[Bug gas/28793] New: [RISC-V] DW_cfa_advance_offset is not correct

[lifang_xia at linux dot alibaba.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28793

            Bug ID: 28793
           Summary: [RISC-V] DW_cfa_advance_offset is not correct
           Product: binutils
           Version: 2.38 (HEAD)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: lifang_xia at linux dot alibaba.com
  Target Milestone: ---

Created attachment 13915
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13915&action=edit
pic of eh_frame

commit: HEAD
========
build config: 
../configure --disable-gdb --target=riscv64-unknown-linux-gnu
========
test:
.global hello
hello:
        .cfi_startproc
        nop
        addi    sp,sp,-32
        .cfi_def_cfa_offset 32
        sd      ra,24(sp)
        sd      s0,16(sp)
        sd      s1,8(sp)
        .cfi_offset 1, -8
        .cfi_offset 8, -16
        .cfi_offset 9, -24

ld      ra,24(sp)
.LXXXXX:
        .cfi_remember_state
        .cfi_restore 1
ld      s0,16(sp)
        .cfi_restore 8
ld      s1,8(sp)
        .cfi_restore 9
        addi    sp,sp,32
.LXXXXA:
        .cfi_def_cfa_offset 0
        jr      ra
.LVL1034:
        .align  2
.L1035:
        .cfi_restore_state
.LEHB7:
        jalr    a5
.LVL1035:
.LBE2445:
.LBE2448:
ld      ra,24(sp)
        .cfi_remember_state
        .cfi_restore 1
ld      s0,16(sp)
        .cfi_restore 8
ld      s1,8(sp)
        .cfi_restore 9
        addi    sp,sp,32
        .cfi_def_cfa_offset 0
        jr      ra
        .cfi_restore_state

        .cfi_endproc
========
command:
./gas/as-new -o a.o a.s -march=rv64gc
./ld/ld-new -o a a.o -e hello
./binutils/objdump -d a
./binutils/readelf -w a
========
eh_frame
In the picture, the DW_CFA_advance_loc should be 0x100c4, but the result is
0x100c6;
If delete the nop in the head of the source. The DW_CFA_advance_loc is 0x100c4.
========
why
".align 2" in .LVL1034 will create a relocation in the .o, and the nop for
alignment will be remove in linker. But the DW_CFA_advance_loc is fixed while
assembling.

We need to start a new frag after alignment. It is same like the instruction
that can be optimized away or compressed by the linker during relaxation. 
=========
patch

diff --git a/gas/config/tc-riscv.c b/gas/config/tc-riscv.c
index 390aaf1710b..ed1e771d290 100644
--- a/gas/config/tc-riscv.c
+++ b/gas/config/tc-riscv.c
@@ -4462,6 +4462,21 @@ s_variant_cc (int ignored ATTRIBUTE_UNUSED)
   elfsym->internal_elf_sym.st_other |= STO_RISCV_VARIANT_CC;
 }

+/* Split frag after alignment.  */
+static void
+s_riscv_align (int arg)
+{
+  s_align_ptwo (arg);
+
+  /* We need to start a new frag after alignment which may be remove  by the
+     linker during relaxation, to prevent the assembler from computing static
+     offsets.
+     This is necessary to get correct EH info.  */
+
+  frag_wane (frag_now);
+  frag_new (0);
+}
+
 /* Same as elf_copy_symbol_attributes, but without copying st_other.
    This is needed so RISC-V specific st_other values can be independently
    specified for an IFUNC resolver (that is called by the dynamic linker)
@@ -4507,6 +4522,7 @@ static const pseudo_typeS riscv_pseudo_table[] =
   {"insn", s_riscv_insn, 0},
   {"attribute", s_riscv_attribute, 0},
   {"variant_cc", s_variant_cc, 0},
+  {"align", s_riscv_align, 0},

   { NULL, NULL, 0 },
 };

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