add error injection demo

README.md

@@ -121,6 +121,10 @@ More bcc/libbpf-tools examples can be found in [example/libbpf-tools](https://gi
 
 You can also run bpftime with `bpftrace`, we've test it on [this commit](https://github.com/iovisor/bpftrace/commit/75aca47dd8e1d642ff31c9d3ce330e0c616e5b96). More details about how to run bpftrace in usespace, can be found in [example/bpftrace](https://github.com/eunomia-bpf/bpftime/tree/master/example/bpftrace).
 
+### Error injections
+
+- [`error-injection`](https://github.com/eunomia-bpf/bpftime/tree/master/example/error-inject) Inject errors into a userspace function to test its error handling capabilities.
+
 > ⚠️ **Note**: `bpftime` is actively under development, and it's not yet recommended for production use. See our [roadmap](#roadmap) for details. We'd love to hear your feedback and suggestions! Please feel free to open an issue or [Contact us](#contact-and-citations).
 
 ## In-Depth

example/error-inject/.gitignore

@@ -1,2 +1,3 @@
 error_inject
-.output/
+.output/
+victim

example/error-inject/README.md

@@ -0,0 +1,19 @@
+# error-inject
+
+bpftime can allow you override the execution of a function in userspace, and return a value you specify, or error injection in the system call.
+
+It's useful for testing the error handling of your program.
+
+## Run for override userspace function
+
+server
+
+```sh
+LD_PRELOAD=~/.bpftime/libbpftime-syscall-server.so ./error_inject
+```
+
+client
+
+```sh
+LD_PRELOAD=~/.bpftime/libbpftime-agent.so ./victim
+```

example/error-inject/error_inject.bpf.c

@@ -6,8 +6,13 @@
 SEC("uprobe")
 int do_error_inject_patch(struct pt_regs *ctx)
 {
-	bpf_printk("target_func called is overrided.\n");
-	bpf_override_return(ctx, 0);
+	int rand = bpf_get_prandom_u32();
+	if (rand % 2 == 0) {
+		bpf_printk("bpf: Inject error. Target func will not exec.\n");
+		bpf_override_return(ctx, -1);
+		return 0;
+	}
+	bpf_printk("bpf: Continue.\n");
 	return 0;
 }
 

example/error-inject/victim.c

@@ -0,0 +1,23 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+int target_func()
+{
+	int res = open("/dev/null");
+	printf("target_func is running\n");
+	close(res);
+	return 0;
+}
+
+int main(int argc, char *argv[])
+{
+	while (1) {
+		sleep(1);
+		int res = target_func();
+		if (res != 0) {
+			printf("got error %d\n", res);
+		}
+	}
+	return 0;
+}

runtime/src/bpf_helper.cpp

@@ -68,6 +68,11 @@ uint64_t bpftime_probe_read(uint64_t dst, uint64_t size, uint64_t ptr, uint64_t,
 	return 0;
 }
 
+uint64_t bpftime_get_prandom_u32()
+{
+	return (uint32_t)rand();
+}
+
 uint64_t bpftime_ktime_get_coarse_ns(uint64_t, uint64_t, uint64_t, uint64_t,
 				     uint64_t)
 {
@@ -613,6 +618,12 @@ const bpftime_helper_group kernel_helper_group = {
 		    .name = "bpf_trace_printk",
 		    .fn = (void *)bpftime_trace_printk,
 	    } },
+	  { BPF_FUNC_get_prandom_u32,
+	    bpftime_helper_info{
+		    .index = BPF_FUNC_get_prandom_u32,
+		    .name = "bpf_get_prandom_u32",
+		    .fn = (void *)bpftime_get_prandom_u32,
+	    } },
 	  { BPF_FUNC_get_current_pid_tgid,
 	    bpftime_helper_info{
 		    .index = BPF_FUNC_get_current_pid_tgid,
@@ -629,7 +640,7 @@ const bpftime_helper_group kernel_helper_group = {
 		    .name = "bpf_get_current_comm",
 		    .fn = (void *)bpftime_get_current_comm,
 	    } },
-	{ BPF_FUNC_override_return,
+	  { BPF_FUNC_override_return,
 	    bpftime_helper_info{
 		    .index = BPF_FUNC_override_return,
 		    .name = "bpf_override_return",