ld.so.8: Tweaks to H.J. Lu's patch

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man8/ld.so.8 b/man8/ld.so.8
index da3340499e13bc67ca542e172f70e511ba15f741..430b3908431866df1a02a31eaaf80f6c1ae42cdb 100644 (file)
--- a/man8/ld.so.8
+++ b/man8/ld.so.8
@@ -474,13 +474,22 @@ If set to a nonempty string, warn about unresolved symbols.
 .TP
 .B LD_PREFER_MAP_32BIT_EXEC
 (x86-64 only)(glibc since 2.23)
-According to Silvermont software optimization guide, for 64-bit
+According to the Intel Silvermont software optimization guide, for 64-bit
 applications, branch prediction performance can be negatively impacted
 when the target of a branch is more than 4GB away from the branch.
-If set, ld.so will try to map executable pages with MAP_32BIT first.
-NB: MAP_32BIT will map to lower 2GB, not lower 4GB, address.  Since
-MAP_32BIT reduces bits available for address space layout randomization
-(ASLR), LD_PREFER_MAP_32BIT_EXEC is always disabled for SUID programs.
+If this environment variable is set (to any value),
+.BR ld.so
+will first try to map executable pages using the
+.BR mmap (2)
+.BR MAP_32BIT
+flag, and fall back to mapping without that flag if that attempt fails.
+NB: MAP_32BIT will map to the low 2GB (not 2GB) of the address space.
+Because
+.B MAP_32BIT
+reduces the address range available for address space layout
+randomization (ASLR),
+.B LD_PREFER_MAP_32BIT_EXEC
+is always disabled in secure-execution mode.
 .TP
 .B LDD_ARGV0
 (libc5)