PING: [PATCH] x86: Force __x86_indirect_thunk_reg for function call via GOT

H.J. Lu hjl.tools@gmail.com
Mon Mar 5 12:20:00 GMT 2018


On Tue, Feb 27, 2018 at 11:39 AM, H.J. Lu <hongjiu.lu@intel.com> wrote:
> For x86 targets, when -fno-plt is used, external functions are called
> via GOT slot, in 64-bit mode:
>
>         [bnd] call/jmp *foo@GOTPCREL(%rip)
>
> and in 32-bit mode:
>
>         [bnd] call/jmp *foo@GOT[(%reg)]
>
> With -mindirect-branch=, they are converted to, in 64-bit mode:
>
>         pushq          foo@GOTPCREL(%rip)
>         [bnd] jmp      __x86_indirect_thunk[_bnd]
>
> and in 32-bit mode:
>
>         pushl          foo@GOT[(%reg)]
>         [bnd] jmp      __x86_indirect_thunk[_bnd]
>
> which were incompatible with CFI.  In 64-bit mode, since R11 is a scratch
> register, we generate:
>
>         movq           foo@GOTPCREL(%rip), %r11
>         [bnd] call/jmp __x86_indirect_thunk_[bnd_]r11
>
> instead.  We do it in ix86_output_indirect_branch so that we can use
> the newly proposed R_X86_64_THUNK_GOTPCRELX relocation:
>
> https://groups.google.com/forum/#!topic/x86-64-abi/eED5lzn3_Mg
>
>         movq           foo@OTPCREL_THUNK(%rip), %r11
>         [bnd] call/jmp __x86_indirect_thunk_[bnd_]r11
>
> to load GOT slot into R11.  If foo is defined locally, linker can can
> convert
>
>         movq           foo@GOTPCREL_THUNK(%rip), %reg
>         call/jmp       __x86_indirect_thunk_reg
>
> to
>
>         call/jmp       foo
>         nop            0L(%rax)
>
> In 32-bit mode, since all caller-saved registers, EAX, EDX and ECX, may
> used to function parameters, there is no scratch register available.  For
> -fno-plt -fno-pic -mindirect-branch=, we expand external function call
> to:
>
>         movl           foo@GOT, %reg
>         [bnd] call/jmp *%reg
>
> so that it can be converted to
>
>         movl           foo@GOT, %reg
>         [bnd] call/jmp __x86_indirect_thunk_[bnd_]reg
>
> in ix86_output_indirect_branch.  Since this is performed during RTL
> expansion, other instructions may be inserted between movl and call/jmp.
> Linker optimization isn't always possible.
>
> Tested on i686 and x86-64.  OK for trunk?
>
>
> H.J.
> ---
> gcc/
>
>         PR target/83970
>         * config/i386/constraints.md (Bs): Allow GOT_memory_operand
>         for TARGET_LP64 with indirect branch conversion.
>         (Bw): Likewise.
>         * config/i386/i386.c (ix86_expand_call): Handle -fno-plt with
>         -mindirect-branch=.
>         (ix86_nopic_noplt_attribute_p): Likewise.
>         (ix86_output_indirect_branch): In 64-bit mode, convert function
>         call via GOT with R11 as a scratch register using
>         __x86_indirect_thunk_r11.
>         (ix86_output_call_insn): In 64-bit mode, set xasm to NULL when
>         calling ix86_output_indirect_branch with function call via GOT.
>         * config/i386/i386.md (*call_got_thunk): New call pattern for
>         TARGET_LP64 with indirect branch conversion.
>         (*call_value_got_thunk): Likewise.
>
> gcc/testsuite/
>
>         PR target/83970
>         * gcc.target/i386/indirect-thunk-5.c: Updated.
>         * gcc.target/i386/indirect-thunk-6.c: Likewise.
>         * gcc.target/i386/indirect-thunk-bnd-3.c: Likewise.
>         * gcc.target/i386/indirect-thunk-bnd-4.c: Likewise.
>         * gcc.target/i386/indirect-thunk-extern-5.c: Likewise.
>         * gcc.target/i386/indirect-thunk-extern-6.c: Likewise.
>         * gcc.target/i386/indirect-thunk-inline-5.c: Likewise.
>         * gcc.target/i386/indirect-thunk-inline-6.c: Likewise.
>         * gcc.target/i386/indirect-thunk-13.c: New test.
>         * gcc.target/i386/indirect-thunk-14.c: Likewise.
>         * gcc.target/i386/indirect-thunk-bnd-5.c: Likewise.
>         * gcc.target/i386/indirect-thunk-bnd-6.c: Likewise.
>         * gcc.target/i386/indirect-thunk-extern-11.c: Likewise.
>         * gcc.target/i386/indirect-thunk-extern-12.c: Likewise.
>         * gcc.target/i386/indirect-thunk-inline-8.c: Likewise.
>         * gcc.target/i386/indirect-thunk-inline-9.c: Likewise.

PING:

https://gcc.gnu.org/ml/gcc-patches/2018-02/msg01527.html


-- 
H.J.



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