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 <christophe.l...@st.com>
Mickaël Guêné <mickael.gu...@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: 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
