 1 0xffffb2b1edfc (user) 1 0xffff800008462834 __arm64_sys_ppoll 1 0xffff8000084b87f4 eventfd_read 1 0xffffb28e6788 (user) 1 0xffff8000081e96d8 rcu_all_qs 1 0xffffb2ada878 (user) 1 ... Signed-off-by: Rong Tao Link: https://lore.kernel.org/r/tencent_A0E82E0BEE925285F8156D540731DF805F05@qq.com Signed-off-by: Alexei Starovoitov --- samples/bpf/sampleip_user.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) (limited to 'samples/bpf/sampleip_user.c') diff --git a/samples/bpf/sampleip_user.c b/samples/bpf/sampleip_user.c index 921c505bb567..9283f47844fb 100644 --- a/samples/bpf/sampleip_user.c +++ b/samples/bpf/sampleip_user.c @@ -21,10 +21,10 @@ #define DEFAULT_FREQ 99 #define DEFAULT_SECS 5 #define MAX_IPS 8192 -#define PAGE_OFFSET 0xffff880000000000 static int map_fd; static int nr_cpus; +static long _text_addr; static void usage(void) { @@ -108,7 +108,7 @@ static void print_ip_map(int fd) /* sort and print */ qsort(counts, max, sizeof(struct ipcount), count_cmp); for (i = 0; i < max; i++) { - if (counts[i].ip > PAGE_OFFSET) { + if (counts[i].ip > _text_addr) { sym = ksym_search(counts[i].ip); if (!sym) { printf("ksym not found. Is kallsyms loaded?\n"); @@ -169,6 +169,13 @@ int main(int argc, char **argv) return 2; } + /* used to determine whether the address is kernel space */ + _text_addr = ksym_get_addr("_text"); + if (!_text_addr) { + fprintf(stderr, "ERROR: no '_text' in /proc/kallsyms\n"); + return 3; + } + /* create perf FDs for each CPU */ nr_cpus = sysconf(_SC_NPROCESSORS_ONLN); links = calloc(nr_cpus, sizeof(struct bpf_link *)); -- cgit