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tools/nolibc: make __nolibc_enosys() a compile time error

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Functions which are known at compile-time to result in ENOSYS can be
surprising to the user. For example using old UAPI headers might mean
that stat() will always fail although the kernel would have the system
call available at runtime. Nowadays __nolibc_enosys() should never be
called for normal applications.

Switch the silent ENOSYS return into a compile-time error, so the user
is aware about the issue. Prefer the 'error' attribute as it provides
the best diagnostics. If the users defines NOLIBC_COMPILE_TIME_ENOSYS
the old, silent fallback is kept.

Also add a test which validates that the error can be optimized away.

Reported-by: Willy Tarreau <w@1wt.eu>
Closes: https://lore.kernel.org/lkml/acizRIq2xrFUNHNS@1wt.eu/
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://patch.msgid.link/20260404-nolibc-enosys-v1-1-e0aba47bdee4@weissschuh.net
This commit is contained in:
Thomas Weißschuh
2026-04-04 17:26:05 +02:00
parent 80e5de852e
commit e635b0459a
2 changed files with 34 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

18
tools/include/nolibc/sys.h
View File

@@ -45,16 +45,30 @@
: __sysret_arg; /* return original value */ \
})
/* Syscall ENOSYS helper: Avoids unused-parameter warnings and provides a
* debugging hook.
/* Syscall ENOSYS helper: Avoids unused-parameter warnings, provides compile
* time validation and a debugging hook.
*/
#if defined(NOLIBC_COMPILE_TIME_ENOSYS)
static __inline__ int __nolibc_enosys(const char *syscall, ...)
{
(void)syscall;
return -ENOSYS;
}
#elif __nolibc_has_attribute(error)
__attribute__((error("system call not implemented")))
extern int __nolibc_enosys(const char *syscall, ...);
#else
static __inline__ int __nolibc_enosys(const char *syscall, ...)
{
extern int __nolibc_enosys_error;
(void)syscall;
return __nolibc_enosys_error;
}
#endif
/* Functions in this file only describe syscalls. They're declared static so
* that the compiler usually decides to inline them while still being allowed

18
tools/testing/selftests/nolibc/nolibc-test.c
View File

@@ -1299,6 +1299,23 @@ int test_openat(void)
return 0;
}
int test_nolibc_enosys(void)
{
if (true)
return 0;
#if defined(NOLIBC)
/*
* __nolibc_enosys() will fail the compilation.
* Make sure it can be optimized away if not actually called.
*/
if (__nolibc_enosys("something") != -ENOSYS)
return 1;
#endif
return 0;
}
int test_namespace(void)
{
int original_ns, new_ns, ret;
@@ -1467,6 +1484,7 @@ int run_syscall(int min, int max)
CASE_TEST(munmap_bad); EXPECT_SYSER(1, munmap(NULL, 0), -1, EINVAL); break;
CASE_TEST(mmap_munmap_good); EXPECT_SYSZR(1, test_mmap_munmap()); break;
CASE_TEST(nanosleep); ts.tv_nsec = -1; EXPECT_SYSER(1, nanosleep(&ts, NULL), -1, EINVAL); break;
CASE_TEST(nolibc_enosys); EXPECT_ZR(is_nolibc, test_nolibc_enosys()); break;
CASE_TEST(open_tty); EXPECT_SYSNE(1, tmp = open("/dev/null", O_RDONLY), -1); if (tmp != -1) close(tmp); break;
CASE_TEST(open_blah); EXPECT_SYSER(1, tmp = open("/proc/self/blah", O_RDONLY), -1, ENOENT); if (tmp != -1) close(tmp); break;
CASE_TEST(openat_dir); EXPECT_SYSZR(1, test_openat()); break;