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arch/arm: stop boards silently discarding --fixed-r10 #19508

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2c153b0
arch/arm: stop boards silently discarding --fixed-r10
casaroli Jul 23, 2026
7498ef2
tools: exempt the "*.siz" gsize comment from codespell
casaroli Jul 23, 2026
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1 change: 1 addition & 0 deletions .codespell-ignore-lines
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Original file line number Diff line number Diff line change
Expand Up @@ -179,3 +179,4 @@ libs/libc/tre-mem.c
/* Followed by one or more ND options */
* message using the Neighbor Discovery (ND) protocol. It then listens
PIO DUE SCHEM. PIN MAPPING SAM3X DUE SCHEM. BOARD LABEL
# instruct the gsize to generate a "*.siz" file that contains the detailed section size
19 changes: 19 additions & 0 deletions arch/arm/src/common/Toolchain.defs
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Expand Up @@ -584,6 +584,25 @@ CELFFLAGS = $(CFLAGS) -fvisibility=hidden -mlong-calls # --target1-abs
CXXELFFLAGS = $(CXXFLAGS)-fvisibility=hidden -mlong-calls

ifeq ($(CONFIG_PIC),y)
# NOTE: nearly every board Make.defs includes this file and then assigns
#
# CFLAGS := $(ARCHCFLAGS) $(ARCHOPTIMIZATION) $(ARCHCPUFLAGS) ...
#
# with ':=', which silently discards this flag. A board enabling
# CONFIG_PIC has to re-apply it after that assignment, and then filter it
# back out of CPICFLAGS and CELFFLAGS, because GCC rejects --fixed-r10
# alongside the -mpic-register=r10 those carry. See
# boards/arm/mps/mps3-an547/scripts/Make.defs for the pattern.
#
# The flag cannot simply move to ARCHCPUFLAGS to survive the ':=', because
# the module flags derive from CFLAGS and would then hit exactly that
# rejected combination.
#
# Losing it is silent and the symptom is remote from the cause: the build
# succeeds, and only a callback from base firmware into module code
# misbehaves, reading its data through a register the firmware has since
# felt free to reuse.

CFLAGS += --fixed-r10

@xiaoxiang781216 xiaoxiang781216 Jul 23, 2026 •
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let's move to ARCHCFLAGS instead. it's better to fix the root cause directly.

@casaroli casaroli Jul 23, 2026 •
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I agree that your suggestion is the correct fix, however we need to change all 500 arm files, so that ARCHPICFLAGS and CPICFLAGS all move to Toolchain.defs

This is a huge change, so I have prepared the fix in a separate PR so you can analyze and compare, and we can check the CI status:

#19510

CELFFLAGS += $(PICFLAGS) -mpic-register=r10
CXXELFFLAGS += $(PICFLAGS) -mpic-register=r10
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22 changes: 21 additions & 1 deletion boards/arm/mps/mps3-an547/scripts/Make.defs
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Expand Up @@ -28,7 +28,27 @@ LDSCRIPT = flash.ld
ARCHSCRIPT += $(BOARD_DIR)$(DELIM)scripts$(DELIM)$(LDSCRIPT)

CFLAGS := $(ARCHCFLAGS) $(ARCHOPTIMIZATION) $(ARCHCPUFLAGS) $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS)
CPICFLAGS = $(ARCHPICFLAGS) $(CFLAGS)

ifeq ($(CONFIG_PIC),y)
# Toolchain.defs adds this, but the ':=' above discards it.
#
# A PIC module reaches its own data through r10, and that register has to
# survive a call into the base firmware: a base firmware routine that
# calls back into module code -- qsort() with a module comparison function
# is the standard case -- must arrive there with the module's data base
# still in r10, which it will not if the compiler was free to allocate r10
# while building the base firmware.

CFLAGS += --fixed-r10
endif

# The module itself already reserves r10 via -mpic-register=r10, and GCC
# rejects a command line carrying both that and --fixed-r10 ("unable to use
# 'r10' for PIC register"). Since both of these derive from CFLAGS, the
# flag has to be filtered back out of them.

CPICFLAGS = $(ARCHPICFLAGS) $(filter-out --fixed-r10,$(CFLAGS))
CELFFLAGS := $(filter-out --fixed-r10,$(CELFFLAGS))
CXXFLAGS := $(ARCHCXXFLAGS) $(ARCHOPTIMIZATION) $(ARCHCPUFLAGS) $(ARCHXXINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS)
CXXPICFLAGS = $(ARCHPICFLAGS) $(CXXFLAGS)
CPPFLAGS := $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS)
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