compile error on LD_PRELOAD version

[zcuder]

following instructions by https://cloud.tencent.com/developer/article/2278480 using branch dev
But got compile errors:
./ff_declare_syscalls.h:25:22: error: conflicting types for ‘ioctl’; have ‘int(int, long unsigned int, long unsigned int)’
25 | FF_SYSCALL_DECL(int, ioctl, (int, unsigned long, unsigned long));
| ^~~~~
ff_hook_syscall.c:37:28: note: in definition of macro ‘strong_alias’
37 | extern __typeof (name) aliasname attribute ((alias (#name)));
| ^~~~~~~~~
./ff_declare_syscalls.h:25:1: note: in expansion of macro ‘FF_SYSCALL_DECL’
25 | FF_SYSCALL_DECL(int, ioctl, (int, unsigned long, unsigned long));
| ^~~~~~~~~~~~~~~
In file included from /usr/include/sys/epoll.h:22,
from ff_hook_syscall.c:4:
/usr/include/sys/ioctl.h:42:12: note: previous declaration of ‘ioctl’ with type ‘int(int, long unsigned int, ...)’
42 | extern int ioctl (int __fd, unsigned long int __request, ...) __THROW;
| ^~~~~
make: *** [Makefile:129: ff_hook_syscall.o] Error 1
uname -r
5.15.178-120.180.amzn2.x86_64

It looks to me ioctl has always been variable paramerters. int ioctl (int __fd, unsigned long int __request, ...) https://man7.org/linux/man-pages/man2/ioctl.2.html
I am wondering how actually does this work, and any expert could help fix this?

[jfb8856606]

Thank you for the detailed report!

Root Cause Analysis:

The compile error is caused by a type conflict in adapter/syscall/ff_declare_syscalls.h:

// Current declaration in f-stack (fixed args):
FF_SYSCALL_DECL(int, ioctl, (int, unsigned long, unsigned long));

// glibc standard declaration (variadic):
extern int ioctl (int __fd, unsigned long int __request, ...) __THROW;

The strong_alias macro expands this into a function declaration with fixed parameters (int, unsigned long, unsigned long), which conflicts with glibc's variadic ioctl(int, unsigned long, ...).

Newer GCC versions (especially on Amazon Linux 2 / kernel 5.15+) enforce stricter type-checking for __attribute__((alias(...))), causing this error to surface.

Current Status:

This issue has not yet been fixed in the dev branch. The ff_declare_syscalls.h file was last modified on 2025-06-08 (only added select support), but the ioctl declaration remains unchanged.

Suggested Fix:

Since ioctl is truly variadic in practice, the cleanest fix is to handle it separately rather than through FF_SYSCALL_DECL. One approach:

1. Remove ioctl from ff_declare_syscalls.h
2. Declare the alias manually using a wrapper that matches the variadic signature, e.g.:

// In ff_hook_syscall.c, replace the macro-generated alias with:
int ioctl(int fd, unsigned long req, ...) __attribute__((alias("ff_hook_ioctl")));

Or alternatively, change ff_hook_ioctl to also be variadic and use va_arg to extract the third argument.

Workaround (temporary):

If you need to compile immediately, you can comment out the ioctl line in ff_declare_syscalls.h and manually add an alias declaration with variadic signature.

We will track this for a proper fix. Thanks again for the report!

[jfb8856606]

Fix Available — PR #1047

A fix has been submitted in PR #1047.

Root Cause (clarified)

The error is environment-dependent. It triggers when sys/ioctl.h is pulled in transitively (via epoll.h or other headers) before the strong_alias macro expansion in ff_hook_syscall.c.

• On older glibc (≤ 2.26, e.g. Amazon Linux 2): epoll.h indirectly includes ioctl.h, so ioctl is already declared as variadic when FF_SYSCALL_DECL(int, ioctl, ...) expands → compile error.
• On newer glibc (≥ 2.38, e.g. TencentOS/Ubuntu 22+): epoll.h does not include ioctl.h → no conflict → compiles fine.

The underlying issue is that ioctl(2) has a variadic signature in glibc:

extern int ioctl(int __fd, unsigned long int __request, ...) __THROW;

but ff_declare_syscalls.h registered it as a fixed-arg function, which is incompatible with strong_alias / __typeof on systems where the variadic declaration is already visible.

Fix Summary (4 files)

File	Change
ff_declare_syscalls.h	Remove FF_SYSCALL_DECL(int, ioctl, ...)
ff_hook_syscall.c	Add explicit variadic ioctl() wrapper using va_arg, forwarding to ff_hook_ioctl()
ff_linux_syscall.h	Add explicit declaration of ff_linux_ioctl()
ff_linux_syscall.c	Add manual pf_ioctl struct member and dlsym("ioctl") load

Temporary Workaround

If you need to compile immediately before the PR is merged, add #include <sys/ioctl.h> at the top of your application and apply a local patch removing the ioctl line from ff_declare_syscalls.h.

[jfb8856606]

Fix Available — PR #1048

PR #1047 was closed due to incorrect base branch. The correct fix is in PR #1048.

Root Cause (clarified)

The error is environment-dependent. It triggers when sys/ioctl.h is pulled in transitively (via epoll.h or other headers) before the strong_alias macro expansion in ff_hook_syscall.c.

• On older glibc (≤ 2.26, e.g. Amazon Linux 2): epoll.h indirectly includes ioctl.h, so ioctl is already declared as variadic when FF_SYSCALL_DECL(int, ioctl, ...) expands → compile error.
• On newer glibc (≥ 2.38, e.g. TencentOS/Ubuntu 22+): epoll.h does not include ioctl.h → no conflict → compiles fine.

The underlying issue is that ioctl(2) has a variadic signature in glibc:

extern int ioctl(int __fd, unsigned long int __request, ...) __THROW;

but ff_declare_syscalls.h registered it as a fixed-arg function, which is incompatible with strong_alias / __typeof on systems where the variadic declaration is already visible.

Fix Summary (4 files)

File	Change
ff_declare_syscalls.h	Remove FF_SYSCALL_DECL(int, ioctl, ...)
ff_hook_syscall.c	Add explicit variadic ioctl() wrapper using va_arg, forwarding to ff_hook_ioctl()
ff_linux_syscall.h	Add explicit declaration of ff_linux_ioctl()
ff_linux_syscall.c	Add manual pf_ioctl struct member and dlsym("ioctl") load

Temporary Workaround

If you need to compile immediately before the PR is merged, remove the ioctl line from ff_declare_syscalls.h and apply the changes from PR #1048 manually.

[jfb8856606]

PR #1048 已合并（merge commit: 2958b02），修复了 ioctl conflicting types 在旧版 glibc 上的编译错误，此 issue 现在关闭。