[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)