After upgrading to Debian trixie (currently "testing") and thus GCC
13.2.1, inttypes.h doesn't define the 64-bit format specifiers such as
PRIi64 anymore, as demonstrated and explained by the following program:

// $ arm-none-eabi-gcc --version
// arm-none-eabi-gcc (15:13.2.rel1-2) 13.2.1 20231009
//
// $ arm-none-eabi-gcc -c test.c
// test.c: In function 'main':
// test.c:21:31: error: expected ')' before 'PRIi64'
//    21 |         printf("the answer: %" PRIi64 "\n", i);
//       |               ~               ^~~~~~~
//       |                               )
// test.c:18:1: note: 'PRIi64' is defined in header '<inttypes.h>'; did you forget to '#include <inttypes.h>'?
//    17 | #include <inttypes.h>
//   +++ |+#include <inttypes.h>
//    18 |

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>

int main(void) {
	int64_t i = 42;
	printf("the answer: %" PRIi64 "\n", i);
	return 0;
}

//
// /usr/include/newlib/machine/_default_types.h correctly defines ___int64_t_defined,
// (indentation for emphasis mine, in all code excerpts):
//
// #ifdef __INT64_TYPE__
//  typedef __INT64_TYPE__ __int64_t;
//  #ifdef __UINT64_TYPE__
//   typedef __UINT64_TYPE__ __uint64_t;
//  #else
//   typedef unsigned __INT64_TYPE__ __uint64_t;
//  #endif
//  #define ___int64_t_defined 1
// #elif __EXP(LONG_MAX) > 0x7fffffff
//  typedef signed long __int64_t;
//  typedef unsigned long __uint64_t;
//  #define ___int64_t_defined 1
//  ...
//
//
// Next, __int64_t_defined would be set in /usr/include/newlib/sys/_stdint.h:
//
// #ifdef ___int64_t_defined
//  #ifndef _INT64_T_DECLARED
//   typedef __int64_t int64_t ;
//   #define _INT64_T_DECLARED
//  #endif
//  #ifndef _UINT64_T_DECLARED
//   typedef __uint64_t uint64_t ;
//   #define _UINT64_T_DECLARED
//  #endif
//  #define __int64_t_defined 1
// #endif /* ___int64_t_defined */
//
//
// sys/_stdint.h would be included via <stdint.h>, but that doesn't happen
// because GCC picks the wrong stdint.h, from /usr/lib/gcc/arm-none-eabi/13.2.1/include/stdint.h.
//
// Finally, PRIi64 and similar macros are not defined in
// /usr/include/newlib/inttypes.h, because __int64_t_defined wasn't defined:
//
// #if __int64_t_defined
//  #define PRId64          __PRI64(d)
//  #define PRIi64          __PRI64(i)
//  #define PRIo64          __PRI64(o)
//  #define PRIu64          __PRI64(u)
//  #define PRIx64          __PRI64(x)
//  #define PRIX64          __PRI64(X)
//
//  #define SCNd64          __SCN64(d)
//  #define SCNi64          __SCN64(i)
//  #define SCNo64          __SCN64(o)
//  #define SCNu64          __SCN64(u)
//  #define SCNx64          __SCN64(x)
// #endif
//
//
// As a workaround, #include <sys/_stdint.h> before #include <inttypes.h> fixes the issue.

Debian team -

My team just hit this bug on production code.
https://github.com/BerkeleyLab/Marble-MMC
Ugly, ugly, ugly.  Thanks, Jonathan, for the thorough
analysis and usable workaround.  I also confirmed that adding
the extra #include <sys/_stdint.h> does not break our build
on Debian stable (Bookworm).

  - Larry

We believe that the bug you reported is fixed in the latest version of
gcc-arm-none-eabi, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1067692@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Keith Packard <keithp@keithp.com> (supplier of updated gcc-arm-none-eabi package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Fri, 31 Jul 2026 17:46:41 -0700
Source: gcc-arm-none-eabi
Architecture: source
Version: 15:15.3.rel1-1
Distribution: unstable
Urgency: medium
Maintainer: Keith Packard <keithp@keithp.com>
Changed-By: Keith Packard <keithp@keithp.com>
Closes: 953844 1067692
Changes:
 gcc-arm-none-eabi (15:15.3.rel1-1) unstable; urgency=medium
 .
   * New upstream release.
   * Switched to picolibc. (Closes: #953844, #1067692)
   * Remove autogen dependency. (Closes #1076254)
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package: gcc-arm-none-eabi

Hi,

I can confirm this bug is still reproducible on current Ubuntu (26.04) with
a
newer toolchain. The same root cause documented here is hit by our CI build
of
an embedded firmware project (STM32 Cortex-M, libudpard/cyphal based)
whenever
the code uses the base-64-bit format macros from <inttypes.h>.

Environment:

   $ arm-none-eabi-gcc --version
   arm-none-eabi-gcc (15:14.2.rel1-1) 14.2.1 20241119

   $ grep PRETTY /etc/os-release
   PRETTY_NAME="Ubuntu 26.04 LTS"

Minimal reproducer (test.c):

   #include <stdint.h>
   #include <inttypes.h>
   #include <stdio.h>
   int main(void){ uint64_t x = 0x0123456789abcdefULL; printf("%016" PRIx64
"\n", x); return 0; }

Compile with the same flags we use for firmware:

   $ arm-none-eabi-gcc -std=c2x -Werror -mthumb -mcpu=cortex-m7 -c test.c
   test.c: In function 'main':
   test.c:4:66: error: expected ')' before 'PRIx64'
       4 | ... printf("%016" PRIx64 ...
         |                          ^~~~~~~
   test.c:4:1: note: 'PRIx64' is defined in header '<inttypes.h>'; this is
probably fixable by adding '#include <inttypes.h>'

(The compiler suggestion is misleading: PRIx64 IS defined in inttypes.h but
only conditionally.)

Root cause is exactly as described above: the header search picks up GCC's
own self-contained <stdint.h> ahead of the newlib one:

   $ arm-none-eabi-gcc -E -v -x c /dev/null 2>&1 | sed -n "/#include <...>
search/,/End of search list/p"
   /usr/lib/gcc/arm-none-eabi/14.2.1/include
   /usr/lib/gcc/arm-none-eabi/14.2.1/include-fixed
   /usr/lib/gcc/arm-none-eabi/14.2.1/../../../arm-none-eabi/include

so `#include <stdint.h>` resolves to
/usr/lib/gcc/arm-none-eabi/14.2.1/include/stdint.h (guarded by
`_GCC_STDINT_H`), which does not include_next <stdint.h>. newlib's
`sys/_stdint.h` (which defines `__int64_t_defined` at line 63) is therefore
never reached, and `/usr/include/newlib/inttypes.h` gates all the
PRI64/SCN64
macros behind `#if __int64_t_defined` at line 216, so none of them are
emitted.

Confirming the include resolution:

   $ printf "#include <stdint.h>\n" | arm-none-eabi-gcc -MM -H -x c -o
/dev/null -
   . /usr/lib/gcc/arm-none-eabi/14.2.1/include/stdint.h

Workaround, for other people hitting the same CI failure: we chain GCC's
stdint.h into newlib's by appending `#include_next <stdint.h>` to
$(arm-none-eabi-gcc -print-file-name=include/stdint.h), which restores the
behavior of the old wrapper and makes PRIx64/PRId64/PRIu64 all compile.

It would be great if the packaging could either restore the `#include_next
<stdint.h>` wrapper that Debian's `provide-stdint-for-embedded` used to
carry,
or coordinate with libnewlib so that `inttypes.h` does not depend on a macro
that only newlib's own <stdint.h> can define.

Thanks for the excellent analysis already in this bug; please let me know if
you need anything else reproduced.

*Erik Rainey*
erik.rainey@gmail.com

The bug is marked as fixed in version 15:15.3.rel1-1, you're still
running an older version.