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authorDaniel T. Lee <danieltimlee@gmail.com>2022-12-24 10:15:25 +0300
committerAndrii Nakryiko <andrii@kernel.org>2022-12-30 01:22:34 +0300
commit2e5c4dd7f81545a98e9f06317347e760749c020b (patch)
treebab392fe3292538b735249d3782b80fa97856359 /samples
parentd4fffba4d04b8d605ff07f1ed987399f6af0ad5b (diff)
downloadlinux-2e5c4dd7f81545a98e9f06317347e760749c020b.tar.xz
samples/bpf: Fix tracex2 by using BPF_KSYSCALL macro
Currently, there is a problem with tracex2, as it doesn't print the histogram properly and the results are misleading. (all results report as 0) The problem is caused by a change in arguments of the function to which the kprobe connects. This tracex2 bpf program uses kprobe (attached to __x64_sys_write) to figure out the size of the write system call. In order to achieve this, the third argument 'count' must be intact. The following is a prototype of the sys_write variant. (checked with pfunct) ~/git/linux$ pfunct -P fs/read_write.o | grep sys_write ssize_t ksys_write(unsigned int fd, const char * buf, size_t count); long int __x64_sys_write(const struct pt_regs * regs); ... cross compile with s390x ... long int __s390_sys_write(struct pt_regs * regs); Since the nature of SYSCALL_WRAPPER function wraps the argument once, additional process of argument extraction is required to properly parse the argument. #define BPF_KSYSCALL(name, args...) ... snip ... struct pt_regs *regs = LINUX_HAS_SYSCALL_WRAPPER \ ? (struct pt_regs *)PT_REGS_PARM1(ctx) \ : ctx; \ In order to fix this problem, the BPF_SYSCALL macro has been used. This reduces the hassle of parsing arguments from pt_regs. Since the macro uses the CORE version of argument extraction, additional portability comes too. Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20221224071527.2292-5-danieltimlee@gmail.com
Diffstat (limited to 'samples')
-rw-r--r--samples/bpf/tracex2.bpf.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/samples/bpf/tracex2.bpf.c b/samples/bpf/tracex2.bpf.c
index a712eefc742e..0a5c75b367be 100644
--- a/samples/bpf/tracex2.bpf.c
+++ b/samples/bpf/tracex2.bpf.c
@@ -8,6 +8,7 @@
#include <linux/version.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_core_read.h>
struct {
__uint(type, BPF_MAP_TYPE_HASH);
@@ -76,14 +77,13 @@ struct {
} my_hist_map SEC(".maps");
SEC("ksyscall/write")
-int bpf_prog3(struct pt_regs *ctx)
+int BPF_KSYSCALL(bpf_prog3, unsigned int fd, const char *buf, size_t count)
{
- long write_size = PT_REGS_PARM3(ctx);
long init_val = 1;
long *value;
struct hist_key key;
- key.index = log2l(write_size);
+ key.index = log2l(count);
key.pid_tgid = bpf_get_current_pid_tgid();
key.uid_gid = bpf_get_current_uid_gid();
bpf_get_current_comm(&key.comm, sizeof(key.comm));