Messages in this thread | | | From | Ard Biesheuvel <> | Date | Tue, 24 Apr 2018 08:13:57 +0200 | Subject | Re: [PATCH] perf tools: set kernel end address properly |
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On 23 April 2018 at 23:43, Kim Phillips <kim.phillips@arm.com> wrote: > On Fri, 20 Apr 2018 10:10:32 +0200 > Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > >> On 20 April 2018 at 01:33, Kim Phillips <kim.phillips@arm.com> wrote: >> > On Thu, 19 Apr 2018 11:54:24 +0900 >> > Namhyung Kim <namhyung@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. > > Sorry about that. The problem is that perf test 1 ("vmlinux > symtab matches kallsyms") is failing, because > module_emit_adrp_veneer exists in /boot/vmlinux but doesn't exist > in /proc/kallsyms, and, sure enough, it's not in the latter. > >> 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. > ... >> > >> 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. > > OK, thanks, so AFAICT this means the function module_emit_adrp_veneer() > should still show up in /proc/kallsyms, but it's not. I'm also seeing > some weird characters, e.g., here there's a byte with a binary 02 value > following a weird symbol named 'L14472' (part of the xfs module?): > > $ grep L1 /proc/kallsyms | hexdump -C | head > <snip> > 00000540 30 30 30 30 30 20 72 20 2e 4c 31 34 34 37 32 02 |00000 r .L14472.| > <snip> > > arch__normalize_symbol_name() is a place where architecture code can > clean up symbol names in perf, and I thought module_emit_adrp_veneer() > was a veneer itself, but it seems that's not the case, so the > literal string check for it shouldn't be needed. The test is still > failing though because it doesn't show up in kallsyms... >
This turns out to be an unintended side effect of the fact that we (I?) taught kallsyms to disregard symbols ending in "_veneer"
So we should probably rename the function, and everything will be fine.
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