On 03/08/2026 12:56, Torbjorn SVENSSON wrote: > > > On 2026-08-03 13:54, Jakub Jelinek wrote: >> On Mon, Aug 03, 2026 at 01:50:18PM +0200, Torbjorn SVENSSON wrote: >>> This change introduces new failures for arm-none-eabi using >>> thumb/arch=armv6s-m/cpu=cortex-m0/float-abi=soft/fpu=auto. >>> >>> Testing torture/bitint-100.c, -O0 >>> doing compile >>> Executing on host: /build/install-native/bin/arm-none-eabi-gcc >>> /build/gcc_src/gcc/testsuite/gcc.dg/torture/bitint-100.c -mthumb >>> -march=armv6s-m -mcpu=cortex-m0 -mfloat-abi=soft -mfpu=auto -dumpbase "" >>> -fdiagnostics-plain-output -O0 -std=c23 -pedantic-errors >>> --specs=rdimon.specs -Wl,--start-group -lc -lm -Wl,--end-group >>> --specs=nosys.specs -Wl,--allow-multiple-definition >>> -Wl,-u,_isatty,-u,_fstat -Wl,-wrap,exit -Wl,-wrap,_exit -Wl,-wrap,main >>> -Wl,-wrap,abort -Wl,gcc_tg.o -lm -T qemu.ld -o ./bitint-100.exe (timeout >>> = 800) >>> spawn -ignore SIGHUP /build/install-native/bin/arm-none-eabi-gcc >>> /build/gcc_src/gcc/testsuite/gcc.dg/torture/bitint-100.c -mthumb >>> -march=armv6s-m -mcpu=cortex-m0 -mfloat-abi=soft -mfpu=auto -dumpbase >>> -fdiagnostics-plain-output -O0 -std=c23 -pedantic-errors >>> --specs=rdimon.specs -Wl,--start-group -lc -lm -Wl,--end-group >>> --specs=nosys.specs -Wl,--allow-multiple-definition >>> -Wl,-u,_isatty,-u,_fstat -Wl,-wrap,exit -Wl,-wrap,_exit -Wl,-wrap,main >>> -Wl,-wrap,abort -Wl,gcc_tg.o -lm -T qemu.ld -o ./bitint-100.exe >>> pid is 1478576 -1478576 >>> /build/install-native/arm-none-eabi/bin/ld: /tmp/ccgSaSgH.o: in function >>> `f1': >>> bitint-100.c:(.text+0x5a): undefined reference to >>> `__atomic_compare_exchange_4' >>> /build/install-native/arm-none-eabi/bin/ld: (__atomic_compare_exchange_4): >>> Unknown destination type (ARM/Thumb) in /tmp/ccgSaSgH.o >>> bitint-100.c:(.text+0x5a): dangerous relocation: unsupported relocation >>> /build/install-native/arm-none-eabi/bin/ld: /tmp/ccgSaSgH.o: in function >>> `f2': >>> bitint-100.c:(.text+0xa4): undefined reference to >>> `__atomic_compare_exchange_4' >>> /build/install-native/arm-none-eabi/bin/ld: (__atomic_compare_exchange_4): >>> Unknown destination type (ARM/Thumb) in /tmp/ccgSaSgH.o >>> bitint-100.c:(.text+0xa4): dangerous relocation: unsupported relocation >>> ... >>> collect2: error: ld returned 1 exit status >>> status 1 >>> compiler exited with status 1 >>> FAIL: gcc.dg/torture/bitint-100.c -O0 (test for excess errors) >>> >>> Same failure exist on both trunk and releases/gcc-16. >> >> I thought gcc has been changed to add -latomic_asneeded by default. >> Or is this because the linker doesn't support it in this configuration? > To my knowledge, there is no atomic support for armv6s-m, but I can be wrong. >
armv6-m has a DMB sync instruction, but that's all. On earlier systems the only support we have for atomics is via __sync_synchronize. That will always be a lib-call if we don't know for sure that we have the DMB sync. If at link time, we can determine that the core is single-threaded only, then the call will become a no-op, otherwise (eg we end up linking for a later architecture) we will use the atomic primitive appropriate for the final architecture. This is all handled in libgcc through the code in arm/lib1funcs.asm. R. > Kind regards, > Torbjörn
