Hi
I would like to have a stack check for threads with small stack space
for each thread.
(I'm using a ARM Cortex-M3 microcontroller with a stack size of a 1
KByte per Thread.)
Each thread having its own limit address.
The thread scheduler can then calculate the limit and store this value
inside of a global variable.
The compiler may generate code to check the stack for overflow at
function entry.
In principal this can be done this way:
- push registers as usual
- figure out if one or two work registers, that can be used directly
without extra push
- if not enough registers found push required work registers to stack
- load limit address into first working register
- load value of limit address (into the same register)
- if stack pointer will go to extend the stack (e.g. for local
variables) load this size value too
(here the second work register can be used)
- compare for overflow
- if overflow occur "call" stack_failure function
- pop work registers that are pushed before
- continue function prologue as usual e.g. extend stack pointer
The ARM target has an option "-mapcs-stack-check" but this is more or
less not working. (implementaion missing)
There are also architecture independent options like
"-fstack-check=generic", "-fstack-limit-symbol=current_stack_limit" or
"-fstack-limit-register=r6"
that can be used.
The generic stack check is doing a probe at end of function prologue phase
(e.g by writing 12K ahead the current stack pointer position).
If this stack space is not available the probe may generates a fault.
This require that the CPU is having a MPU or a MMU.
For machines with small memory space an additional mechanism should be
available.
The option "-fstack-check" can be extend by the switches "direct" and
"indirect" to emit compare code in function prologue.
If switch "direct" is given the address of "-fstack-limit-symbol"
represents the limit itself.
If switch "indirect" is given "-fstack-limit-symbol" is a kind of global
variable that needs be read before compare.
I have add an proposal to show how an integrateion of this behavior can
be done at ARM architecture.
Is there interest to have such a feature at GCC side?
Is there someone with write permission who is willing to play the role
as a volunteer for this task?
Is the code still small enough to be acceptable or is additional
paperwork required first?
The generated code itself will be small
e.g. if using "-fstack-check=indirect -fstack-limit-symbol=stack_limit_var"
-> push {r0}
-> ldr r0, =stack_limit_var
-> ldr r0, [r0]
-> cmp sp, r0
-> bhs 1f
-> push {lr}
-> bl __thumb_stack_failure @ stack check
->.align
->.ltorg
->1:
-> pop {r0}
The rest of the implementation overhead is only GCC specific.
Regards
Thomas Klein
PS
Here are some more implementation hints.
introduce new parameters "direct" and "indirect" in gcc/opts.c and
gcc/flag-types.h
gcc/explow.c function allocate_dynamic_stack_space:
- suppress stack probing if parameter "direct", "indirect" or if a
stack-limit is given
- do additional read of limit value if parameter "indirect" and a
stack-limit symbol is given
gcc/config/arm/arm.c
- new function "stack_check_output_function" to write the stack check
to the assember file
- new function "stack_check_work_registers" to find possible working
registers (only used by "stack check")
- integration for ARM and Thumb-2 in function arm_expand_prologue
- integration for Thumb-1 in function thumb1_output_function_prologue
gcc/config/arm/arm.md
- probe_stack: do not emit code when parameters "direct" or "indirect"
given
emit code as in gcc/explow.c
- probe_stack_done: dummy to make sure probe_stack insns are not
optimized away
- check_stack: if stack-limit and parameter "generic" is given use the
limit the same way as in function allocate_dynamic_stack_space
- stack_check: ARM/Thumb-2 insn to output function
stack_check_output_function
- trap: failure call used in function allocate_dynamic_stack_space
Index: gcc/opts.c
===================================================================
--- gcc/opts.c (revision 168762)
+++ gcc/opts.c (working copy)
@@ -1616,6 +1616,12 @@ common_handle_option (struct gcc_options *opts,
: STACK_CHECK_STATIC_BUILTIN
? STATIC_BUILTIN_STACK_CHECK
: GENERIC_STACK_CHECK;
+ else if (!strcmp (arg, "indirect"))
+ /* This is an other stack checking method. */
+ opts->x_flag_stack_check = INDIRECT_STACK_CHECK;
+ else if (!strcmp (arg, "direct"))
+ /* This is an other stack checking method. */
+ opts->x_flag_stack_check = DIRECT_STACK_CHECK;
else
warning_at (loc, 0, "unknown stack check parameter \"%s\"", arg);
break;
Index: gcc/flag-types.h
===================================================================
--- gcc/flag-types.h (revision 168762)
+++ gcc/flag-types.h (working copy)
@@ -153,7 +153,11 @@ enum stack_check_type
/* Check the stack and entirely rely on the target configuration
files, i.e. do not use the generic mechanism at all. */
- FULL_BUILTIN_STACK_CHECK
+ FULL_BUILTIN_STACK_CHECK,
+
+ /* Check the stack after allocation at each function entry */
+ DIRECT_STACK_CHECK,
+ INDIRECT_STACK_CHECK
};
/* Names for the different levels of -Wstrict-overflow=N. The numeric
Index: gcc/explow.c
===================================================================
--- gcc/explow.c (revision 168762)
+++ gcc/explow.c (working copy)
@@ -1395,7 +1395,12 @@ allocate_dynamic_stack_space (rtx size, unsigned s
/* If needed, check that we have the required amount of stack. Take
into
account what has already been checked. */
- if (STACK_CHECK_MOVING_SP)
+ if ( STACK_CHECK_MOVING_SP
+#ifdef HAVE_check_stack
+ || crtl->limit_stack
+#endif
+ || flag_stack_check == DIRECT_STACK_CHECK
+ || flag_stack_check == INDIRECT_STACK_CHECK)
;
else if (flag_stack_check == GENERIC_STACK_CHECK)
probe_stack_range (STACK_OLD_CHECK_PROTECT +
STACK_CHECK_MAX_FRAME_SIZE,
@@ -1437,15 +1442,23 @@ allocate_dynamic_stack_space (rtx size, unsigned s
/* Check stack bounds if necessary. */
if (crtl->limit_stack)
{
+ rtx limit_rtx;
rtx available;
rtx space_available = gen_label_rtx ();
+ if ( GET_CODE (stack_limit_rtx) == SYMBOL_REF
+ && flag_stack_check == INDIRECT_STACK_CHECK)
+ limit_rtx = expand_unop (Pmode, mov_optab,
+ gen_rtx_MEM (Pmode, stack_limit_rtx),
+ NULL_RTX, 1);
+ else
+ limit_rtx = stack_limit_rtx;
#ifdef STACK_GROWS_DOWNWARD
available = expand_binop (Pmode, sub_optab,
- stack_pointer_rtx, stack_limit_rtx,
+ stack_pointer_rtx, limit_rtx,
NULL_RTX, 1, OPTAB_WIDEN);
#else
available = expand_binop (Pmode, sub_optab,
- stack_limit_rtx, stack_pointer_rtx,
+ limit_rtx, stack_pointer_rtx,
NULL_RTX, 1, OPTAB_WIDEN);
#endif
emit_cmp_and_jump_insns (available, size, GEU, NULL_RTX, Pmode, 1,
Index: gcc/config/arm/arm.c
===================================================================
--- gcc/config/arm/arm.c (revision 168762)
+++ gcc/config/arm/arm.c (working copy)
@@ -14472,6 +14472,136 @@ arm_output_function_prologue (FILE *f, HOST_WIDE_I
}
+void
+stack_check_output_function (FILE *f, int reg0, int reg1, unsigned amount,
+ unsigned numregs)
+{
+ unsigned amount_needsreg, amount_const_ok, issym=0;
+
+ if (TARGET_THUMB1)
+ amount_const_ok = (amount < 256);
+ else
+ amount_const_ok = const_ok_for_arm (amount);
+
+ if(GET_CODE (stack_limit_rtx) == SYMBOL_REF) /*stack_limit_rtx*/
+ {
+ issym = 1;
+ amount_needsreg = !amount_const_ok;
+ }
+ else
+ amount_needsreg = (amount > 0);
+
+ if (issym && amount) /*need temp regs for limit and amount*/
+ {
+ if (numregs >= 2)
+ ; /*no need to push*/
+ else if (numregs == 1)
+ {
+ if (amount_needsreg)
+ {
+ /*push temp reg for amount*/
+ if (TARGET_ARM)
+ asm_fprintf (f, "\tstr\t%r, [%r, #-4]!\n", reg1,
SP_REGNUM);
+ else
+ asm_fprintf (f, "\tpush\t{%r}\n", reg1);
+ }
+ }
+ else
+ {
+ /*push temp regs for limit and amount*/
+ if (TARGET_ARM)
+ asm_fprintf (f, "\tstmfd\t%r, {%r,%r}\n", SP_REGNUM, reg0,
reg1);
+ else
+ asm_fprintf (f, "\tpush\t{%r,%r}\n", reg0, reg1);
+ }
+ }
+ else if ((issym || amount_needsreg) && numregs == 0)
+ { /*push temp reg either for limit or amount*/
+ if (TARGET_ARM)
+ asm_fprintf (f, "\tstr\t%1, [%0, #-4]!\n", reg0, SP_REGNUM);
+ else
+ asm_fprintf (f, "\tpush\t{%r}\n", reg0);
+ }
+
+ if (issym)
+ {
+ char *str ;
+ str = (char *) XSTR (stack_limit_rtx, 0);
+
+ asm_fprintf (f, "\tldr\t%r, =%s\n", reg0, str);
+ if (flag_stack_check == INDIRECT_STACK_CHECK)
+ asm_fprintf (f, "\tldr\t%r, [%r]\n", reg0, reg0);
+ if (amount)
+ {
+ if (amount_const_ok)
+ {
+ asm_fprintf (f, "\tadds\t%r, %r, #%d\n", reg0, reg0, amount);
+ }
+ else
+ {
+ asm_fprintf (f, "\tldr\t%r, =#%d\n", reg1, amount);
+ asm_fprintf (f, "\tadd\t%r, %r, %r\n", reg0, reg0, reg1);
+ }
+ }
+ asm_fprintf (f, "\tcmp\t%r, %r\n", SP_REGNUM, reg0);
+ }
+ else if (amount)
+ {
+ if (amount_const_ok)
+ asm_fprintf (f, "\tmov\t%r, =#%d\n", reg0, amount);
+ else
+ asm_fprintf (f, "\tldr\t%r, =#%d\n", reg0, amount);
+ asm_fprintf (f, "\tadd\t%r, %r, %r\n", reg0, reg0,
REGNO(stack_limit_rtx));
+ asm_fprintf (f, "\tcmp\t%r, %r\n", SP_REGNUM, reg0);
+ }
+ else
+ asm_fprintf (f, "\tcmp\t%r, %r\n", SP_REGNUM, REGNO(stack_limit_rtx));
+ asm_fprintf (f, "\tbhs\t1f\n");
+ if (TARGET_ARM)
+ {
+ asm_fprintf (f, "\stmfd\t%r, {%r}\n", SP_REGNUM, LR_REGNUM);
+ asm_fprintf (f, "\tbl\t__arm_stack_failure\t%@ stack check\n");
+ }
+ else
+ {
+ asm_fprintf (f, "\tpush\t{%r}\n", LR_REGNUM);
+ asm_fprintf (f, "\tbl\t__thumb_stack_failure\t%@ stack check\n");
+ }
+
+ if (issym || amount) /*temp regs: collect values from here*/
+ asm_fprintf (f, ".align\n.ltorg\n");
+ asm_fprintf (f, "1:\n");
+ if (issym && amount) /*pop temp regs used by limit and amount*/
+ {
+ if (numregs >= 2)
+ ; /*no need to pop*/
+ else if (numregs == 1)
+ {
+ if (amount_needsreg)
+ {
+ if (TARGET_ARM)
+ asm_fprintf (f, "\tldr\t%r, [%r, #4]!\n", reg1, SP_REGNUM);
+ else
+ asm_fprintf (f, "\tpop\t{%r}\n", reg1);
+ }
+ }
+ else
+ {
+ if (TARGET_ARM)
+ asm_fprintf (f, "\tldmfd\t%r, {%r,%r}\n", SP_REGNUM, reg0,
reg1);
+ else
+ asm_fprintf (f, "\tpop\t{%r,%r}\n", reg0, reg1);
+ }
+ }
+ else if ((issym || amount_needsreg) && numregs == 0)
+ { /*pop temp reg used by limit or amount*/
+ if (TARGET_ARM)
+ asm_fprintf (f, "\tldr\t%r, [%r, #4]!\n", reg0, SP_REGNUM);
+ else
+ asm_fprintf (f, "\tpop\t{%r}\n", reg0);
+ }
+}
+
const char *
arm_output_epilogue (rtx sibling)
{
@@ -15616,6 +15746,72 @@ thumb_set_frame_pointer (arm_stack_offsets *offset
RTX_FRAME_RELATED_P (insn) = 1;
}
+/*search for possible work registers for stack-check operation at prologue
+ return the number of register that can be used without extra push/pop */
+
+static int
+stack_check_work_registers (rtx *workreg)
+{
+ int reg, i, k, n, nregs;
+
+ if (crtl->args.info.pcs_variant <= ARM_PCS_AAPCS_LOCAL)
+ {
+ nregs = crtl->args.info.aapcs_next_ncrn;
+ }
+ else
+ nregs = crtl->args.info.nregs;
+
+
+ n = 0;
+ i = 0;
+ /* check if we can use one of the argument registers r0..r3 as long
as they
+ * not holding data*/
+ for (reg = 0; reg <= LAST_ARG_REGNUM && i < 2; reg++)
+ {
+ if ( !df_regs_ever_live_p (reg)
+ || (cfun->machine->uses_anonymous_args &&
crtl->args.pretend_args_size
+ > (LAST_ARG_REGNUM - reg) * UNITS_PER_WORD)
+ || (!cfun->machine->uses_anonymous_args && nregs < reg + 1)
+ )
+ {
+ workreg[i++] = gen_rtx_REG (SImode, reg);
+ n = (reg + 1) % 4;
+ }
+ }
+
+ /* otherwise try to use r4..r7*/
+ for (reg = LAST_ARG_REGNUM + 1; reg <= LAST_LO_REGNUM && i < 2; reg++)
+ {
+ if ( df_regs_ever_live_p (reg)
+ && !fixed_regs[reg]
+ && reg != FP_REGNUM )
+ {
+ workreg[i++] = gen_rtx_REG (SImode, reg);
+ }
+ }
+
+ if (TARGET_32BIT)
+ {
+ /* ARM and Thumb-2 can use high regs. */
+ for (reg = FIRST_HI_REGNUM; reg <= LAST_HI_REGNUM && i < 2; reg ++)
+ if ( df_regs_ever_live_p (reg)
+ && !fixed_regs[reg]
+ && reg != FP_REGNUM )
+ {
+ workreg[i++] = gen_rtx_REG (SImode, reg);
+ }
+ }
+
+ k = i;
+ /* if not enough found to be uses without extra push,
+ * collect next from r0..r4*/
+ for ( ; i<2; i++)
+ workreg[i] = gen_rtx_REG (SImode, n++);
+
+ return k;
+}
+
+
/* Generate the prologue instructions for entry into an ARM or Thumb-2
function. */
void
@@ -15865,6 +16061,24 @@ arm_expand_prologue (void)
current_function_static_stack_size
= offsets->outgoing_args - offsets->saved_args;
+ if ( crtl->limit_stack
+ && !(IS_INTERRUPT (func_type))
+ && ( flag_stack_check == DIRECT_STACK_CHECK
+ || flag_stack_check == INDIRECT_STACK_CHECK)
+ && (offsets->outgoing_args - offsets->saved_args) > 0
+ )
+ {
+ rtx reg[2], num_temp_regs;
+
+ amount = GEN_INT (offsets->outgoing_args - saved_regs
+ - offsets->saved_args);
+ num_temp_regs = GEN_INT (stack_check_work_registers(reg));
+ insn = gen_stack_check (stack_pointer_rtx,
+ reg[0], reg[1], stack_limit_rtx,
+ amount, num_temp_regs);
+ insn = emit_insn (insn);
+ }
+
if (offsets->outgoing_args != offsets->saved_args + saved_regs)
{
/* This add can produce multiple insns for a large constant, so we
@@ -21050,6 +21264,26 @@ thumb1_output_function_prologue (FILE *f, HOST_WID
thumb_pushpop (f, pushable_regs, 1, &cfa_offset, real_regs_mask);
}
}
+
+ if( crtl->limit_stack
+ && ( flag_stack_check == DIRECT_STACK_CHECK
+ || flag_stack_check == INDIRECT_STACK_CHECK)
+ && (offsets->outgoing_args - offsets->saved_args)
+ )
+ {
+ unsigned amount, numregs;
+ int reg0, reg1;
+ rtx reg[2];
+
+ amount = offsets->outgoing_args - offsets->saved_regs;
+ amount -= 4 * thumb1_extra_regs_pushed (offsets, true);
+
+ numregs = stack_check_work_registers(reg);
+ reg0 = REGNO (reg[0]);
+ reg1 = REGNO (reg[1]);
+
+ stack_check_output_function (f, reg0, reg1, amount, numregs);
+ }
}
/* Handle the case of a double word load into a low register from
Index: gcc/config/arm/arm.md
===================================================================
--- gcc/config/arm/arm.md (revision 168762)
+++ gcc/config/arm/arm.md (working copy)
@@ -104,6 +104,7 @@
(UNSPEC_SYMBOL_OFFSET 27) ; The offset of the start of the symbol from
; another symbolic address.
(UNSPEC_MEMORY_BARRIER 28) ; Represent a memory barrier.
+ (UNSPEC_PROBE_STACK 29) ; probe stack memory reference
]
)
@@ -10581,6 +10582,108 @@
[(set_attr "conds" "clob")]
)
+(define_expand "probe_stack"
+ [(match_operand 0 "memory_operand" "")]
+ "TARGET_EITHER"
+{
+ if ( flag_stack_check == DIRECT_STACK_CHECK
+ || flag_stack_check == INDIRECT_STACK_CHECK)
+ ;
+ else
+ {
+ emit_move_insn (operands[0], const0_rtx);
+ emit_insn (gen_probe_stack_done (operands[0]));
+ emit_insn (gen_blockage ());
+ }
+ DONE;
+}
+)
+
+(define_insn "probe_stack_done"
+ [(set (match_operand 0 "memory_operand" "=m")
+ (unspec [(const_int 0)] UNSPEC_PROBE_STACK))]
+ "TARGET_EITHER"
+ "@ probe stack done"
+ [(set_attr "type" "store1")]
+)
+
+(define_expand "check_stack"
+ [(match_operand 0 "memory_operand" "")]
+ "crtl->limit_stack
+ && flag_stack_check != DIRECT_STACK_CHECK
+ && flag_stack_check != INDIRECT_STACK_CHECK"
+{
+ rtx label = gen_label_rtx ();
+ rtx addr = copy_rtx (operands[0]);
+ addr = gen_rtx_fmt_ee (MINUS, Pmode, addr, GEN_INT (0));
+ addr = force_operand (addr, NULL_RTX);
+ emit_insn (gen_blockage ());
+ emit_cmp_and_jump_insns (stack_limit_rtx, addr, LEU, NULL_RTX, Pmode, 1,
+ label);
+ emit_insn (gen_trap ());
+ emit_label (label);
+ emit_insn (gen_blockage ());
+ DONE;
+}
+)
+
+
+(define_insn "stack_check"
+ [(set
+ (match_operand:SI 0 "register_operand" "=k")
+ (match_operand:SI 3 "general_operand" "sr")
+ )
+ (match_operand:SI 1 "register_operand" "r")
+ (match_operand:SI 2 "register_operand" "r")
+ (match_operand:SI 4 "general_operand" "i")
+ (match_operand:SI 5 "general_operand" "i")
+ (clobber (reg:CC CC_REGNUM))
+ ]
+ "TARGET_32BIT
+ && (operands[3] == stack_limit_rtx)
+ && (GET_CODE (operands[4]) == CONST_INT)
+ && (GET_CODE (operands[5]) == CONST_INT)"
+ "*
+ {
+ int reg0, reg1;
+ unsigned amount, numregs;
+
+ reg0 = REGNO (operands[1]);
+ reg1 = REGNO (operands[2]);
+ amount = INTVAL (operands[4]);
+ numregs = INTVAL (operands[5]);
+
+ stack_check_output_function (asm_out_file, reg0, reg1, amount,
numregs);
+ }
+ return \"\";
+ "
+ [(set_attr "conds" "clob")]
+)
+
+(define_insn "trap"
+ [(trap_if (const_int 1) (const_int 0))]
+ "TARGET_EITHER"
+ "*
+ {
+ rtx ops[2];
+
+ ops[0] = stack_pointer_rtx;
+ ops[1] = gen_rtx_REG (SImode, LR_REGNUM);
+ if (TARGET_ARM)
+ {
+ output_asm_insn (\"str\\t%1, [%0, #-4]!\", ops);
+ output_asm_insn (\"bl\\t__arm_stack_failure\\t%@ trap call\", ops);
+ }
+ else
+ {
+ output_asm_insn (\"push\\t{%1}\", ops);
+ output_asm_insn (\"bl\\t__thumb_stack_failure\\t%@ trap call\",
ops);
+ }
+ }
+ return \"\";
+ "
+)
+
(define_insn "*arm_movtas_ze"
[(set (zero_extract:SI (match_operand:SI 0 "s_register_operand" "+r")
(const_int 16)
