Compile error after changing examples/uretprobe 's target from amd64 to arm64.

[xiaoziv]

In file examples/uretprobe/main.go, I changed the code //go:build amd64 to //go:build arm64 in line 5, and change the target parameter from -target amd64 to -target arm64.

Error occurs when I rerun the go generate command, here is the error:

uretprobe git:(main) ✗ go generate
/Volumes/TuyaExt/work/github/ebpf/examples/uretprobe/uretprobe.c:26:58: error: incomplete definition of type 'struct user_pt_regs'
        bpf_probe_read(&event.line, sizeof(event.line), (void *)PT_REGS_RC(ctx));
                                                                ^~~~~~~~~~~~~~~
../headers/bpf_tracing.h:209:46: note: expanded from macro 'PT_REGS_RC'
#define PT_REGS_RC(x) (((PT_REGS_ARM64 *)(x))->regs[0])
                       ~~~~~~~~~~~~~~~~~~~~~~^
/Volumes/TuyaExt/work/github/ebpf/examples/uretprobe/uretprobe.c:26:58: note: forward declaration of 'struct user_pt_regs'
../headers/bpf_tracing.h:209:26: note: expanded from macro 'PT_REGS_RC'
#define PT_REGS_RC(x) (((PT_REGS_ARM64 *)(x))->regs[0])
                         ^
../headers/bpf_tracing.h:200:45: note: expanded from macro 'PT_REGS_ARM64'
#define PT_REGS_ARM64 const volatile struct user_pt_regs
                                            ^
1 error generated.
Error: can't execute clang: exit status 1
exit status 1
main.go:25: running "go": exit status 1

Does something wrong with the definition of PT_REGS_RC in arm64 architecture in headers/bpf_tracing.h file?

[florianl]

In examples/headers/bpf_tracing.h you see, that arm64 uses user_pt_regs instead of pt_regs.

ebpf/examples/headers/bpf_tracing.h

Lines 198 to 200 in 01ebd4c

	/* arm64 provides struct user_pt_regs instead of struct pt_regs to userspace */
	struct pt_regs;
	#define PT_REGS_ARM64 const volatile struct user_pt_regs

But in examples/headers/common.h only struct pt_regs for aarch64 is defined.

ebpf/examples/headers/common.h

Lines 113 to 114 in 01ebd4c

	#if defined(__TARGET_ARCH_x86)
	struct pt_regs {

The definition for struct user_pt_regs on arm64 is not provided in the headers. Overall, I think, the examples do have a focus on aarch64.

[xiaoziv]

Sorry for my unfamiliarity with the c macro code.
I want to use PT_REGS_RC to extract return value of kretprobe, the code may like

SEC("kretprobe/tcp_sendpage")
int kretprobe__tcp_sendpage(struct pt_regs *ctx)
{
    int size = PT_REGS_RC(ctx);
    if (size > 0)
        return tcp_sendstat(size);
    else
        return 0;
}

Furthermore, I want to compile the code into both x86 and arm64 architecture.
Is there any way to approach this as PT_REGS_RC doesn't work well in arm64?

[xiaoziv]

I have solved this problem by appending the following snippet to headers/common.h.
@florianl thanks.

#if defined(__TARGET_ARCH_arm64)
struct user_pt_regs {
	__u64		regs[31];
	__u64		sp;
	__u64		pc;
	__u64		pstate;
};
struct pt_regs {
	union {
		struct user_pt_regs user_regs;
		struct {
			u64 regs[31];
			u64 sp;
			u64 pc;
			u64 pstate;
		};
	};
	u64 orig_x0;
#ifdef __AARCH64EB__
	u32 unused2;
	s32 syscallno;
#else
	s32 syscallno;
	u32 unused2;
#endif
	u64 sdei_ttbr1;
	/* Only valid when ARM64_HAS_GIC_PRIO_MASKING is enabled. */
	u64 pmr_save;
	u64 stackframe[2];

	/* Only valid for some EL1 exceptions. */
	u64 lockdep_hardirqs;
	u64 exit_rcu;
};
#endif