In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table changing from their dot prefixed variant to the non-prefixed ones.
Since ftrace prefixes a dot to the syscall names when matching them to build its syscall event list, this resulted in no syscall events being available.
Remove the PPC64_ELF_ABI_V1 specific version of arch_syscall_match_sym_name to have the same behavior across all powerpc variants.
Fixes: 68b34588e202 ("powerpc/64/sycall: Implement syscall entry/exit logic in C") Cc: stable@vger.kernel.org # v5.7+ Cc: Steven Rostedt rostedt@goodmis.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Michael Ellerman mpe@ellerman.id.au Cc: Nicholas Piggin npiggin@gmail.com Cc: Christophe Leroy christophe.leroy@csgroup.eu Cc: Michal Suchanek msuchanek@suse.de Cc: linuxppc-dev@lists.ozlabs.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Michael Jeanson mjeanson@efficios.com Reviewed-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com --- arch/powerpc/include/asm/ftrace.h | 12 ------------ 1 file changed, 12 deletions(-)
diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h index 3cee7115441b..e3d1f377bc5b 100644 --- a/arch/powerpc/include/asm/ftrace.h +++ b/arch/powerpc/include/asm/ftrace.h @@ -64,17 +64,6 @@ void ftrace_graph_func(unsigned long ip, unsigned long parent_ip, * those. */ #define ARCH_HAS_SYSCALL_MATCH_SYM_NAME -#ifdef CONFIG_PPC64_ELF_ABI_V1 -static inline bool arch_syscall_match_sym_name(const char *sym, const char *name) -{ - /* We need to skip past the initial dot, and the __se_sys alias */ - return !strcmp(sym + 1, name) || - (!strncmp(sym, ".__se_sys", 9) && !strcmp(sym + 6, name)) || - (!strncmp(sym, ".ppc_", 5) && !strcmp(sym + 5, name + 4)) || - (!strncmp(sym, ".ppc32_", 7) && !strcmp(sym + 7, name + 4)) || - (!strncmp(sym, ".ppc64_", 7) && !strcmp(sym + 7, name + 4)); -} -#else static inline bool arch_syscall_match_sym_name(const char *sym, const char *name) { return !strcmp(sym, name) || @@ -83,7 +72,6 @@ static inline bool arch_syscall_match_sym_name(const char *sym, const char *name (!strncmp(sym, "ppc32_", 6) && !strcmp(sym + 6, name + 4)) || (!strncmp(sym, "ppc64_", 6) && !strcmp(sym + 6, name + 4)); } -#endif /* CONFIG_PPC64_ELF_ABI_V1 */ #endif /* CONFIG_FTRACE_SYSCALLS */
#if defined(CONFIG_PPC64) && defined(CONFIG_FUNCTION_TRACER)
Michael Jeanson mjeanson@efficios.com writes:
In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table changing from their dot prefixed variant to the non-prefixed ones.
Since ftrace prefixes a dot to the syscall names when matching them to build its syscall event list, this resulted in no syscall events being available.
Remove the PPC64_ELF_ABI_V1 specific version of arch_syscall_match_sym_name to have the same behavior across all powerpc variants.
This doesn't seem to work for me.
Event with it applied I still don't see anything in /sys/kernel/debug/tracing/events/syscalls
Did we break it in some other way recently?
cheers
Fixes: 68b34588e202 ("powerpc/64/sycall: Implement syscall entry/exit logic in C") Cc: stable@vger.kernel.org # v5.7+ Cc: Steven Rostedt rostedt@goodmis.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Michael Ellerman mpe@ellerman.id.au Cc: Nicholas Piggin npiggin@gmail.com Cc: Christophe Leroy christophe.leroy@csgroup.eu Cc: Michal Suchanek msuchanek@suse.de Cc: linuxppc-dev@lists.ozlabs.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Michael Jeanson mjeanson@efficios.com Reviewed-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com
arch/powerpc/include/asm/ftrace.h | 12 ------------ 1 file changed, 12 deletions(-)
diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h index 3cee7115441b..e3d1f377bc5b 100644 --- a/arch/powerpc/include/asm/ftrace.h +++ b/arch/powerpc/include/asm/ftrace.h @@ -64,17 +64,6 @@ void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
- those.
*/ #define ARCH_HAS_SYSCALL_MATCH_SYM_NAME -#ifdef CONFIG_PPC64_ELF_ABI_V1 -static inline bool arch_syscall_match_sym_name(const char *sym, const char *name) -{
- /* We need to skip past the initial dot, and the __se_sys alias */
- return !strcmp(sym + 1, name) ||
(!strncmp(sym, ".__se_sys", 9) && !strcmp(sym + 6, name)) ||(!strncmp(sym, ".ppc_", 5) && !strcmp(sym + 5, name + 4)) ||(!strncmp(sym, ".ppc32_", 7) && !strcmp(sym + 7, name + 4)) ||(!strncmp(sym, ".ppc64_", 7) && !strcmp(sym + 7, name + 4));-} -#else static inline bool arch_syscall_match_sym_name(const char *sym, const char *name) { return !strcmp(sym, name) || @@ -83,7 +72,6 @@ static inline bool arch_syscall_match_sym_name(const char *sym, const char *name (!strncmp(sym, "ppc32_", 6) && !strcmp(sym + 6, name + 4)) || (!strncmp(sym, "ppc64_", 6) && !strcmp(sym + 6, name + 4)); } -#endif /* CONFIG_PPC64_ELF_ABI_V1 */ #endif /* CONFIG_FTRACE_SYSCALLS */
#if defined(CONFIG_PPC64) && defined(CONFIG_FUNCTION_TRACER)
2.34.1
On 2022-12-05 00:34, Michael Ellerman wrote:
Michael Jeanson mjeanson@efficios.com writes:
In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table changing from their dot prefixed variant to the non-prefixed ones.
Since ftrace prefixes a dot to the syscall names when matching them to build its syscall event list, this resulted in no syscall events being available.
Remove the PPC64_ELF_ABI_V1 specific version of arch_syscall_match_sym_name to have the same behavior across all powerpc variants.
This doesn't seem to work for me.
Event with it applied I still don't see anything in /sys/kernel/debug/tracing/events/syscalls
Did we break it in some other way recently?
cheers
I've just tried this change on top of v6.1-rc8 in qemu with a base config of 'corenet32_smp_defconfig' and these options on top:
CONFIG_FTRACE=y CONFIG_FTRACE_SYSCALLS=y
And I can trace syscalls with ftrace.
What kernel tree and config are you using?
Thanks for looking into this.
Fixes: 68b34588e202 ("powerpc/64/sycall: Implement syscall entry/exit logic in C") Cc: stable@vger.kernel.org # v5.7+ Cc: Steven Rostedt rostedt@goodmis.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Michael Ellerman mpe@ellerman.id.au Cc: Nicholas Piggin npiggin@gmail.com Cc: Christophe Leroy christophe.leroy@csgroup.eu Cc: Michal Suchanek msuchanek@suse.de Cc: linuxppc-dev@lists.ozlabs.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Michael Jeanson mjeanson@efficios.com Reviewed-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com
arch/powerpc/include/asm/ftrace.h | 12 ------------ 1 file changed, 12 deletions(-)
diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h index 3cee7115441b..e3d1f377bc5b 100644 --- a/arch/powerpc/include/asm/ftrace.h +++ b/arch/powerpc/include/asm/ftrace.h @@ -64,17 +64,6 @@ void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
- those.
*/ #define ARCH_HAS_SYSCALL_MATCH_SYM_NAME -#ifdef CONFIG_PPC64_ELF_ABI_V1 -static inline bool arch_syscall_match_sym_name(const char *sym, const char *name) -{
- /* We need to skip past the initial dot, and the __se_sys alias */
- return !strcmp(sym + 1, name) ||
(!strncmp(sym, ".__se_sys", 9) && !strcmp(sym + 6, name)) ||(!strncmp(sym, ".ppc_", 5) && !strcmp(sym + 5, name + 4)) ||(!strncmp(sym, ".ppc32_", 7) && !strcmp(sym + 7, name + 4)) ||(!strncmp(sym, ".ppc64_", 7) && !strcmp(sym + 7, name + 4));-} -#else static inline bool arch_syscall_match_sym_name(const char *sym, const char *name) { return !strcmp(sym, name) || @@ -83,7 +72,6 @@ static inline bool arch_syscall_match_sym_name(const char *sym, const char *name (!strncmp(sym, "ppc32_", 6) && !strcmp(sym + 6, name + 4)) || (!strncmp(sym, "ppc64_", 6) && !strcmp(sym + 6, name + 4)); } -#endif /* CONFIG_PPC64_ELF_ABI_V1 */ #endif /* CONFIG_FTRACE_SYSCALLS */
#if defined(CONFIG_PPC64) && defined(CONFIG_FUNCTION_TRACER)
2.34.1
Le 05/12/2022 à 19:19, Michael Jeanson a écrit :
[Vous ne recevez pas souvent de courriers de mjeanson@efficios.com. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
On 2022-12-05 00:34, Michael Ellerman wrote:
Michael Jeanson mjeanson@efficios.com writes:
In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table changing from their dot prefixed variant to the non-prefixed ones.
Since ftrace prefixes a dot to the syscall names when matching them to build its syscall event list, this resulted in no syscall events being available.
Remove the PPC64_ELF_ABI_V1 specific version of arch_syscall_match_sym_name to have the same behavior across all powerpc variants.
This doesn't seem to work for me.
Event with it applied I still don't see anything in /sys/kernel/debug/tracing/events/syscalls
Did we break it in some other way recently?
cheers
I've just tried this change on top of v6.1-rc8 in qemu with a base config of 'corenet32_smp_defconfig' and these options on top:
CONFIG_FTRACE=y CONFIG_FTRACE_SYSCALLS=y
And I can trace syscalls with ftrace.
What kernel tree and config are you using?
If you are using a ppc32 config, CONFIG_PPC64_ELF_ABI_V1 won't be set, so it doesn't matter whether this change is there or not.
You should try corenet64_smp_defconfig if you want CONFIG_PPC64_ELF_ABI_V1 to be set.
You can also use ppc64_defconfig, that's a different platform but it also has CONFIG_PPC64_ELF_ABI_V1.
Christophe
Thanks for looking into this.
Fixes: 68b34588e202 ("powerpc/64/sycall: Implement syscall entry/exit logic in C") Cc: stable@vger.kernel.org # v5.7+ Cc: Steven Rostedt rostedt@goodmis.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Michael Ellerman mpe@ellerman.id.au Cc: Nicholas Piggin npiggin@gmail.com Cc: Christophe Leroy christophe.leroy@csgroup.eu Cc: Michal Suchanek msuchanek@suse.de Cc: linuxppc-dev@lists.ozlabs.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Michael Jeanson mjeanson@efficios.com Reviewed-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com
arch/powerpc/include/asm/ftrace.h | 12 ------------ 1 file changed, 12 deletions(-)
diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h index 3cee7115441b..e3d1f377bc5b 100644 --- a/arch/powerpc/include/asm/ftrace.h +++ b/arch/powerpc/include/asm/ftrace.h @@ -64,17 +64,6 @@ void ftrace_graph_func(unsigned long ip, unsigned long parent_ip, * those. */ #define ARCH_HAS_SYSCALL_MATCH_SYM_NAME -#ifdef CONFIG_PPC64_ELF_ABI_V1 -static inline bool arch_syscall_match_sym_name(const char *sym, const char *name) -{ - /* We need to skip past the initial dot, and the __se_sys alias */ - return !strcmp(sym + 1, name) || - (!strncmp(sym, ".__se_sys", 9) && !strcmp(sym + 6, name)) || - (!strncmp(sym, ".ppc_", 5) && !strcmp(sym + 5, name + 4)) || - (!strncmp(sym, ".ppc32_", 7) && !strcmp(sym + 7, name + 4)) || - (!strncmp(sym, ".ppc64_", 7) && !strcmp(sym + 7, name + 4)); -} -#else static inline bool arch_syscall_match_sym_name(const char *sym, const char *name) { return !strcmp(sym, name) || @@ -83,7 +72,6 @@ static inline bool arch_syscall_match_sym_name(const char *sym, const char *name (!strncmp(sym, "ppc32_", 6) && !strcmp(sym + 6, name + 4)) || (!strncmp(sym, "ppc64_", 6) && !strcmp(sym + 6, name + 4)); } -#endif /* CONFIG_PPC64_ELF_ABI_V1 */ #endif /* CONFIG_FTRACE_SYSCALLS */
#if defined(CONFIG_PPC64) && defined(CONFIG_FUNCTION_TRACER)
2.34.1
On 2022-12-05 13:56, Christophe Leroy wrote:
Le 05/12/2022 à 19:19, Michael Jeanson a écrit :
[Vous ne recevez pas souvent de courriers de mjeanson@efficios.com. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
On 2022-12-05 00:34, Michael Ellerman wrote:
Michael Jeanson mjeanson@efficios.com writes:
In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table changing from their dot prefixed variant to the non-prefixed ones.
Since ftrace prefixes a dot to the syscall names when matching them to build its syscall event list, this resulted in no syscall events being available.
Remove the PPC64_ELF_ABI_V1 specific version of arch_syscall_match_sym_name to have the same behavior across all powerpc variants.
This doesn't seem to work for me.
Event with it applied I still don't see anything in /sys/kernel/debug/tracing/events/syscalls
Did we break it in some other way recently?
cheers
I've just tried this change on top of v6.1-rc8 in qemu with a base config of 'corenet32_smp_defconfig' and these options on top:
CONFIG_FTRACE=y CONFIG_FTRACE_SYSCALLS=y
And I can trace syscalls with ftrace.
What kernel tree and config are you using?
If you are using a ppc32 config, CONFIG_PPC64_ELF_ABI_V1 won't be set, so it doesn't matter whether this change is there or not.
You should try corenet64_smp_defconfig if you want CONFIG_PPC64_ELF_ABI_V1 to be set.
You can also use ppc64_defconfig, that's a different platform but it also has CONFIG_PPC64_ELF_ABI_V1.
You are absolutely right, I used the wrong environment, I blame Monday morning. I tested again this time using 'corenet64_smp_defconfig' with the same options and syscall tracing with ftrace also works.
I double checked that /proc/config.gz contained CONFIG_PPC64_ELF_ABI_V1 to be sure.
Christophe
Thanks for looking into this.
On 2022-12-05 15:11, Michael Jeanson wrote:
Michael Jeanson mjeanson@efficios.com writes:
In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table changing from their dot prefixed variant to the non-prefixed ones.
Since ftrace prefixes a dot to the syscall names when matching them to build its syscall event list, this resulted in no syscall events being available.
Remove the PPC64_ELF_ABI_V1 specific version of arch_syscall_match_sym_name to have the same behavior across all powerpc variants.
This doesn't seem to work for me.
Event with it applied I still don't see anything in /sys/kernel/debug/tracing/events/syscalls
Did we break it in some other way recently?
cheers
I did some further testing, my config also enabled KALLSYMS_ALL, when I remove it there is indeed no syscall events.
Michael Jeanson mjeanson@efficios.com writes:
On 2022-12-05 15:11, Michael Jeanson wrote:
Michael Jeanson mjeanson@efficios.com writes:
In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table changing from their dot prefixed variant to the non-prefixed ones.
Since ftrace prefixes a dot to the syscall names when matching them to build its syscall event list, this resulted in no syscall events being available.
Remove the PPC64_ELF_ABI_V1 specific version of arch_syscall_match_sym_name to have the same behavior across all powerpc variants.
This doesn't seem to work for me.
Event with it applied I still don't see anything in /sys/kernel/debug/tracing/events/syscalls
Did we break it in some other way recently?
cheers
I did some further testing, my config also enabled KALLSYMS_ALL, when I remove it there is indeed no syscall events.
Aha, OK that explains it I guess.
I was using ppc64_guest_defconfig which has ABI_V1 and FTRACE_SYSCALLS, but does not have KALLSYMS_ALL. So I guess there's some other bug lurking in there.
cheers
On 2022-12-05 17:50, Michael Ellerman wrote:
Michael Jeanson mjeanson@efficios.com writes:
On 2022-12-05 15:11, Michael Jeanson wrote:
Michael Jeanson mjeanson@efficios.com writes: > In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on > PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table > changing from their dot prefixed variant to the non-prefixed ones. > > Since ftrace prefixes a dot to the syscall names when matching them to > build its syscall event list, this resulted in no syscall events being > available. > > Remove the PPC64_ELF_ABI_V1 specific version of > arch_syscall_match_sym_name to have the same behavior across all powerpc > variants.
This doesn't seem to work for me.
Event with it applied I still don't see anything in /sys/kernel/debug/tracing/events/syscalls
Did we break it in some other way recently?
cheers
I did some further testing, my config also enabled KALLSYMS_ALL, when I remove it there is indeed no syscall events.
Aha, OK that explains it I guess.
I was using ppc64_guest_defconfig which has ABI_V1 and FTRACE_SYSCALLS, but does not have KALLSYMS_ALL. So I guess there's some other bug lurking in there.
I don't have the setup handy to validate it, but I suspect it is caused by the way scripts/kallsyms.c:symbol_valid() checks whether a symbol entry needs to be integrated into the assembler output when --all-symbols is not specified. It only keeps symbols which addresses are in the text range. On PPC64_ELF_ABI_V1, this means only the dot-prefixed symbols will be kept (those point to the function begin), leaving out the non-dot-prefixed symbols (those point to the function descriptors).
So I see two possible solutions there: either we ensure that FTRACE_SYSCALLS selects KALLSYMS_ALL on PPC64_ELF_ABI_V1, or we modify scripts/kallsyms.c:symbol_valid() to also include function descriptor symbols. This would mean accepting symbols pointing into the .opd ELF section.
IMHO the second option would be better because it does not increase the kernel image size as much as KALLSYMS_ALL.
Thoughts ?
Thanks,
Mathieu
Le 06/12/2022 à 15:38, Mathieu Desnoyers a écrit :
On 2022-12-05 17:50, Michael Ellerman wrote:
Michael Jeanson mjeanson@efficios.com writes:
On 2022-12-05 15:11, Michael Jeanson wrote:
> Michael Jeanson mjeanson@efficios.com writes: >> In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on >> PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table >> changing from their dot prefixed variant to the non-prefixed ones. >> >> Since ftrace prefixes a dot to the syscall names when matching >> them to >> build its syscall event list, this resulted in no syscall events >> being >> available. >> >> Remove the PPC64_ELF_ABI_V1 specific version of >> arch_syscall_match_sym_name to have the same behavior across all >> powerpc >> variants. > > This doesn't seem to work for me. > > Event with it applied I still don't see anything in > /sys/kernel/debug/tracing/events/syscalls > > Did we break it in some other way recently? > > cheers
I did some further testing, my config also enabled KALLSYMS_ALL, when I remove it there is indeed no syscall events.
Aha, OK that explains it I guess.
I was using ppc64_guest_defconfig which has ABI_V1 and FTRACE_SYSCALLS, but does not have KALLSYMS_ALL. So I guess there's some other bug lurking in there.
I don't have the setup handy to validate it, but I suspect it is caused by the way scripts/kallsyms.c:symbol_valid() checks whether a symbol entry needs to be integrated into the assembler output when --all-symbols is not specified. It only keeps symbols which addresses are in the text range. On PPC64_ELF_ABI_V1, this means only the dot-prefixed symbols will be kept (those point to the function begin), leaving out the non-dot-prefixed symbols (those point to the function descriptors).
So I see two possible solutions there: either we ensure that FTRACE_SYSCALLS selects KALLSYMS_ALL on PPC64_ELF_ABI_V1, or we modify scripts/kallsyms.c:symbol_valid() to also include function descriptor symbols. This would mean accepting symbols pointing into the .opd ELF section.
IMHO the second option would be better because it does not increase the kernel image size as much as KALLSYMS_ALL.
Yes, seems to be the best solution.
Maybe the only thing to do is to add a new range to text_ranges, something like (untested):
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c index 03fa07ad45d9..decf31c497f5 100644 --- a/scripts/kallsyms.c +++ b/scripts/kallsyms.c @@ -64,6 +64,7 @@ static unsigned long long relative_base; static struct addr_range text_ranges[] = { { "_stext", "_etext" }, { "_sinittext", "_einittext" }, + { "__start_opd", "__end_opd" }, }; #define text_range_text (&text_ranges[0]) #define text_range_inittext (&text_ranges[1])
--- Christophe
Mathieu Desnoyers mathieu.desnoyers@efficios.com writes:
On 2022-12-05 17:50, Michael Ellerman wrote:
Michael Jeanson mjeanson@efficios.com writes:
On 2022-12-05 15:11, Michael Jeanson wrote:
> Michael Jeanson mjeanson@efficios.com writes: >> In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on >> PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table >> changing from their dot prefixed variant to the non-prefixed ones. >> >> Since ftrace prefixes a dot to the syscall names when matching them to >> build its syscall event list, this resulted in no syscall events being >> available. >> >> Remove the PPC64_ELF_ABI_V1 specific version of >> arch_syscall_match_sym_name to have the same behavior across all powerpc >> variants. > > This doesn't seem to work for me. > > Event with it applied I still don't see anything in > /sys/kernel/debug/tracing/events/syscalls > > Did we break it in some other way recently? > > cheers
I did some further testing, my config also enabled KALLSYMS_ALL, when I remove it there is indeed no syscall events.
Aha, OK that explains it I guess.
I was using ppc64_guest_defconfig which has ABI_V1 and FTRACE_SYSCALLS, but does not have KALLSYMS_ALL. So I guess there's some other bug lurking in there.
I don't have the setup handy to validate it, but I suspect it is caused by the way scripts/kallsyms.c:symbol_valid() checks whether a symbol entry needs to be integrated into the assembler output when --all-symbols is not specified. It only keeps symbols which addresses are in the text range. On PPC64_ELF_ABI_V1, this means only the dot-prefixed symbols will be kept (those point to the function begin), leaving out the non-dot-prefixed symbols (those point to the function descriptors).
OK. So I guess it never worked without KALLSYMS_ALL.
It seems like most distros enable KALLSYMS_ALL, so I guess that's why we've never noticed.
So I see two possible solutions there: either we ensure that FTRACE_SYSCALLS selects KALLSYMS_ALL on PPC64_ELF_ABI_V1, or we modify scripts/kallsyms.c:symbol_valid() to also include function descriptor symbols. This would mean accepting symbols pointing into the .opd ELF section.
My only worry is that will cause some other breakage, because .opd symbols are not really "text" in the normal sense, ie. you can't execute them directly.
On the other hand the help for KALLSYMS_ALL says:
"Normally kallsyms only contains the symbols of functions"
But without .opd included that's not really true. In practice it probably doesn't really matter, because eg. backtraces will point to dot symbols which can be resolved.
IMHO the second option would be better because it does not increase the kernel image size as much as KALLSYMS_ALL.
Yes I agree.
Even if that did break something, any breakage would be limited to arches which uses function descriptors, which are now all rare.
Relatedly we have a patch in next to optionally use ABIv2 for 64-bit big endian builds.
cheers
On 2022-12-06 21:09, Michael Ellerman wrote:
Mathieu Desnoyers mathieu.desnoyers@efficios.com writes:
On 2022-12-05 17:50, Michael Ellerman wrote:
Michael Jeanson mjeanson@efficios.com writes:
On 2022-12-05 15:11, Michael Jeanson wrote:
>> Michael Jeanson mjeanson@efficios.com writes: >>> In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on >>> PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table >>> changing from their dot prefixed variant to the non-prefixed ones. >>> >>> Since ftrace prefixes a dot to the syscall names when matching them to >>> build its syscall event list, this resulted in no syscall events being >>> available. >>> >>> Remove the PPC64_ELF_ABI_V1 specific version of >>> arch_syscall_match_sym_name to have the same behavior across all powerpc >>> variants. >> >> This doesn't seem to work for me. >> >> Event with it applied I still don't see anything in >> /sys/kernel/debug/tracing/events/syscalls >> >> Did we break it in some other way recently? >> >> cheers
I did some further testing, my config also enabled KALLSYMS_ALL, when I remove it there is indeed no syscall events.
Aha, OK that explains it I guess.
I was using ppc64_guest_defconfig which has ABI_V1 and FTRACE_SYSCALLS, but does not have KALLSYMS_ALL. So I guess there's some other bug lurking in there.
I don't have the setup handy to validate it, but I suspect it is caused by the way scripts/kallsyms.c:symbol_valid() checks whether a symbol entry needs to be integrated into the assembler output when --all-symbols is not specified. It only keeps symbols which addresses are in the text range. On PPC64_ELF_ABI_V1, this means only the dot-prefixed symbols will be kept (those point to the function begin), leaving out the non-dot-prefixed symbols (those point to the function descriptors).
OK. So I guess it never worked without KALLSYMS_ALL.
I suspect it worked prior to kernel v5.7, because back then the PPC64 ABIv1 system call table contained pointers to the text section (beginning of functions) rather than function descriptors.
So changing this system call table to point to C functions introduced the dot-prefix match issue for syscall tracing as well as a dependency on KALLSYMS_ALL.
It seems like most distros enable KALLSYMS_ALL, so I guess that's why we've never noticed.
Or very few people run recent PPC64 ABIv1 kernels :)
So I see two possible solutions there: either we ensure that FTRACE_SYSCALLS selects KALLSYMS_ALL on PPC64_ELF_ABI_V1, or we modify scripts/kallsyms.c:symbol_valid() to also include function descriptor symbols. This would mean accepting symbols pointing into the .opd ELF section.
My only worry is that will cause some other breakage, because .opd symbols are not really "text" in the normal sense, ie. you can't execute them directly.
AFAIU adding the .opd section to scripts/kallsyms.c text_ranges will only affect the result of symbol_valid(), which decides which symbols get pulled into a KALLSYMS=n/KALLSYMS_ALL=n kernel build. Considering that a KALLSYMS_ALL=y build pulls those function descriptor symbols into the image without breaking anything, I don't see why adding the .opd section to this script text_ranges would have any ill side-effect.
On the other hand the help for KALLSYMS_ALL says:
"Normally kallsyms only contains the symbols of functions"
But without .opd included that's not really true. In practice it probably doesn't really matter, because eg. backtraces will point to dot symbols which can be resolved.
Indeed, I don't see this affecting backtraces, but as soon as a lookup depends on comparing the C function pointer to a function descriptor, the .opd symbols are needed. Not having those function descriptor symbols in KALLSYMS_ALL=n builds seems rather error-prone.
IMHO the second option would be better because it does not increase the kernel image size as much as KALLSYMS_ALL.
Yes I agree.
Even if that did break something, any breakage would be limited to arches which uses function descriptors, which are now all rare.
Yes, it would only impact those arches using function descriptors, which are broken today with respect to system call tracing. Are you aware of other architectures other than PPC64 ELF ABI v1 supported by the Linux kernel that use function descriptors ?
Relatedly we have a patch in next to optionally use ABIv2 for 64-bit big endian builds.
Interesting. Does it require a matching user-space ? (built with PPC64 ABIv2 ?) Does it handle legacy PPC32 executables ?
Thanks,
Mathieu
Hello,
On Wed, Dec 07, 2022 at 10:18:13AM -0500, Mathieu Desnoyers wrote:
On 2022-12-06 21:09, Michael Ellerman wrote:
Mathieu Desnoyers mathieu.desnoyers@efficios.com writes:
On 2022-12-05 17:50, Michael Ellerman wrote:
Relatedly we have a patch in next to optionally use ABIv2 for 64-bit big endian builds.
Interesting. Does it require a matching user-space ? (built with PPC64 ABIv2
No, the kernel and userspace ABI is separate.
?) Does it handle legacy PPC32 executables ?
Theoretically it should. No idea if anybody has tested it.
Thanks
Michal
Le 07/12/2022 à 16:18, Mathieu Desnoyers a écrit :
On 2022-12-06 21:09, Michael Ellerman wrote:
Mathieu Desnoyers mathieu.desnoyers@efficios.com writes:
On 2022-12-05 17:50, Michael Ellerman wrote: IMHO the second option would be better because it does not increase the kernel image size as much as KALLSYMS_ALL.
Yes I agree.
Even if that did break something, any breakage would be limited to arches which uses function descriptors, which are now all rare.
Yes, it would only impact those arches using function descriptors, which are broken today with respect to system call tracing. Are you aware of other architectures other than PPC64 ELF ABI v1 supported by the Linux kernel that use function descriptors ?
$ git grep "select HAVE_FUNCTION_DESCRIPTORS" arch/ arch/ia64/Kconfig: select HAVE_FUNCTION_DESCRIPTORS arch/parisc/Kconfig: select HAVE_FUNCTION_DESCRIPTORS if 64BIT arch/powerpc/Kconfig: select HAVE_FUNCTION_DESCRIPTORS if PPC64_ELF_ABI_V1
Christophe
On Thu, 1 Dec 2022 11:14:42 -0500, Michael Jeanson wrote:
In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table changing from their dot prefixed variant to the non-prefixed ones.
Since ftrace prefixes a dot to the syscall names when matching them to build its syscall event list, this resulted in no syscall events being available.
[...]
Applied to powerpc/next.
[1/1] powerpc/ftrace: fix syscall tracing on PPC64_ELF_ABI_V1 https://git.kernel.org/powerpc/c/ad050d2390fccb22aa3e6f65e11757ce7a5a7ca5
cheers
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Michael Ellerman -
Michael Ellerman -
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Michal Suchánek