[PATCH] RISC-V: fix setting up std streams in init_semihosting()

["Ram Nalamothu (QUIC)" <quic_vnalamot@quicinc.com>]

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Without this patch, the following simple test would fail to run as expected.

#include <stdio.h>
int main() {
  int n;
  printf("Enter a number\n");
  scanf("%d", &n);
  printf("Entered number: %d\n", n);
  return 0;
}

If the patch looks good, could someone please commit it on behalf of me as I don't have commit rights.

-- 8< --

Currently init_semihosting() assumes the return value from _open()
call as the file descriptor handle and that is incorrect.

The semihost _open() call returns the fdtable index returned by the
__add_fdentry() for the file opened.

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From 966aa280a1c51759ff8ab8e6cdda225a2093f17b Mon Sep 17 00:00:00 2001
From: Venkata Ramanaiah Nalamothu <quic_vnalamot@quicinc.com>
Date: Wed, 3 Jan 2024 12:22:16 +0530
Subject: [PATCH] RISC-V: fix setting up std streams in init_semihosting()
To: newlib@sourceware.org,
    kito.cheng@sifive.com,
    craig.blackmore@embecosm.com

Currently init_semihosting() assumes the return value from _open()
call as the file descriptor handle and that is incorrect.

The semihost _open() call returns the fdtable index returned by the
__add_fdentry() for the file opened.
---
 libgloss/riscv/semihost-sys_fdtable.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/libgloss/riscv/semihost-sys_fdtable.c b/libgloss/riscv/semihost-sys_fdtable.c
index 152c92d15..d62e3f970 100644
--- a/libgloss/riscv/semihost-sys_fdtable.c
+++ b/libgloss/riscv/semihost-sys_fdtable.c
@@ -24,25 +24,26 @@ static struct fdentry fdtable[RISCV_MAX_OPEN_FILES];
 void __attribute__ ((constructor))
 init_semihosting ()
 {
-  int handle;
+  int i;
 
-  for (int i=0; i<RISCV_MAX_OPEN_FILES; i++)
+  for (i=0; i<RISCV_MAX_OPEN_FILES; i++)
     fdtable[i].handle = -1;
 
-  /* Set up std streams.  */
+  /* Set up std streams. Note that the semihost _open() call returns an index
+     into the fdtable.  */
   /* stdin.  */
-  handle = _open (":tt", O_RDONLY);
-  fdtable[STDIN_FILENO].handle = handle;
+  i = _open (":tt", O_RDONLY);
+  fdtable[STDIN_FILENO].handle = fdtable[i].handle;
   fdtable[STDIN_FILENO].pos = 0;
 
   /* stdout.  */
-  handle = _open (":tt", O_WRONLY|O_CREAT|O_TRUNC);
-  fdtable[STDOUT_FILENO].handle = handle;
+  i = _open (":tt", O_WRONLY|O_CREAT|O_TRUNC);
+  fdtable[STDOUT_FILENO].handle = fdtable[i].handle;
   fdtable[STDOUT_FILENO].pos = 0;
 
   /* stderr.  */
-  handle = _open (":tt", O_WRONLY|O_CREAT|O_APPEND);
-  fdtable[STDERR_FILENO].handle = handle;
+  i = _open (":tt", O_WRONLY|O_CREAT|O_APPEND);
+  fdtable[STDERR_FILENO].handle = fdtable[i].handle;
   fdtable[STDERR_FILENO].pos = 0;
 }
 
-- 
2.17.1