From 41d3081c4ac0a79a4ad292957ead84f8477eaa55 Mon Sep 17 00:00:00 2001
From: Sertonix
Date: Sat, 11 Oct 2025 18:25:20 +0200
Subject: Add `swab`

Make the overlap check pedantic only since some software seems to rely
on glibc working when src and dest are the same.
---
 README.md                         |  1 +
 include/unistd.h                  | 26 ++++++++++++++++++++++++++
 tests/Makefile                    |  4 ++++
 tests/test_swab_dynamic_read.c    | 18 ++++++++++++++++++
 tests/test_swab_dynamic_write.c   | 18 ++++++++++++++++++
 tests/test_swab_overwrite_over.c  | 17 +++++++++++++++++
 tests/test_swab_overwrite_under.c | 17 +++++++++++++++++
 tests/test_swab_static_read.c     | 18 ++++++++++++++++++
 tests/test_swab_static_write.c    | 18 ++++++++++++++++++
 9 files changed, 137 insertions(+)
 create mode 100644 tests/test_swab_dynamic_read.c
 create mode 100644 tests/test_swab_dynamic_write.c
 create mode 100644 tests/test_swab_overwrite_over.c
 create mode 100644 tests/test_swab_overwrite_under.c
 create mode 100644 tests/test_swab_static_read.c
 create mode 100644 tests/test_swab_static_write.c

diff --git a/README.md b/README.md
index e187776..8f8824a 100644
--- a/README.md
+++ b/README.md
@@ -116,6 +116,7 @@ At this point, the program will safely and loudly crash.
 - `strncat`
 - `strncpy`
 - `strrchr`
+- `swab`
 - `tmpfile` 
 - `ttyname_r`
 - `umask` 
diff --git a/include/unistd.h b/include/unistd.h
index f6d4e87..b91dc56 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -178,6 +178,32 @@ _FORTIFY_FN(readlinkat) ssize_t readlinkat(int __f, const char *__p,
 	return __orig_readlinkat(__f, __p, __s, __n);
 }
 
+#if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+#undef swab
+
+__fh_access(read_only, 1, 3)
+__fh_access(write_only, 2, 3)
+#if __has_builtin(__builtin_swab)
+__diagnose_as_builtin(__builtin_swab, 1, 2, 3)
+#endif
+_FORTIFY_FN(swab) void swab(const void *restrict  _FORTIFY_POS0 __os,
+                                 void *restrict _FORTIFY_POS0 __od, ssize_t __n)
+__error_if((__fh_bos(__od, 0) < __n), "'swab' called with `n` bigger than the size of `d`.")
+{
+	__fh_size_t __bs = __fh_bos(__os, 0);
+	__fh_size_t __bd = __fh_bos(__od, 0);
+
+#if defined FORTIFY_PEDANTIC_CHECKS
+	if (__n > 0 && __fh_overlap(__os, __n, __od, __n))
+		__builtin_trap();
+#endif
+	if (__n > __bs || __n > __bd)
+		__builtin_trap();
+	return __orig_swab(__os, __od, __n);
+}
+
+#endif
+
 __fh_access(write_only, 2, 3)
 #if __has_builtin(__builtin_ttyname_r)
 __diagnose_as_builtin(__builtin_ttyname_r, 1, 2, 3)
diff --git a/tests/Makefile b/tests/Makefile
index e9e52dc..b4ea242 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -126,6 +126,10 @@ RUNTIME_TARGETS= \
 	test_strncpy_static_write    \
 	test_strrchr_dynamic_read    \
 	test_strrchr_static_read     \
+	test_swab_dynamic_read       \
+	test_swab_dynamic_write      \
+	test_swab_overwrite_over     \
+	test_swab_static_read        \
 	test_ttyname_r_dynamic       \
 	test_ttyname_r_static        \
 	test_umask                   \
diff --git a/tests/test_swab_dynamic_read.c b/tests/test_swab_dynamic_read.c
new file mode 100644
index 0000000..402dc4e
--- /dev/null
+++ b/tests/test_swab_dynamic_read.c
@@ -0,0 +1,18 @@
+#define _XOPEN_SOURCE
+
+#include "common.h"
+
+#include <unistd.h>
+
+int main(int argc, char** argv) {
+  char buffer[12] = {0};
+  swab("1234567890", buffer, sizeof(buffer) - 1);
+  puts(buffer);
+
+  CHK_FAIL_START
+  swab("123456", buffer, argc);
+  CHK_FAIL_END
+
+  puts(buffer);
+  return ret;
+}
diff --git a/tests/test_swab_dynamic_write.c b/tests/test_swab_dynamic_write.c
new file mode 100644
index 0000000..21725b7
--- /dev/null
+++ b/tests/test_swab_dynamic_write.c
@@ -0,0 +1,18 @@
+#define _XOPEN_SOURCE
+
+#include "common.h"
+
+#include <unistd.h>
+
+int main(int argc, char** argv) {
+  char buffer[8] = {0};
+  swab("1234567890", buffer, sizeof(buffer) - 1);
+  puts(buffer);
+
+  CHK_FAIL_START
+  swab("1234567890", buffer, argc);
+  CHK_FAIL_END
+
+  puts(buffer);
+  return ret;
+}
diff --git a/tests/test_swab_overwrite_over.c b/tests/test_swab_overwrite_over.c
new file mode 100644
index 0000000..997f6d1
--- /dev/null
+++ b/tests/test_swab_overwrite_over.c
@@ -0,0 +1,17 @@
+#define _XOPEN_SOURCE
+
+#include "common.h"
+
+#include <unistd.h>
+
+int main(int argc, char** argv) {
+  char buffer[9] = {'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', '\0'};
+  puts(buffer);
+
+  CHK_FAIL_START
+  swab(buffer+1, buffer, 5);
+  CHK_FAIL_END
+
+  puts(buffer);
+  return ret;
+}
diff --git a/tests/test_swab_overwrite_under.c b/tests/test_swab_overwrite_under.c
new file mode 100644
index 0000000..1d69545
--- /dev/null
+++ b/tests/test_swab_overwrite_under.c
@@ -0,0 +1,17 @@
+#define _XOPEN_SOURCE
+
+#include "common.h"
+
+#include <unistd.h>
+
+int main(int argc, char** argv) {
+  char buffer[9] = {'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', '\0'};
+  puts(buffer);
+
+  CHK_FAIL_START
+  swab(buffer-1, buffer, 5);
+  CHK_FAIL_END
+
+  puts(buffer);
+  return ret;
+}
diff --git a/tests/test_swab_static_read.c b/tests/test_swab_static_read.c
new file mode 100644
index 0000000..f7fffcb
--- /dev/null
+++ b/tests/test_swab_static_read.c
@@ -0,0 +1,18 @@
+#define _XOPEN_SOURCE
+
+#include "common.h"
+
+#include <unistd.h>
+
+int main(int argc, char** argv) {
+  char buffer[8] = {0};
+  swab("123456", buffer, 4);
+  puts(buffer);
+
+  CHK_FAIL_START
+  swab("123456", buffer, sizeof(buffer));
+  CHK_FAIL_END
+
+  puts(buffer);
+  return ret;
+}
diff --git a/tests/test_swab_static_write.c b/tests/test_swab_static_write.c
new file mode 100644
index 0000000..b5a63c6
--- /dev/null
+++ b/tests/test_swab_static_write.c
@@ -0,0 +1,18 @@
+#define _XOPEN_SOURCE
+
+#include "common.h"
+
+#include <unistd.h>
+
+int main(int argc, char** argv) {
+  char buffer[8] = {0};
+  swab("1234567890", buffer, sizeof(buffer) - 1);
+  puts(buffer);
+
+  CHK_FAIL_START
+  swab("1234567890", buffer, sizeof(buffer) + 1);
+  CHK_FAIL_END
+
+  puts(buffer);
+  return ret;
+}
-- 
cgit v1.3