Hi, Would you please help on how to generate correct epilogue dwarf info? Without correct dwarf info, when shrink-wrap is enabled, it tends to ICE at dwarf2cfi.c: function maybe_record_trace_start.
/* We ought to have the same state incoming to a given trace no
matter how we arrive at the trace. Anything else means we've
got some kind of optimization error. */
gcc_checking_assert (cfi_row_equal_p (cur_row, ti->beg_row));
Issues:
1) pretend_args
The attached pretend_arg.c shows an example about pretend_args dwarf info
push {r2, r3}
.cfi_def_cfa_offset 8
.cfi_offset 2, -8
.cfi_offset 3, -4
use r3
push {r4, r5, lr}
...
pop {r4, r5, lr}
add sp, sp, #8
//No instruction here to restore r2 and r3
Can we RESTORE r2 and r3?
* If we notes to RESTORE r2 and r3, it might lead to wrong info for
GDB since no instruction restores them.
* If we do not RESTORE them, the reg_save dwarf info will not be
cleared. Then the dwarf check will fail when the function is
shrink-wrapped.
2) frame_pointer_needed
In prologue, we set fp like
fp = sp + INT
After this instruction, cfi_def_cfa_register is set to fp
In epilogue. we have
fp += INT
sp = fp
Can we reset cfi_def_cfa_register back to sp?
* If we set it back to sp, how to handle it in arm_unwind_emit_set,
which assumes sp can not be set from other register?
/* A stack increment. */
if (GET_CODE (e1) != PLUS
|| !REG_P (XEXP (e1, 0))
|| REGNO (XEXP (e1, 0)) != SP_REGNUM
|| !CONST_INT_P (XEXP (e1, 1)))
abort ();
* If we do not set it back, to get correct dwarf info for POP after
"sp = fp", we have to add notes " sp = fp + INT" for dwarf-info while
we have "sp = sp + INT" in the insn. Here is the workaround POP RTL
example for the attached alloca,c:
(insn/f 62 61 66 3 (parallel [
(set/f (reg/f:SI 13 sp) // sp = sp + 8
(plus:SI (reg/f:SI 13 sp)
(const_int 8 [0x8])))
(set/f (reg:SI 3 r3)
(mem/c:SI (reg/f:SI 13 sp) [3 S4 A32]))
(set/f (reg/f:SI 7 r7)
(mem/c:SI (plus:SI (reg/f:SI 13 sp)
(const_int 4 [0x4])) [3 S4 A32]))
]) alloca.c:8 329 {*load_multiple_with_writeback}
(expr_list:REG_UNUSED (reg:SI 3 r3)
(expr_list:REG_CFA_ADJUST_CFA (set (reg/f:SI 13 sp)
(plus:SI (reg/f:SI 7 r7) // sp = fp + 8
(const_int 8 [0x8])))
(expr_list:REG_CFA_RESTORE (reg/f:SI 7 r7)
(expr_list:REG_CFA_RESTORE (reg:SI 3 r3)
(nil))))))
(3) No idea for
if (crtl->calls_eh_return)
emit_insn (gen_addsi3 (stack_pointer_rtx,
stack_pointer_rtx,
gen_rtx_REG (SImode, ARM_EH_STACKADJ_REGNUM)));
Currently I have no shrink-wrapped test case which
crtl->calls_eh_return is true.
Thanks!
-Zhenqiang
#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
#define DEBUG_BUFFER_SIZE 80
int unifi_debug = 5;
void unifi_trace(void* ospriv, int level, const char *fmt, ...)
{
static char s[DEBUG_BUFFER_SIZE];
va_list args;
unsigned int len;
if (!ospriv) return;
if(unifi_debug >= level)
{
va_start(args, fmt);
len = vsnprintf(&(s)[0], (DEBUG_BUFFER_SIZE), fmt, args);
va_end(args);
if (len >= DEBUG_BUFFER_SIZE)
{
(s)[DEBUG_BUFFER_SIZE - 2] = '\n';
(s)[DEBUG_BUFFER_SIZE - 1] = 0;
}
printf("%s", s);
}
}
pretend_arg.s
Description: Binary data
extern int * alloca(int);
int *p;
void test(int a)
{
if (a > 0)
p = alloca(4);
}
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