Hello,

I am currently developing on Intel TGLRVP-UP3, but this should be relevant for other TGL-based platforms and possibly all other that set CONFIG_IDT_IN_EVERY_STAGE=y:

When I try to use the GDB stub for my debug attempts on TGL (CONFIG_GDB_STUB=y), I get the following 'undefined reference' errors during the bootblock linkage process:

src/arch/x86/exception.c:225: undefined reference to `gdb_tx_byte'
src/arch/x86/exception.c:225: undefined reference to `gdb_tx_byte'
src/arch/x86/exception.c:225: undefined reference to `gdb_tx_byte'
src/arch/x86/exception.c:230: undefined reference to `gdb_tx_flush'
src/arch/x86/exception.c:230: undefined reference to `gdb_tx_flush'
src/arch/x86/exception.c:230: undefined reference to `gdb_tx_flush'
src/arch/x86/exception.c:235: undefined reference to `gdb_rx_byte'
util/crossgcc/xgcc/bin/i386-elf-ld.bfd: src/arch/x86/exception.c:225: undefined reference to `gdb_tx_byte'
util/crossgcc/xgcc/bin/i386-elf-ld.bfd: src/arch/x86/exception.c:225: undefined reference to `gdb_tx_byte'
util/crossgcc/xgcc/bin/i386-elf-ld.bfd: src/arch/x86/exception.c:225: undefined reference to `gdb_tx_byte'
util/crossgcc/xgcc/bin/i386-elf-ld.bfd: src/arch/x86/exception.c:225: undefined reference to `gdb_tx_byte'
util/crossgcc/xgcc/bin/i386-elf-ld.bfd: src/arch/x86/exception.c:235: undefined reference to `gdb_rx_byte'
util/crossgcc/xgcc/bin/i386-elf-ld.bfd: src/arch/x86/exception.c:235: undefined reference to `gdb_rx_byte'
util/crossgcc/xgcc/bin/i386-elf-ld.bfd: src/arch/x86/exception.c:235: undefined reference to `gdb_rx_byte'
util/crossgcc/xgcc/bin/i386-elf-ld.bfd: src/arch/x86/exception.c:235: undefined reference to `gdb_rx_byte'

The gdb_*() functions used in exception.c are defined in src/console/console.c. Nevertheless, the problem with the functions in question is that they're defined under '#if CONFIG(GDB_STUB) && (ENV_ROMSTAGE || ENV_RAMSTAGE)' which obviously doesn't allow them to be compiled into the bootblock code while they're unconditionally (there's only the IDT_IN_EVERY_STAGE condition) referenced in exception.c

Looking at src/arch/x86/Makefile.inc (filtering out only the lines of interest), it's apparent that exception.c is linked in all stages when the IDT_IN_EVERY_STAGE option is set:

76:  bootblock-$(CONFIG_IDT_IN_EVERY_STAGE) += exception.c
111: verstage-$(CONFIG_IDT_IN_EVERY_STAGE) += exception.c
148: romstage-$(CONFIG_IDT_IN_EVERY_STAGE) += exception.c
187: postcar-$(CONFIG_IDT_IN_EVERY_STAGE) += exception.c
229: ramstage-y += exception.c
291: smm-$(CONFIG_IDT_IN_EVERY_STAGE) += exception.c

The behavior appears in revision b90aba43c1405d3d2cb7cba05e68906e979dcda3 (master).

To reproduce,
- run 'make menuconfig',
- select 'Mainboard ->Mainboard Vendor': 'Intel',
- select 'Mainboard -> Mainboard Model': 'Tiger Lake UP3 RVP',
- select 'Debugging -> GDB debugging support': 'y'.
- run 'make'.

What do you think would be the best approach to make the GDB stub work on these platforms?

P.S. My bug tracker registration is currently pending an approval, I could be able to create a ticket afterwards.

Regards,
Jan
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