* [PATCH] perf symbol: ignore $a/$d symbols for ARM modules @ 2021-10-27 9:52 Lexi Shao 2021-10-27 10:23 ` James Clark 2021-10-28 8:44 ` [PATCH] perf symbol: ignore $a/$d symbols for ARM modules James Clark 0 siblings, 2 replies; 12+ messages in thread From: Lexi Shao @ 2021-10-27 9:52 UTC (permalink / raw) To: linux-perf-users, linux-kernel Cc: acme, mark.rutland, peterz, mingo, alexander.shishkin, jolsa, namhyung, shaolexi, qiuxi1, nixiaoming, wangbing6 On ARM machine, kernel symbols from modules can be resolved to $a instead of printing the actual symbol name. Ignore symbols starting with "$" when building kallsyms rbtree. A sample stacktrace is shown as follows: c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) bf4a66d8 $a+0x78 ([test_module]) c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) On ARM machine, $a/$d symbols are used by the compiler to mark the beginning of code/data part in code section. These symbols are filtered out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but are left on modules. So there are $a symbols in /proc/kallsyms which share the same addresses with the actual module symbols and confuses perf when resolving symbols. After this patch, the module symbol name is printed: c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) bf4a66d8 test_func+0x78 ([test_module]) c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) Signed-off-by: Lexi Shao <shaolexi@huawei.com> --- tools/perf/util/symbol.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c index 0fc9a5410739..35116aed74eb 100644 --- a/tools/perf/util/symbol.c +++ b/tools/perf/util/symbol.c @@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name, if (!symbol_type__filter(type)) return 0; + /* Ignore local symbols for ARM modules */ + if (name[0] == '$') + return 0; + /* * module symbols are not sorted so we add all * symbols, setting length to 0, and rely on -- 2.12.3 ^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules 2021-10-27 9:52 [PATCH] perf symbol: ignore $a/$d symbols for ARM modules Lexi Shao @ 2021-10-27 10:23 ` James Clark 2021-10-27 12:31 ` Lexi Shao 2021-10-28 8:44 ` [PATCH] perf symbol: ignore $a/$d symbols for ARM modules James Clark 1 sibling, 1 reply; 12+ messages in thread From: James Clark @ 2021-10-27 10:23 UTC (permalink / raw) To: Lexi Shao, linux-perf-users, linux-kernel Cc: acme, mark.rutland, peterz, mingo, alexander.shishkin, jolsa, namhyung, qiuxi1, nixiaoming, wangbing6 On 27/10/2021 10:52, Lexi Shao wrote: > On ARM machine, kernel symbols from modules can be resolved to $a > instead of printing the actual symbol name. Ignore symbols starting with > "$" when building kallsyms rbtree. > > A sample stacktrace is shown as follows: > > c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) > bf4a66d8 $a+0x78 ([test_module]) > c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) > c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) > > On ARM machine, $a/$d symbols are used by the compiler to mark the > beginning of code/data part in code section. These symbols are filtered > out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but > are left on modules. So there are $a symbols in /proc/kallsyms which > share the same addresses with the actual module symbols and confuses perf > when resolving symbols. Hi Lexi, Is it worth using or re-implementing the entire is_ignored_symbol() function from scripts/kallsyms.c? It seems like this change only fixes one occurrence, but is_ignored_symbol() has a big list of other cases. Unless those cases are different? Thanks James > > After this patch, the module symbol name is printed: > > c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) > bf4a66d8 test_func+0x78 ([test_module]) > c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) > c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) > > Signed-off-by: Lexi Shao <shaolexi@huawei.com> > --- > tools/perf/util/symbol.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c > index 0fc9a5410739..35116aed74eb 100644 > --- a/tools/perf/util/symbol.c > +++ b/tools/perf/util/symbol.c > @@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name, > if (!symbol_type__filter(type)) > return 0; > > + /* Ignore local symbols for ARM modules */ > + if (name[0] == '$') > + return 0; > + > /* > * module symbols are not sorted so we add all > * symbols, setting length to 0, and rely on > ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules 2021-10-27 10:23 ` James Clark @ 2021-10-27 12:31 ` Lexi Shao 2021-10-27 15:10 ` James Clark 0 siblings, 1 reply; 12+ messages in thread From: Lexi Shao @ 2021-10-27 12:31 UTC (permalink / raw) To: james.clark Cc: acme, alexander.shishkin, jolsa, linux-kernel, linux-perf-users, mark.rutland, mingo, namhyung, nixiaoming, peterz, qiuxi1, shaolexi, wangbing6 On 27/10/2021 18:24, James Clark wrote: >On 27/10/2021 10:52, Lexi Shao wrote: >> On ARM machine, kernel symbols from modules can be resolved to $a >> instead of printing the actual symbol name. Ignore symbols starting with >> "$" when building kallsyms rbtree. >> >> A sample stacktrace is shown as follows: >> >> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) >> bf4a66d8 $a+0x78 ([test_module]) >> c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) >> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) >> >> On ARM machine, $a/$d symbols are used by the compiler to mark the >> beginning of code/data part in code section. These symbols are filtered >> out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but >> are left on modules. So there are $a symbols in /proc/kallsyms which >> share the same addresses with the actual module symbols and confuses perf >> when resolving symbols. > >Hi Lexi, > >Is it worth using or re-implementing the entire is_ignored_symbol() function >from scripts/kallsyms.c? It seems like this change only fixes one occurrence, >but is_ignored_symbol() has a big list of other cases. > >Unless those cases are different? > >Thanks >James Hi James, I don't think it's necessary to cover all the cases listed in is_ignored_symbol(). As long as the symbols are unique and not overlapping with each other, they should't cause problems in resolving symbols. So most of the cases in is_ignored_symbol() should be irrelevant. Lexi > >> >> After this patch, the module symbol name is printed: >> >> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) >> bf4a66d8 test_func+0x78 ([test_module]) >> c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) >> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) >> >> Signed-off-by: Lexi Shao <shaolexi@huawei.com> >> --- >> tools/perf/util/symbol.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c >> index 0fc9a5410739..35116aed74eb 100644 >> --- a/tools/perf/util/symbol.c >> +++ b/tools/perf/util/symbol.c >> @@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name, >> if (!symbol_type__filter(type)) >> return 0; >> >> + /* Ignore local symbols for ARM modules */ >> + if (name[0] == '$') >> + return 0; >> + >> /* >> * module symbols are not sorted so we add all >> * symbols, setting length to 0, and rely on >> > ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules 2021-10-27 12:31 ` Lexi Shao @ 2021-10-27 15:10 ` James Clark 2021-10-28 2:05 ` Lexi Shao 0 siblings, 1 reply; 12+ messages in thread From: James Clark @ 2021-10-27 15:10 UTC (permalink / raw) To: Lexi Shao Cc: acme, alexander.shishkin, jolsa, linux-kernel, linux-perf-users, mark.rutland, mingo, namhyung, nixiaoming, peterz, qiuxi1, wangbing6 On 27/10/2021 13:31, Lexi Shao wrote: > On 27/10/2021 18:24, James Clark wrote: >> On 27/10/2021 10:52, Lexi Shao wrote: >>> On ARM machine, kernel symbols from modules can be resolved to $a >>> instead of printing the actual symbol name. Ignore symbols starting with >>> "$" when building kallsyms rbtree. >>> >>> A sample stacktrace is shown as follows: >>> >>> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) >>> bf4a66d8 $a+0x78 ([test_module]) >>> c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) >>> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) >>> >>> On ARM machine, $a/$d symbols are used by the compiler to mark the >>> beginning of code/data part in code section. These symbols are filtered >>> out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but >>> are left on modules. So there are $a symbols in /proc/kallsyms which >>> share the same addresses with the actual module symbols and confuses perf >>> when resolving symbols. >> >> Hi Lexi, >> >> Is it worth using or re-implementing the entire is_ignored_symbol() function >>from scripts/kallsyms.c? It seems like this change only fixes one occurrence, >> but is_ignored_symbol() has a big list of other cases. >> >> Unless those cases are different? >> >> Thanks >> James > > Hi James, > > I don't think it's necessary to cover all the cases listed in > is_ignored_symbol(). As long as the symbols are unique and not overlapping > with each other, they should't cause problems in resolving symbols. So most > of the cases in is_ignored_symbol() should be irrelevant. Is it possible to do the filtering of the module symbols somewhere else like in kernel/kallsyms.c? I'm not that familiar with it but it seems like at one point when populating kallsyms '$...' functions are filtered out, but when modules are loaded the symbols are not filtered because another code path is used? If kallsyms has some duplicate addresses in there then isn't the bug in kallsyms rather than perf? And another tool could get confused too. James > > Lexi > >> >>> >>> After this patch, the module symbol name is printed: >>> >>> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) >>> bf4a66d8 test_func+0x78 ([test_module]) >>> c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) >>> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) >>> >>> Signed-off-by: Lexi Shao <shaolexi@huawei.com> >>> --- >>> tools/perf/util/symbol.c | 4 ++++ >>> 1 file changed, 4 insertions(+) >>> >>> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c >>> index 0fc9a5410739..35116aed74eb 100644 >>> --- a/tools/perf/util/symbol.c >>> +++ b/tools/perf/util/symbol.c >>> @@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name, >>> if (!symbol_type__filter(type)) >>> return 0; >>> >>> + /* Ignore local symbols for ARM modules */ >>> + if (name[0] == '$') >>> + return 0; >>> + >>> /* >>> * module symbols are not sorted so we add all >>> * symbols, setting length to 0, and rely on >>> >> ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules 2021-10-27 15:10 ` James Clark @ 2021-10-28 2:05 ` Lexi Shao 2021-10-28 8:42 ` James Clark 0 siblings, 1 reply; 12+ messages in thread From: Lexi Shao @ 2021-10-28 2:05 UTC (permalink / raw) To: james.clark Cc: acme, alexander.shishkin, jolsa, linux-kernel, linux-perf-users, mark.rutland, mingo, namhyung, nixiaoming, peterz, qiuxi1, shaolexi, wangbing6 On 27/10/2021 23:10, James Clark wrote: >On 27/10/2021 13:31, Lexi Shao wrote: >> On 27/10/2021 18:24, James Clark wrote: >>> On 27/10/2021 10:52, Lexi Shao wrote: >>>> On ARM machine, kernel symbols from modules can be resolved to $a >>>> instead of printing the actual symbol name. Ignore symbols starting with >>>> "$" when building kallsyms rbtree. >>>> >>>> A sample stacktrace is shown as follows: >>>> >>>> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) >>>> bf4a66d8 $a+0x78 ([test_module]) >>>> c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) >>>> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) >>>> >>>> On ARM machine, $a/$d symbols are used by the compiler to mark the >>>> beginning of code/data part in code section. These symbols are filtered >>>> out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but >>>> are left on modules. So there are $a symbols in /proc/kallsyms which >>>> share the same addresses with the actual module symbols and confuses perf >>>> when resolving symbols. >>> >>> Hi Lexi, >>> >>> Is it worth using or re-implementing the entire is_ignored_symbol() function >>>from scripts/kallsyms.c? It seems like this change only fixes one occurrence, >>> but is_ignored_symbol() has a big list of other cases. >>> >>> Unless those cases are different? >>> >>> Thanks >>> James >> >> Hi James, >> >> I don't think it's necessary to cover all the cases listed in >> is_ignored_symbol(). As long as the symbols are unique and not overlapping >> with each other, they should't cause problems in resolving symbols. So most >> of the cases in is_ignored_symbol() should be irrelevant. > >Is it possible to do the filtering of the module symbols somewhere else like >in kernel/kallsyms.c? I'm not that familiar with it but it seems like >at one point when populating kallsyms '$...' functions are filtered out, but >when modules are loaded the symbols are not filtered because another code path is >used? > >If kallsyms has some duplicate addresses in there then isn't the bug in kallsyms >rather than perf? And another tool could get confused too. > >James Yes we can filter these symbols out when adding module symbols to the kallsyms list. I will send another patch that modifies module.c to ignore '$' symbols when loading module. I think it's worth applying this patch in the sense that perf userspace tool can be used on all 5.x kernels, and people don't have to update the kernel to fix it. Lexi > >> >> Lexi >> >>> >>>> >>>> After this patch, the module symbol name is printed: >>>> >>>> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) >>>> bf4a66d8 test_func+0x78 ([test_module]) >>>> c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) >>>> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) >>>> >>>> Signed-off-by: Lexi Shao <shaolexi@huawei.com> >>>> --- >>>> tools/perf/util/symbol.c | 4 ++++ >>>> 1 file changed, 4 insertions(+) >>>> >>>> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c >>>> index 0fc9a5410739..35116aed74eb 100644 >>>> --- a/tools/perf/util/symbol.c >>>> +++ b/tools/perf/util/symbol.c >>>> @@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name, >>>> if (!symbol_type__filter(type)) >>>> return 0; >>>> >>>> + /* Ignore local symbols for ARM modules */ >>>> + if (name[0] == '$') >>>> + return 0; >>>> + >>>> /* >>>> * module symbols are not sorted so we add all >>>> * symbols, setting length to 0, and rely on >>>> >>> ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules 2021-10-28 2:05 ` Lexi Shao @ 2021-10-28 8:42 ` James Clark 2021-10-29 6:50 ` [PATCH v2 0/2] kallsyms: Ignore $a/$d symbols in kallsyms for ARM Lexi Shao 0 siblings, 1 reply; 12+ messages in thread From: James Clark @ 2021-10-28 8:42 UTC (permalink / raw) To: Lexi Shao Cc: acme, alexander.shishkin, jolsa, linux-kernel, linux-perf-users, mark.rutland, mingo, namhyung, nixiaoming, peterz, qiuxi1, wangbing6 On 28/10/2021 03:05, Lexi Shao wrote: > On 27/10/2021 23:10, James Clark wrote: >> On 27/10/2021 13:31, Lexi Shao wrote: >>> On 27/10/2021 18:24, James Clark wrote: >>>> On 27/10/2021 10:52, Lexi Shao wrote: >>>>> On ARM machine, kernel symbols from modules can be resolved to $a >>>>> instead of printing the actual symbol name. Ignore symbols starting with >>>>> "$" when building kallsyms rbtree. >>>>> >>>>> A sample stacktrace is shown as follows: >>>>> >>>>> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) >>>>> bf4a66d8 $a+0x78 ([test_module]) >>>>> c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) >>>>> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) >>>>> >>>>> On ARM machine, $a/$d symbols are used by the compiler to mark the >>>>> beginning of code/data part in code section. These symbols are filtered >>>>> out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but >>>>> are left on modules. So there are $a symbols in /proc/kallsyms which >>>>> share the same addresses with the actual module symbols and confuses perf >>>>> when resolving symbols. >>>> >>>> Hi Lexi, >>>> >>>> Is it worth using or re-implementing the entire is_ignored_symbol() function >>> >from scripts/kallsyms.c? It seems like this change only fixes one occurrence, >>>> but is_ignored_symbol() has a big list of other cases. >>>> >>>> Unless those cases are different? >>>> >>>> Thanks >>>> James >>> >>> Hi James, >>> >>> I don't think it's necessary to cover all the cases listed in >>> is_ignored_symbol(). As long as the symbols are unique and not overlapping >>> with each other, they should't cause problems in resolving symbols. So most >>> of the cases in is_ignored_symbol() should be irrelevant. >> >> Is it possible to do the filtering of the module symbols somewhere else like >> in kernel/kallsyms.c? I'm not that familiar with it but it seems like >> at one point when populating kallsyms '$...' functions are filtered out, but >> when modules are loaded the symbols are not filtered because another code path is >> used? >> >> If kallsyms has some duplicate addresses in there then isn't the bug in kallsyms >> rather than perf? And another tool could get confused too. >> >> James > > Yes we can filter these symbols out when adding module symbols to the kallsyms > list. I will send another patch that modifies module.c to ignore '$' symbols > when loading module. > That sounds great thanks. > I think it's worth applying this patch in the sense that perf userspace tool > can be used on all 5.x kernels, and people don't have to update the kernel > to fix it. Yes you are right. In that case I will add a review tag to this change. Thanks James > > Lexi > >> >>> >>> Lexi >>> >>>> >>>>> >>>>> After this patch, the module symbol name is printed: >>>>> >>>>> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) >>>>> bf4a66d8 test_func+0x78 ([test_module]) >>>>> c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) >>>>> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) >>>>> >>>>> Signed-off-by: Lexi Shao <shaolexi@huawei.com> >>>>> --- >>>>> tools/perf/util/symbol.c | 4 ++++ >>>>> 1 file changed, 4 insertions(+) >>>>> >>>>> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c >>>>> index 0fc9a5410739..35116aed74eb 100644 >>>>> --- a/tools/perf/util/symbol.c >>>>> +++ b/tools/perf/util/symbol.c >>>>> @@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name, >>>>> if (!symbol_type__filter(type)) >>>>> return 0; >>>>> >>>>> + /* Ignore local symbols for ARM modules */ >>>>> + if (name[0] == '$') >>>>> + return 0; >>>>> + >>>>> /* >>>>> * module symbols are not sorted so we add all >>>>> * symbols, setting length to 0, and rely on >>>>> >>>> > ^ permalink raw reply [flat|nested] 12+ messages in thread
* [PATCH v2 0/2] kallsyms: Ignore $a/$d symbols in kallsyms for ARM 2021-10-28 8:42 ` James Clark @ 2021-10-29 6:50 ` Lexi Shao 2021-10-29 6:50 ` [PATCH v2 1/2] perf symbol: ignore $a/$d symbols for ARM modules Lexi Shao 2021-10-29 6:50 ` [PATCH v2 2/2] kallsyms: ignore arm mapping symbols when loading module Lexi Shao 0 siblings, 2 replies; 12+ messages in thread From: Lexi Shao @ 2021-10-29 6:50 UTC (permalink / raw) To: linux-kernel, linux-perf-users Cc: james.clark, acme, alexander.shishkin, jolsa, mark.rutland, mingo, namhyung, nixiaoming, peterz, qiuxi1, shaolexi, wangbing6, jeyu, ast, daniel, andrii, kafai, songliubraving, yhs, john.fastabend, kpsingh, natechancellor, ndesaulniers, bpf, clang-built-linux On ARM machine, $a/$d symbols are used by the compiler to mark the beginning of code/data part in code section. These symbols are filtered out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but are left on modules. So there are $a symbols in /proc/kallsyms whose address overlap with the actual module symbols and can confuse tools such as perf when resolving kernel symbols. A sample stacktrace shown by perf script: c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) bf4a66d8 $a+0x78 ([test_module]) // $a is shown instead of actual sym name c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) This patch set contains 2 patches to fix such problem: The 1st patch modifies perf userspace tools to ignore $a/$d symbols from /proc/kallsyms. So people can use new perf tool to get correct kernel symbol on arm machines instead of updating kernel image. The 2nd patch modifies the logic of loading modules to ignore arm mapping symbols in the first place. Being left out in vmlinux and kernelspace API (e.g. module_kallsyms_on_each_symbol) means these symbols are not used anywhere, so it should be safe to remove them from module kallsyms list. v2: - Add 2nd patch as discussed with James Clark, see: https://lore.kernel.org/all/c7dfbd17-85fd-b914-b90f-082abc64c9d1@arm.com/ Lexi Shao (2): perf symbol: ignore $a/$d symbols for ARM modules kallsyms: ignore arm mapping symbols when loading module kernel/module.c | 19 +++++++++++-------- tools/perf/util/symbol.c | 4 ++++ 2 files changed, 15 insertions(+), 8 deletions(-) -- 2.12.3 ^ permalink raw reply [flat|nested] 12+ messages in thread
* [PATCH v2 1/2] perf symbol: ignore $a/$d symbols for ARM modules 2021-10-29 6:50 ` [PATCH v2 0/2] kallsyms: Ignore $a/$d symbols in kallsyms for ARM Lexi Shao @ 2021-10-29 6:50 ` Lexi Shao 2021-10-29 6:50 ` [PATCH v2 2/2] kallsyms: ignore arm mapping symbols when loading module Lexi Shao 1 sibling, 0 replies; 12+ messages in thread From: Lexi Shao @ 2021-10-29 6:50 UTC (permalink / raw) To: linux-kernel, linux-perf-users Cc: james.clark, acme, alexander.shishkin, jolsa, mark.rutland, mingo, namhyung, nixiaoming, peterz, qiuxi1, shaolexi, wangbing6, jeyu, ast, daniel, andrii, kafai, songliubraving, yhs, john.fastabend, kpsingh, natechancellor, ndesaulniers, bpf, clang-built-linux On ARM machine, kernel symbols from modules can be resolved to $a instead of printing the actual symbol name. Ignore symbols starting with "$" when building kallsyms rbtree. A sample stacktrace is shown as follows: c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) bf4a66d8 $a+0x78 ([test_module]) c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) On ARM machine, $a/$d symbols are used by the compiler to mark the beginning of code/data part in code section. These symbols are filtered out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but are left on modules. So there are $a symbols in /proc/kallsyms which share the same addresses with the actual module symbols and confuses perf when resolving symbols. After this patch, the module symbol name is printed: c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) bf4a66d8 test_func+0x78 ([test_module]) c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) Signed-off-by: Lexi Shao <shaolexi@huawei.com> Reviewed-by: James Clark <james.clark@arm.com> --- tools/perf/util/symbol.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c index 0fc9a5410739..35116aed74eb 100644 --- a/tools/perf/util/symbol.c +++ b/tools/perf/util/symbol.c @@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name, if (!symbol_type__filter(type)) return 0; + /* Ignore local symbols for ARM modules */ + if (name[0] == '$') + return 0; + /* * module symbols are not sorted so we add all * symbols, setting length to 0, and rely on -- 2.12.3 ^ permalink raw reply related [flat|nested] 12+ messages in thread
* [PATCH v2 2/2] kallsyms: ignore arm mapping symbols when loading module 2021-10-29 6:50 ` [PATCH v2 0/2] kallsyms: Ignore $a/$d symbols in kallsyms for ARM Lexi Shao 2021-10-29 6:50 ` [PATCH v2 1/2] perf symbol: ignore $a/$d symbols for ARM modules Lexi Shao @ 2021-10-29 6:50 ` Lexi Shao 2021-11-02 9:43 ` James Clark 1 sibling, 1 reply; 12+ messages in thread From: Lexi Shao @ 2021-10-29 6:50 UTC (permalink / raw) To: linux-kernel, linux-perf-users Cc: james.clark, acme, alexander.shishkin, jolsa, mark.rutland, mingo, namhyung, nixiaoming, peterz, qiuxi1, shaolexi, wangbing6, jeyu, ast, daniel, andrii, kafai, songliubraving, yhs, john.fastabend, kpsingh, natechancellor, ndesaulniers, bpf, clang-built-linux Arm modules contains mapping symbols(e.g. $a $d) which are ignored in module_kallsyms_on_each_symbol. However, these symbols are still displayed when catting /proc/kallsyms. This confuses tools(e.g. perf) that resolves kernel symbols with address using information from /proc/kallsyms. See discussion in Link: https://lore.kernel.org/all/c7dfbd17-85fd-b914-b90f-082abc64c9d1@arm.com/ Being left out in vmlinux(see scripts/kallsyms.c is_ignored_symbol) and kernelspace API implies that these symbols are not used in any cases. So we can ignore them in the first place by not adding them to module kallsyms. Signed-off-by: Lexi Shao <shaolexi@huawei.com> --- kernel/module.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/kernel/module.c b/kernel/module.c index 5c26a76e800b..b30cbbe144c7 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -2662,16 +2662,22 @@ static char elf_type(const Elf_Sym *sym, const struct load_info *info) return '?'; } -static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs, - unsigned int shnum, unsigned int pcpundx) +static inline int is_arm_mapping_symbol(const char *str); +static bool is_core_symbol(const Elf_Sym *src, const struct load_info *info) { const Elf_Shdr *sec; + const Elf_Shdr *sechdrs = info->sechdrs; + unsigned int shnum = info->hdr->e_shnum; + unsigned int pcpundx = info->index.pcpu; if (src->st_shndx == SHN_UNDEF || src->st_shndx >= shnum || !src->st_name) return false; + if (is_arm_mapping_symbol(&info->strtab[src->st_name])) + return false; + #ifdef CONFIG_KALLSYMS_ALL if (src->st_shndx == pcpundx) return true; @@ -2714,8 +2720,7 @@ static void layout_symtab(struct module *mod, struct load_info *info) /* Compute total space required for the core symbols' strtab. */ for (ndst = i = 0; i < nsrc; i++) { if (i == 0 || is_livepatch_module(mod) || - is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum, - info->index.pcpu)) { + is_core_symbol(src+i, info)) { strtab_size += strlen(&info->strtab[src[i].st_name])+1; ndst++; } @@ -2778,8 +2783,7 @@ static void add_kallsyms(struct module *mod, const struct load_info *info) for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) { mod->kallsyms->typetab[i] = elf_type(src + i, info); if (i == 0 || is_livepatch_module(mod) || - is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum, - info->index.pcpu)) { + is_core_symbol(src+i, info)) { mod->core_kallsyms.typetab[ndst] = mod->kallsyms->typetab[i]; dst[ndst] = src[i]; @@ -4246,8 +4250,7 @@ static const char *find_kallsyms_symbol(struct module *mod, * We ignore unnamed symbols: they're uninformative * and inserted at a whim. */ - if (*kallsyms_symbol_name(kallsyms, i) == '\0' - || is_arm_mapping_symbol(kallsyms_symbol_name(kallsyms, i))) + if (*kallsyms_symbol_name(kallsyms, i) == '\0') continue; if (thisval <= addr && thisval > bestval) { -- 2.12.3 ^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH v2 2/2] kallsyms: ignore arm mapping symbols when loading module 2021-10-29 6:50 ` [PATCH v2 2/2] kallsyms: ignore arm mapping symbols when loading module Lexi Shao @ 2021-11-02 9:43 ` James Clark 0 siblings, 0 replies; 12+ messages in thread From: James Clark @ 2021-11-02 9:43 UTC (permalink / raw) To: Lexi Shao, linux-kernel, linux-perf-users Cc: acme, alexander.shishkin, jolsa, mark.rutland, mingo, namhyung, nixiaoming, peterz, qiuxi1, wangbing6, jeyu, ast, daniel, andrii, kafai, songliubraving, yhs, john.fastabend, kpsingh, natechancellor, ndesaulniers, bpf, clang-built-linux On 29/10/2021 07:50, Lexi Shao wrote: > Arm modules contains mapping symbols(e.g. $a $d) which are ignored in > module_kallsyms_on_each_symbol. However, these symbols are still > displayed when catting /proc/kallsyms. This confuses tools(e.g. perf) > that resolves kernel symbols with address using information from > /proc/kallsyms. See discussion in Link: > https://lore.kernel.org/all/c7dfbd17-85fd-b914-b90f-082abc64c9d1@arm.com/ > > Being left out in vmlinux(see scripts/kallsyms.c is_ignored_symbol) and > kernelspace API implies that these symbols are not used in any cases. > So we can ignore them in the first place by not adding them to module > kallsyms. > > Signed-off-by: Lexi Shao <shaolexi@huawei.com> I tested this and it has removed the $ symbols from kallsyms where I saw them before. Reviewed-by: James Clark <james.clark@arm.com> > --- > kernel/module.c | 19 +++++++++++-------- > 1 file changed, 11 insertions(+), 8 deletions(-) > > diff --git a/kernel/module.c b/kernel/module.c > index 5c26a76e800b..b30cbbe144c7 100644 > --- a/kernel/module.c > +++ b/kernel/module.c > @@ -2662,16 +2662,22 @@ static char elf_type(const Elf_Sym *sym, const struct load_info *info) > return '?'; > } > > -static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs, > - unsigned int shnum, unsigned int pcpundx) > +static inline int is_arm_mapping_symbol(const char *str); > +static bool is_core_symbol(const Elf_Sym *src, const struct load_info *info) > { > const Elf_Shdr *sec; > + const Elf_Shdr *sechdrs = info->sechdrs; > + unsigned int shnum = info->hdr->e_shnum; > + unsigned int pcpundx = info->index.pcpu; > > if (src->st_shndx == SHN_UNDEF > || src->st_shndx >= shnum > || !src->st_name) > return false; > > + if (is_arm_mapping_symbol(&info->strtab[src->st_name])) > + return false; > + > #ifdef CONFIG_KALLSYMS_ALL > if (src->st_shndx == pcpundx) > return true; > @@ -2714,8 +2720,7 @@ static void layout_symtab(struct module *mod, struct load_info *info) > /* Compute total space required for the core symbols' strtab. */ > for (ndst = i = 0; i < nsrc; i++) { > if (i == 0 || is_livepatch_module(mod) || > - is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum, > - info->index.pcpu)) { > + is_core_symbol(src+i, info)) { > strtab_size += strlen(&info->strtab[src[i].st_name])+1; > ndst++; > } > @@ -2778,8 +2783,7 @@ static void add_kallsyms(struct module *mod, const struct load_info *info) > for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) { > mod->kallsyms->typetab[i] = elf_type(src + i, info); > if (i == 0 || is_livepatch_module(mod) || > - is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum, > - info->index.pcpu)) { > + is_core_symbol(src+i, info)) { > mod->core_kallsyms.typetab[ndst] = > mod->kallsyms->typetab[i]; > dst[ndst] = src[i]; > @@ -4246,8 +4250,7 @@ static const char *find_kallsyms_symbol(struct module *mod, > * We ignore unnamed symbols: they're uninformative > * and inserted at a whim. > */ > - if (*kallsyms_symbol_name(kallsyms, i) == '\0' > - || is_arm_mapping_symbol(kallsyms_symbol_name(kallsyms, i))) > + if (*kallsyms_symbol_name(kallsyms, i) == '\0') > continue; > > if (thisval <= addr && thisval > bestval) { > ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules 2021-10-27 9:52 [PATCH] perf symbol: ignore $a/$d symbols for ARM modules Lexi Shao 2021-10-27 10:23 ` James Clark @ 2021-10-28 8:44 ` James Clark 2021-11-06 19:48 ` Arnaldo Carvalho de Melo 1 sibling, 1 reply; 12+ messages in thread From: James Clark @ 2021-10-28 8:44 UTC (permalink / raw) To: Lexi Shao, linux-perf-users, linux-kernel Cc: acme, mark.rutland, peterz, mingo, alexander.shishkin, jolsa, namhyung, qiuxi1, nixiaoming, wangbing6 On 27/10/2021 10:52, Lexi Shao wrote: > On ARM machine, kernel symbols from modules can be resolved to $a > instead of printing the actual symbol name. Ignore symbols starting with > "$" when building kallsyms rbtree. > > A sample stacktrace is shown as follows: > > c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) > bf4a66d8 $a+0x78 ([test_module]) > c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) > c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) > > On ARM machine, $a/$d symbols are used by the compiler to mark the > beginning of code/data part in code section. These symbols are filtered > out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but > are left on modules. So there are $a symbols in /proc/kallsyms which > share the same addresses with the actual module symbols and confuses perf > when resolving symbols. > > After this patch, the module symbol name is printed: > > c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) > bf4a66d8 test_func+0x78 ([test_module]) > c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) > c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) > > Signed-off-by: Lexi Shao <shaolexi@huawei.com> Reviewed-by: James Clark <james.clark@arm.com> > --- > tools/perf/util/symbol.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c > index 0fc9a5410739..35116aed74eb 100644 > --- a/tools/perf/util/symbol.c > +++ b/tools/perf/util/symbol.c > @@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name, > if (!symbol_type__filter(type)) > return 0; > > + /* Ignore local symbols for ARM modules */ > + if (name[0] == '$') > + return 0; > + > /* > * module symbols are not sorted so we add all > * symbols, setting length to 0, and rely on > ^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules 2021-10-28 8:44 ` [PATCH] perf symbol: ignore $a/$d symbols for ARM modules James Clark @ 2021-11-06 19:48 ` Arnaldo Carvalho de Melo 0 siblings, 0 replies; 12+ messages in thread From: Arnaldo Carvalho de Melo @ 2021-11-06 19:48 UTC (permalink / raw) To: James Clark Cc: Lexi Shao, linux-perf-users, linux-kernel, mark.rutland, peterz, mingo, alexander.shishkin, jolsa, namhyung, qiuxi1, nixiaoming, wangbing6 Em Thu, Oct 28, 2021 at 09:44:26AM +0100, James Clark escreveu: > > > On 27/10/2021 10:52, Lexi Shao wrote: > > On ARM machine, kernel symbols from modules can be resolved to $a > > instead of printing the actual symbol name. Ignore symbols starting with > > "$" when building kallsyms rbtree. > > > > A sample stacktrace is shown as follows: > > > > c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) > > bf4a66d8 $a+0x78 ([test_module]) > > c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) > > c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) > > > > On ARM machine, $a/$d symbols are used by the compiler to mark the > > beginning of code/data part in code section. These symbols are filtered > > out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but > > are left on modules. So there are $a symbols in /proc/kallsyms which > > share the same addresses with the actual module symbols and confuses perf > > when resolving symbols. > > > > After this patch, the module symbol name is printed: > > > > c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) > > bf4a66d8 test_func+0x78 ([test_module]) > > c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) > > c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) > > > > Signed-off-by: Lexi Shao <shaolexi@huawei.com> > > Reviewed-by: James Clark <james.clark@arm.com> Thanks, applied. - Arnaldo ^ permalink raw reply [flat|nested] 12+ messages in thread
end of thread, other threads:[~2021-11-06 19:49 UTC | newest] Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-10-27 9:52 [PATCH] perf symbol: ignore $a/$d symbols for ARM modules Lexi Shao 2021-10-27 10:23 ` James Clark 2021-10-27 12:31 ` Lexi Shao 2021-10-27 15:10 ` James Clark 2021-10-28 2:05 ` Lexi Shao 2021-10-28 8:42 ` James Clark 2021-10-29 6:50 ` [PATCH v2 0/2] kallsyms: Ignore $a/$d symbols in kallsyms for ARM Lexi Shao 2021-10-29 6:50 ` [PATCH v2 1/2] perf symbol: ignore $a/$d symbols for ARM modules Lexi Shao 2021-10-29 6:50 ` [PATCH v2 2/2] kallsyms: ignore arm mapping symbols when loading module Lexi Shao 2021-11-02 9:43 ` James Clark 2021-10-28 8:44 ` [PATCH] perf symbol: ignore $a/$d symbols for ARM modules James Clark 2021-11-06 19:48 ` Arnaldo Carvalho de Melo
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