ESP-IDF compiles every component with -ffunction-sections/-fdata-sections and
links with -Wl,--gc-sections, so that code and data nothing references does not
reach the image. With CONFIG_COMPILER_LTO_LINKTIME the object files carry GIMPLE
instead of machine code and code generation is deferred to the link, where those
two options no longer apply. The LTO partition is therefore emitted as a single
.text/.rodata, and since --gc-sections works at section granularity it can only
keep or drop that section as a whole. Some function in it is always live, so
nothing is dropped.
The options are recorded in the object file (in the .gnu.lto_.opts section), but
they do not reach the code generator. Code generation at link time runs as a
separate compiler invocation (LTRANS) whose command line lto-wrapper
reconstructs from those recorded options, and append_compiler_options() in
gcc/lto-wrapper.cc forwards only CL_TARGET options plus a small hard-coded list:
-fPIC/-fpic/-fPIE/-fpie, -fcommon, -fgnu-tm, -fopenmp/-fopenacc, -fcf-protection=,
(-fasynchronous-)unwind-tables, -g, -O/-Os/-Og/-Ofast/-Oz and the diagnostics
formatting options. Everything else hits the default arm and is dropped.
-ffunction-sections/-fdata-sections are neither. They are plain Common options in
common.opt without the Optimization marker, so they are not part of the
per-function state that is streamed with each function (which is why -O2 and -Os
do survive per translation unit under LTO), and they are not target options
either. They reach LTRANS only if they are repeated on the link command line.
Pass them next to -flto=auto, in both build systems.
This can be verified on any LTO build by adding -save-temps to the link options
and inspecting the generated <output>.ltrans.mk, which contains the literal
LTRANS command line:
grep -o -- "-ffunction-sections\|-fdata-sections" build/*.ltrans.mk
Measured on esp32c3 with -Os and CONFIG_COMPILER_LTO_COMPILETIME, application
binary size in bytes:
no LTO LTO LTO+fix fix saves
hello_world 116112 119792 115808 -3984 (-3.33%)
wifi/getting_started 734720 792960 732976 -59984 (-7.56%)
Without this change, enabling LTO produces a larger image than not using LTO at
all; with it, LTO is size neutral to slightly positive.
Two effects contribute. The dead code inside the partition itself stays, which
scales with how much code was compiled with LTO. On top of that, every function
retained this way keeps whatever it references alive as well, transitively and
across object boundaries: constant data, other functions, and sections of objects
that were not compiled with LTO at all. That second effect is not bounded by the
size of the LTO partition and can dominate. In the wifi/getting_started case a
single retained function, esp_crt_bundle_attach(), is the only referrer of the
mbedTLS certificate bundle, so a 55 KB .rodata blob stayed in an application that
never uses TLS. A plain non-LTO build collects all of it, which is what this
change restores.
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>
The generated assembly emitted <name>_length immediately after the raw
payload bytes, so the 32-bit word landed misaligned whenever the data
size was not a multiple of 4. Consumers declare it as a 32-bit object
(e.g. `extern const size_t <name>_length` in the ULP firmware loaders),
so the compiler emits an alignment-assuming word load, which is a
misaligned flash read prone to spurious load faults on chips with
SOC_CPU_MISALIGNED_ACCESS_ON_PMP_MISMATCH_ISSUE (ESP32-C6/H2/H21).
ldgen skips regeneration when a fingerprint over the section names, the
linker fragment files, sdkconfig and Kconfig is unchanged. The linker
script template was not part of that fingerprint, even though everything
outside its mapping placeholders is copied into the generated script
verbatim.
The build system regenerates the preprocessed template whenever any of
its inputs changes, not only when a linker fragment changes. When such a
change reaches ldgen but leaves the section names alone, the fingerprint
still matches, generation is skipped, and the image is linked against the
previously generated script. The skip path updates the mtime of the
output, so nothing in the build output shows that the change was dropped.
Add the template to the fingerprint so that regenerating it always
regenerates the linker script.
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>
Trim bootloader size by moving some logs to DEBUG. Allows
compiling bootloader on P4 with CONFIG_ESPTOOLPY_FLASHMODE_QIO
without changing partition table offset
On some Windows systems, antivirus, endpoint-security or DLP/encryption
software intercepts short-lived toolchain processes and strips their
stdout when the build captures it through a pipe, while the same command
prints its output normally when run by hand. The tool exits successfully
but returns nothing, and each build step that reads toolchain output then
failed with a different, cryptic error far from the real cause:
- CMake configuration aborted with "Unknown arguments specified" in
components/xtensa/project_include.cmake, or "check_expected_tool_version
invoked with incorrect arguments" in components/esp_common.
- ldgen turned the empty objdump output into an opaque pyparsing
"Expected 'In archive'" traceback.
- idf_tools.py silently reported the compiler/debugger version as
"unknown", sending users into a fruitless reinstall loop.
Detect the empty result at each consumer and fail (or warn) with an
actionable message that names the likely cause and the remedy:
- tools/cmake/compiler_query.cmake: new __compiler_query() helper runs a
compiler query and fails with a clear error on empty or failed output.
It is a standalone module included by both the cmakev1 and cmakev2
utilities, since the esp_common and xtensa project_include.cmake that
call it are shared by both build systems. The xtensa if() arguments are
now quoted so an empty result no longer collapses into a parse error.
- tools/ldgen/ldgen.py: _run_objdump() rejects empty objdump output, and
non-empty-but-unparsable section info is caught and re-raised as a clear
LdGenFailure instead of a raw pyparsing traceback.
- tools/idf_tools.py: empty version output now warns with the cause and
returns UNKNOWN_VERSION instead of silently reporting "unknown".
Closes https://github.com/espressif/esp-idf/issues/18727
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>
FastMCP was renamed to MCPServer in mcp 2.0, which made idf.py mcp-server
report a false "MCP dependencies not available" error. Prefer MCPServer
and keep a FastMCP fallback for mcp 1.x.
Closes https://github.com/espressif/esp-idf/issues/18904
Co-authored-by: Cursor <cursoragent@cursor.com>
idf_build_library() captured the LINK_OPTIONS build property before including
the components, so a link option a component appended while it was processed was
dropped from the executable link. Read the property as a generator expression so
these options are included.
This file predates the adoption of ruff-format and was never reformatted,
because pre-commit only runs on the files touched by a change. GitHub PR
#18871 bumps the copyright year here, which pulls the file into the hook's
scope and makes check_pre_commit fail on a pre-existing formatting
violation unrelated to that change.
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>
Legacy ulp_embed_binary() call-site sources were attached directly to the CMake v2 child executable. However, the ULP runtime is linked with WHOLE_ARCHIVE through target_link_options(), which CMake emits before executable objects. This reversed the CMake v1 order, changed ULP code placement, and allowed runtime weak definitions to take precedence over legacy strong handlers.
Build the call-site sources as a dedicated static archive and place its whole-archive option before the runtime archive. Preserve the parent sdkconfig and include view, including FSM-specific include behavior, without generating a synthetic component tree.
Factor linker-specific whole-archive handling into a shared CMake v2 helper for GNU, Darwin, and ULP FSM linkers. Link the archive target normally as well so CMake tracks build and relink dependencies when a legacy ULP source changes.
Add test apps for binary size tracking:
- esp_timer size_metrics app with minimal/full sdkconfig variants
- minimal_baseline app to establish the platform binary size floor
nilesh.kale
linruihao
Jakub Kocka
morris
Sudeep MohantyandCursor
Evgeny Torbin
Frantisek Hrbata
Fu Hanxi
Marius Vikhammer
Stefan Stipanovic
Mahavir Jain
Ashish Sharma
Renz Christian Bagaporo
Alexey Lapshin
Renz Bagaporo
Marek Fiala
Michael (XIAO Xufeng)
Alexey Gerenkov
Roland Dobai