[RISC-V] epilogue_begin is set incorrectly #120553
Description
For the following test,
int main(int argc, char **argv)
{
int foo = 1;
return 0;
}
GCC (riscv32) generates (https://godbolt.org/z/Wqze6n8Gs):
main:
.LFB0:
.file 1 "/app/example.c"
.loc 1 2 1
.cfi_startproc
addi sp,sp,-48
.cfi_def_cfa_offset 48
sw ra,44(sp)
sw s0,40(sp)
.cfi_offset 1, -4
.cfi_offset 8, -8
addi s0,sp,48
.cfi_def_cfa 8, 0
sw a0,-36(s0)
sw a1,-40(s0)
.loc 1 3 7
li a5,1
sw a5,-20(s0)
.loc 1 5 10
li a5,0
.loc 1 6 1
mv a0,a5
lw ra,44(sp)
.cfi_restore 1
lw s0,40(sp)
.cfi_restore 8
.cfi_def_cfa 2, 48
addi sp,sp,48
.cfi_def_cfa_offset 0
jr ra
.cfi_endproc
.LFE0:
.size main, .-main
and Clang riscv32 generates (https://godbolt.org/z/TMGPsr44s):
main:
.Lfunc_begin0:
.file 0 "/app" "/app/example.c" md5 0x8aa04db627be45b3215ab92eac2e23c5
.file 1 "example.c" md5 0x8aa04db627be45b3215ab92eac2e23c5
.loc 1 2 0
.cfi_sections .debug_frame
.cfi_startproc
addi sp, sp, -32
.cfi_def_cfa_offset 32
sw ra, 28(sp)
sw s0, 24(sp)
.cfi_offset ra, -4
.cfi_offset s0, -8
addi s0, sp, 32
.cfi_def_cfa s0, 0
mv a2, a0
li a0, 0
sw a0, -12(s0)
sw a2, -16(s0)
sw a1, -20(s0)
li a1, 1
.Ltmp0:
.loc 1 3 7 prologue_end
sw a1, -24(s0)
.cfi_def_cfa sp, 32
lw ra, 28(sp) <<<<<<<<<<
lw s0, 24(sp)
.cfi_restore ra
.cfi_restore s0
.loc 1 5 3 epilogue_begin <<<<<<<<<<
addi sp, sp, 32
.cfi_def_cfa_offset 0
ret
.Ltmp1:
.Lfunc_end0:
.size main, .Lfunc_end0-main
As can be seen from the Clang's output, the epilogue_begin is set after the epilogue has actually begun. This creates a problem if we single step from line 3, or set a breakpoint on line 5, the FP has been restored to the parent frame's FP, and accessing variables goes to the wrong place.
$ gdb main.gcc
(gdb) b main
Breakpoint 1 at 0x10444: file main.c, line 3.
(gdb) c
Continuing.
Breakpoint 1, main (argc=1, argv=0x40800004) at main.c:3
3 int foo = 1;
(gdb) si
0x00010446 3 int foo = 1;
(gdb) p foo
$1 = 0
(gdb) si
5 return 0;
(gdb) p foo
$2 = 1
(gdb) s
6 }
(gdb) p foo
$3 = 1
(gdb)
$ gdb main.llvm
(gdb) b main
Breakpoint 1 at 0x10496: file main.c, line 3.
(gdb) c
Continuing.
Breakpoint 1, main (argc=1, argv=0x407ffff4) at main.c:3
3 int foo = 1;
(gdb) si
0x0001049a 3 int foo = 1;
(gdb) p foo
$1 = 1
(gdb) si
0x0001049c 3 int foo = 1;
(gdb) p foo
$2 = 1
(gdb) s
5 return 0;
(gdb) p foo
$3 = -1242739775
(gdb)