On Wed, May 27, 2020 at 6:45 AM Robin Murphy <robin.mur...@arm.com> wrote: > > On 2020-05-26 18:31, Nick Desaulniers wrote: > > Custom toolchains that modify the default target to -mthumb cannot > > compile the arm64 compat vdso32, as > > arch/arm64/include/asm/vdso/compat_gettimeofday.h > > contains assembly that's invalid in -mthumb. Force the use of -marm, > > always. > > FWIW, this seems suspicious - the only assembly instructions I see there > are SWI(SVC), MRRC, and a MOV, all of which exist in Thumb for the > -march=armv7a baseline that we set. > > On a hunch, I've just bodged "VDSO_CFLAGS += -mthumb" into my tree and > built a Thumb VDSO quite happily with Ubuntu 19.04's > gcc-arm-linux-gnueabihf. What was the actual failure you saw?
>From the link in the commit message: `write to reserved register 'R7'` https://godbolt.org/z/zwr7iZ IIUC r7 is reserved for the frame pointer in THUMB? What is the implicit default of your gcc-arm-linux-gnueabihf at -O2? -mthumb, or -marm? -- Thanks, ~Nick Desaulniers
