[ARM/FDPIC,v2,09/21,ARM] FDPIC: Add support for taking address of nested function

Message ID 20180713161136.29104-10-christophe.lyon@st.com
State New
Headers show
Series
  • FDPIC ABI for ARM
Related show

Commit Message

Christophe Lyon July 13, 2018, 4:11 p.m.
From: Christophe Lyon <christophe.lyon@linaro.org>


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]
	   .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.

2018-XX-XX  Christophe Lyon  <christophe.lyon@st.com>
	Mickaël Guêné <mickael.guene@st.com>

	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: I4b5127261a9aefa0f0318f110574ec07a856aeb1

-- 
2.6.3

Comments

Kyrill Tkachov Aug. 29, 2018, 11:01 a.m. | #1
Hi Christophe,

On 13/07/18 17:11, christophe.lyon@st.com wrote:
> From: Christophe Lyon <christophe.lyon@linaro.org>

>

> 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]


The comment in the code says the last one is:
ldr           pc,  [pc, #8] ; #4 for Thumb2

I'm assuming the code one is correct.

>            .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.

>

> 2018-XX-XX  Christophe Lyon  <christophe.lyon@st.com>

>         Mickaël Guêné <mickael.guene@st.com>

>

>         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: I4b5127261a9aefa0f0318f110574ec07a856aeb1

>

> diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c

> index 51da2bc..ffc9128 100644

> --- a/gcc/config/arm/arm.c

> +++ b/gcc/config/arm/arm.c

> @@ -3950,13 +3950,50 @@ 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

> +*/

>  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_assert ( !TARGET_ARM && !TARGET_THUMB2);

> +


This cannot trigger based on the two clauses above. I think you want to just make it 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);

> +      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);

> @@ -3997,12 +4034,37 @@ 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));

> +      rtx trampoline_code_start

> +       = plus_constant (Pmode, XEXP (m_tramp, 0), TARGET_THUMB2 ? 9 : 8);


9? Can you comment on this value?

> +

> +      /* 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"),

> @@ -4016,7 +4078,9 @@ 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 4671d64..22a65a1 100644

> --- a/gcc/config/arm/arm.h

> +++ b/gcc/config/arm/arm.h

> @@ -1581,7 +1581,7 @@ 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

>
Christophe Lyon Aug. 31, 2018, 2:17 p.m. | #2
On Wed, 29 Aug 2018 at 13:01, Kyrill Tkachov
<kyrylo.tkachov@foss.arm.com> wrote:
>

> Hi Christophe,

>

> On 13/07/18 17:11, christophe.lyon@st.com wrote:

> > From: Christophe Lyon <christophe.lyon@linaro.org>

> >

> > 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]

>

> The comment in the code says the last one is:

> ldr           pc,  [pc, #8] ; #4 for Thumb2

>

> I'm assuming the code one is correct.


Right, it looks like a typo in the commit message.

>

> >            .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.

> >

> > 2018-XX-XX  Christophe Lyon  <christophe.lyon@st.com>

> >         Mickaël Guêné <mickael.guene@st.com>

> >

> >         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: I4b5127261a9aefa0f0318f110574ec07a856aeb1

> >

> > diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c

> > index 51da2bc..ffc9128 100644

> > --- a/gcc/config/arm/arm.c

> > +++ b/gcc/config/arm/arm.c

> > @@ -3950,13 +3950,50 @@ 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

> > +*/

> >  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_assert ( !TARGET_ARM && !TARGET_THUMB2);

> > +

>

> This cannot trigger based on the two clauses above. I think you want to just make it gcc_unreachable ().

>

OK

> > +      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);

> > +      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);

> > @@ -3997,12 +4034,37 @@ 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));

> > +      rtx trampoline_code_start

> > +       = plus_constant (Pmode, XEXP (m_tramp, 0), TARGET_THUMB2 ? 9 : 8);

>

> 9? Can you comment on this value?

>

The function start address is a offset 8, but in Thumb mode we want
bit 0 set to 1 to indicate thumb-ness.

> > +

> > +      /* 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"),

> > @@ -4016,7 +4078,9 @@ 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 4671d64..22a65a1 100644

> > --- a/gcc/config/arm/arm.h

> > +++ b/gcc/config/arm/arm.h

> > @@ -1581,7 +1581,7 @@ 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

> >

>

Patch

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 51da2bc..ffc9128 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -3950,13 +3950,50 @@  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
+*/
 
 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_assert ( !TARGET_ARM && !TARGET_THUMB2);
+
+      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);
+      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);
@@ -3997,12 +4034,37 @@  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));
+      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"),
@@ -4016,7 +4078,9 @@  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 4671d64..22a65a1 100644
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -1581,7 +1581,7 @@  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