Created attachment 15271 [details]
propsed patch

After closing "Bug 30770 - serial.c does not preserve errno correctly"
https://sourceware.org/bugzilla/show_bug.cgi?id=30770
remote debugging became impossible due to an attempt to recv() by a call intended for the socket, and not for the character device file. The documentation implicitly states that it is possible to use the read() call to work with a socket. But this does not mean in the general case that it is permissible to use recv in the case of a non-socket.

condition:
os:
  Distributor ID:	Ubuntu
  Description:	Ubuntu 23.10
  Release:	23.10
  Codename:	mantic

libc:  
   ldd (Ubuntu GLIBC 2.38-1ubuntu6) 2.38
kernel:
   Linux klen-dev-um790pro 6.5.0-14-generic #14-Ubuntu SMP PREEMPT_DYNAMIC Tue Nov 14 14:59:49 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
gdb: build from trank at 15.0.50.20231226-git

GDB output:
$ arm-kgp-eabi-gdb
GNU gdb (Klen's_GNU_package_(KGP)_for_target::arm-kgp-eabi<rmprofile/lto>_host::x86_64-kgp-linux-gnu_znver4-avx512<<ílex>>) 15.0.50.20231226-git
....
(gdb) tar ext /dev/ttyACM1
Remote debugging using /dev/ttyACM1
Remote communication error.  Target disconnected: error while reading: Socket operation on non-socket.
(gdb)

after fix gdb work fine

$ arm-kgp-eabi-gdb -q
(gdb) tar ext /dev/ttyACM0
Remote debugging using /dev/ttyACM0
(gdb) mon swd
Target voltage: 0.0V
Available Targets:
No. Att Driver
 1      STM32F40x M4
(gdb) att 1
Attaching to Remote target
warning: No executable has been specified and target does not support
determining executable automatically.  Try using the "file" command.
0x08020c80 in ?? ()
(gdb)


propsed patch

diff --git a/gdb/ser-unix.c b/gdb/ser-unix.c
index 07cd8b7b5b4..57dcf6c7cf3 100644
--- a/gdb/ser-unix.c
+++ b/gdb/ser-unix.c
@@ -574,7 +574,7 @@ when debugging using remote targets."),
 int
 ser_unix_read_prim (struct serial *scb, size_t count)
 {
-  int result = recv (scb->fd, scb->buf, count, 0);
+  int result = read (scb->fd, scb->buf, count);
   if (result == -1 && errno != EINTR)
     perror_with_name ("error while reading");
   return result;