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ld.so.8: Document LD_PREFER_MAP_32BIT_EXEC 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
H.J. Lu 2015-12-16 14:40:40 +01:00 committed by Michael Kerrisk
parent cc15860198
commit 5b479f37b6
1 changed files with 10 additions and 0 deletions
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man8/ld.so.8
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@ -472,6 +472,16 @@ environment variable has been set.
(ELF only)(glibc since 2.1.3)
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
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.
.TP
.B LDD_ARGV0
(libc5)
.IR argv [0]