riscv: eliminate unreliable __builtin_frame_address(1)

riscv: eliminate unreliable __builtin_frame_address(1)

I tried different pieces of code which uses __builtin_frame_address(1)
(with both gcc version 7.5.0 and 10.3.0) to verify whether it works as
expected on riscv64. The result is negative.

What the compiler had generated is as below:
31                      fp = (unsigned long)__builtin_frame_address(1);
   0xffffffff80006024 <+200>:   ld      s1,0(s0)

It takes '0(s0)' as the address of frame 1 (caller), but the actual address
should be '-16(s0)'.

          |       ...       | <-+
          +-----------------+   |
          | return address  |   |
          | previous fp     |   |
          | saved registers |   |
          | local variables |   |
  $fp --> |       ...       |   |
          +-----------------+   |
          | return address  |   |
          | previous fp --------+
          | saved registers |
  $sp --> | local variables |
          +-----------------+

This leads the kernel can not dump the full stack trace on riscv.

[    7.222126][    T1] Call Trace:
[    7.222804][    T1] [<ffffffff80006058>] dump_backtrace+0x2c/0x3a

This problem is not exposed on most riscv builds just because the '0(s0)'
occasionally is the address frame 2 (caller's caller), if only ra and fp
are stored in frame 1 (caller).

          |       ...       | <-+
          +-----------------+   |
          | return address  |   |
  $fp --> | previous fp     |   |
          +-----------------+   |
          | return address  |   |
          | previous fp --------+
          | saved registers |
  $sp --> | local variables |
          +-----------------+

This could be a *bug* of gcc that should be fixed. But as noted in gcc
manual "Calling this function with a nonzero argument can have
unpredictable effects, including crashing the calling program.", let's
remove the '__builtin_frame_address(1)' in backtrace code.

With this fix now it can show full stack trace:
[   10.444838][    T1] Call Trace:
[   10.446199][    T1] [<ffffffff8000606c>] dump_backtrace+0x2c/0x3a
[   10.447711][    T1] [<ffffffff800060ac>] show_stack+0x32/0x3e
[   10.448710][    T1] [<ffffffff80a005c0>] dump_stack_lvl+0x58/0x7a
[   10.449941][    T1] [<ffffffff80a005f6>] dump_stack+0x14/0x1c
[   10.450929][    T1] [<ffffffff804c04ee>] ubsan_epilogue+0x10/0x5a
[   10.451869][    T1] [<ffffffff804c092e>] __ubsan_handle_load_invalid_value+0x6c/0x78
[   10.453049][    T1] [<ffffffff8018f834>] __pagevec_release+0x62/0x64
[   10.455476][    T1] [<ffffffff80190830>] truncate_inode_pages_range+0x132/0x5be
[   10.456798][    T1] [<ffffffff80190ce0>] truncate_inode_pages+0x24/0x30
[   10.457853][    T1] [<ffffffff8045bb04>] kill_bdev+0x32/0x3c
...

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Fixes: eac2f3059e02 ("riscv: stacktrace: fix the riscv stacktrace when CONFIG_FRAME_POINTER enabled")
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>