feature_test_macros.7: Further tweaks to _REENTRANT description

Reviewed-by: Zack Weinberg <zackw@panix.com>
Reported-by: Zack Weinberg <zackw@panix.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man7/feature_test_macros.7 b/man7/feature_test_macros.7
index 1deb8fd4d7629e520170f10c6df4a81630de18e9..ef004e36e28e4b8cd471d92e72240270dc9c0256 100644 (file)
--- a/man7/feature_test_macros.7
+++ b/man7/feature_test_macros.7
@@ -529,8 +529,13 @@ and
 .BR _SVID_SOURCE .
 .TP
 .B _REENTRANT
-Historically, it was necessary to define this macro in all
+Historically, on various C libraries
+it was necessary to define this macro in all
 multithreaded code.
+.\" Zack Weinberg
+.\"     There did once exist C libraries where it was necessary. The ones
+.\"     I remember were proprietary Unix vendor libcs from the mid-1990s
+.\"     You would get completely unlocked stdio without _REENTRANT.
 (Some C libraries may still require this.)
 In glibc,
 this macro also exposed definitions of certain reentrant functions.
@@ -543,10 +548,11 @@ are also enabled by defining
 .BR _POSIX_C_SOURCE
 with a value of 199606L or greater.
 
-In glibc 2.25 and later,
 .B _REENTRANT
-is deprecated.
-Defining it is equivalent to defining
+is now obsolete.
+In glibc 2.25 and later, defining
+.B _REENTRANT
+is equivalent to defining
 .B _POSIX_C_SOURCE
 with the value 199606L.
 If a higher POSIX conformance level is
@@ -557,11 +563,11 @@ itself,
 .BR _DEFAULT_SOURCE ,
 or
 .BR _GNU_SOURCE ),
-then
+then defining
 .B _REENTRANT
 has no effect.
 
-This flag is automatically defined if one compiles with
+This macro is automatically defined if one compiles with
 .IR "cc\ \-pthread" .
 .TP
 .B _THREAD_SAFE