On Mon, May 11, 2015 at 10:05:37AM +0100, Christoffer Dall wrote: > On Sat, May 09, 2015 at 10:10:56PM +0200, Ard Biesheuvel wrote: > > On 9 May 2015 at 22:07, Christoffer Dall <christoffer.dall@xxxxxxxxxx> wrote: > > > On Fri, May 08, 2015 at 05:08:42PM +0100, Russell King wrote: > > >> BSYM() should only be used when refering to local symbols in the same > > >> assembly file which are resolved by the assembler, and not for > > >> linker-fixed up symbols. The use of BSYM() with panic is incorrect as > > >> the linker is involved in fixing up this relocation, and it knows > > >> whether panic() is ARM or Thumb. > > >> > > >> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx> > > >> --- > > >> arch/arm/kvm/interrupts.S | 2 +- > > >> 1 file changed, 1 insertion(+), 1 deletion(-) > > >> > > >> diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S > > >> index 79caf79b304a..87847d2c5f99 100644 > > >> --- a/arch/arm/kvm/interrupts.S > > >> +++ b/arch/arm/kvm/interrupts.S > > >> @@ -309,7 +309,7 @@ ENTRY(kvm_call_hyp) > > >> THUMB( orr r2, r2, #PSR_T_BIT ) > > >> msr spsr_cxsf, r2 > > >> mrs r1, ELR_hyp > > >> - ldr r2, =BSYM(panic) > > >> + ldr r2, =panic > > >> msr ELR_hyp, r2 > > >> ldr r0, =\panic_str > > >> clrex @ Clear exclusive monitor > > >> -- > > >> 1.8.3.1 > > >> > > > Indeed, the linker figures it out as it should. It does seem like the > > > right result is produced with the BSYM() macro as well so not sure what > > > the harm is. > > > > > > > BSYM() is defined as 'sym + 1' not 'sym | 1', so if the symbol has the > > thumb bit set already, the result is incorrect. > > > yeah, but the linker will look at the result of 'sym + 1', so on my > system it ends up with 'sym + 1' after the linker has done its thing > (verified by looking at the disassembly of vmlinux); I assume the > linker logic is that it's branching to a thumb function but the target > is already the +1 so no action necessary, as opposed to just blindly > adding 1. There are a few overlapping confusions. ldr= will do the right thing *if* the target symbol's type is correctly annotated. This means that ldr =some_local_code_symbol does the right thing for branch target addresses if and only if some_local_code_symbol is marked with .type %function (or ENDPROC). The fact that a symbol is in a code section is *not* enough. For ARM code this never mattered, so local symbols in .S files are probably under-annotated in general. BSYM() might have been used to work around this in some cases. We should check that all the BSYMs removed by this series from ldr= and .long/.word etc. point to a correctly annotated symbol, and add the annotations if not. Cheers ---Dave -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
