git: 917c0541e4cc - main - cross-tools: Document a rather bizarre looking construct

The branch main has been updated by imp:

URL: https://cgit.FreeBSD.org/src/commit/?id=917c0541e4cc60fc4ea6fe434dabe0699ca7c2fd

commit 917c0541e4cc60fc4ea6fe434dabe0699ca7c2fd
Author:     Warner Losh <imp@FreeBSD.org>
AuthorDate: 2024-05-26 17:38:46 +0000
Commit:     Warner Losh <imp@FreeBSD.org>
CommitDate: 2024-05-26 17:38:46 +0000

    cross-tools: Document a rather bizarre looking construct
    
    On Linux, stddef.h will define __size_t to something when size_t is
    defined. On FreeBSD, __size_t is an actual typedef which we need for
    other parts of the system. If __size_t isn't defined, that tells us we
    need to define the fallback __size_t typedef (if it is defined, then we
    can't easily redefine it without issues because glob.h will define it to
    something different than stddef.h defines it). Add a comment to this
    effect.
    
    Sponsored by:           Netflix
    Reviewed by:            val_packett.cool
    Differential Revision:  https://reviews.freebsd.org/D45350
---
 tools/build/cross-build/include/linux/sys/types.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/build/cross-build/include/linux/sys/types.h b/tools/build/cross-build/include/linux/sys/types.h
index 770b3057f8a8..222560167a71 100644
--- a/tools/build/cross-build/include/linux/sys/types.h
+++ b/tools/build/cross-build/include/linux/sys/types.h
@@ -37,6 +37,13 @@
 
 #include_next <sys/types.h>
 
+/*
+ * stddef.h for both gcc and clang will define __size_t when size_t has
+ * been defined (except on *BSD where it doesn't touch __size_t). So if
+ * we're building on Linux, we know that if that's not defined, we have
+ * to typedef __size_t for FreeBSD's use of __size_t in places to work
+ * during bootstrapping.
+ */
 #ifndef __size_t
 typedef __SIZE_TYPE__ __size_t;
 #endif