Hi Brian,

It is the expected behavior of LTO. The whole project should be built with LTO enabled if any library used is enabled with LTO. We met a similar issue when we tried to optimize one component in TF-M with LTO.

IIRC, no pre-built binaries (maybe CMSIS ones) required by TF-M is built with LTO. It should be unnecessary for TF-M to explicitly disable LTO in linker configuration.

Please correct me if I misunderstood your case. You link TF-M secure image to those binaries with LTO enabled. Imho, TF-M may be built with LTO enabled then in your case. But it might not be a common case in TF-M as I mentioned above.

Best regards,

David

From: Quach, Brian via TF-M <tf-m@lists.trustedfirmware.org>
Sent: Wednesday, April 2, 2025 5:11 PM
To: Jackson Cooper-Driver <Jackson.Cooper-Driver@arm.com>; tf-m@lists.trustedfirmware.org; Antonio De Angelis <Antonio.DeAngelis@arm.com>
Subject: [TF-M] Re: Link Time Optimization

Hi Jackson,

The issue is that some of our libraries which are linked into the secure image have LTO enabled.

Per https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html:

The important thing to keep in mind is that to enable link-time optimizations you need to use the GCC driver to perform the link step. GCC automatically performs link-time optimization if any of the objects involved were compiled with the -flto command-line option. You can always override the automatic decision to do link-time optimization by passing -fno-lto to the link command.

So it seems that the -fno-lto flag must be used to explicitly opt out of LTO.

It might be wise to add that flag to toolchain_GNUARM.cmake to ensure no one is unknowingly having LTO enabled as you have not analyzed the impact.

Regards,
Brian

From: Jackson Cooper-Driver <Jackson.Cooper-Driver@arm.com>
Sent: Wednesday, April 2, 2025 1:46 AM
To: tf-m@lists.trustedfirmware.org; Quach, Brian <brian@ti.com>; Antonio De Angelis <Antonio.DeAngelis@arm.com>
Subject: [EXTERNAL] Re: Link Time Optimization

Hi Brian, Worth just saying that GCC does not enable any optimizations by default. LTO needs to be explicitly enabled on the command line using -flto - see the GCC docs here - https: //gcc. gnu. org/onlinedocs/gcc/Optimize-Options. html CMake also

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Hi Brian,

Worth just saying that GCC does not enable any optimizations by default. LTO needs to be explicitly enabled on the command line using -flto - see the GCC docs here - https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

CMake also has a way to enable LTO using a specific CMake flag which you can set - details here - https://stackoverflow.com/questions/31355692/how-do-i-enable-link-time-optimization-lto-with-cmake

But we do not currently do that in TF-M

Thanks,

Jackson

From: Antonio De Angelis via TF-M <tf-m@lists.trustedfirmware.org>
Sent: 01 April 2025 22:44
To: tf-m@lists.trustedfirmware.org <tf-m@lists.trustedfirmware.org>; Quach, Brian <brian@ti.com>
Subject: [TF-M] Re: Link Time Optimization

Hi Brian,

no, TF-M does not use it (on purpose), i.e. if GCC enables it by default, the impact of LTO has not been assessed.

Thanks, Antonio

From: Quach, Brian via TF-M <tf-m@lists.trustedfirmware.org>
Sent: Tuesday, April 1, 2025 16:01
To: tf-m@lists.trustedfirmware.org <tf-m@lists.trustedfirmware.org>
Subject: [TF-M] Link Time Optimization

Hi, does TF-M use LTO? I didn’t see any flags to disable it in toolchain_GNUARM.cmake. I think for GCC, it’s enabled by default if no flag is set.

Regards,

Brian Quach

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