[Bug target/64953] Compiling sourcecode for STM32F103 causes USB errors with some optimization settings

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64953

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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             Status|REOPENED                    |RESOLVED
         Resolution|---                         |INVALID

--- Comment #16 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
You need to compile with -mno-unaligned-access when compiling the firmware.
This is mentioned in https://gcc.gnu.org/gcc-4.7/changes.html:
On ARM, when compiling for ARMv6 (but not ARMv6-M), ARMv7-A, ARMv7-R, or
ARMv7-M, the new option -munaligned-access is active by default, which for some
sources generates code that accesses memory on unaligned addresses. This
requires the kernel of those systems to enable such accesses (controlled by
CP15 register c1, refer to ARM documentation). Alternatively, or for
compatibility with kernels where unaligned accesses are not supported, all code
has to be compiled with -mno-unaligned-access. Upstream Linux kernel releases
have automatically and unconditionally supported unaligned accesses as emitted
by GCC due to this option being active since version 2.6.28.