How to make ARM GCC linker put a version number at a fixed address at the end of a memory section?

I'm developing firmware update code for a Cortex-M4 based system and need a way for my firmware to obtain the version number of the separately-linked boot loader so I can determine if it must be updated. The makefile I inherited currently puts the build date/time at the end of the code, but it moves if code is added or removed.

I attempted to do this by defining a new memory section called .version and modifying the loader script to place it near the end of flash memory just before an existing section call .binfo, and including a header file containing the version number with a attribute that puts it in that section in main.c. The loader script I started with looks like this (with extraneous parts replaced by "...").

MEMORY{  rom      (rx)  : ORIGIN = 0x00000000, LENGTH = 16K  ram      (rwx) : ORIGIN = 0x20000000, LENGTH = 192K...    . = ALIGN(4);    _end = . ;    _binfo_start = 16K - 4 * 4;    .binfo _binfo_start : {      KEEP(*(.binfo)) ;    } > rom}

I changed this to:

MEMORY  rom      (rx)  : ORIGIN = 0x00000000, LENGTH = 16K  ram      (rwx) : ORIGIN = 0x20000000, LENGTH = 192K...    . = ALIGN(4);    _end = . ;    _version_start = 16K - 4 * 4 - 2;    /* new, intended to reserve 2 bytes for .version before .binfo */    .version _version_start : {      KEEP(*(._version)) ;    } > rom                              /* end new */    _binfo_start = 16K - 4 * 4;    .binfo _binfo_start : {      KEEP(*(.binfo)) ;    } > rom}

I understand the "> rom" after .binfo to constrain .binfo to lie entiredly inside rom, so I omitted it bootloaderVersion.h in included in main.c, and looks like this:

#ifndef BLVERSION_H#define BLVERSION_H#define BLVERSIONMAJOR 0x00#define BLVERSIONMINOR 0x01#define BLVERSION (BLVERSIONMAJOR << 8 | BLVERSIONMINOR) __attribute__((section(".version"))) __attribute__((__used__)) const uint16_t blVersion = BLVERSION;#endif

It builds, but I don't see anything in the .bin file before 0x3FF0 (where binfo resides). When I look at the loader with Segger Ozone I see that bootloaderVersion.h was included but consumed no memory.

What am I doing wrong?

Incidentally, binfo is filled as follows:

__attribute__((section(".binfo"))) __attribute__((__used__)) const UF2_BInfo binfo = {#if USE_MSC_HANDOVER    .handoverMSC = handover,#endif#if USE_HID_HANDOVER    .handoverHID = hidHandoverLoop,#endif    .info_uf2 = infoUf2File,};