On 20 April 2018 at 01:33, Kim Phillips <kim.phill...@arm.com> wrote:
> On Thu, 19 Apr 2018 11:54:24 +0900
> Namhyung Kim <namhy...@kernel.org> wrote:
>
>> On Wed, Apr 18, 2018 at 07:37:59PM -0500, Kim Phillips wrote:
>> > diff --git a/tools/perf/arch/arm64/util/sym-handling.c
>> > b/tools/perf/arch/arm64/util/sym-handling.c
>> > index 0051b1ee8450..5c4a2e208bbc 100644
>> > --- a/tools/perf/arch/arm64/util/sym-handling.c
>> > +++ b/tools/perf/arch/arm64/util/sym-handling.c
>> > @@ -20,3 +20,16 @@ bool elf__needs_adjust_symbols(GElf_Ehdr ehdr)
>> > ehdr.e_type == ET_DYN;
>> > }
>> > #endif
>> > +
>> > +const char *arch__normalize_symbol_name(const char *name)
>> > +{
>> > + /*
>> > + * arm64 kernels compensating for a CPU erratum can put up a
>> > + * module_emit_adrp_veneer in place of a module_emit_plt_entry
>> > + */
>> > + if (name && strlen(name) >= 23 &&
>> > + !strncmp(name, "module_emit_adrp_veneer", 23))
>> > + return "module_emit_plt_entry";
>> > +
>> > + return name;
>> > +}
>>
>> I don't know it's always preferable or just for the test. It it's the
>> latter it may be better to move it to the test code.
>
> AFACT, the veneer is a moniker and doesn't technically exist, and
> shouldn't be being looked-up. Both chunks of this diff are needed to
> pass perf test 1: this chunk above is because in
> arch__normalize_symbol_name(), we squash the perf test 1's "<veneer>
> not in *kallsyms*" problem, and in the below chunk, we prevent it
> coming up when the test code iterates over the *vmlinux* symbols. I.e.
> we need to prevent the veneer from coming up in both kallsyms *and*
> vmlinux.
>
I don't have all the context here, so I don't know what exactly
arch__normalize_symbol_name() is trying to accomplish.
What I do know is that module_emit_adrp_veneer() and
module_emit_plt_entry() are not part of the veneer themselves: they
are ordinary routines that are part of the module loader, and which
populate the allocated veneer space on demand when encountering ADRP
instructions that need to be rerouted.
>> > diff --git a/tools/perf/tests/vmlinux-kallsyms.c
>> > b/tools/perf/tests/vmlinux-kallsyms.c
>> > index 1e5adb65632a..07064e76947d 100644
>> > --- a/tools/perf/tests/vmlinux-kallsyms.c
>> > +++ b/tools/perf/tests/vmlinux-kallsyms.c
>> > @@ -163,6 +163,29 @@ int test__vmlinux_matches_kallsyms(struct test *test
>> > __maybe_unused, int subtest
>> >
>> > continue;
>> > }
>> > + } else if (pair) {
>> > + s64 skew = mem_start - UM(pair->start);
>> > + struct map *kmap =
>> > map_groups__find(&kallsyms.kmaps, type, mem_start);
>> > + struct map *vmap =
>> > map_groups__find(&vmlinux.kmaps, type, mem_start);
>> > +
>> > + /*
>> > + * arm64 kernels compensating for a CPU erratum
>> > can put up a
>> > + * module_emit_adrp_veneer in place of a
>> > module_emit_plt_entry
>> > + */
>> > + if (llabs(skew) < page_size)
>>
>> It seems that we needs to check it's the ARM64 at least. If it's a
>
> OK.
>
>> rare case we might need to add more paranoid checks.
>
> It's certainly rare: Adding the authors of the veneer to cc for
> comments:
>
> Will, Ard, how probable are veneer-style symbols such as the
> one introduced in commit a257e0257 "arm64/kernel: don't ban ADRP to
> work around Cortex-A53 erratum #843419" to happen again in the future?
>
Distro kernels typically enable full KASLR, so on systems that
implement EFI_RNG_PROTOCOL, all function calls from modules into the
kernel proper are redirected via veneers. (Note that these are bl
instructions not adrp instructions though).
> I would have thought WARNing on within-a-pagesize would be OK,
> Namhyung. Are you suggesting checking instead for a hardcoded veneer
> symbol string?
>
Veneers don't have symbol strings. Veneers are anonymous sequences of
instructions living in a patch of R-X mapped module space somewhere.
The only symbol strings are for the routines that generate these
veneers, not for the veneers themselves.
>> > + pr_debug("NO ERR FOR SKEW %ld: %#" PRIx64
>> > ": diff start addr v: %s k: %#" PRIx64 " %s\n",
>> > + skew, mem_start, sym->name,
>> > UM(pair->start), pair->name);
>> > + continue;
>> > + }
>> > +
>> > + pr_debug("ERR : %#" PRIx64 ": diff start addr v:
>> > %s k: %#" PRIx64 " %s\n",
>> > + mem_start, sym->name, UM(pair->start),
>> > pair->name);
>> > +
>> > + if (kmap && vmap) {
>> > + pr_debug(" : map v: %s k: %s\n",
>> > + vmap->dso->short_name,
>> > kmap->dso->short_name);
>> > + }
>> > } else
>> > pr_debug("ERR : %#" PRIx64 ": %s not on
>> > kallsyms\n",
>> > mem_start, sym->name);
