From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 94093 invoked by alias); 16 Jul 2019 11:18:15 -0000 Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Received: (qmail 94079 invoked by uid 89); 16 Jul 2019 11:18:14 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-14.1 required=5.0 tests=AWL,BAYES_00,GIT_PATCH_0,GIT_PATCH_1,GIT_PATCH_2,GIT_PATCH_3,SEM_URI,SEM_URIRED autolearn=ham version=3.3.1 spammy=pc, Setup X-HELO: foss.arm.com Received: from foss.arm.com (HELO foss.arm.com) (217.140.110.172) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Tue, 16 Jul 2019 11:18:12 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D81E12B; Tue, 16 Jul 2019 04:18:05 -0700 (PDT) Received: from [10.2.206.47] (e120808-lin.cambridge.arm.com [10.2.206.47]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7FC343F71A; Tue, 16 Jul 2019 04:18:05 -0700 (PDT) Subject: Re: [ARM/FDPIC v5 09/21] [ARM] FDPIC: Add support for taking address of nested function To: Christophe Lyon , "gcc-patches@gcc.gnu.org" References: <20190515124006.25840-1-christophe.lyon@st.com> <20190515124006.25840-10-christophe.lyon@st.com> From: Kyrill Tkachov Message-ID: <21a7e3bb-40ab-8b7e-1c66-b991231eb808@foss.arm.com> Date: Tue, 16 Jul 2019 11:53:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.1 MIME-Version: 1.0 In-Reply-To: <20190515124006.25840-10-christophe.lyon@st.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-SW-Source: 2019-07/txt/msg01111.txt.bz2 Hi Christophe On 5/15/19 1:39 PM, Christophe Lyon wrote: > In FDPIC mode, the trampoline generated to support pointers to nested > functions looks like: > >            .word trampoline address >            .word trampoline GOT address >            ldr            r12, [pc, #8] >            ldr            r9, [pc, #8] >            ldr           pc, [pc, #8] >            .word static chain value >            .word GOT address >            .word function's address > > because in FDPIC function pointers are actually pointers to function > descriptors, we have to actually generate a function descriptor for > the trampoline. > > 2019-XX-XX  Christophe Lyon  >         Mickaël Guêné > >         gcc/ >         * config/arm/arm.c (arm_asm_trampoline_template): Add FDPIC >         support. >         (arm_trampoline_init): Likewise. >         (arm_trampoline_init): Likewise. >         * config/arm/arm.h (TRAMPOLINE_SIZE): Likewise. > > Change-Id: Idc4d5f629ae4f8d79bdf9623517481d524a0c144 > > diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c > index 40e3f3b..99d13bf 100644 > --- a/gcc/config/arm/arm.c > +++ b/gcc/config/arm/arm.c > @@ -3976,13 +3976,50 @@ arm_warn_func_return (tree decl) >             .word static chain value >             .word function's address >     XXX FIXME: When the trampoline returns, r8 will be clobbered.  */ > +/* In FDPIC mode, the trampoline looks like: > +          .word trampoline address > +          .word trampoline GOT address > +          ldr            r12, [pc, #8] ; #4 for Thumb2 > +          ldr            r9,  [pc, #8] ; #4 for Thumb2 > +          ldr           pc,  [pc, #8] ; #4 for Thumb2 > +          .word static chain value > +          .word GOT address > +          .word function's address > +*/ I think this comment is not right for Thumb2. These load instructionshave 32-bit encodings, even in Thumb2 (they use high registers). Also, please merge this comment with the one above (no separate /**/) > >  static void >  arm_asm_trampoline_template (FILE *f) >  { >    fprintf (f, "\t.syntax unified\n"); > > -  if (TARGET_ARM) > +  if (TARGET_FDPIC) > +    { > +      /* The first two words are a function descriptor pointing to the > +        trampoline code just below.  */ > +      if (TARGET_ARM) > +       fprintf (f, "\t.arm\n"); > +      else if (TARGET_THUMB2) > +       fprintf (f, "\t.thumb\n"); > +      else > +       /* Only ARM and Thumb-2 are supported.  */ > +       gcc_unreachable (); > + > +      assemble_aligned_integer (UNITS_PER_WORD, const0_rtx); > +      assemble_aligned_integer (UNITS_PER_WORD, const0_rtx); > +      /* Trampoline code which sets the static chain register but also > +        PIC register before jumping into real code.  */ > +      asm_fprintf (f, "\tldr\t%r, [%r, #%d]\n", > +                  STATIC_CHAIN_REGNUM, PC_REGNUM, > +                  TARGET_THUMB2 ? 8 : 4); > +      asm_fprintf (f, "\tldr\t%r, [%r, #%d]\n", > +                  PIC_OFFSET_TABLE_REGNUM, PC_REGNUM, > +                  TARGET_THUMB2 ? 8 : 4); > +      asm_fprintf (f, "\tldr\t%r, [%r, #%d]\n", > +                  PC_REGNUM, PC_REGNUM, > +                  TARGET_THUMB2 ? 8 : 4); As above, I think the offset should be 8 for both Arm and Thumb2. Thanks, Kyrill > +      assemble_aligned_integer (UNITS_PER_WORD, const0_rtx); > +    } > +  else if (TARGET_ARM) >      { >        fprintf (f, "\t.arm\n"); >        asm_fprintf (f, "\tldr\t%r, [%r, #0]\n", STATIC_CHAIN_REGNUM, > PC_REGNUM); > @@ -4023,12 +4060,40 @@ arm_trampoline_init (rtx m_tramp, tree fndecl, > rtx chain_value) >    emit_block_move (m_tramp, assemble_trampoline_template (), >                     GEN_INT (TRAMPOLINE_SIZE), BLOCK_OP_NORMAL); > > -  mem = adjust_address (m_tramp, SImode, TARGET_32BIT ? 8 : 12); > -  emit_move_insn (mem, chain_value); > +  if (TARGET_FDPIC) > +    { > +      rtx funcdesc = XEXP (DECL_RTL (fndecl), 0); > +      rtx fnaddr = gen_rtx_MEM (Pmode, funcdesc); > +      rtx gotaddr = gen_rtx_MEM (Pmode, plus_constant (Pmode, > funcdesc, 4)); > +      /* The function start address is at offset 8, but in Thumb mode > +        we want bit 0 set to 1 to indicate Thumb-ness, hence 9 > +        below.  */ > +      rtx trampoline_code_start > +       = plus_constant (Pmode, XEXP (m_tramp, 0), TARGET_THUMB2 ? 9 : 8); > + > +      /* Write initial funcdesc which points to the trampoline.  */ > +      mem = adjust_address (m_tramp, SImode, 0); > +      emit_move_insn (mem, trampoline_code_start); > +      mem = adjust_address (m_tramp, SImode, 4); > +      emit_move_insn (mem, gen_rtx_REG (Pmode, PIC_OFFSET_TABLE_REGNUM)); > +      /* Setup static chain.  */ > +      mem = adjust_address (m_tramp, SImode, 20); > +      emit_move_insn (mem, chain_value); > +      /* GOT + real function entry point.  */ > +      mem = adjust_address (m_tramp, SImode, 24); > +      emit_move_insn (mem, gotaddr); > +      mem = adjust_address (m_tramp, SImode, 28); > +      emit_move_insn (mem, fnaddr); > +    } > +  else > +    { > +      mem = adjust_address (m_tramp, SImode, TARGET_32BIT ? 8 : 12); > +      emit_move_insn (mem, chain_value); > > -  mem = adjust_address (m_tramp, SImode, TARGET_32BIT ? 12 : 16); > -  fnaddr = XEXP (DECL_RTL (fndecl), 0); > -  emit_move_insn (mem, fnaddr); > +      mem = adjust_address (m_tramp, SImode, TARGET_32BIT ? 12 : 16); > +      fnaddr = XEXP (DECL_RTL (fndecl), 0); > +      emit_move_insn (mem, fnaddr); > +    } > >    a_tramp = XEXP (m_tramp, 0); >    emit_library_call (gen_rtx_SYMBOL_REF (Pmode, "__clear_cache"), > @@ -4042,7 +4107,9 @@ arm_trampoline_init (rtx m_tramp, tree fndecl, > rtx chain_value) >  static rtx >  arm_trampoline_adjust_address (rtx addr) >  { > -  if (TARGET_THUMB) > +  /* For FDPIC don't fix trampoline address since it's a function > +     descriptor and not a function address.  */ > +  if (TARGET_THUMB && !TARGET_FDPIC) >      addr = expand_simple_binop (Pmode, IOR, addr, const1_rtx, >                                  NULL, 0, OPTAB_LIB_WIDEN); >    return addr; > diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h > index 45c0e2b..f80df63 100644 > --- a/gcc/config/arm/arm.h > +++ b/gcc/config/arm/arm.h > @@ -1602,7 +1602,7 @@ typedef struct >  #define INIT_EXPANDERS  arm_init_expanders () > >  /* Length in units of the trampoline for entering a nested function.  */ > -#define TRAMPOLINE_SIZE  (TARGET_32BIT ? 16 : 20) > +#define TRAMPOLINE_SIZE  (TARGET_FDPIC ? 32 : (TARGET_32BIT ? 16 : 20)) > >  /* Alignment required for a trampoline in bits.  */ >  #define TRAMPOLINE_ALIGNMENT  32 > -- > 2.6.3 >