Hi David,
Your understanding is correct. For our specific use case, we link
link TF-M secure image to a library which has LTO enabled
(we don’t have an LTO-disabled version of the library).
Since TFM was not tested with LTO, I want to ensure that it is disabled. If explicitly disabling LTO at link time is an option, it seems worthwhile to add the flag just in case.
How did you overcome the issue: “We met a similar issue when we tried to optimize one component in TF-M with LTO.”?
AFAIK, using LTO for a single component is something that is feasible (but not as effective as using it for the whole project).
Regards,
Brian
From: David Hu <David.Hu2@arm.com>
Sent: Wednesday, April 2, 2025 11:44 AM
To: Quach, Brian <brian@ti.com>; Jackson Cooper-Driver <Jackson.Cooper-Driver@arm.com>; tf-m@lists.trustedfirmware.org; Antonio De Angelis <Antonio.DeAngelis@arm.com>
Cc: nd <nd@arm.com>
Subject: [EXTERNAL] RE: Link Time Optimization
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
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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
SimpleLink MCU
Texas Instruments Inc.
12500 TI Blvd, MS F-4000
Dallas, TX 75243
214-479-4076