Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> writes: > Hi Carlos, > > ----- On Mar 22, 2019, at 4:09 PM, Carlos O'Donell codonell@xxxxxxxxxx wrote: ... > > [...] >>> +++ b/sysdeps/unix/sysv/linux/powerpc/bits/rseq.h > [...] >>> +/* Signature required before each abort handler code. */ >>> +#define RSEQ_SIG 0x53053053 >> >> Why isn't this an opcode specific to power? > > On powerpc 32/64, the abort is placed in a __rseq_failure executable section: > > #define RSEQ_ASM_DEFINE_ABORT(label, abort_label) \ > ".pushsection __rseq_failure, \"ax\"\n\t" \ > ".long " __rseq_str(RSEQ_SIG) "\n\t" \ > __rseq_str(label) ":\n\t" \ > "b %l[" __rseq_str(abort_label) "]\n\t" \ > ".popsection\n\t" > > That section only contains snippets of those trampolines. Arguably, it would be > good if disassemblers could find valid instructions there. Boqun Feng could perhaps > shed some light on this signature choice ? Now would be a good time to decide > once and for all whether a valid instruction would be a better choice. I'm a bit vague on what we're trying to do here. But it seems like you want some sort of "eye catcher" prior to the branch? That value is a valid instruction on current CPUs (rlwimi. r5,r24,6,1,9), and even if it wasn't it could become one in future. If you change it to 0x8053530 that is both a valid instruction and is a nop (conditional trap immediate but with no conditions set). cheers
