On 3 Mar 2021, at 14:55, Andrew Turner <and...@freebsd.org> wrote: > >> On 3 Mar 2021, at 14:37, Jessica Clarke <jrt...@freebsd.org> wrote: >> >> On 3 Mar 2021, at 14:29, Jessica Clarke <jrt...@freebsd.org> wrote: >>> On 3 Mar 2021, at 14:26, Andrew Turner <and...@freebsd.org> wrote: >>>> >>>> The branch main has been updated by andrew: >>>> >>>> URL: >>>> https://cgit.FreeBSD.org/src/commit/?id=28d945204ea1014d7de6906af8470ed8b3311335 >>>> >>>> commit 28d945204ea1014d7de6906af8470ed8b3311335 >>>> Author: Andrew Turner <and...@freebsd.org> >>>> AuthorDate: 2021-01-13 11:08:19 +0000 >>>> Commit: Andrew Turner <and...@freebsd.org> >>>> CommitDate: 2021-03-03 14:18:03 +0000 >>>> >>>> Handle functions that use a nop in the arm64 fbt >>>> >>>> To trace leaf asm functions we can insert a single nop instruction as >>>> the first instruction in a function and trigger off this. >>>> >>>> Reviewed by: gnn >>>> Sponsored by: Innovate UK >>>> Differential Revision: https://reviews.freebsd.org/D28132 >>>> --- >>>> sys/arm64/include/asm.h | 8 +++- >>>> .../contrib/opensolaris/uts/common/sys/dtrace.h | 2 + >>>> sys/cddl/dev/dtrace/aarch64/dtrace_subr.c | 5 +++ >>>> sys/cddl/dev/fbt/aarch64/fbt_isa.c | 51 >>>> ++++++++++++++-------- >>>> 4 files changed, 46 insertions(+), 20 deletions(-) >>>> >>>> diff --git a/sys/arm64/include/asm.h b/sys/arm64/include/asm.h >>>> index 05e618500e59..32b79d256e80 100644 >>>> --- a/sys/arm64/include/asm.h >>>> +++ b/sys/arm64/include/asm.h >>>> @@ -38,9 +38,15 @@ >>>> >>>> #define _C_LABEL(x) x >>>> >>>> +#ifdef KDTRACE_HOOKS >>>> +#define DTRACE_NOP nop >>>> +#else >>>> +#define DTRACE_NOP >>>> +#endif >>>> + >>>> #define LENTRY(sym) \ >>>> .text; .align 2; .type sym,#function; sym: \ >>>> - .cfi_startproc >>>> + .cfi_startproc; DTRACE_NOP >>>> #define ENTRY(sym) \ >>>> .globl sym; LENTRY(sym) >>> >>> Doesn't this mean ENTRY incorrectly also has the nop? >> >> Hm, right, the L in LENTRY means local not leaf. Isn't this a problem >> though? (L)ENTRY are perfectly legal to use for non-leaf assembly >> functions today. Shouldn't there be separate ones specifically for leaf >> functions if you want to treat them differently? > > Other than early boot handling, pmap_switch, and the exception handlers I > think we only have a few non-leaf asm functions on arm64. The only ones I can > think of use tail recursion, e.g. memmove -> memcpy when possible. Other than > exception handlers these functions don’t have the needed instructions to > manage the stack frame as they don’t use any stack space. I decided it was > easier to add the nop instruction to the start of function than try to create > an unneeded stack frame.
I don't contest that. My problem is that there is now a hidden requirement that (L)ENTRY only be used for leaf functions lest you get broken FBT for them. That is a surprising restriction, which to me should be indicated by having a different macro name from the generic (L)ENTRY shared across most (all?) ports. Despite its flaws, MIPS does have special LEAF macros that are distinct from the others. Jess _______________________________________________ dev-commits-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/dev-commits-src-all To unsubscribe, send any mail to "dev-commits-src-all-unsubscr...@freebsd.org"
