Messages in this thread | | | Date | Wed, 21 Mar 2018 15:09:58 +0100 | From | Stefan Agner <> | Subject | Re: [PATCH 3/5] ARM: trusted_foundations: do not use naked function |
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On 21.03.2018 13:13, Robin Murphy wrote: > On 20/03/18 23:02, Stefan Agner wrote: >> As documented in GCC naked functions should only use Basic asm >> syntax. The Extended asm or mixture of Basic asm and "C" code is >> not guaranteed. Currently this works because it was hard coded >> to follow and check GCC behavior for arguments and register >> placement. >> >> Furthermore with clang using parameters in Extended asm in a >> naked function is not supported: >> arch/arm/firmware/trusted_foundations.c:47:10: error: parameter >> references not allowed in naked functions >> : "r" (type), "r" (arg1), "r" (arg2) >> ^ >> >> Use a regular function to be more portable. This aligns also with >> the other smc call implementations e.g. in qcom_scm-32.c and >> bcm_kona_smc.c. >> >> Additionally also make sure all callee-saved registers get saved >> as it has been done before. >> >> Signed-off-by: Stefan Agner <stefan@agner.ch> >> --- >> arch/arm/firmware/trusted_foundations.c | 12 +++++++----- >> 1 file changed, 7 insertions(+), 5 deletions(-) >> >> diff --git a/arch/arm/firmware/trusted_foundations.c b/arch/arm/firmware/trusted_foundations.c >> index 3fb1b5a1dce9..426d732e6591 100644 >> --- a/arch/arm/firmware/trusted_foundations.c >> +++ b/arch/arm/firmware/trusted_foundations.c >> @@ -31,21 +31,23 @@ >> static unsigned long cpu_boot_addr; >> -static void __naked tf_generic_smc(u32 type, u32 arg1, u32 arg2) >> +static void tf_generic_smc(u32 type, u32 arg1, u32 arg2) >> { >> + register u32 r0 asm("r0") = type; >> + register u32 r1 asm("r1") = arg1; >> + register u32 r2 asm("r2") = arg2; >> + >> asm volatile( >> ".arch_extension sec\n\t" >> - "stmfd sp!, {r4 - r11, lr}\n\t" >> __asmeq("%0", "r0") >> __asmeq("%1", "r1") >> __asmeq("%2", "r2") >> "mov r3, #0\n\t" >> "mov r4, #0\n\t" >> "smc #0\n\t" >> - "ldmfd sp!, {r4 - r11, pc}" >> : >> - : "r" (type), "r" (arg1), "r" (arg2) >> - : "memory"); >> + : "r" (r0), "r" (r1), "r" (r2) >> + : "memory", "r3", "r4", "r5", "r6", "r7", "r8", "r9", "r10"); > > I may be missing a subtlety, but it looks like we no longer have a > guarantee that r11 will be caller-saved as it was previously. I don't > know the Trusted Foundations ABI to say whether that matters or not, > but if it is the case that it never needed preserving anyway, that > might be worth calling out in the commit message.
Adding r11 (fp) to the clobber list causes an error when using gcc and CONFIG_FRAME_POINTER=y: arch/arm/firmware/trusted_foundations.c: In function ‘tf_generic_smc’: arch/arm/firmware/trusted_foundations.c:51:1: error: fp cannot be used in asm here
Not sure what ABI Trusted Foundations follow.
[adding Stephen, Thierry and Dmitry] Maybe someone more familiar with NVIDIA Tegra SoCs can help?
When CONFIG_FRAME_POINTER=y fp gets saved anyway. So we could add r11 to clobber list ifndef CONFIG_FRAME_POINTER...
-- Stefan
> > Robin. > >> } >> static int tf_set_cpu_boot_addr(int cpu, unsigned long boot_addr) >>
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