Debug Mode Adds Unsupported `-g2` Flag to Assembler, Causing Fatal Error

Description:

When attempting to debug a project created with STM32Cube in PlatformIO, the assembler (arm-none-eabi-as) receives the -g2 flag, which it does not recognize, resulting in a fatal error. This issue prevents successful debugging even though the project compiles without errors in normal build mode.

Environment:

• PlatformIO Version: 6.1.16
• Platform: ST STM32
• Board: genericSTM32F103ZE
• Toolchain: arm-none-eabi-gcc (version 12.3.1)
• Operating System: Windows 11

Build Configuration (platformio.ini):

[env:genericSTM32F103ZE]
platform = ststm32
board = genericSTM32F103ZE
build_flags =
  -g

Problem:

When initiating a debug session using pio debug -v, PlatformIO automatically adds the -g2 and -ggdb2 flags to both the GCC compiler and the assembler. While the compiler accepts these flags, the assembler (arm-none-eabi-as) does not recognize -g2, leading to the following fatal error:

Assembler messages:
Fatal error: unknown option `-g2'
*** [path_to_output.o] Error 1

Even though I forced the -g option in build_flags, it did not take effect.I added the following content to the configuration file, and the debug debugging can be used normally.

debug_build_flags =
    -g

Steps to Reproduce:

Create a new STM32Cube project using PlatformIO with the genericSTM32F103ZE board. In platformio.ini, set -g as the debug flag. Include an assembly startup file (e.g., startup_stm32f103zetx.s) in the project. Build the project to confirm that it compiles without issues. Start a debug session using pio debug -v. Observe the assembler error related to the -g2 flag.

Log Output:

CONFIGURATION: https://docs.platformio.org/page/boards/ststm32/genericSTM32F103ZE.html
PLATFORM: ST STM32 (17.6.0) > STM32F103ZE (64k RAM. 512k Flash)
HARDWARE: STM32F103ZET6 72MHz, 64KB RAM, 512KB Flash
DEBUG: Current (stlink) External (blackmagic, cmsis-dap, jlink, stlink)
PACKAGES:
 - toolchain-gccarmnoneeabi @ 1.120301.0 (12.3.1)
LDF: Library Dependency Finder -> https://bit.ly/configure-pio-ldf
LDF Modes: Finder ~ chain, Compatibility ~ soft
Found 11 compatible libraries
Scanning dependencies...
[Dependency graph information]
Building in debug mode
arm-none-eabi-as -mthumb -mcpu=cortex-m3 -g2 -ggdb2 -o .pio\build\genericSTM32F103ZE\src\N1OS\Startup\startup_stm32f103zetx.o Startup\startup_stm32f103zetx.s
arm-none-eabi-gcc -o .pio\build\genericSTM32F103ZE\src\N1OS\Users\App\User\Program\app.o -c [additional flags including -g2 -ggdb2]
Assembler messages:
Fatal error: unknown option `-g2'
*** [.pio\build\genericSTM32F103ZE\src\N1OS\Startup\startup_stm32f103zetx.o] Error 1

Expected Behavior:

PlatformIO should respect the build_flags specified in the platformio.ini file and avoid adding unsupported flags like -g2 to the assembler. The debugger should initiate successfully without modifying the assembler flags in an incompatible way.

Actual Behavior:

During the debug build process, PlatformIO adds -g2 and -ggdb2 flags to both the GCC compiler and the assembler. While GCC handles these flags gracefully, the assembler does not recognize -g2, resulting in a fatal error and preventing the debug session from starting.