----- On Apr 24, 2019, at 6:06 PM, Paul Burton paul.burton@xxxxxxxx wrote: > Hi Mathieu, > > On Wed, Apr 24, 2019 at 11:25:02AM -0400, Mathieu Desnoyers wrote: >> diff --git a/tools/testing/selftests/rseq/rseq-mips.h >> b/tools/testing/selftests/rseq/rseq-mips.h >> index fe3eabcdcbe5..eb53a6adfbbb 100644 >> --- a/tools/testing/selftests/rseq/rseq-mips.h >> +++ b/tools/testing/selftests/rseq/rseq-mips.h >> @@ -7,7 +7,11 @@ >> * (C) Copyright 2016-2018 - Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> >> */ >> >> -#define RSEQ_SIG 0x53053053 >> +/* >> + * RSEQ_SIG uses the break instruction. The instruction pattern is >> + * 0350000d break 0x350 >> + */ >> +#define RSEQ_SIG 0x0350000d > > My apologies for taking a while to get back to you on the various ISAs & > endian issues here, but I think we'll want this to be something like: > > #if defined(__nanomips__) > # ifdef __MIPSEL__ > # define RSEQ_SIG 0x03500010 > # else > # define RSEQ_SIG 0x00100350 > # endif > #elif defined(__mips_micromips) > # ifdef __MIPSEL__ > # define RSEQ_SIG 0xd4070000 > # else > # define RSEQ_SIG 0x0000d407 > # endif > #else > # define RSEQ_SIG 0x0350000d > #endif > > For plain old MIPS the .word directive will be fine endian-wise, but for > microMIPS & nanoMIPS we need to take into account that the instruction > stream is encoded as 16b halfwords & swap those accordingly for little > endian. Considering that we have micromips and nanomips already, I guess something along the lines of "picomips" is not that far away... I've tried to figure out if we could find a way to have RSEQ_SIG left undefined if it's not on the plain mips environment, but could not find anything that would be #defined on plain mips, but #undefined on both micromips and nanomips. What I'd like to do is e.g.: #if defined(__nanomips__) # ifdef __MIPSEL__ # define RSEQ_SIG 0x03500010 # else # define RSEQ_SIG 0x00100350 # endif #elif defined(__mips_micromips) # ifdef __MIPSEL__ # define RSEQ_SIG 0xd4070000 # else # define RSEQ_SIG 0x0000d407 # endif #elif defined(__mips__) # define RSEQ_SIG 0x0350000d #else /* Leave RSEQ_SIG as is. */ #endif The idea here is to not allow code targeting future MIPS ISA to compile with the wrong signature. The delta between compiling without/with -mmicromips on a gcc-8 compiler is only: > #define __mips_micromips 1 Some interesting delta when compiling for plain little-endian mips with gcc-8 compared to the nanomips compiler is: < #define __mips__ 1 < #define _mips 1 < #define MIPSEL 1 > #define __nanomips__ 1 < #define __mips_isa_rev 2 > #define __mips_isa_rev 6 So let's say we have a picomips introduced in the future, can we rely on it not defining __mips__ like the nanomips compiler does ? If so, my "#elif defined(__mips__)" approach would indeed leave RSEQ_SIG undefined as expected. Thoughts ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
