[PATCH] x86: Do not dump DS/CS segment overrides for branch hints
H.J. Lu
hjl.tools@gmail.com
Sun Nov 29 12:25:16 GMT 2020
On Sun, Nov 29, 2020 at 3:45 AM Borislav Petkov <bp@alien8.de> wrote:
>
> From: Borislav Petkov <bp@suse.de>
>
> The previous change
>
> "x86: Ignore CS/DS/ES/SS segment-override prefixes in 64-bit mode"
>
> to ignore segment override prefixes in 64-bit mode lead to dumping
> branch hints as excessive prefixes:
>
> ffffffff8109d5a0 <vmx_get_rflags>:
> ...
> ffffffff8109d601: 3e 77 0a ds ja,pt ffffffff8109d60e <vmx_get_rflags+0x6e>
> ^^^^^
>
> In this particular case, those prefixes are not excessive but are used
> to provide branch hints - taken/not-taken - to the CPU.
>
> Assign active_seg_prefix in that particular case to consume them.
>
> gas/
>
> 2002-11-29 Borislav Petkov <bp@suse.de>
>
> * testsuite/gas/i386/branch.d: Add new branch insns test.
> * testsuite/gas/i386/branch.s: Likewise.
> * testsuite/gas/i386/i386.exp: Insert the new branch test.
> * testsuite/gas/i386/x86-64-branch.d: Test for branch hints insns.
> * testsuite/gas/i386/x86-64-branch.s: Likewise.
> * testsuite/gas/i386/ilp32/x86-64-branch.d: Likewise.
>
> opcodes /
>
> 2020-11-28 Borislav Petkov <bp@suse.de>
>
> * i386-dis.c (print_insn): Set active_seg_prefix for branch hint insns
> to not dump branch hint prefixes 0x2E and 0x3E as unused prefixes.
> ---
> gas/ChangeLog | 9 +++++++++
> gas/testsuite/gas/i386/branch.d | 12 ++++++++++++
> gas/testsuite/gas/i386/branch.s | 4 ++++
> gas/testsuite/gas/i386/i386.exp | 1 +
> gas/testsuite/gas/i386/ilp32/x86-64-branch.d | 2 ++
> gas/testsuite/gas/i386/x86-64-branch.d | 2 ++
> gas/testsuite/gas/i386/x86-64-branch.s | 4 ++++
> opcodes/ChangeLog | 5 +++++
> opcodes/i386-dis.c | 10 ++++++++--
> 9 files changed, 47 insertions(+), 2 deletions(-)
> create mode 100644 gas/testsuite/gas/i386/branch.d
> create mode 100644 gas/testsuite/gas/i386/branch.s
>
> diff --git a/gas/ChangeLog b/gas/ChangeLog
> index 97754267be9b..8d07dc9bbb9a 100644
> --- a/gas/ChangeLog
> +++ b/gas/ChangeLog
> @@ -1,3 +1,12 @@
> +2002-11-29 Borislav Petkov <bp@suse.de>
> +
> + * testsuite/gas/i386/branch.d: Add new branch insns test.
> + * testsuite/gas/i386/branch.s: Likewise.
> + * testsuite/gas/i386/i386.exp: Insert the new branch test.
> + * testsuite/gas/i386/x86-64-branch.d: Test for branch hints insns.
> + * testsuite/gas/i386/x86-64-branch.s: Likewise.
> + * testsuite/gas/i386/ilp32/x86-64-branch.d: Likewise.
> +
> 2020-11-27 Jozef Lawrynowicz <jozef.l@mittosystems.com>
>
> * testsuite/gas/elf/elf.exp: Run new tests.
> diff --git a/gas/testsuite/gas/i386/branch.d b/gas/testsuite/gas/i386/branch.d
> new file mode 100644
> index 000000000000..6d25b950830f
> --- /dev/null
> +++ b/gas/testsuite/gas/i386/branch.d
> @@ -0,0 +1,12 @@
> +#as: -J
> +#objdump: -dw
> +#name: i386 branch
> +
> +.*: +file format .*
> +
> +Disassembly of section .text:
> +
> +0+ <.text>:
> +[ ]*[a-f0-9]+: 3e 74 03[ ]+je,pt +0x[0-9a-f]+
> +[ ]*[a-f0-9]+: 2e 74 00[ ]+je,pn +0x[0-9a-f]+
> +#pass
> diff --git a/gas/testsuite/gas/i386/branch.s b/gas/testsuite/gas/i386/branch.s
> new file mode 100644
> index 000000000000..968a1818970f
> --- /dev/null
> +++ b/gas/testsuite/gas/i386/branch.s
> @@ -0,0 +1,4 @@
> +.text
> + jz,pt .Llabel
> + jz,pn .Llabel
> +.Llabel:
> diff --git a/gas/testsuite/gas/i386/i386.exp b/gas/testsuite/gas/i386/i386.exp
> index c85ced1c9181..432cf0192d49 100644
> --- a/gas/testsuite/gas/i386/i386.exp
> +++ b/gas/testsuite/gas/i386/i386.exp
> @@ -565,6 +565,7 @@ if [gas_32_check] then {
> run_dump_test "lfence-ret-c"
> run_dump_test "lfence-ret-d"
> run_dump_test "lfence-byte"
> + run_dump_test "branch"
>
> # These tests require support for 8 and 16 bit relocs,
> # so we only run them for ELF and COFF targets.
> diff --git a/gas/testsuite/gas/i386/ilp32/x86-64-branch.d b/gas/testsuite/gas/i386/ilp32/x86-64-branch.d
> index 8be91de922f3..d5f2358546fc 100644
> --- a/gas/testsuite/gas/i386/ilp32/x86-64-branch.d
> +++ b/gas/testsuite/gas/i386/ilp32/x86-64-branch.d
> @@ -25,6 +25,8 @@ Disassembly of section .text:
> [ ]*[a-f0-9]+: 66 0f 82 00 00 00 00 data16 jb 0x37 33: R_X86_64_PLT32 foo-0x4
> [ ]*[a-f0-9]+: 66 c3 data16 ret *
> [ ]*[a-f0-9]+: 66 c2 08 00 data16 ret \$0x8
> +[ ]*[a-f0-9]+: 3e 74 03[ ]+je,pt +0x[0-9a-f]+
> +[ ]*[a-f0-9]+: 2e 74 00[ ]+je,pn +0x[0-9a-f]+
> [ ]*[a-f0-9]+: ff d0 call \*%rax
> [ ]*[a-f0-9]+: ff d0 call \*%rax
> [ ]*[a-f0-9]+: 66 ff d0 data16 call \*%rax
> diff --git a/gas/testsuite/gas/i386/x86-64-branch.d b/gas/testsuite/gas/i386/x86-64-branch.d
> index 2618134b4011..b963f9f051e4 100644
> --- a/gas/testsuite/gas/i386/x86-64-branch.d
> +++ b/gas/testsuite/gas/i386/x86-64-branch.d
> @@ -24,6 +24,8 @@ Disassembly of section .text:
> [ ]*[a-f0-9]+: 66 0f 82 00 00 00 00 data16 jb (0x37|37 <.text\+0x37>)
> [ ]*[a-f0-9]+: 66 c3 data16 ret *
> [ ]*[a-f0-9]+: 66 c2 08 00 data16 ret \$0x8
> +[ ]*[a-f0-9]+: 3e 74 03[ ]+je,pt +0x[0-9a-f]+
> +[ ]*[a-f0-9]+: 2e 74 00[ ]+je,pn +0x[0-9a-f]+
> [ ]*[a-f0-9]+: ff d0 call \*%rax
> [ ]*[a-f0-9]+: ff d0 call \*%rax
> [ ]*[a-f0-9]+: 66 ff d0 data16 call \*%rax
> diff --git a/gas/testsuite/gas/i386/x86-64-branch.s b/gas/testsuite/gas/i386/x86-64-branch.s
> index eb40dd4d4cd1..496e1bb089fb 100644
> --- a/gas/testsuite/gas/i386/x86-64-branch.s
> +++ b/gas/testsuite/gas/i386/x86-64-branch.s
> @@ -22,6 +22,10 @@
> retw
> retw $8
>
> + jz,pt .Llabel
> + jz,pn .Llabel
> +.Llabel:
> +
> .intel_syntax noprefix
> call rax
> callq rax
> diff --git a/opcodes/ChangeLog b/opcodes/ChangeLog
> index 1e7e40fd9664..02fd2f5b5837 100644
> --- a/opcodes/ChangeLog
> +++ b/opcodes/ChangeLog
> @@ -1,3 +1,8 @@
> +2020-11-28 Borislav Petkov <bp@suse.de>
> +
> + * i386-dis.c (print_insn): Set active_seg_prefix for branch hint insns
> + to not dump branch hint prefixes 0x2E and 0x3E as unused prefixes.
> +
> 2020-11-16 Przemyslaw Wirkus <przemyslaw.wirkus@arm.com>
>
> * aarch64-tbl.h (FLAGM): Handle for FLAGM feature.
> diff --git a/opcodes/i386-dis.c b/opcodes/i386-dis.c
> index 58cf001080bc..d1b3f50f7b70 100644
> --- a/opcodes/i386-dis.c
> +++ b/opcodes/i386-dis.c
> @@ -10910,10 +10910,16 @@ putop (const char *in_template, int sizeflag)
> used_prefixes |= prefixes & (PREFIX_CS | PREFIX_DS);
> *obufp++ = ',';
> *obufp++ = 'p';
> - if (prefixes & PREFIX_DS)
> +
> + /* Set active_seg_prefix even if not set in 64-bit mode because
> + * here it is a valid branch hint. */
> + if (prefixes & PREFIX_DS) {
Please put { on a separate line.
> + active_seg_prefix = PREFIX_DS;
> *obufp++ = 't';
> - else
> + } else {
Please put { and } on separate lines.
> + active_seg_prefix = PREFIX_CS;
> *obufp++ = 'n';
> + }
> }
> break;
> case 'K':
> --
> 2.21.0
>
OK with these changes.
Thanks.
--
H.J.
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