On Thu, Nov 18, 2021 at 12:25 AM Uros Bizjak <ubiz...@gmail.com> wrote: > > On Wed, Nov 17, 2021 at 2:47 PM H.J. Lu <hjl.to...@gmail.com> wrote: > > > > Add -mindirect-branch-cs-prefix to add CS prefix to call and jmp to thunk > > via r8-r15 registers when converting indirect call and jump to increase > > the instruction length to 6, allowing the non-thunk form to be inlined. > > > > gcc/ > > > > PR target/102952 > > * config/i386/i386.c (ix86_output_jmp_thunk_or_indirect): Emit > > CS prefix for -mindirect-branch-cs-prefix. > > (ix86_output_indirect_branch_via_reg): Likewise. > > * config/i386/i386.opt: Add -mindirect-branch-cs-prefix. > > * doc/invoke.texi: Document -mindirect-branch-cs-prefix. > > > > gcc/testsuite/ > > > > PR target/102952 > > * gcc.target/i386/indirect-thunk-cs-prefix-1.c: New test. > > * gcc.target/i386/indirect-thunk-cs-prefix-2.c: Likewise. > > It is hard for me to parse the description, both in the commit message > and in the option description and documentation. Can you please reword > them to be more comprehensible? > >
Here is the v3 patch with updated description. OK for master? Thanks. -- H.J.
From ed12d22089b7ee75f20e504f9e7c898dd2b92215 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" <hjl.to...@gmail.com> Date: Wed, 27 Oct 2021 06:27:15 -0700 Subject: [PATCH v3] x86: Add -mindirect-branch-cs-prefix Add -mindirect-branch-cs-prefix to add CS prefix to call and jmp to indirect thunk with branch target in r8-r15 registers so that the call and jmp instruction length is 6 bytes to allow them to be replaced with "lfence; call *%r8-r15" or "lfence; jmp *%r8-r15" at run-time. gcc/ PR target/102952 * config/i386/i386.c (ix86_output_jmp_thunk_or_indirect): Emit CS prefix for -mindirect-branch-cs-prefix. (ix86_output_indirect_branch_via_reg): Likewise. * config/i386/i386.opt: Add -mindirect-branch-cs-prefix. * doc/invoke.texi: Document -mindirect-branch-cs-prefix. gcc/testsuite/ PR target/102952 * gcc.target/i386/indirect-thunk-cs-prefix-1.c: New test. * gcc.target/i386/indirect-thunk-cs-prefix-2.c: Likewise. --- gcc/config/i386/i386.c | 6 ++++++ gcc/config/i386/i386.opt | 4 ++++ gcc/doc/invoke.texi | 10 +++++++++- .../gcc.target/i386/indirect-thunk-cs-prefix-1.c | 14 ++++++++++++++ .../gcc.target/i386/indirect-thunk-cs-prefix-2.c | 15 +++++++++++++++ 5 files changed, 48 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-1.c create mode 100644 gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-2.c diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c index c246c8736f5..7fe271b1b94 100644 --- a/gcc/config/i386/i386.c +++ b/gcc/config/i386/i386.c @@ -15982,6 +15982,9 @@ ix86_output_jmp_thunk_or_indirect (const char *thunk_name, const int regno) { if (thunk_name != NULL) { + if (REX_INT_REGNO_P (regno) + && ix86_indirect_branch_cs_prefix) + fprintf (asm_out_file, "\tcs\n"); fprintf (asm_out_file, "\tjmp\t"); assemble_name (asm_out_file, thunk_name); putc ('\n', asm_out_file); @@ -16031,6 +16034,9 @@ ix86_output_indirect_branch_via_reg (rtx call_op, bool sibcall_p) { if (thunk_name != NULL) { + if (REX_INT_REGNO_P (regno) + && ix86_indirect_branch_cs_prefix) + fprintf (asm_out_file, "\tcs\n"); fprintf (asm_out_file, "\tcall\t"); assemble_name (asm_out_file, thunk_name); putc ('\n', asm_out_file); diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt index 2b6d8aab101..3e67c537bb7 100644 --- a/gcc/config/i386/i386.opt +++ b/gcc/config/i386/i386.opt @@ -1076,6 +1076,10 @@ Enum(indirect_branch) String(thunk-inline) Value(indirect_branch_thunk_inline) EnumValue Enum(indirect_branch) String(thunk-extern) Value(indirect_branch_thunk_extern) +mindirect-branch-cs-prefix +Target Var(ix86_indirect_branch_cs_prefix) Init(0) +Add CS prefix to call and jmp to indirect thunk with branch target in r8-r15 registers. + mindirect-branch-register Target Var(ix86_indirect_branch_register) Init(0) Force indirect call and jump via register. diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index d62ec08150e..5fed1dd6a31 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -1427,7 +1427,8 @@ See RS/6000 and PowerPC Options. -mstack-protector-guard-symbol=@var{symbol} @gol -mgeneral-regs-only -mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop @gol -mindirect-branch=@var{choice} -mfunction-return=@var{choice} @gol --mindirect-branch-register -mharden-sls=@var{choice} -mneeded} +-mindirect-branch-register -mharden-sls=@var{choice} @gol +-mindirect-branch-cs-prefix -mneeded} @emph{x86 Windows Options} @gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol @@ -32416,6 +32417,13 @@ hardening. @samp{return} enables SLS hardening for function return. @samp{indirect-branch} enables SLS hardening for indirect branch. @samp{all} enables all SLS hardening. +@item -mindirect-branch-cs-prefix +@opindex mindirect-branch-cs-prefix +Add CS prefix to call and jmp to indirect thunk with branch target in +r8-r15 registers so that the call and jmp instruction length is 6 bytes +to allow them to be replaced with @samp{lfence; call *%r8-r15} or +@samp{lfence; jmp *%r8-r15} at run-time. + @end table These @samp{-m} switches are supported in addition to the above diff --git a/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-1.c b/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-1.c new file mode 100644 index 00000000000..db2f3416823 --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-1.c @@ -0,0 +1,14 @@ +/* { dg-do compile { target { ! ia32 } } } */ +/* { dg-options "-O2 -ffixed-rax -ffixed-rbx -ffixed-rcx -ffixed-rdx -ffixed-rdi -ffixed-rsi -mindirect-branch-cs-prefix -mindirect-branch=thunk-extern" } */ +/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */ + +extern void (*fptr) (void); + +void +foo (void) +{ + fptr (); +} + +/* { dg-final { scan-assembler-times "jmp\[ \t\]+_?__x86_indirect_thunk_r\[0-9\]+" 1 } } */ +/* { dg-final { scan-assembler-times "\tcs" 1 } } */ diff --git a/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-2.c b/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-2.c new file mode 100644 index 00000000000..adfc39a49d4 --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-2.c @@ -0,0 +1,15 @@ +/* { dg-do compile { target { ! ia32 } } } */ +/* { dg-options "-O2 -ffixed-rax -ffixed-rbx -ffixed-rcx -ffixed-rdx -ffixed-rdi -ffixed-rsi -mindirect-branch-cs-prefix -mindirect-branch=thunk-extern" } */ +/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */ + +extern void (*bar) (void); + +int +foo (void) +{ + bar (); + return 0; +} + +/* { dg-final { scan-assembler-times "call\[ \t\]+_?__x86_indirect_thunk_r\[0-9\]+" 1 } } */ +/* { dg-final { scan-assembler-times "\tcs" 1 } } */ -- 2.33.1