From 6b116cbb0a84f467e1419385a271ecbc1963ffc1 Mon Sep 17 00:00:00 2001 From: Christophe Lyon Date: Thu, 8 Feb 2018 14:34:20 +0100 Subject: [ARM/FDPIC v6 09/24] [ARM] FDPIC: Add support for taking address of nested function MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 bd09536..4827988 100644 --- a/gcc/config/arm/arm.c +++ b/gcc/config/arm/arm.c @@ -3974,14 +3974,52 @@ arm_warn_func_return (tree decl) ldr pc, [pc] .word static chain value .word function's address - XXX FIXME: When the trampoline returns, r8 will be clobbered. */ + 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 Arm mode + ldr r9, [pc, #8] ; #4 for Arm mode + ldr pc, [pc, #8] ; #4 for Arm mode + .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_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); @@ -4022,12 +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"), @@ -4041,7 +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