How can I get arm-none-eabi-gcc V6 via APT?

Just recently, there was an update to the GCC toolchain to version 7.

For whatever reason… this broke my code. I have a wrapper around `vsniprintf` that transmits syslog (RFC5424) messages, and this code instead of reporting log messages like this:

2017-12-21T02:40:00Z 11f47b5800124b00 scheduler Beginning poll at 1513824000
2017-12-21T02:40:00Z 11f47b5800124b00 scheduler Writing at 1513824000: 0x1ffe
2017-12-21T02:40:15Z 11f47b5800124b00 scheduler Beginning poll at 1513824015
2017-12-21T02:40:15Z 11f47b5800124b00 scheduler Writing at 1513824015: 0x1ffe
2017-12-21T02:40:30Z 11f47b5800124b00 scheduler Beginning poll at 1513824030
2017-12-21T02:40:30Z 11f47b5800124b00 scheduler Writing at 1513824030: 0x1ffe

started instead reporting log messages like this:

2017-12-21T02:46:32Z 11f47b5800124b00 scheduler Beginning poll at 536900368
2017-12-21T02:46:32Z 11f47b5800124b00 scheduler Writing at -7: 0x5a3b2086
2017-12-21T02:46:45Z 11f47b5800124b00 scheduler Beginning poll at 2300141
2017-12-21T02:46:45Z 11f47b5800124b00 scheduler Writing at 0: 0x5a3b2095
2017-12-21T02:47:00Z 11f47b5800124b00 scheduler Beginning poll at 2300141
2017-12-21T02:47:00Z 11f47b5800124b00 scheduler Writing at -7: 0x5a3b20a4

The function call that generates these messages looks like this:

  syslog_send(instance, SCHEDULER_FACILITY,
    SYSLOG_SEV_INFO,
    SCHEDULER_PROC,
    "Beginning poll at %ld",
    schedule_current);
…
  syslog_send(instance, SCHEDULER_FACILITY,
    SYSLOG_SEV_INFO,
    SCHEDULER_PROC,
    "Writing at %ld: 0x%04x",
    schedule_current, schedule_todo);

schedule_todo is a uint16_t… it is IMPOSSIBLE for it to have the value 0x5a3b20a4. schedule_current is a time_t. The code behind `syslog_send`:

/*!
 * Send a syslog message (varadic version).
 */
static inline int syslog_send(otInstance* instance,
  uint8_t facility, uint8_t severity,
  const char* app, const char* fmt, ...) {
 int res;
 va_list fmt_args;
 va_start(fmt_args, fmt);
 res = syslog_send_va(instance, facility, severity, app, fmt, fmt_args);
 va_end(fmt_args);
 return res;
}

/*!
 * Send a syslog message.
 */
int syslog_send_va(otInstance* instance,
  uint8_t facility, uint8_t severity,
  const char* app, const char* fmt, va_list fmt_args) {

 /* Retrieve the current system time */
 struct timeval tv;
 int res = gettimeofday(&tv, NULL);
 if (res < 0) {
  return res;
 }

 char buffer[SYSLOG_BUF_SZ];
 int16_t sz = syslog_format(instance, buffer, sizeof(buffer),
   tv.tv_sec, facility, severity, app, fmt, fmt_args);
 if (sz < 0) {
  return sz;
 }
…

/*!
 * Format a received message into a log buffer and return its size.
 */
static int16_t syslog_format(
  otInstance* instance,
  char* buffer, uint16_t buf_sz,
  time_t timestamp, uint8_t facility, uint8_t severity,
  const char* app, const char* fmt, va_list fmt_args) {
 /* Sum of bytes written */
 int16_t sum = 0;

 /* Converted timestamp */
 struct tm tm;
 if (!gmtime_r(&timestamp, &tm)) {
  /* Invalid timestamp arguments given */
  return -errno;
 }

#ifdef SYSLOG_TRACE
#ifdef SYSLOG_TRACE_FORMAT
 iprintf("%s:%d Format message %s\r\n",
  __FILE__, __LINE__, fmt);
#endif
#endif

 /* Format the message header first. */
 int fmt_sz = sniprintf(buffer, buf_sz,
   "<%d>1 %04d-%02d-%02dT%02d:%02d:%02dZ ",
   /* Priority value */
   (facility << 3) | (severity & 0x07),
   /* Timestamp */
   tm.tm_year + 1900,
   tm.tm_mon + 1,
   tm.tm_mday,
   tm.tm_hour,
   tm.tm_min,
   tm.tm_sec);

#ifdef SYSLOG_TRACE
#ifdef SYSLOG_TRACE_FORMAT
 iprintf("%s:%d Size: %d Buffer: %s\r\n",
  __FILE__, __LINE__, fmt_sz, buffer);
#endif
#endif

 buf_sz -= fmt_sz;
 buffer += fmt_sz;
 sum += fmt_sz;

 /* Append hostname */
 hostname(instance, buffer, buf_sz);
#ifdef SYSLOG_TRACE
#ifdef SYSLOG_TRACE_FORMAT
 iprintf("%s:%d Size: %d Buffer: %s\r\n",
  __FILE__, __LINE__, HOSTNAME_LEN, buffer);
#endif
#endif
 buffer += HOSTNAME_LEN;
 buf_sz -= HOSTNAME_LEN;
 sum += HOSTNAME_LEN;

 /* Append remainder of header */
 fmt_sz = sniprintf(buffer, buf_sz,
   " %s - - - ", app);
#ifdef SYSLOG_TRACE
#ifdef SYSLOG_TRACE_FORMAT
 iprintf("%s:%d Size: %d Buffer: %s\r\n",
  __FILE__, __LINE__, fmt_sz, buffer);
#endif
#endif

 buffer += fmt_sz;
 buf_sz -= fmt_sz;
 sum += fmt_sz;

 /* Append message */
 fmt_sz = vsniprintf(buffer, buf_sz, fmt, fmt_args); /* <-- vsniprintf is HERE */
#ifdef SYSLOG_TRACE
#ifdef SYSLOG_TRACE_FORMAT
 iprintf("%s:%d Size: %d Buffer: %s\r\n",
  __FILE__, __LINE__, fmt_sz, buffer);
#endif
#endif
 sum += fmt_sz;

 /* We're done */
#ifdef SYSLOG_TRACE
#ifdef SYSLOG_TRACE_FORMAT
 iprintf("%s:%d Total %u\r\n",
  __FILE__, __LINE__, sum);
#endif
#endif
 return sum;
}

It is clear that, at the very least, vsniprintf and/or the implementation behind stdarg.h… is misbehaving badly. Possibly other things too: maybe the optimiser is being a bit overzealous, I don't know.

I can reproduce the same problem with both the Debian package version of arm-none-eabi-gcc v7 (on Debian Jessie), and the tarball binary from the upstream developers (on Gentoo). Rolling back to gcc v6 (on my Gentoo-based workstation) fixes the problem.

Unfortunately, looking in the repository, I do not see a package for GCC v6, and I do not have the time to migrate the code to GCC v7 prior to my workplace closing for the year (tomorrow around 11:00 UTC+10). If the old package were still in the repository, it'd be possible for me to work-around things by just forcing `apt-get` to install the older version. Without that there, I can do nothing, and mirroring the APT repository makes a mockery of using it in the first place.

It is not possible to download the tarball automatically as pointing `wget` or `curl` at the links that ARM provide simply gives me the HTML page that the file is linked to… and running a web browser is not viable from within a CI environment. The URI is also a moving target. The CI environment builds the following Docker image:

https://hub.docker.com/r/vrtsystems/widesky-openthread-build-env/

… which is then used to build our code. If you could point me to the APT repository where you keep the older binaries, that would be most appreciated.