From: Rabin Vincent <[email protected]>
ARM has a few system calls (most notably mmap) for which the names of
the functions which are referenced in the syscall table do not match the
names of the syscall tracepoints. As a consequence of this, these
tracepoints are not made available. Implement
arch_syscall_match_sym_name to fix this and allow tracing even these
system calls.
Signed-off-by: Rabin Vincent <[email protected]>
---
arch/arm/include/asm/ftrace.h | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index bfe2a2f..8467909 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -54,6 +54,27 @@ static inline void *return_address(unsigned int level)
#define ftrace_return_address(n) return_address(n)
+#define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
+
+static inline bool arch_syscall_match_sym_name(const char *sym,
+ const char *name)
+{
+ /* Skip sys_ */
+ sym += 4;
+ name += 4;
+
+ if (!strcmp(sym, "mmap2"))
+ sym = "mmap_pgoff";
+ else if (!strcmp(sym, "statfs64_wrapper"))
+ sym = "statfs64";
+ else if (!strcmp(sym, "fstatfs64_wrapper"))
+ sym = "fstatfs64";
+ else if (!strcmp(sym, "arm_fadvise64_64"))
+ sym = "fadvise64_64";
+
+ return !strcmp(sym, name);
+}
+
#endif /* ifndef __ASSEMBLY__ */
#endif /* _ASM_ARM_FTRACE */
--
2.1.4
On Mon, Nov 14, 2016 at 02:03:45PM +0100, Rabin Vincent wrote:
> From: Rabin Vincent <[email protected]>
>
> ARM has a few system calls (most notably mmap) for which the names of
> the functions which are referenced in the syscall table do not match the
> names of the syscall tracepoints. As a consequence of this, these
> tracepoints are not made available. Implement
> arch_syscall_match_sym_name to fix this and allow tracing even these
> system calls.
>
> Signed-off-by: Rabin Vincent <[email protected]>
> ---
> arch/arm/include/asm/ftrace.h | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
> index bfe2a2f..8467909 100644
> --- a/arch/arm/include/asm/ftrace.h
> +++ b/arch/arm/include/asm/ftrace.h
> @@ -54,6 +54,27 @@ static inline void *return_address(unsigned int level)
>
> #define ftrace_return_address(n) return_address(n)
>
> +#define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
> +
> +static inline bool arch_syscall_match_sym_name(const char *sym,
> + const char *name)
> +{
> + /* Skip sys_ */
> + sym += 4;
> + name += 4;
Is this really safe? What guarantees that we can wind forward four
bytes here? If it's always safe, it needs a better comment than just
two words.
> +
> + if (!strcmp(sym, "mmap2"))
> + sym = "mmap_pgoff";
> + else if (!strcmp(sym, "statfs64_wrapper"))
> + sym = "statfs64";
> + else if (!strcmp(sym, "fstatfs64_wrapper"))
> + sym = "fstatfs64";
> + else if (!strcmp(sym, "arm_fadvise64_64"))
> + sym = "fadvise64_64";
> +
> + return !strcmp(sym, name);
> +}
> +
> #endif /* ifndef __ASSEMBLY__ */
>
> #endif /* _ASM_ARM_FTRACE */
> --
> 2.1.4
>
--
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On Mon, 14 Nov 2016 13:40:17 +0000
Russell King - ARM Linux <[email protected]> wrote:
> On Mon, Nov 14, 2016 at 02:03:45PM +0100, Rabin Vincent wrote:
> > From: Rabin Vincent <[email protected]>
> >
> > ARM has a few system calls (most notably mmap) for which the names of
> > the functions which are referenced in the syscall table do not match the
> > names of the syscall tracepoints. As a consequence of this, these
> > tracepoints are not made available. Implement
> > arch_syscall_match_sym_name to fix this and allow tracing even these
> > system calls.
> >
> > Signed-off-by: Rabin Vincent <[email protected]>
> > ---
> > arch/arm/include/asm/ftrace.h | 21 +++++++++++++++++++++
> > 1 file changed, 21 insertions(+)
> >
> > diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
> > index bfe2a2f..8467909 100644
> > --- a/arch/arm/include/asm/ftrace.h
> > +++ b/arch/arm/include/asm/ftrace.h
> > @@ -54,6 +54,27 @@ static inline void *return_address(unsigned int level)
> >
> > #define ftrace_return_address(n) return_address(n)
> >
> > +#define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
> > +
> > +static inline bool arch_syscall_match_sym_name(const char *sym,
> > + const char *name)
> > +{
> > + /* Skip sys_ */
> > + sym += 4;
> > + name += 4;
>
> Is this really safe? What guarantees that we can wind forward four
> bytes here? If it's always safe, it needs a better comment than just
> two words.
I believe it is, but a comment would do well.
The "sym" comes from kallsyms_lookup(syscall-address...)
Which it becomes the syscall function. Mostly defined by:
include/linux/syscalls.h:
#define SYSCALL_DEFINEx(x, name)
asmlinkage long sys_##name(...)
But there are cases that archs can define their own system calls
outside of this method. But then again, those system calls wont have
tracepoints attached to them, and they wont be called with this
function.
The "name" part comes from the system call tracepoint.
#define SYSCALL_METADATA(sname, ...)
static struct syscall_metadata
__syscall_meta_##sname = {
.name = "sys"#sname,
It too appends the "sys" to the name. Note, sname here is called with
appending "_" to name, so the .name will start with "sys_" as well.
I'm guessing that there's an issue if more than one function name is
used for the same function, that is, the symbol maps to the same IP.
Then kallsyms_lookup() can return different function names for the same
function being called, and I'm guessing that's what this is trying to
fix.
-- Steve
>
> > +
> > + if (!strcmp(sym, "mmap2"))
> > + sym = "mmap_pgoff";
> > + else if (!strcmp(sym, "statfs64_wrapper"))
> > + sym = "statfs64";
> > + else if (!strcmp(sym, "fstatfs64_wrapper"))
> > + sym = "fstatfs64";
> > + else if (!strcmp(sym, "arm_fadvise64_64"))
> > + sym = "fadvise64_64";
> > +
> > + return !strcmp(sym, name);
> > +}
> > +
> > #endif /* ifndef __ASSEMBLY__ */
> >
> > #endif /* _ASM_ARM_FTRACE */
> > --
> > 2.1.4
> >
>
On Mon, 14 Nov 2016 10:40:08 -0500
Steven Rostedt <[email protected]> wrote:
> > Is this really safe? What guarantees that we can wind forward four
> > bytes here? If it's always safe, it needs a better comment than just
> > two words.
>
> I believe it is, but a comment would do well.
Also, the generic function that is called if the arch does not define
ARCH_HAS_SYSCALL_MATCH_SYM_NAME does this too.
return !strcmp(sym + 3, name + 3);
And looking at this, it really should be + 4 and not + 3, because it
doesn't match the comment above, where it says it can handle both
".SyS" and "SyS", but it doesn't handle ".SyS" compared to ".sys".
-- Steve
From: Rabin Vincent <[email protected]>
ARM has a few system calls (most notably mmap) for which the names of
the functions which are referenced in the syscall table do not match the
names of the syscall tracepoints. As a consequence of this, these
tracepoints are not made available. Implement
arch_syscall_match_sym_name to fix this and allow tracing even these
system calls.
Signed-off-by: Rabin Vincent <[email protected]>
---
v2: get rid of unsafe-looking pointer adjustment
arch/arm/include/asm/ftrace.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index bfe2a2f..22b7311 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -54,6 +54,24 @@ static inline void *return_address(unsigned int level)
#define ftrace_return_address(n) return_address(n)
+#define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
+
+static inline bool arch_syscall_match_sym_name(const char *sym,
+ const char *name)
+{
+ if (!strcmp(sym, "sys_mmap2"))
+ sym = "sys_mmap_pgoff";
+ else if (!strcmp(sym, "sys_statfs64_wrapper"))
+ sym = "sys_statfs64";
+ else if (!strcmp(sym, "sys_fstatfs64_wrapper"))
+ sym = "sys_fstatfs64";
+ else if (!strcmp(sym, "sys_arm_fadvise64_64"))
+ sym = "sys_fadvise64_64";
+
+ /* Ignore case since sym may start with "SyS" instead of "sys" */
+ return !strcasecmp(sym, name);
+}
+
#endif /* ifndef __ASSEMBLY__ */
#endif /* _ASM_ARM_FTRACE */
--
2.1.4
On Mon, Nov 14, 2016 at 10:40:08AM -0500, Steven Rostedt wrote:
> On Mon, 14 Nov 2016 13:40:17 +0000
> Russell King - ARM Linux <[email protected]> wrote:
> > On Mon, Nov 14, 2016 at 02:03:45PM +0100, Rabin Vincent wrote:
> > > +static inline bool arch_syscall_match_sym_name(const char *sym,
> > > + const char *name)
> > > +{
> > > + /* Skip sys_ */
> > > + sym += 4;
> > > + name += 4;
> >
> > Is this really safe? What guarantees that we can wind forward four
> > bytes here? If it's always safe, it needs a better comment than just
> > two words.
>
> I believe it is, but a comment would do well.
I ended up just getting rid of the skip and comparing the whole name
instead. I've sent a v2.