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    SubjectRe: [PATCH 3/4] ftrace syscalls: Allow arch specific syscall symbol matching
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    On Thu, 2010-05-13 at 17:43 +1000, Ian Munsie wrote:
    > From: Ian Munsie <imunsie@au1.ibm.com>
    >
    > Some architectures have unusual symbol names and the generic code to
    > match the symbol name with the function name for the syscall metadata
    > will fail. For example, symbols on PPC64 start with a period and the
    > generic code will fail to match them.
    >
    > This patch splits out the match logic into a standalone weak function
    > that can be overridden on archs with unusual symbol names.
    >
    > Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
    > ---

    Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    ---

    Ian, I assume you will implement the support for the "special" ppc_*
    syscalls via a subsequent patch and not a respin of this one right ?

    Cheers,
    Ben.

    > Documentation/trace/ftrace-design.txt | 3 +++
    > include/linux/ftrace.h | 1 +
    > kernel/trace/trace_syscalls.c | 19 ++++++++++++-------
    > 3 files changed, 16 insertions(+), 7 deletions(-)
    >
    > diff --git a/Documentation/trace/ftrace-design.txt b/Documentation/trace/ftrace-design.txt
    > index 8369a1c..3936d5f 100644
    > --- a/Documentation/trace/ftrace-design.txt
    > +++ b/Documentation/trace/ftrace-design.txt
    > @@ -247,6 +247,9 @@ You need very few things to get the syscalls tracing in an arch.
    > - If the system call table on this arch is more complicated than a simple array
    > of addresses of the system calls, implement an arch_syscall_addr to return
    > the address of a given system call.
    > +- If the symbol names of the system calls do not match the function names on
    > + this arch, implement an arch_syscall_match_sym_name with the appropriate
    > + logic to return true if the function name corresponds with the symbol name.
    > - Tag this arch as HAVE_SYSCALL_TRACEPOINTS.
    >
    >
    > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
    > index e0ae83b..26ad1f5 100644
    > --- a/include/linux/ftrace.h
    > +++ b/include/linux/ftrace.h
    > @@ -534,6 +534,7 @@ static inline void trace_hw_branch_oops(void) {}
    > #ifdef CONFIG_FTRACE_SYSCALLS
    >
    > unsigned long arch_syscall_addr(int nr);
    > +bool arch_syscall_match_sym_name(const char *sym, const char *name);
    >
    > #endif /* CONFIG_FTRACE_SYSCALLS */
    >
    > diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
    > index 1c231d0..ebbc74d 100644
    > --- a/kernel/trace/trace_syscalls.c
    > +++ b/kernel/trace/trace_syscalls.c
    > @@ -32,13 +32,7 @@ static struct syscall_metadata *find_syscall_meta(unsigned long syscall)
    > kallsyms_lookup(syscall, NULL, NULL, NULL, str);
    >
    > for ( ; start < stop; start++) {
    > - /*
    > - * Only compare after the "sys" prefix. Archs that use
    > - * syscall wrappers may have syscalls symbols aliases prefixed
    > - * with "SyS" instead of "sys", leading to an unwanted
    > - * mismatch.
    > - */
    > - if (start->name && !strcmp(start->name + 3, str + 3))
    > + if (start->name && arch_syscall_match_sym_name(str, start->name))
    > return start;
    > }
    > return NULL;
    > @@ -408,6 +402,17 @@ unsigned long __init __weak arch_syscall_addr(int nr)
    > return (unsigned long)sys_call_table[nr];
    > }
    >
    > +bool __weak arch_syscall_match_sym_name(const char *sym, const char *name)
    > +{
    > + /*
    > + * Only compare after the "sys" prefix. Archs that use
    > + * syscall wrappers may have syscalls symbols aliases prefixed
    > + * with "SyS" instead of "sys", leading to an unwanted
    > + * mismatch.
    > + */
    > + return (!strcmp(sym + 3, name + 3));
    > +}
    > +
    > int __init init_ftrace_syscalls(void)
    > {
    > struct syscall_metadata *meta;




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