i386: Generate lfence with load/indirect branch/ret [CVE-2020-0551]

[deliverable/binutils-gdb.git] / gas / doc / c-i386.texi

diff --git a/gas/doc/c-i386.texi b/gas/doc/c-i386.texi
index c536759cb3848b32fc346573516e2d7a12a51a27..1dd99f91bb0e97f220c17cacedbe5c4f71cfe8d1 100644 (file)
--- a/gas/doc/c-i386.texi
+++ b/gas/doc/c-i386.texi
@@ -464,6 +464,49 @@ on an instruction.  It is equivalent to
 @option{-malign-branch-prefix-size=5}.
 The default doesn't align branches.
 
+@cindex @samp{-mlfence-after-load=} option, i386
+@cindex @samp{-mlfence-after-load=} option, x86-64
+@item -mlfence-after-load=@var{no}
+@itemx -mlfence-after-load=@var{yes}
+These options control whether the assembler should generate lfence
+after load instructions.  @option{-mlfence-after-load=@var{yes}} will
+generate lfence.  @option{-mlfence-after-load=@var{no}} will not generate
+lfence, which is the default.
+
+@cindex @samp{-mlfence-before-indirect-branch=} option, i386
+@cindex @samp{-mlfence-before-indirect-branch=} option, x86-64
+@item -mlfence-before-indirect-branch=@var{none}
+@item -mlfence-before-indirect-branch=@var{all}
+@item -mlfence-before-indirect-branch=@var{register}
+@itemx -mlfence-before-indirect-branch=@var{memory}
+These options control whether the assembler should generate lfence
+after indirect near branch instructions.
+@option{-mlfence-before-indirect-branch=@var{all}} will generate lfence
+after indirect near branch via register and issue a warning before
+indirect near branch via memory.
+@option{-mlfence-before-indirect-branch=@var{register}} will generate
+lfence after indirect near branch via register.
+@option{-mlfence-before-indirect-branch=@var{memory}} will issue a
+warning before indirect near branch via memory.
+@option{-mlfence-before-indirect-branch=@var{none}} will not generate
+lfence nor issue warning, which is the default.  Note that lfence won't
+be generated before indirect near branch via register with
+@option{-mlfence-after-load=@var{yes}} since lfence will be generated
+after loading branch target register.
+
+@cindex @samp{-mlfence-before-ret=} option, i386
+@cindex @samp{-mlfence-before-ret=} option, x86-64
+@item -mlfence-before-ret=@var{none}
+@item -mlfence-before-ret=@var{or}
+@itemx -mlfence-before-ret=@var{not}
+These options control whether the assembler should generate lfence
+before ret.  @option{-mlfence-before-ret=@var{or}} will generate
+generate or instruction with lfence.
+@option{-mlfence-before-ret=@var{not}} will generate not instruction
+with lfence.
+@option{-mlfence-before-ret=@var{none}} will not generate lfence,
+which is the default.
+
 @cindex @samp{-mx86-used-note=} option, i386
 @cindex @samp{-mx86-used-note=} option, x86-64
 @item -mx86-used-note=@var{no}