From 1a77c71303b552140613d49595baebdff1a4716e Mon Sep 17 00:00:00 2001 From: Sunil Dora Date: Tue, 17 Mar 2026 01:58:55 -0700 Subject: [PATCH] PR gdb/33747: gdb/ser-unix: modernize Linux custom baud rate support The Linux custom baud rate implementation previously accessed the struct termios members c_ispeed and c_ospeed directly. These fields exist in glibc but are not exposed by musl, causing builds to fail on musl-based systems. Update set_custom_baudrate_linux to use a capability-based approach, with three distinct code paths: 1) If POSIX cfsetispeed/cfsetospeed accept arbitrary baud rates (HAVE_CFSETSPEED_ARBITRARY), use them to set input and output speeds. 2) Else if Linux termios2 interface is available (TCGETS2/BOTHER), use it to support arbitrary baud rates. 3) Else if legacy struct termios supports c_ispeed/c_ospeed, use the TCGETS/TCSETS fallback (primarily for glibc on older architectures). 4) Otherwise, emit an error indicating that custom baud rates are unsupported on this platform. This preserves existing behavior on glibc systems while restoring build compatibility with musl and other libc implementations. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33747 Upstream-Status: Submitted [https://sourceware.org/pipermail/gdb-patches/2026-March/225952.html] Suggested-by: Kevin Buettner Suggested-by: Maciej W. Rozycki Signed-off-by: Sunil Dora --- gdb/config.in | 6 ++++++ gdb/configure | 52 +++++++++++++++++++++++++++++++++++++++++++++ gdb/configure.ac | 22 +++++++++++++++++++ gdb/ser-unix.c | 55 ++++++++++++++++++++++++++++++++++-------------- 4 files changed, 119 insertions(+), 16 deletions(-) diff --git a/gdb/config.in b/gdb/config.in index efc3100cb9e..b2469c8dabd 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 @@ -517,6 +520,9 @@ /* Define to 1 if `st_blocks' is a member of `struct stat'. */ #undef HAVE_STRUCT_STAT_ST_BLOCKS +/* Define to 1 if `c_ospeed' is a member of `struct termios'. */ +#undef HAVE_STRUCT_TERMIOS_C_OSPEED + /* Define to 1 if `td_pcb' is a member of `struct thread'. */ #undef HAVE_STRUCT_THREAD_TD_PCB diff --git a/gdb/configure b/gdb/configure index d0bdba6eb36..8a0e2fa2771 100755 --- a/gdb/configure +++ b/gdb/configure @@ -27336,6 +27336,58 @@ if test "$ac_res" != no; then : 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 +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 + +$as_echo "#define HAVE_CFSETSPEED_ARBITRARY 1" >>confdefs.h + +fi + +# Check for members required by the legacy Linux custom baud rate path. +ac_fn_c_check_member "$LINENO" "struct termios" "c_ospeed" "ac_cv_member_struct_termios_c_ospeed" "#include +" +if test "x$ac_cv_member_struct_termios_c_ospeed" = xyes; then : + +cat >>confdefs.h <<_ACEOF +#define HAVE_STRUCT_TERMIOS_C_OSPEED 1 +_ACEOF + + +fi + + # Check whether --with-jit-reader-dir was given. diff --git a/gdb/configure.ac b/gdb/configure.ac index 52924106bca..26e8d1ee276 100644 --- a/gdb/configure.ac +++ b/gdb/configure.ac @@ -733,6 +733,28 @@ AC_CONFIG_FILES([jit-reader.h:jit-reader.in]) AC_SEARCH_LIBS(dlopen, dl) +# Check whether cfsetispeed/cfsetospeed accept arbitrary baud rates. +AC_CACHE_CHECK([whether cfsetispeed/cfsetospeed accept arbitrary baud rates], + [gdb_cv_cfsetspeed_arbitrary], [ + AC_COMPILE_IFELSE( + [AC_LANG_PROGRAM([[#include ]], + [[ + #if B9600 != 9600 + #error B-constants are not numeric symbols + #endif + ]])], + [gdb_cv_cfsetspeed_arbitrary=yes], + [gdb_cv_cfsetspeed_arbitrary=no]) +]) + +if test "$gdb_cv_cfsetspeed_arbitrary" = yes; then + AC_DEFINE([HAVE_CFSETSPEED_ARBITRARY], [1], + [Define if cfsetispeed/cfsetospeed accept arbitrary baud rates]) +fi + +# Check for members required by the legacy Linux custom baud rate path. +AC_CHECK_MEMBERS([struct termios.c_ospeed], [], [], [[#include ]]) + 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 6f2766518be..fbd73970dbb 100644 --- a/gdb/ser-unix.c +++ b/gdb/ser-unix.c @@ -508,36 +508,59 @@ set_baudcode_baudrate (struct serial *scb, int baud_code) #if HAVE_CUSTOM_BAUDRATE_SUPPORT && defined(BOTHER) -/* Set a custom baud rate using the termios BOTHER. */ +/* Set a custom baud rate. + + Prefer the POSIX cfsetispeed/cfsetospeed interface when it accepts + arbitrary baud rates. Otherwise fall back to Linux-specific termios2 + (BOTHER) or legacy termios interfaces. */ static void set_custom_baudrate_linux (int fd, int rate) { -#ifdef TCGETS2 - struct termios2 tio; - const unsigned long req_get = TCGETS2; - const unsigned long req_set = TCSETS2; -#else +#if defined(HAVE_CFSETSPEED_ARBITRARY) struct termios tio; - const unsigned long req_get = TCGETS; - const unsigned long req_set = TCSETS; -#endif + if (tcgetattr (fd, &tio) < 0) + perror_with_name (_("Cannot get current baud rate")); + + cfsetispeed (&tio, rate); + cfsetospeed (&tio, rate); + + if (tcsetattr (fd, TCSANOW, &tio) < 0) + perror_with_name (_("Cannot set custom baud rate")); + +#elif defined(TCGETS2) + struct termios2 tio2; + if (ioctl (fd, TCGETS2, &tio2) < 0) + perror_with_name (_("Cannot get current baud rate")); + + tio2.c_cflag &= ~CBAUD; + tio2.c_cflag |= BOTHER; + tio2.c_ospeed = rate; + tio2.c_cflag &= ~(CBAUD << IBSHIFT); + tio2.c_cflag |= BOTHER << IBSHIFT; + tio2.c_ispeed = rate; - if (ioctl (fd, req_get, &tio) < 0) - perror_with_name (_("Can not get current baud rate")); + if (ioctl (fd, TCSETS2, &tio2) < 0) + perror_with_name (_("Cannot set custom baud rate")); + +#elif defined(HAVE_STRUCT_TERMIOS_C_OSPEED) + struct termios tio; + if (ioctl (fd, TCGETS, &tio) < 0) + perror_with_name (_("Cannot get current baud rate")); - /* Clear the current output baud rate and fill a new value. */ tio.c_cflag &= ~CBAUD; tio.c_cflag |= BOTHER; tio.c_ospeed = rate; - - /* Clear the current input baud rate and fill a new value. */ tio.c_cflag &= ~(CBAUD << IBSHIFT); tio.c_cflag |= BOTHER << IBSHIFT; tio.c_ispeed = rate; - if (ioctl (fd, req_set, &tio) < 0) - perror_with_name (_("Can not set custom baud rate")); + if (ioctl (fd, TCSETS, &tio) < 0) + perror_with_name (_("Cannot set custom baud rate")); + +#else + error (_("Custom baud rate not supported on this platform")); +#endif } #elif HAVE_CUSTOM_BAUDRATE_SUPPORT && defined(IOSSIOSPEED) -- 2.49.0