[binutils-gdb/gdb-17-branch] gdb/ser-unix: add POSIX cfsetispeed/cfsetospeed support for custom baud rates
Sam James
sjames@sourceware.org
Sun Apr 19 16:30:39 GMT 2026
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=17d05df7da13f7b0942e4e6b5f952f66c29338a2
commit 17d05df7da13f7b0942e4e6b5f952f66c29338a2
Author: Sunil Dora <sunilkumar.dora@windriver.com>
Date: Tue Mar 24 09:45:27 2026 -0700
gdb/ser-unix: add POSIX cfsetispeed/cfsetospeed support for custom baud rates
glibc 2.42 and later, and GNU Hurd, accept arbitrary baud rates
directly via cfsetispeed and cfsetospeed. This behaviour is expected
to be standardized in a future POSIX revision.
Introduce a configure-time test (HAVE_CFSETSPEED_ARBITRARY) that
detects this capability and add a new platform-agnostic helper
set_custom_baudrate_posix. The main dispatcher now prefers the POSIX
path when it is available, falling back to the existing Linux (BOTHER)
or Darwin (IOSSIOSPEED) implementations otherwise.
The HAVE_CUSTOM_BAUDRATE_SUPPORT guard is extended to also cover the
new POSIX case.
Suggested-by: Kevin Buettner <kevinb@redhat.com>
Suggested-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Sunil Dora <sunilkumar.dora@windriver.com>
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Approved-by: Kevin Buettner <kevinb@redhat.com>
(cherry picked from commit 7d53467645b0430e94a3cfd13fc3c16ef19efda5)
Diff:
---
gdb/config.in | 3 +++
gdb/configure | 39 +++++++++++++++++++++++++++++++++++++++
gdb/configure.ac | 19 +++++++++++++++++++
gdb/ser-unix.c | 49 ++++++++++++++++++++++++++++++++++++++++---------
4 files changed, 101 insertions(+), 9 deletions(-)
diff --git a/gdb/config.in b/gdb/config.in
index 62ceb846824..e66127a427d 100644
--- a/gdb/config.in
+++ b/gdb/config.in
@@ -110,6 +110,9 @@
the CoreFoundation framework. */
#undef HAVE_CFPREFERENCESCOPYAPPVALUE
+/* Define if cfsetispeed/cfsetospeed accept arbitrary baud rates. */
+#undef HAVE_CFSETSPEED_ARBITRARY
+
/* Define if compiling support to gdb compile. */
#undef HAVE_COMPILE
diff --git a/gdb/configure b/gdb/configure
index 3c321d6220b..ef645210301 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -27349,6 +27349,45 @@ _ACEOF
fi
+# Check whether cfsetispeed/cfsetospeed accept arbitrary baud rates.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether cfsetispeed/cfsetospeed accept arbitrary baud rates" >&5
+$as_echo_n "checking whether cfsetispeed/cfsetospeed accept arbitrary baud rates... " >&6; }
+if ${gdb_cv_cfsetspeed_arbitrary+:} false; then :
+ $as_echo_n "(cached) " >&6
+else
+
+ cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h. */
+#include <termios.h>
+int
+main ()
+{
+
+ #if B9600 != 9600
+ #error B-constants are not numeric symbols
+ #endif
+
+ ;
+ return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+ gdb_cv_cfsetspeed_arbitrary=yes
+else
+ gdb_cv_cfsetspeed_arbitrary=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $gdb_cv_cfsetspeed_arbitrary" >&5
+$as_echo "$gdb_cv_cfsetspeed_arbitrary" >&6; }
+
+if test "$gdb_cv_cfsetspeed_arbitrary" = yes; then
+
+$as_echo "#define HAVE_CFSETSPEED_ARBITRARY 1" >>confdefs.h
+
+fi
+
# Check whether --with-jit-reader-dir was given.
diff --git a/gdb/configure.ac b/gdb/configure.ac
index 9d3377f3c40..dfa40d34c10 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -736,6 +736,25 @@ AC_SEARCH_LIBS(dlopen, dl)
# Check for members required by the legacy Linux custom baud rate path.
AC_CHECK_MEMBERS([struct termios.c_ospeed], [], [], [[#include <termios.h>]])
+# Check whether cfsetispeed/cfsetospeed accept arbitrary baud rates.
+AC_CACHE_CHECK([whether cfsetispeed/cfsetospeed accept arbitrary baud rates],
+ [gdb_cv_cfsetspeed_arbitrary], [
+ AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM([[#include <termios.h>]],
+ [[
+ #if B9600 != 9600
+ #error B-constants are not numeric symbols
+ #endif
+ ]])],
+ [gdb_cv_cfsetspeed_arbitrary=yes],
+ [gdb_cv_cfsetspeed_arbitrary=no])
+])
+
+if test "$gdb_cv_cfsetspeed_arbitrary" = yes; then
+ AC_DEFINE([HAVE_CFSETSPEED_ARBITRARY], [1],
+ [Define if cfsetispeed/cfsetospeed accept arbitrary baud rates.])
+fi
+
GDB_AC_WITH_DIR([JIT_READER_DIR], [jit-reader-dir],
[directory to load the JIT readers from],
[${libdir}/gdb])
diff --git a/gdb/ser-unix.c b/gdb/ser-unix.c
index ffd721ad599..5ec664df1f3 100644
--- a/gdb/ser-unix.c
+++ b/gdb/ser-unix.c
@@ -53,9 +53,10 @@
#include "gdbsupport/scoped_ignore_sigttou.h"
-#if (defined(HAVE_SYS_IOCTL_H) \
- && ((defined(BOTHER) && defined(HAVE_STRUCT_TERMIOS_C_OSPEED)) \
- || defined(IOSSIOSPEED)))
+#if (defined(HAVE_CFSETSPEED_ARBITRARY) \
+ || (defined(HAVE_SYS_IOCTL_H) \
+ && ((defined(BOTHER) && defined(HAVE_STRUCT_TERMIOS_C_OSPEED)) \
+ || defined(IOSSIOSPEED))))
# define HAVE_CUSTOM_BAUDRATE_SUPPORT 1
#endif
@@ -508,7 +509,32 @@ set_baudcode_baudrate (struct serial *scb, int baud_code)
perror_with_name (_("could not set tty state"));
}
-#if HAVE_CUSTOM_BAUDRATE_SUPPORT && defined(BOTHER)
+#if HAVE_CUSTOM_BAUDRATE_SUPPORT && defined(HAVE_CFSETSPEED_ARBITRARY)
+
+/* Set a custom baud rate using the POSIX cfsetispeed/cfsetospeed
+ interface. Supported in glibc 2.42 and later and expected to be
+ standardized in a future POSIX revision. It is platform-agnostic
+ and also covers systems like GNU Hurd that do not provide BOTHER. */
+
+static void
+set_custom_baudrate_posix (int fd, int rate)
+{
+ struct termios tio;
+
+ if (tcgetattr (fd, &tio) < 0)
+ perror_with_name (_("Cannot get current baud rate"));
+
+ if (cfsetispeed (&tio, rate) < 0)
+ perror_with_name (_("Cannot set custom input baud rate"));
+
+ if (cfsetospeed (&tio, rate) < 0)
+ perror_with_name (_("Cannot set custom output baud rate"));
+
+ if (tcsetattr (fd, TCSANOW, &tio) < 0)
+ perror_with_name (_("Cannot set custom baud rate"));
+}
+
+#elif HAVE_CUSTOM_BAUDRATE_SUPPORT && defined(BOTHER)
/* Set a custom baud rate using the termios BOTHER. */
@@ -555,19 +581,24 @@ set_custom_baudrate_darwin (int fd, int rate)
}
#endif /* HAVE_CUSTOM_BAUDRATE_SUPPORT
- && (defined(BOTHER) || defined(IOSSIOSPEED)) */
+ && (defined(HAVE_CFSETSPEED_ARBITRARY)
+ || defined(BOTHER)
+ || defined(IOSSIOSPEED)) */
#if HAVE_CUSTOM_BAUDRATE_SUPPORT
/* Set a baud rate that differs from the OS B_codes.
- This is possible if one of the following macros is available:
- - BOTHER (Linux).
- - IOSSIOSPEED (Darwin). */
+ Prefer the POSIX cfsetispeed/cfsetospeed interface when the host
+ libc accepts arbitrary baud rates. Otherwise fall back to
+ Linux-specific (BOTHER) or Darwin-specific (IOSSIOSPEED)
+ interfaces. */
static void
set_custom_baudrate (int fd, int rate)
{
-#if defined(BOTHER)
+#if defined(HAVE_CFSETSPEED_ARBITRARY)
+ set_custom_baudrate_posix (fd, rate);
+#elif defined(BOTHER)
set_custom_baudrate_linux (fd, rate);
#elif defined(IOSSIOSPEED)
set_custom_baudrate_darwin (fd, rate);
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