Messages in this thread | | | From | Ian Rogers <> | Date | Sat, 30 Jul 2022 08:21:10 -0700 | Subject | Re: [PATCH v3 1/2] perf symbol: Correct address for bss symbols |
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On Sat, Jul 30, 2022 at 2:38 AM Leo Yan <leo.yan@linaro.org> wrote: > > Hi Ian, > > On Fri, Jul 29, 2022 at 10:13:04PM -0700, Ian Rogers wrote: > > [...] > > > I am seeing a problem with this patch with jvmti. To repro: > > > > 1) download a Java workload dacapo-9.12-MR1-bach.jar from > > https://sourceforge.net/projects/dacapobench/ > > 2) build perf such as "make -C tools/perf O=/tmp/perf NO_LIBBFD=1" it > > should detect Java and create /tmp/perf/libperf-jvmti.so > > 3) run perf with the jvmti agent: > > /tmp/perf/perf record -k 1 java -agentpath:/tmp/perf/libperf-jvmti.so > > -jar dacapo-9.12-MR1-bach.jar -n 10 fop > > 4) run perf inject: > > /tmp/perf/perf inject -i perf.data -o perf-injected.data -j > > 5) run perf report > > /tmp/perf/perf report -i perf-injected.data | grep org.apache.fop > > > > With this patch reverted I see lots of symbols like: > > 0.00% java jitted-388040-4656.so [.] > > org.apache.fop.fo.FObj.bind(org.apache.fop.fo.PropertyList) > > > > With the patch I see lots of: > > dso__load_sym_internal: failed to find program header for symbol: > > Lorg/apache/fop/fo/FObj;bind(Lorg/apache/fop/fo/PropertyList;)V > > st_value: 0x40 > > Thanks for sharing the steps, I can reproduce the issue. > > I tried to add more logs to dump and hope can find specific pattern for > these symbols, one thing I observed that if a symbol fails to find > program header, it has the same values for st_value, shdr.sh_addr and > shdr.sh_offset: all of them are 0x40. So that means if with you > proposed change in below, then we will get the file address is: > > file_addr = st_value - shdr.sh_addr + shdr.sh_offset = 0x40 > > Seems to me this is not reasonable: perf tries to add many symbols > with the same file address 0x40. > > > Combining the old and new behaviors fixes the issue for me, wdyt? > > So far we don't answer a question is what's the purpose for these JAVA > symbols. I checked these symbols and concluded as: > > - They are not label, this is because sym.st_info is 0x2, so its > symbol type is STT_FUNC; > - They are from ".text" section; > - Symbol visibility is STV_DEFAULT; > - Symbol's section index number is 0x1, which is different from some > special sections (STV_DEFAULT/SHN_COMMON/SHN_UNDEF/SHN_XINDEX). > > This is a rough summary, these symbols are likewise the normal function > symbols, but they have special st_value (0x40) and has no matched the > program header for them. > > If we rollback to use old offsets to calculate the symbol file address, > it still is incorrect. > > I list all relevant symbols in: https://termbin.com/s0fb, for a reliable > fixing, could anyone with java experience shed some lights for handling > the symbols? > > On the other hand, I can accept to simply change pr_warning() to > pr_debug4() to avoid warning flood, the log still can help us to find > potential symbol parsing issue, so far they are not false-positive > reporting.
Thanks, I suspect the ELF that the Java agent has created isn't good. The Java agent is part of perf as and so is the ELF file generation code: https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/perf/util/genelf.c?h=perf/core#n367 I took a quick look but most of the logic is in libelf - it seems less obvious the bug would be there rather than perf. Could you take a look? Ideally there'd be a quick fix that keeps all the benefits of your change and the jvmti code working.
Thanks, Ian
> Thanks, > Leo > > > ``` > > --- a/tools/perf/util/symbol-elf.c > > +++ b/tools/perf/util/symbol-elf.c > > @@ -1305,16 +1305,21 @@ dso__load_sym_internal(struct dso *dso, struct > > map *map, struct symsrc *syms > > _ss, > > > > if (elf_read_program_header(syms_ss->elf, > > (u64)sym.st_value, &phdr)) { > > - pr_warning("%s: failed to find program > > header for " > > + pr_debug4("%s: failed to find program > > header for " > > "symbol: %s st_value: %#" PRIx64 "\n", > > __func__, elf_name, > > (u64)sym.st_value); > > - continue; > > + pr_debug4("%s: adjusting symbol: > > st_value: %#" PRIx64 " " > > + "sh_addr: %#" PRIx64 " > > sh_offset: %#" PRIx64 "\n", > > + __func__, (u64)sym.st_value, > > (u64)shdr.sh_addr, > > + (u64)shdr.sh_offset); > > + sym.st_value -= shdr.sh_addr - shdr.sh_offset; > > + } else { > > + pr_debug4("%s: adjusting symbol: > > st_value: %#" PRIx64 " " > > + "p_vaddr: %#" PRIx64 " > > p_offset: %#" PRIx64 "\n", > > + __func__, (u64)sym.st_value, > > (u64)phdr.p_vaddr, > > + (u64)phdr.p_offset); > > + sym.st_value -= phdr.p_vaddr - phdr.p_offset; > > } > > - pr_debug4("%s: adjusting symbol: st_value: %#" > > PRIx64 " " > > - "p_vaddr: %#" PRIx64 " p_offset: %#" > > PRIx64 "\n", > > - __func__, (u64)sym.st_value, > > (u64)phdr.p_vaddr, > > - (u64)phdr.p_offset); > > - sym.st_value -= phdr.p_vaddr - phdr.p_offset; > > } > > > > demangled = demangle_sym(dso, kmodule, elf_name); > > ``` > > > > Thanks, > > Ian > > > > > > > > demangled = demangle_sym(dso, kmodule, elf_name); > > > -- > > > 2.25.1 > > >
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