Fix embedded images built with the clang compiler by danielinux · Pull Request #730 · wolfSSL/wolfBoot

danielinux · 2026-03-19T22:43:06Z

zd21378

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Pull request overview

This PR addresses oversized/sparse embedded images produced when building with clang by adjusting linking and objcopy behavior for clang-based builds.

Changes:

Add clang-specific objcopy section filtering to avoid producing huge sparse binary/hex/srec outputs.
Switch clang builds to use the GNU linker driver to preserve LMAs in the linker script.
Relax clang build warnings around unknown attributes.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
test-app/Makefile	Introduces clang-specific `objcopy` flags and applies them to image artifact generation to prevent sparse outputs.
arch.mk	Changes clang toolchain linking to use GNU linker driver and adds clang warning suppressions for unknown attributes.

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test-app/Makefile

arch.mk

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arch.mk

test-app/Makefile

Makefile

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arch.mk

.github/workflows/test-build.yml

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arch.mk

.github/workflows/test-build.yml

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test-app/Makefile

options.mk

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src/clang_sections.S

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test-app/Makefile

Copilot · 2026-04-03T15:59:51Z

src/clang_sections.S

+/* Workaround for GNU ld mishandling AT() on output sections when no input
+ * object contributes a matching section.  Clang does not emit empty .data/.bss
+ * sections in object files (GCC does), so GNU ld fails to assign the correct
+ * LMA for the .data output section, producing a huge sparse binary.
+ * Including this object ensures .data and .bss exist as inputs.


The header comment attributes the sparse-binary issue to “GNU ld”, but Clang builds now force -fuse-ld=lld in arch.mk. If the real failure mode is tied to the linker being used with USE_CLANG=1, consider updating this comment to describe the problem more generally (or name the specific linker/toolchain combination that still needs the workaround) so future maintenance doesn’t incorrectly assume GNU ld is still involved.

Suggested change

/* Workaround for GNU ld mishandling AT() on output sections when no input

* object contributes a matching section. Clang does not emit empty .data/.bss

* sections in object files (GCC does), so GNU ld fails to assign the correct

* LMA for the .data output section, producing a huge sparse binary.

* Including this object ensures .data and .bss exist as inputs.

/* Workaround for the linker used with Clang builds mishandling AT() on

* output sections when no input object contributes a matching section.

* Clang does not emit empty .data/.bss sections in object files (GCC does),

* so the linker can assign the wrong LMA for the .data output section,

* producing a huge sparse binary. Including this object ensures .data and

* .bss exist as inputs.

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Copilot · 2026-04-03T16:17:21Z

src/clang_sections.S

+/* Workaround for GNU ld mishandling AT() on output sections when no input
+ * object contributes a matching section.  Clang does not emit empty .data/.bss
+ * sections in object files (GCC does), so GNU ld fails to assign the correct
+ * LMA for the .data output section, producing a huge sparse binary.
+ * Including this object ensures .data and .bss exist as inputs.
+ */


This new assembly file is missing the project’s standard wolfBoot GPL license header comment that appears at the top of other assembly sources. Add the usual license boilerplate (and any required file-level copyright line) to keep licensing consistent across the codebase.

Copilot · 2026-04-03T16:17:22Z

.github/workflows/test-build.yml

+          inputs.config-file == './config/examples/stm32u5-nonsecure-dualbank.config' ||
+          inputs.config-file == './config/examples/stm32n567.config'


The Clang rebuild condition includes ./config/examples/stm32n567.config, but that config file is not present in this repository. This makes the workflow inconsistent and will fail if the reusable workflow is ever called with that inputs.config-file value; either add the missing config file or remove/rename this entry to an existing config path.

Suggested change

inputs.config-file == './config/examples/stm32u5-nonsecure-dualbank.config' ||

inputs.config-file == './config/examples/stm32n567.config'

inputs.config-file == './config/examples/stm32u5-nonsecure-dualbank.config'

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danielinux added 9 commits April 3, 2026 18:09

Fix embedded images built with the clang compiler

ed15e3a

Added explicit discard list for clang compiler

6082543

Added clang pass for arm build tests

cd556ce

Discard volatile sections during app objcopy when compiling with clang

f6ec476

Fix stdlib in clang, limit test to a few targets

f7b2e5a

Exclude stm32c0 (too small for clang) and stm32h5 (no ARMORED support)

9982734

Concentrate flags for clang in arch.mk

8583a87

Fixed Clang sections in TZEN images

bcd4d8b

CLANG: fix sparse image for test-app in trustzone

ce24cd2

danielinux and others added 7 commits April 3, 2026 18:09

Removed clang install + fix path in tests

92ed25d

test-app: add dummy .data and .bss sections when using clang

7591d67

Undo redundant workarounds

82e8148

Don't override OBJCOPY_IMAGE_FLAGS

1bcac24

Remove redundant comment

9778552

Use LLVM LDD with clang

8572e20

Use llvm-ar, llvm-objcopy, llvm-size when USE_CLANG=1

a0a3dae

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mattia-moffa added 2 commits April 3, 2026 18:51

Update test container to 1.3

5cd5a19

Explicitly place .keystore

8bfdf5b

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Fix CI tests

e01c613

mattia-moffa self-assigned this Apr 3, 2026

-/* Workaround for GNU ld mishandling AT() on output sections when no input
- * object contributes a matching section.  Clang does not emit empty .data/.bss
- * sections in object files (GCC does), so GNU ld fails to assign the correct
- * LMA for the .data output section, producing a huge sparse binary.
- * Including this object ensures .data and .bss exist as inputs.
+/* Workaround for the linker used with Clang builds mishandling AT() on
+ * output sections when no input object contributes a matching section.
+ * Clang does not emit empty .data/.bss sections in object files (GCC does),
+ * so the linker can assign the wrong LMA for the .data output section,
+ * producing a huge sparse binary.  Including this object ensures .data and
+ * .bss exist as inputs.

		inputs.config-file == './config/examples/stm32u5-nonsecure-dualbank.config' \|\|
		inputs.config-file == './config/examples/stm32n567.config'

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