SDCC does output OMF51, but only as a secondary "byproduct", and of course only the original Intel version, without Keil's "proprietary" (what a funny buzzword replacement for "we don't give it away because of competition") extensions.

Contrary to Keil's extension to OMF51, SDCC's native object format, CDB, is well documented (there's an online version, of that document too). It should be fairly easy to read and parse it instead of OMF51. IIRC the Ramtron Versa debugger does exactly that.

Given the nature of open source, it is not impossible even to modify or expand on the existing format, or create and implement a wholly new one, if needed. The "industry standard" is of course ELF/DWARF, but that's maybe a bit more than needed for '51.

JW