[Bug gas/23126] New: SVC instruction is rejected for ARM Cortex-M0

[freddie_chopin at op dot pl]

https://sourceware.org/bugzilla/show_bug.cgi?id=23126

            Bug ID: 23126
           Summary: SVC instruction is rejected for ARM Cortex-M0
           Product: binutils
           Version: 2.30
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: freddie_chopin at op dot pl
  Target Milestone: ---
            Target: arm-none-eabi

New binutils 2.30 rejects `svc 0` (as part of `asm volatile(...)` in C++ source
file):

-- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 --

arm-none-eabi-g++ -Wall -Wextra -Wshadow -std=gnu++11 -mcpu=cortex-m0 -mthumb
-g -ggdb3 -O2  -fno-use-cxa-atexit -ffunction-sections -fdata-sections
-fno-rtti -fno-exceptions   -Ioutput/include -Iinclude
-Isource/architecture/ARM/ARMv6-M-ARMv7-M/include
-Isource/architecture/ARM/ARMv6-M-ARMv7-M/external/CMSIS
-Isource/chip/STM32/include -Isource/chip/STM32/STM32F0/include
-Isource/chip/STM32/peripherals/GPIOv2/include
-Isource/chip/STM32/peripherals/SPIv2/include
-Isource/chip/STM32/peripherals/USARTv2/include
-Isource/chip/STM32/STM32F0/external/CMSIS-STM32F0  -MD -MP -c
source/architecture/ARM/ARMv6-M-ARMv7-M/ARMv6-M-ARMv7-M-supervisorCall.cpp -o
output/source/architecture/ARM/ARMv6-M-ARMv7-M/ARMv6-M-ARMv7-M-supervisorCall.o
/tmp/cchwMvG1.s: Assembler messages:
/tmp/cchwMvG1.s:41: Error: SVC is not permitted on this architecture
make: *** [Makefile:261:
output/source/architecture/ARM/ARMv6-M-ARMv7-M/ARMv6-M-ARMv7-M-supervisorCall.o]
Error 1

-- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 --

This code was accepted in previous binutils (for years). SVC is listed with no
notes about any special conditions in:
- Thumb ® 16-bit Instruction Set Quick Reference Card
- ARMv6-M Architecture Reference Manual

Additionally "ARMv6-M Architecture Reference Manual" says ("A4.9
Exception-generating instructions"):

-- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 --
In an ARMv6-M implementation that does not include the Unprivileged/Privileged
Extension,
execution is always privileged. However in such an implementation, application
code might use
supervisor calls to maintain a software hierarchy with a system kernel.
-- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 --

Adding `-march=armv6s-m` to the compilation flags makes the error go away, but
I don't think that requiring it is a good solution.

Related problems:
https://sourceware.org/bugzilla/show_bug.cgi?id=12296
https://bugs.launchpad.net/gcc-arm-embedded/+bug/1449610

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