[newlib-cygwin/main] RISC-V: Initialize the jvt CSR

[newlib-cygwin/main] RISC-V: Initialize the jvt CSR

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=573458e7fc4f5247874b139a17e7e54827c92440

commit 573458e7fc4f5247874b139a17e7e54827c92440
Author:     Hau Hsu <hau.hsu@sifive.com>
AuthorDate: Fri Jan 5 15:06:39 2024 +0800
Commit:     Corinna Vinschen <corinna@vinschen.de>
CommitDate: Mon Jan 8 13:12:06 2024 +0100

    RISC-V: Initialize the jvt CSR
    
    Set symbol '__jvt_base$' as weak. So if the symbol is not set in the
    linker script, the address would be 0. We initialize jvt CSR only if
    the address is not 0.
    
    Also use csr number directly instead of using symbolic name to prevent the
    backward incompatible issue.
    
    psabi reference:
    https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/2d770815dc9a8b11e61ea1abd487cb25ee56ad5e/riscv-elf.adoc#table-jump-relaxation

Diff:
---
 libgloss/riscv/crt0.S | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/libgloss/riscv/crt0.S b/libgloss/riscv/crt0.S
index 7a4e4e32c146..f1c5419a5eb4 100644
--- a/libgloss/riscv/crt0.S
+++ b/libgloss/riscv/crt0.S
@@ -26,6 +26,17 @@ _start:
   addi  gp, gp, %pcrel_lo(1b)
 .option pop
 
+  /* Initialize jvt CSR (reg addr: 0x0017) */
+  .weak __jvt_base$
+  lla a0, __jvt_base$
+  beqz a0, .Ljvt_init_end
+.option push
+.option norelax
+.option arch, +zicsr
+  csrw 0x17, a0
+.option pop
+.Ljvt_init_end:
+
   # Clear the bss segment
   la      a0, __bss_start
   la      a2, _end