[Bug libc/29749] New: clarify usage of .cfi_label in riscv start.S

["alex.fan.q at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29749

            Bug ID: 29749
           Summary: clarify usage of .cfi_label in riscv start.S
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: alex.fan.q at gmail dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

riscv's start.S includes a `.cfi_label dummy` directive in [1]. The comment
above it says 
> use a dummy .cfi_label to force starting the FDE.`
but as I understand it, `ENTRY (ENTRY_POINT)` macro includes a
`.cfi_startproc`, which should already do the same thing as comment suggests.

This directive was introduced in
https://sourceware.org/bugzilla/show_bug.cgi?id=23125 , but the original patch
in the first comment didn't include cfi_label and works as reported.

Zig compilation gets stuck on this directive as clang doesn't support it [2].

Can I get some help to clarify this directive and whether it is okay to remove
it?

[1]
https://github.com/bminor/glibc/blob/8c77e26ba8b360c851b2b9485bb4431aacc51ad1/sysdeps/riscv/start.S#L48
[2] https://github.com/ziglang/zig/issues/3340

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