[PATCH 8/9] tools/nolibc: emit a detailed error when missing alternate syscall number definitions

[Willy Tarreau]

Some syscalls can be implemented from different __NR_* variants. For
example, sys_dup2() can be implemented based on __NR_dup3 or __NR_dup2.
In this case it's useful to produce an error message when neither are
detected, mentioning the supported alternatives. In case of trouble with
includes, it will help the user search for the right one (e.g __NR_dup3)
instead of just the fallback (__NR_dup2) which might simply not exist on
the platform.
[This is nolibc's upstream commit a21080d2ba41]

Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
Link: https://lore.kernel.org/lkml/20210120145447.GC77728@C02TD0UTHF1T.local/
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 tools/include/nolibc/nolibc.h | 52 ++++++++++++++++++++++++++---------
 1 file changed, 39 insertions(+), 13 deletions(-)

diff --git a/tools/include/nolibc/nolibc.h b/tools/include/nolibc/nolibc.h
index 475d956ed1d6..618acad6c932 100644
--- a/tools/include/nolibc/nolibc.h
+++ b/tools/include/nolibc/nolibc.h
@@ -1446,8 +1446,10 @@ int sys_chmod(const char *path, mode_t mode)
 {
 #ifdef __NR_fchmodat
 	return my_syscall4(__NR_fchmodat, AT_FDCWD, path, mode, 0);
-#else
+#elif defined(__NR_chmod)
 	return my_syscall2(__NR_chmod, path, mode);
+#else
+#error Neither __NR_fchmodat nor __NR_chmod defined, cannot implement sys_chmod()
 #endif
 }
 
@@ -1456,8 +1458,10 @@ int sys_chown(const char *path, uid_t owner, gid_t group)
 {
 #ifdef __NR_fchownat
 	return my_syscall5(__NR_fchownat, AT_FDCWD, path, owner, group, 0);
-#else
+#elif defined(__NR_chown)
 	return my_syscall3(__NR_chown, path, owner, group);
+#else
+#error Neither __NR_fchownat nor __NR_chown defined, cannot implement sys_chown()
 #endif
 }
 
@@ -1492,8 +1496,10 @@ int sys_dup2(int old, int new)
 {
 #ifdef __NR_dup3
 	return my_syscall3(__NR_dup3, old, new, 0);
-#else
+#elif defined(__NR_dup2)
 	return my_syscall2(__NR_dup2, old, new);
+#else
+#error Neither __NR_dup3 nor __NR_dup2 defined, cannot implement sys_dup2()
 #endif
 }
 
@@ -1512,8 +1518,10 @@ pid_t sys_fork(void)
 	 * will not use the rest with no other flag.
 	 */
 	return my_syscall5(__NR_clone, SIGCHLD, 0, 0, 0, 0);
-#else
+#elif defined(__NR_fork)
 	return my_syscall0(__NR_fork);
+#else
+#error Neither __NR_clone nor __NR_fork defined, cannot implement sys_fork()
 #endif
 }
 
@@ -1570,8 +1578,10 @@ int sys_link(const char *old, const char *new)
 {
 #ifdef __NR_linkat
 	return my_syscall5(__NR_linkat, AT_FDCWD, old, AT_FDCWD, new, 0);
-#else
+#elif defined(__NR_link)
 	return my_syscall2(__NR_link, old, new);
+#else
+#error Neither __NR_linkat nor __NR_link defined, cannot implement sys_link()
 #endif
 }
 
@@ -1586,8 +1596,10 @@ int sys_mkdir(const char *path, mode_t mode)
 {
 #ifdef __NR_mkdirat
 	return my_syscall3(__NR_mkdirat, AT_FDCWD, path, mode);
-#else
+#elif defined(__NR_mkdir)
 	return my_syscall2(__NR_mkdir, path, mode);
+#else
+#error Neither __NR_mkdirat nor __NR_mkdir defined, cannot implement sys_mkdir()
 #endif
 }
 
@@ -1596,8 +1608,10 @@ long sys_mknod(const char *path, mode_t mode, dev_t dev)
 {
 #ifdef __NR_mknodat
 	return my_syscall4(__NR_mknodat, AT_FDCWD, path, mode, dev);
-#else
+#elif defined(__NR_mknod)
 	return my_syscall3(__NR_mknod, path, mode, dev);
+#else
+#error Neither __NR_mknodat nor __NR_mknod defined, cannot implement sys_mknod()
 #endif
 }
 
@@ -1613,8 +1627,10 @@ int sys_open(const char *path, int flags, mode_t mode)
 {
 #ifdef __NR_openat
 	return my_syscall4(__NR_openat, AT_FDCWD, path, flags, mode);
-#else
+#elif defined(__NR_open)
 	return my_syscall3(__NR_open, path, flags, mode);
+#else
+#error Neither __NR_openat nor __NR_open defined, cannot implement sys_open()
 #endif
 }
 
@@ -1635,8 +1651,10 @@ int sys_poll(struct pollfd *fds, int nfds, int timeout)
 		t.tv_nsec = (timeout % 1000) * 1000000;
 	}
 	return my_syscall4(__NR_ppoll, fds, nfds, (timeout >= 0) ? &t : NULL, NULL);
-#else
+#elif defined(__NR_poll)
 	return my_syscall3(__NR_poll, fds, nfds, timeout);
+#else
+#error Neither __NR_ppoll nor __NR_poll defined, cannot implement sys_poll()
 #endif
 }
 
@@ -1676,11 +1694,13 @@ int sys_select(int nfds, fd_set *rfds, fd_set *wfds, fd_set *efds, struct timeva
 		t.tv_nsec = timeout->tv_usec * 1000;
 	}
 	return my_syscall6(__NR_pselect6, nfds, rfds, wfds, efds, timeout ? &t : NULL, NULL);
-#else
+#elif defined(__NR__newselect) || defined(__NR_select)
 #ifndef __NR__newselect
 #define __NR__newselect __NR_select
 #endif
 	return my_syscall5(__NR__newselect, nfds, rfds, wfds, efds, timeout);
+#else
+#error None of __NR_select, __NR_pselect6, nor __NR__newselect defined, cannot implement sys_select()
 #endif
 }
 
@@ -1705,8 +1725,10 @@ int sys_stat(const char *path, struct stat *buf)
 #ifdef __NR_newfstatat
 	/* only solution for arm64 */
 	ret = my_syscall4(__NR_newfstatat, AT_FDCWD, path, &stat, 0);
-#else
+#elif defined(__NR_stat)
 	ret = my_syscall2(__NR_stat, path, &stat);
+#else
+#error Neither __NR_newfstatat nor __NR_stat defined, cannot implement sys_stat()
 #endif
 	buf->st_dev     = stat.st_dev;
 	buf->st_ino     = stat.st_ino;
@@ -1730,8 +1752,10 @@ int sys_symlink(const char *old, const char *new)
 {
 #ifdef __NR_symlinkat
 	return my_syscall3(__NR_symlinkat, old, AT_FDCWD, new);
-#else
+#elif defined(__NR_symlink)
 	return my_syscall2(__NR_symlink, old, new);
+#else
+#error Neither __NR_symlinkat nor __NR_symlink defined, cannot implement sys_symlink()
 #endif
 }
 
@@ -1752,8 +1776,10 @@ int sys_unlink(const char *path)
 {
 #ifdef __NR_unlinkat
 	return my_syscall3(__NR_unlinkat, AT_FDCWD, path, 0);
-#else
+#elif defined(__NR_unlink)
 	return my_syscall1(__NR_unlink, path);
+#else
+#error Neither __NR_unlinkat nor __NR_unlink defined, cannot implement sys_unlink()
 #endif
 }
 
-- 
2.28.0